The test is done with a vibration measurement tool. A micro computer is connected to an accelerometer & the results can be made in near real time, under all conditions. This test has been done for years, testing bearing wear in aircraft Carier equipment.
If you want a reliable test, do your comparisons on a downhill stretch of road, with no pedal input. Be sure to do this on a windless day. This will eliminate totally the uncontrolled variables of fatigue and wind.
Global Cycling Network Please test even lower pressures, small and lightweight riders can get away with just 1,2 bar (maybe even less) on a 25 mm tire.
Actually the results are likely less informing then. You would like to have realistic results based on the influence it has on your performance. The effect of rough surfaces quite probably have a tiring effect on the rider because it's uncomfortable as Emma told, which contributes negatively to your performance.
GCN does Science now has a proper scientist. I think for these segments, it might be appropriate to correctly refer to Emma as Dr. Pooley. The force diagrams make this physicist very happy.
Definitely an improvement on gcn does science in the past, but still flawed I think. You only considered rolling onto the bump, and not the force vectors rolling off it again. So, sorry, still haven't understood the whole dynamics of the rolling resistance /tyre pressure thing. Whilst you think about that, you could also try and answer, in a proper physics way, why cadence braking is in anyway advantageous.
Great video! I understand this is a simplification of the mechanisms involved, but I still have a few comments and hand-waving arguments. Early in the video it is said that the vertical movement is a waste of energy, which agree to. However, when decomposing the forces it is said that only the horizontal component causes loss (is unwanted). The vertical component will do work against gravity as the bike goes up - that is energy lost that will only partly be regained as the bike comes down again. One may argue that the net loss is little, but considering the small angles the vertical force will be much greater than the horizontal force, which may imply that the two are comparable. The video also says that only the horizontal force makes the ride uncomfortable. Imagine riding a bike that was shaking only in the horizontal direction...
Emma is the gift that keeps on giving. Woman is a scientist, a good cook, an amazing time-trialist, climbs like a mountain goat, fluent spanish and italian speaker and very good freehand circle doodler (that's harder than you think). My god, what CAN'T this woman do?
Great video. Emma I love the way you have fitted into the GCN approach on the many issues of cycling. I am 75kg, my bikes 8.5kg & I roll on 28mm tyres with tubes. I use 85-90 psi. Any more is bumpy & harsh & less makes climbing sluggish....
_@Emma_ - Great video! The pump height at the end was hilarious. I have the opposite problem -- I'm tall and most pumps are too short for me. Lezyne offers some of its pump models in a "tall" version and I bought one. It's great and pumps more air volume per stroke. Regarding the use of the word "pressure", I wish you hadn't made it the focus of the video. It's the only aspect to the excellent video that could be misleading to cyclists who are not schooled as well in the physics. What you are really trying to do is determine the ideal *compression* for your tyres when traveling on a rough road. As you rightly explained, the pressure you need to achieve the ideal compression will vary from cyclist to cyclist because it depends on their weight. And this was illustrated beautifully when you explained how the front tyre pressure needs to be less than the rear tyre because of the different weight on each wheel. But there's more to it than that. Another _equally important_ factor is the *volume* in each tyre. In other words, smaller tyres need higher pressure than larger tyres to achieve the same compression. This is a challenging subject for most cyclists because -- if they want to get it right -- they must learn to think in terms of tyre compression, then select a pressure that achieves it based on the weight on each wheel *and* the size tyre on each wheel. I use the _Berto Tire Pressure_ app (from Edison Gauss Publishing) for my Android smart phone to calculate the tyre pressure for smooth roads. It's also listed as _Bicycle Tire Pressure Calc_ in the Google Play store. Its calculations are based on a standard 15% compression of the tyre at the contact patch. However, it doesn't allow the user to change the compression amount and I'm not aware of any app that does. This is what we need -- an app that let's the user also select the desired tyre compression. GCN could provide a valuable service by testing different compression levels for various road surfaces from super-smooth indoor tracks to outdoor gravel roads and everything in between. It would also be nice to test some of the outdoor roads in rain to determine "ideal" compression levels for wet roads as well. You could produce the first ever tyre compression table for various road surface types. This is the information that would be needed for someone to update apps like _Berto Tire Pressure_ with easy-to-understand choices for the user. If GCN wanted to go all the way, you could create your own Tyre Pressure app that incorporates all of this information and sell it. If you do, make both an Android and an iOS version. I'll be your first customer!
Well. I’ve cycled for over 50 years and now someone explains the science. Clearly and practically. Supper Emma. Thank you. Very interesting watching your videos. My partner is new to cycling. I’m pointing at all your videos as she always needs to know why !!
Awesome video. I'm no science genius so this was just the amount of detail to make me pay more attention to the pressure in my tires and to not over-inflate. I love Emma as an addition to GCN and it's her cycling credentials and acumen that make it so. Her demeanor, laughter and friendly smile are just a huge bonus.
Just what I was dealing with today - I cut the pressure from 100 to 75 psi on my 700x23 tires for the rough pavement on the back roads - felt smoother and faster. No measurements tho, I’m not consistent enough. Great explanations and diagrams, I now understand it better and will continue to modify to find my ideal. Thanks for this vid.
I’m totally old school and pump up my tires over 100psi. This was great and those force diagrams that Emma drew bring me back to college physics lectures! Very well done and explained!
Thanks, @Emma really great sicence, great to have you as part of the team. I have done my own experiment but being a TOF your approach would be too variable for me as my energy dropped. I think I may have found a better way to check the effect which is: 1) Fine a suitable long gradient which is a rough as you want, potholed 12% Oxfordshire hill in my case 2) Little or no wind 3) Decide on a starting pace at the top of the hill (20Kmph) 4) Coast / Speed down in the same aero position and record either terminal speed or time down the hill. I went for terminal speed as it was very easy to reset. The advantage of this method is it's very repeatable (if you ignore how tired you get cycling back to the top for the next run). I managed 3 before my tired old legs said enough. Dropping the pressure in my case saw the following 100psi = 69.7 Kmph 90psi = 70.2Kmph 80psi = 71.3Kmph I will try still lower pressure when I can face the climb again. (TOF = Tired Old Fart)
OK, I'm putting my own glasses on. Regarding Fv, that's not just a story about comfort, or it's absence. Let's have a look at the entire system bike+rider BR. Fv imparts a vertical acceleration av to BR. Now BR is not a rigid structure, but has a lot of articulated components, some of them soft (tyres, rider). On these, av causes a deformation. Now, what you already mentioned about deformation of the tyre causing energy loss through heat dissipation is even more true for the body. There's much more mass (yes, even in the case of a lightweight like you, Emma), so there is actually much more loss! The science of tyre pressure is balancing the losses in the tyre, which are lower with higher pressure, and the losses due to deformation of the elements of BR, which are lower with lower pressure. As another commenter commented, I'm not sure about the effect of Fh, given as at least part of the loss is regained when rolling off the pebble, as Fv then points forward...
On one bike I ride with 50 mm wide slicks at about 4 bar (lower feels uncomfortable because of sideways movement you get with the rim-tyre combination at lower pressures). Now this is on a recumbent, so the weight distribution is different, far more on the front wheel, pretty much the reverse of a road bike. My other recumbent has a 28 mm front tyre and a 35 mm rear tyre, usually at about 6 bar. The roads around here are pretty decent, but in rain I should decrease that pressure. Then I have a velomobile, which also has 28 mm in front, 35 mm in the rear. 6 bar front, 5 bar rear. Rather high, but a recumbent trike gets to deal with far higher sideways forces. My older velomobile could handle wider tyres, there I had 40 mm front, 47 mm rear. These tyres have a good puncture protection, but need to be inflated to a rather high pressure to get a decent rolling resistance (deformation is expensive on those tyres, but no punctures for about 28000 km is worth something). On the grocery bike I ride between 5 and 2 bar, I usually forget to inflate those tyres until the low pressure gets really noticeable. Those are 47 mm tyres, so 2 bar is still fine.
I've been experimenting with tire pressure for a while. I'm just over 200 lbs and find that 80 psi is fantastic. Used to run 100+ what a pain! 80psi gives lots of response and compliance. Bumps are not as harsh. I can ride much longer now!
Anti- Pops imagine Emma having a sudden misclip moment. Unexpected, then funny, then sort of bittersweet. Of course, Matt is ok and probably happy with the new job, but for us viewers, this has angst potential ) Plus, she is the only one on the crew now with the champion tricolor.
Dr. Pooley, You took me back to dynamics class, 40 years ago! I hate to say it, but Dr. Pooley just makes this channel SUPER! More time riding next time Doc!
To GCN...Fabulous video. Whomever is responsible for the brilliant writing, directing, photography, and production, you have reached the pinnacle of GCN videos to date. Just EXCELLENT. Superb pleasure to watch. Emma, as always your the TOPS. Thank you, thank you, thank you...did I say thanks...
Great information. It's basically trial and error + experience that gives the best results. I've found over the years (on my recumbent trike) that 1.5" tires are the optimum width for trike + my mass. I've run 1.75" tires on the front and boy does that wear me out in a hurry (but it is the most comfortable on rough roads/trails). Not only do they have an extra 1/2" of rubber on the road but they also are 10 psi under the 1.5s. When riding the 1.5" tires at the same psi as the 1.75" tires, I've found that my average speed in the flats is about 3mph faster. Doesn't sound like much but that's nearly 30% faster! In a specific downhill, I could barely hit 30 mph on the 1.75's while I can hit nearly 40 mph on the 1.5's when running at 80 psi (max psi for the tires I use). I run the same routes all the time. So, it was fairly easy to figure out the best psi/width/size for my mass. This was a fun video to watch. You should do a follow up with the differential equations to break it down ;)
I used to ride at 100psi, gained some weight, started to get lots of snake bites (I call them vampire bites). Were generally caused by hitting gravel on paved roads (common in towns) Was told to raise pressure to 110 and this solved the problem. I also tend tyo ride off saddle to better distribute weight in areas where there is gravel on the paved road. So lowering tyre pressure to save a few seconds would result in losing much more time fixing punctures.
Back in the 1970's my silk sew-up Clement Del Mundo tires gave me excellent grip on the wet or dry roads in Santa Cruz CA when I was training 400 miles a week. I miss that kind of performance.
great vid Emma! i tried finding an optimal pressure for my Specialized Roubaix with 28mm gp s4000ii tyres. i'm not a lightweight rider but came to finding around 70psi was good for me and my commute to uni with differing surfaces. 90-100psi just rattled me around and found myself fatiguing earlier in my rides. i also ride a stiff specialized tarmac on 25mm vitorria pro's at 95 -115 psi and find it great, not as comfy as the 28mm's on the more compliant Roubaix of course.
I'm not sure how much of this I would have understood if I hadn't just finished two years of physics. But it's really great to have someone who actually understands what they are explaining. Great work!
Great video Emma, love what you have brought to the GCN team - in particular I like this one and the bike fit videos. Factual and informative, and easy to understand. Keep up the great work!
Bicycle Quarterly readers have known about this for years. On smooth roads, less pressure is just as fast as more pressure. On bumpy roads, wider tires with supple sidewalls (like the kind found on tubulars) combined with lower pressures are definitely faster. I've converted from 700x23 at 120 psi to 700x28 at 75 psi with no loss of speed and an increase in comfort. I consistently out-roll other cyclists on descents where no one is pedaling (well, I could be in a more aero tuck, but I'm not the heaviest).A side benefit is that I've gone from an average of 2 punctures per month (23mm at 120 psi) to one puncture maybe every six months (28mm at 75 psi). And cornering is faster on wider tires. I just love seeing other riders (competitors) on narrower tires running higher pressures! On one rainy ultra-distance event, I was the only rider in my classification who did not puncture! The only difference was tire width. One other note: I think you should reconsider the 60-40 weight distribution assumption. This is under static conditions. I air my tires based on worst case dynamic weight distribution. Anytime you're braking or out of the saddle (as in sprinting), weight distribution changes significantly, with more weight going to the front wheel. Put your bike on two bathroom scales, then hop on. Note the weight distribution while seated, and then when out of the saddle. As a result, I air my tires evenly.
Impressed you got to 29psi. Have ridden a flat before and it is fast enough, just the valve gets annoying and corners are like ice. One time it was both tyres at once, i was fed up with repairing them that day... I love firm rumbling tyres for the record, for the feel of whether i am getting a slow flat mostly. My favourite race tyre was the Panasonic Panaracer Race D. 150psi! Raced it all the time at that pressure and it was great, even rode club rides with it at that. Fast as you like. Only downside was it would strip the tread on the back wheel if you skidded a bit which is bad and no white side walls. Other issue was rims which couldnt cope with that pressure like my Zipps so they went. Did experiment with Michelins at different pressures. Went down to 70psi i think, rode up one half inch step in a cycle path and it gave an instant flat. Plenty of times rode with 60psi after punctures, one time with front and rear patched and it felt so slow and definitely not easy as your experiment showed. Settling for 95-100psi as the middle ground of my tyres limits 78-116psi. Reliability seems best note and a little less bumps. Dont think i would want zero bumps.
They updated their advice recently to not use less than 50% weight distribution on the front tyre pressure calc as the sidewall can 'collapse' under hard braking.
which is a crock, it's too short a period to be useful for rr, as a sometime 107kg rider I've never had very hard braking issues though use 55/45(r/f) split as I'm muscular upper with 47"chest. When braking for shortest stopping you learn to shift your weight backwards anyway so equalising tyre pressure at the front is tosh.
I'm old school and recently got back into regular cycling after a 20 year layoff - I'm 61 now. I would get my bike out occasionally during my layoff, usually when the Tour fired my enthusiasm but that would only last for a week or two. I got my bike out of the shed, fitted new brakes and tyres and of course I went for the skinniest tyres at the highest pressure on my old Raleigh 653 road bike! It was like riding a gatling gun! I have just bought a fixed gear bike for winter riding and it came with 28mm tyres on 700 rims. Out came the track pump and in went 110 psi! A very uncomfortable and tiring ride. After watching this video (and others) I have now reduced my tyre pressure to 90 psi - I weight about 95kg. It was like riding on air today and my average went up by 1 mph for seemingly no more effort. Besides that, my legs feel less tired after the ride today. Everything just seemed easier. Maybe it's psychological but hey, it's a win as far as I'm concerned.
63 kg rider. Rear: 25 mm tyre 5.4 bar. Front: 23 mm tyre 5.1 bar. Latex innertubes. 50 000 kilometers with no puncture, I try to avoid to bike in wet conditions.
12.5 stone (work it out!), 38mm tires, 50 rear 47.5 front. Today I ran them a bit softer for a bit of bribleway riding (only like a mile out of 40+) and on road the rear felt quite draggy. It was just over 45psi rear.
For me, it was a huge improvement in just a slight change of tire pressure from 100 to 110 psi. I weigh 95kg and I use 28C Schwalbe Durano tires with inner tubes. Those tires are so much plushier than 23C and the grip while braking and cornering is so much better. Never had a flat tire. Durano tires have "double down" carcass and they grip well even on wet roads. The bike's drivetrain is compact type meaning a larger cassette.
Great video and explanation. About two months ago, I did a similar tyre pressure experiment to find the optimum pressure for my tyres. I used a 3 mile traffic free segment, in North Bristol, not too far from where the GCN guys are based (www.strava.com/segments/17574664?filter=overall). The tarmac quality is average-to-poor, sadly typical of many UK roads! I held an average power of 160W, with a different pressure each run. I did one repeat. The best pressure was between 70 and 90 psi. However, as shown below, the differences were quite subtle and the same order of magnitude as the repeatability. 110psi: 10:20 / 16.9mph 90psi: 10:14 / 17.1mph 70psi: 10:16 / 17.0mph 50psi: 10:19 / 16.9mph Repeat: 83psi: 10:09 / 17.2 mph The tyres were 25mm Schwalbe Pro Ones and I’m about 70kg.
Super interesting. I'm obsessed with tire pressures because ideal pressure is different from setup to setup and person to person. I believe ideal pressure is finding a compromise between traction, rolling resistance, comfort, road feel, tire reaction, flat resistance, and ultimately preference. Personally, I'm a 70kg rider with a 10kg bike and 7kg backpack (plus 1.2L of water weight) on 28s with 75psi front and 85psi back for rough potholed streets and gravel roads.
Wow those roades look great, lol. Yes Emma I ride on rough roads daily. I ride 25 mm tyres, I have 6.2 bar rear tyre and 5.9 bar in front. Love the Nerd Science vids, bravo Emma👍
Really? I was just thinking how pleasing it was to see that Emma doesn't poke fun at people who can apply a bit of practical maths to real life situations by wearing those glasses or a white lab coat. It's perfectly normal stuff that nobody need be afraid of - why stigmatise it? (and by implication, those who enjoy it)
Emma is a top notch presenter! You could sense the nerves when she started, but shes all ready Si-level pro as far as I'm concerned. I could listen to physics lectures from those two all day long...
I never heard a word you said.....love your spirit and accent Emma. I got lost with the math quiz, when you drew a circle. Is it Venus or Mars with clouds ?
Great video. I'm big, If I tried 29psi my tire would get off and walk and I would be riding on rims. I like the outtakes at the end, more please. Cheers.
This brings me back to high school physics. Great video, excellent explanation, and very clear. Now I know all I'd ever need to know about tire pressures. Thanks!
Si science means wearing nurdy glasses. Emma's science means using charts and using complex words. My copy of 'Bicycling Science' by Wilson/Papadopoulos say's Emma's doing it right and Si isn't.... :.) I have gravitated towards bigger volume tyres and the condition of the roads I ride is just one reason - the smallest tyre I ride is 700x28 and they go all the way up to a set of Schwalbe Super Motos (2.4") that I managed to get working tubeless on my HT 29er and damned nice they are to at just 40psi on tarmac.
Nigel: Wow, that's high! With about 105-110 kg system weight (bike and me with pack), I run the 2,25" tubeless tires on my 29er HT with no more than 32 psi on the roads... That's as harsh as I want to feel those bumps!
Hi, interesting video, but I think you really are missing a piece of the physics. When you roll onto a bump, yes, it slows you down. But when you roll off the bump you should get that energy back again, unless there is more going on - and there is. There is some explanation here: janheine.wordpress.com/2016/08/08/the-missing-piece-suspension-losses/ Basically, the energy from the vibration of the road ends up being absorbed by all the parts of your body that can jiggle about, ultimately resulting in energy loss in your muscles through friction. How can we relate this to what happens when we go over a bump? I.e. why does rolling off the bump not give all your energy back? The answer is that when you hit the bump, the impact has lifts the bike and rider higher off the road. The weight applied by the bike on the bump on the way down is therefore lower than it was on the way up, because the bike has been lifted. If you draw the vectors, this means that the horizontal component of the force is less on the way down the bump, so you don't get all the energy back.You can imagine this getting more extreme until the bike is lifted fully off the ground and you have no help from the bump at all on the way down. The benefit of the softer tyre pressure is, therefore, that it reduces the motion of the bike, and your body up and down. This means the force on the bump is closer to equal on the way up and the way down, therefore resulting in lower suspension loss.
Very good video, but tire rolling resistance results from asymmetrical distribution of the vertical force across the contact patch (as explained, for example, in en.wikipedia.org/wiki/Rolling_resistance), rather than from the bulging of the tire.
Well done! Jan Heine of Bicycle Quarterly advocates 30 psi and 35+ mm tires for randonneur riding. Seems like ideal experiment would be on a variety of tire sizes, each run at “minimum no-pinch-flats” pressure. (Sounds complicated!)
I ride for pleasure only, mainly on canal and river towpaths which are often compacted gravel or cinder tracks, but far from smooth. I have what a few years ago was a top spec full susser mountain bike but was initially surprised how little the suspension did to smooth the ride; it really helped with serious imperfections on the track but made zero difference to the jiggling and vibration caused by surface roughness. So I played around a little and found that dropping the tyre pressure from around 50psi to 25psi made a huge difference and suddenly it was like riding a magic carpet; anything much over 25psi brought the vibration back. My initial thought was that this would require more effort from me to maintain the same speed, but (admittedly) subjectively the opposite seems true. My entirely empirical conclusion is that the suspension will deal with big hits, but that the tyre is responsible for dealing with the lower amplitude and higher frequency of vertical movements caused by small surface imperfections. In effect, I have two independent suspension systems working together. I'm going to make a guess that a hard tyre has little give and therefore a 1cm stone will cause the bike to move vertically up by nearly the same distance, meaning that as I'm pedalling, a portion of my effort goes into raising my entire weight (plus bike) up and down all the time, and with a poor ride as a side effect; a soft tyre may have more rolling resistance on a dead smooth surface, but on the towpath, that same 1cm stone will merely cause the tyre to deform which means that only the mass of a small area of tyre now has to be raised rather than the whole bike. A better ride is a bonus. The jury is out on my susceptibility to punctures though.
Hi Emma, can you do one about crank length comparison as well please? Like most short female riders, we are in between 170-165, even 160 at times. Just wonder how do you make a decision on a crank length that suits your need? Thanks! We love you, Emma!
I don't usually ride a road bike on such bad surfaces, and even when I don't have option to avoid it, I slow down to give myself enough time to avoid potholes, cracks and other pleasures. When road surface gets reasonably smooth, then I return to my usual speeds. So for me and my style of riding, higher pressure is better option. And yes, we do have enough of bad roads here in Croatia.
Oh my, there are times when I forget that GCN has other presenters. Cracken good job Dr. Emma! I wonder why some tires have both a maximum and a minimum pressure. That minimum would certainly keep me from going to 2 bar since my tyre has a minimum pressure of 7 bar.
pretty much exactly that! I mean what's the point of using decimals if you don't have to, might as well use the more precise increments in relation to what were adressing. Similar reasoning to not using inches for bike sizes and miles for ride length...
Suggestions for GCN does science that might be interesting: - Average power to maintain constant speed for an aero bike (frame, cockpit, helmet, wheels) vs traditional road bike in 1st wheel, 2nd wheel, 3rd wheel, 4th wheel. - Average power to maintain constant speed for an aero bike (frame, cockpit, helmet) vs traditional road bike (same wheels) at 0, 5, 10, 15 degrees yaw angle. This would be more enlightening than the data for a solo effort in 0 degrees wind provided by bike and component manufacturers.
Emma, I'm not sure how important the vertical and horizontal component of the pebble impact are, but I'm quite sure the essential question is which part of the impact the tyre takes, and which part is given towards the wheel, frame and rider. At medium pressure, the deflection is almost entirely absorbed by the tyre and because the tyre is elastic, most "spring"-energy is given back afterwards when the pebble is "through". For a hard tyre, the rider takes most, and as Jan Heine points out, we absorb this energy very effectively as heat in our body (ca. 20-100W under normal road conditions and speeds, but people driving tanks have been found to absorb as much as 2000W). However, at very low pressure, the tyre contacting the road is deflecting too much, almost exponentially increasing the rolling resistance with decreasing pressure (in line with the roller experiments in the lab). Silca has a very nice blog where they have published quite an amount of theory and measurements, where you can see how these two effects merge (tyre adsorption -or casing losses- dominating at very low pressures and body absorption -or suspension losses- at higher pressures). They did this for several tyre widths, and also for nylon vs cotton threads. My personal favorite is an app called Berto Tire Pressure, based on the work of Frank Berto, and on the algorithms of Philip Williamson. It gives good advice for tyre pressure for any weight and tyre size. It has a number of pre-programmed frame geometries for weight distribution, but can also be used to enter your own measurements of weight on front and backwheel. It works well for normal roads, for gravel and bad roads one could adapt "on the go"
Suscribirse a GCN en Español: gcn.eu/Suscribirse
Global Cycling Network Were Si's attempts at Spanish names the cause of this?
Love Emma's work.. GCN, any chance she could come back for special appearances?
PLEASE DO A VIDEO ON HIGH PRESSURE+FLEXIBLE FRAME VS LOW PRESSURE+STIFF FRAME
The test is done with a vibration measurement tool. A micro computer is connected to an accelerometer & the results can be made in near real time, under all conditions. This test has been done for years, testing bearing wear in aircraft Carier equipment.
that's a bloody good circle Emma
Talented eh?
Global Cycling Network indeed
For this reason alone I think Emma should do all the GCN science from now on :)
James Pancoast BYE, Si!!! Emma does cloudy roads. Likey
Omg, that’s a fantastic circle. I’ve taught art students for years and that is just damn good!
If you want a reliable test, do your comparisons on a downhill stretch of road, with no pedal input. Be sure to do this on a windless day. This will eliminate totally the uncontrolled variables of fatigue and wind.
One for next time!
Global Cycling Network Please test even lower pressures, small and lightweight riders can get away with just 1,2 bar (maybe even less) on a 25 mm tire.
Or also distance on a horizontal stretch of road with a certain speed and no pedaling
At my age uncontrolled variables of fatigue and wind are inevitable!
Actually the results are likely less informing then. You would like to have realistic results based on the influence it has on your performance. The effect of rough surfaces quite probably have a tiring effect on the rider because it's uncomfortable as Emma told, which contributes negatively to your performance.
2020 and I still don't no why don't we have new Emma's videos. Miss you dr. Pooley!
Gcn should do a video about How to draw a circle like emma
Hahahaha
She did as DaVinci!!!
Emma has been bringing more personality and comedy to her videos...I like!
Ben's Reviewsies totally agree
I loved this because she completely acknowledged the invalidity of her results and did some reeeeal physics!! Good job
Thanks Matt! What else would you like to see Emma investigate?
@@gcn LAZER BEAMS!
GCN does Science now has a proper scientist. I think for these segments, it might be appropriate to correctly refer to Emma as Dr. Pooley. The force diagrams make this physicist very happy.
Thanks Mike
Definitely an improvement on gcn does science in the past, but still flawed I think. You only considered rolling onto the bump, and not the force vectors rolling off it again. So, sorry, still haven't understood the whole dynamics of the rolling resistance /tyre pressure thing. Whilst you think about that, you could also try and answer, in a proper physics way, why cadence braking is in anyway advantageous.
Great video! I understand this is a simplification of the mechanisms involved, but I still have a few comments and hand-waving arguments. Early in the video it is said that the vertical movement is a waste of energy, which agree to. However, when decomposing the forces it is said that only the horizontal component causes loss (is unwanted). The vertical component will do work against gravity as the bike goes up - that is energy lost that will only partly be regained as the bike comes down again. One may argue that the net loss is little, but considering the small angles the vertical force will be much greater than the horizontal force, which may imply that the two are comparable.
The video also says that only the horizontal force makes the ride uncomfortable. Imagine riding a bike that was shaking only in the horizontal direction...
Emma is the gift that keeps on giving. Woman is a scientist, a good cook, an amazing time-trialist, climbs like a mountain goat, fluent spanish and italian speaker and very good freehand circle doodler (that's harder than you think). My god, what CAN'T this woman do?
You really upped the science part of „GCN does science“. 👍🏻👍🏻👍🏻👍🏻
Oh yes! Would be rude not to with Dr Pooley on board!
You could get right into the physics, especially the horizontal component vs vertical vs compression. Force “moments” are not difficult.
Emma does science!
Great video. Emma I love the way you have fitted into the GCN approach on the many issues of cycling.
I am 75kg, my bikes 8.5kg & I roll on 28mm tyres with tubes. I use 85-90 psi. Any more is bumpy & harsh & less makes climbing sluggish....
Cheers Kevin
_@Emma_ - Great video! The pump height at the end was hilarious. I have the opposite problem -- I'm tall and most pumps are too short for me. Lezyne offers some of its pump models in a "tall" version and I bought one. It's great and pumps more air volume per stroke.
Regarding the use of the word "pressure", I wish you hadn't made it the focus of the video. It's the only aspect to the excellent video that could be misleading to cyclists who are not schooled as well in the physics. What you are really trying to do is determine the ideal *compression* for your tyres when traveling on a rough road. As you rightly explained, the pressure you need to achieve the ideal compression will vary from cyclist to cyclist because it depends on their weight. And this was illustrated beautifully when you explained how the front tyre pressure needs to be less than the rear tyre because of the different weight on each wheel. But there's more to it than that. Another _equally important_ factor is the *volume* in each tyre. In other words, smaller tyres need higher pressure than larger tyres to achieve the same compression.
This is a challenging subject for most cyclists because -- if they want to get it right -- they must learn to think in terms of tyre compression, then select a pressure that achieves it based on the weight on each wheel *and* the size tyre on each wheel.
I use the _Berto Tire Pressure_ app (from Edison Gauss Publishing) for my Android smart phone to calculate the tyre pressure for smooth roads. It's also listed as _Bicycle Tire Pressure Calc_ in the Google Play store. Its calculations are based on a standard 15% compression of the tyre at the contact patch. However, it doesn't allow the user to change the compression amount and I'm not aware of any app that does. This is what we need -- an app that let's the user also select the desired tyre compression. GCN could provide a valuable service by testing different compression levels for various road surfaces from super-smooth indoor tracks to outdoor gravel roads and everything in between. It would also be nice to test some of the outdoor roads in rain to determine "ideal" compression levels for wet roads as well. You could produce the first ever tyre compression table for various road surface types. This is the information that would be needed for someone to update apps like _Berto Tire Pressure_ with easy-to-understand choices for the user. If GCN wanted to go all the way, you could create your own Tyre Pressure app that incorporates all of this information and sell it. If you do, make both an Android and an iOS version. I'll be your first customer!
D.Eldon how about 20$ pumps they work too
Thanks D.Eldon and interesting points as usual!
Well. I’ve cycled for over 50 years and now someone explains the science. Clearly and practically. Supper Emma. Thank you. Very interesting watching your videos. My partner is new to cycling. I’m pointing at all your videos as she always needs to know why !!
Awesome video. I'm no science genius so this was just the amount of detail to make me pay more attention to the pressure in my tires and to not over-inflate. I love Emma as an addition to GCN and it's her cycling credentials and acumen that make it so. Her demeanor, laughter and friendly smile are just a huge bonus.
Thanks Bill!
Just what I was dealing with today - I cut the pressure from 100 to 75 psi on my 700x23 tires for the rough pavement on the back roads - felt smoother and faster. No measurements tho, I’m not consistent enough. Great explanations and diagrams, I now understand it better and will continue to modify to find my ideal. Thanks for this vid.
Do you still ride a bike on 75 psi ?
I’m totally old school and pump up my tires over 100psi. This was great and those force diagrams that Emma drew bring me back to college physics lectures! Very well done and explained!
Thanks, @Emma really great sicence, great to have you as part of the team. I have done my own experiment but being a TOF your approach would be too variable for me as my energy dropped. I think I may have found a better way to check the effect which is:
1) Fine a suitable long gradient which is a rough as you want, potholed 12% Oxfordshire hill in my case
2) Little or no wind
3) Decide on a starting pace at the top of the hill (20Kmph)
4) Coast / Speed down in the same aero position and record either terminal speed or time down the hill. I went for terminal speed as it was very easy to reset.
The advantage of this method is it's very repeatable (if you ignore how tired you get cycling back to the top for the next run). I managed 3 before my tired old legs said enough. Dropping the pressure in my case saw the following
100psi = 69.7 Kmph
90psi = 70.2Kmph
80psi = 71.3Kmph
I will try still lower pressure when I can face the climb again.
(TOF = Tired Old Fart)
OK, I'm putting my own glasses on.
Regarding Fv, that's not just a story about comfort, or it's absence. Let's have a look at the entire system bike+rider BR. Fv imparts a vertical acceleration av to BR. Now BR is not a rigid structure, but has a lot of articulated components, some of them soft (tyres, rider). On these, av causes a deformation. Now, what you already mentioned about deformation of the tyre causing energy loss through heat dissipation is even more true for the body. There's much more mass (yes, even in the case of a lightweight like you, Emma), so there is actually much more loss!
The science of tyre pressure is balancing the losses in the tyre, which are lower with higher pressure, and the losses due to deformation of the elements of BR, which are lower with lower pressure.
As another commenter commented, I'm not sure about the effect of Fh, given as at least part of the loss is regained when rolling off the pebble, as Fv then points forward...
On one bike I ride with 50 mm wide slicks at about 4 bar (lower feels uncomfortable because of sideways movement you get with the rim-tyre combination at lower pressures). Now this is on a recumbent, so the weight distribution is different, far more on the front wheel, pretty much the reverse of a road bike.
My other recumbent has a 28 mm front tyre and a 35 mm rear tyre, usually at about 6 bar. The roads around here are pretty decent, but in rain I should decrease that pressure.
Then I have a velomobile, which also has 28 mm in front, 35 mm in the rear. 6 bar front, 5 bar rear. Rather high, but a recumbent trike gets to deal with far higher sideways forces.
My older velomobile could handle wider tyres, there I had 40 mm front, 47 mm rear. These tyres have a good puncture protection, but need to be inflated to a rather high pressure to get a decent rolling resistance (deformation is expensive on those tyres, but no punctures for about 28000 km is worth something).
On the grocery bike I ride between 5 and 2 bar, I usually forget to inflate those tyres until the low pressure gets really noticeable. Those are 47 mm tyres, so 2 bar is still fine.
Mechanical Engineering: Statics 101! A good job GCN and Emma! (but, yeah- randomize your trial runs and add duplicate runs! :) )
I've been experimenting with tire pressure for a while. I'm just over 200 lbs and find that 80 psi is fantastic. Used to run 100+ what a pain! 80psi gives lots of response and compliance. Bumps are not as harsh. I can ride much longer now!
I miss Matt...
Those clipping in moments...
Anti- Pops imagine Emma having a sudden misclip moment. Unexpected, then funny, then sort of bittersweet. Of course, Matt is ok and probably happy with the new job, but for us viewers, this has angst potential ) Plus, she is the only one on the crew now with the champion tricolor.
Its just not the same without him
Yep, i agree with y'all
There was meant to be a video about him ..
Matt Parsons that would be cool...
this is the first time I actually understand this in depth
like I had a pretty solid intuition but I needed the visual : )
GCN Science is so much better since Emma came on board
Dr Emma, that is!
Agree. Always enjoyed it beforehand, but she's definitely a welcome addition.
Dr. Pooley,
You took me back to dynamics class, 40 years ago! I hate to say it, but Dr. Pooley just makes this channel SUPER! More time riding next time Doc!
To GCN...Fabulous video. Whomever is responsible for the brilliant writing, directing, photography, and production, you have reached the pinnacle of GCN videos to date. Just EXCELLENT. Superb pleasure to watch. Emma, as always your the TOPS. Thank you, thank you, thank you...did I say thanks...
Cheers Richard, really great to hear you are enjoying the videos! Remember to let us know what else you would like to see on the channel
Great information. It's basically trial and error + experience that gives the best results. I've found over the years (on my recumbent trike) that 1.5" tires are the optimum width for trike + my mass. I've run 1.75" tires on the front and boy does that wear me out in a hurry (but it is the most comfortable on rough roads/trails). Not only do they have an extra 1/2" of rubber on the road but they also are 10 psi under the 1.5s. When riding the 1.5" tires at the same psi as the 1.75" tires, I've found that my average speed in the flats is about 3mph faster. Doesn't sound like much but that's nearly 30% faster! In a specific downhill, I could barely hit 30 mph on the 1.75's while I can hit nearly 40 mph on the 1.5's when running at 80 psi (max psi for the tires I use). I run the same routes all the time. So, it was fairly easy to figure out the best psi/width/size for my mass.
This was a fun video to watch. You should do a follow up with the differential equations to break it down ;)
50kg?! Very jealous! Emma’s presenting style is awesome by the way, funny and relaxed. The rest of you are funny in a different way... ;)
I used to ride at 100psi, gained some weight, started to get lots of snake bites (I call them vampire bites).
Were generally caused by hitting gravel on paved roads (common in towns)
Was told to raise pressure to 110 and this solved the problem. I also tend tyo ride off saddle to better distribute weight in areas where there is gravel on the paved road.
So lowering tyre pressure to save a few seconds would result in losing much more time fixing punctures.
Spain and Switzerland 120 psi
France 110 psi
Italy and Australia 100 psi
Uk 30 psi
UK hahahahaha
clearly you never ride through French towns and cities, the roads are massively worse than here on average.
@@ynotnilknarf39 clearly you dont understand a joke
I use 90 psi in australia not too soft not too hard
USA 15 psi
Back in the 1970's my silk sew-up Clement Del Mundo tires gave me excellent grip on the wet or dry roads in Santa Cruz CA when I was training 400 miles a week. I miss that kind of performance.
great vid Emma!
i tried finding an optimal pressure for my Specialized Roubaix with 28mm gp s4000ii tyres. i'm not a lightweight rider but came to finding around 70psi was good for me and my commute to uni with differing surfaces. 90-100psi just rattled me around and found myself fatiguing earlier in my rides. i also ride a stiff specialized tarmac on 25mm vitorria pro's at 95 -115 psi and find it great, not as comfy as the 28mm's on the more compliant Roubaix of course.
Glad you enjoyed the video
this video is the best video i have ever watched in gnc youtube channel. thank you lady!
Pre- Emma GCN was pretty damn good. Now GCN is just freakin' awesome.
blairrob cheers!
I'm not sure how much of this I would have understood if I hadn't just finished two years of physics. But it's really great to have someone who actually understands what they are explaining. Great work!
Cheers!
Great video Emma, love what you have brought to the GCN team - in particular I like this one and the bike fit videos. Factual and informative, and easy to understand. Keep up the great work!
Thanks Jamie, glad you enjoyed the video
Emma is a welcomed addition... Hearing her talk (tech) is always a pleasure....
Pantwone 👍
Bicycle Quarterly readers have known about this for years. On smooth roads, less pressure is just as fast as more pressure. On bumpy roads, wider tires with supple sidewalls (like the kind found on tubulars) combined with lower pressures are definitely faster. I've converted from 700x23 at 120 psi to 700x28 at 75 psi with no loss of speed and an increase in comfort. I consistently out-roll other cyclists on descents where no one is pedaling (well, I could be in a more aero tuck, but I'm not the heaviest).A side benefit is that I've gone from an average of 2 punctures per month (23mm at 120 psi) to one puncture maybe every six months (28mm at 75 psi). And cornering is faster on wider tires. I just love seeing other riders (competitors) on narrower tires running higher pressures! On one rainy ultra-distance event, I was the only rider in my classification who did not puncture! The only difference was tire width.
One other note: I think you should reconsider the 60-40 weight distribution assumption. This is under static conditions. I air my tires based on worst case dynamic weight distribution. Anytime you're braking or out of the saddle (as in sprinting), weight distribution changes significantly, with more weight going to the front wheel. Put your bike on two bathroom scales, then hop on. Note the weight distribution while seated, and then when out of the saddle. As a result, I air my tires evenly.
Luis Bernhardt I'm on 100 psi with 25's. It's in the middle of yours
Impressed you got to 29psi. Have ridden a flat before and it is fast enough, just the valve gets annoying and corners are like ice. One time it was both tyres at once, i was fed up with repairing them that day...
I love firm rumbling tyres for the record, for the feel of whether i am getting a slow flat mostly. My favourite race tyre was the Panasonic Panaracer Race D. 150psi! Raced it all the time at that pressure and it was great, even rode club rides with it at that. Fast as you like. Only downside was it would strip the tread on the back wheel if you skidded a bit which is bad and no white side walls. Other issue was rims which couldnt cope with that pressure like my Zipps so they went. Did experiment with Michelins at different pressures. Went down to 70psi i think, rode up one half inch step in a cycle path and it gave an instant flat. Plenty of times rode with 60psi after punctures, one time with front and rear patched and it felt so slow and definitely not easy as your experiment showed. Settling for 95-100psi as the middle ground of my tyres limits 78-116psi. Reliability seems best note and a little less bumps. Dont think i would want zero bumps.
Those two road repair guys did more in 10 seconds, than most of the road crews in the UK do in a day!!!
am I the only one who thinks that she's absolutely adorable?
also, very interesting video btw! :)
Jan Heine from Bicycle Quarterly did a lot of extensive testing on pressures and widths. You should have him on as a guest.
They updated their advice recently to not use less than 50% weight distribution on the front tyre pressure calc as the sidewall can 'collapse' under hard braking.
which is a crock, it's too short a period to be useful for rr, as a sometime 107kg rider I've never had very hard braking issues though use 55/45(r/f) split as I'm muscular upper with 47"chest. When braking for shortest stopping you learn to shift your weight backwards anyway so equalising tyre pressure at the front is tosh.
I'm old school and recently got back into regular cycling after a 20 year layoff - I'm 61 now. I would get my bike out occasionally during my layoff, usually when the Tour fired my enthusiasm but that would only last for a week or two.
I got my bike out of the shed, fitted new brakes and tyres and of course I went for the skinniest tyres at the highest pressure on my old Raleigh 653 road bike! It was like riding a gatling gun!
I have just bought a fixed gear bike for winter riding and it came with 28mm tyres on 700 rims. Out came the track pump and in went 110 psi! A very uncomfortable and tiring ride. After watching this video (and others) I have now reduced my tyre pressure to 90 psi - I weight about 95kg. It was like riding on air today and my average went up by 1 mph for seemingly no more effort. Besides that, my legs feel less tired after the ride today. Everything just seemed easier. Maybe it's psychological but hey, it's a win as far as I'm concerned.
why is Emma no longer with GCN?one of the best apearences in this show
Road-Racing.pl Official Channel , I was asking myself the same.
Hey Emma (and GCN)... this is fabulous! Love and respect from Mumbai, India!
Do you ride on rough roads? Let us know what psi/bar you choose.
63 kg rider.
Rear: 25 mm tyre 5.4 bar.
Front: 23 mm tyre 5.1 bar.
Latex innertubes.
50 000 kilometers with no puncture, I try to avoid to bike in wet conditions.
95 kg rider
Rear: 28 mm Conti GP 4000 4 season 6.0 bar
Front: 25 mm Conti GP 4000 6.5 bar
weight 75 kilos - riding 6 and 6,5 on 25 mm, and 5 and 5,5 on 28 mm, everything above 7 is really uncomfortable
I am 70kg.
25mm Conti GP 4000 II front and rear at 100 psi
12.5 stone (work it out!), 38mm tires, 50 rear 47.5 front. Today I ran them a bit softer for a bit of bribleway riding (only like a mile out of 40+) and on road the rear felt quite draggy. It was just over 45psi rear.
For me, it was a huge improvement in just a slight change of tire pressure from 100 to 110 psi. I weigh 95kg and I use 28C Schwalbe Durano tires with inner tubes. Those tires are so much plushier than 23C and the grip while braking and cornering is so much better. Never had a flat tire. Durano tires have "double down" carcass and they grip well even on wet roads. The bike's drivetrain is compact type meaning a larger cassette.
27.5" rules!!!!
Oh, wait, wrong channel...
Until 30.5's come out!
36er is the king
Great video and explanation. About two months ago, I did a similar tyre pressure experiment to find the optimum pressure for my tyres. I used a 3 mile traffic free segment, in North Bristol, not too far from where the GCN guys are based (www.strava.com/segments/17574664?filter=overall). The tarmac quality is average-to-poor, sadly typical of many UK roads! I held an average power of 160W, with a different pressure each run. I did one repeat. The best pressure was between 70 and 90 psi. However, as shown below, the differences were quite subtle and the same order of magnitude as the repeatability.
110psi: 10:20 / 16.9mph
90psi: 10:14 / 17.1mph
70psi: 10:16 / 17.0mph
50psi: 10:19 / 16.9mph
Repeat:
83psi: 10:09 / 17.2 mph
The tyres were 25mm Schwalbe Pro Ones and I’m about 70kg.
Since the roads are well maintained in the Netherlandz, i opt for ~6.5 bar in my back wheel and ~5.5 bar in my front wheel.
Super interesting. I'm obsessed with tire pressures because ideal pressure is different from setup to setup and person to person. I believe ideal pressure is finding a compromise between traction, rolling resistance, comfort, road feel, tire reaction, flat resistance, and ultimately preference. Personally, I'm a 70kg rider with a 10kg bike and 7kg backpack (plus 1.2L of water weight) on 28s with 75psi front and 85psi back for rough potholed streets and gravel roads.
"This video isn't about the risk of slipping out"
I've seen that video. It's not on RUclips
Well played
I love your honesty and your pick of music .
Great content Emma.
Can you do test runs on smooth asphalt as well?
Would be interesting to see combinations of tyre width and pressure.
That's a really good shout Jans!
Wow those roades look great, lol. Yes Emma I ride on rough roads daily. I ride 25 mm tyres, I have 6.2 bar rear tyre and 5.9 bar in front. Love the Nerd Science vids, bravo Emma👍
I think a GCN lab coat should be on order for the science bits 🤣
Maybe one for the GCN shop!
Really? I was just thinking how pleasing it was to see that Emma doesn't poke fun at people who can apply a bit of practical maths to real life situations by wearing those glasses or a white lab coat. It's perfectly normal stuff that nobody need be afraid of - why stigmatise it? (and by implication, those who enjoy it)
Can't imagine the rest of the team being able to explain that one quite so well! Excellent video :)
At 2 bars, my tires will probably fall of the rim. I usually go at 6.5-7 bar rear and 0.5 bar less at front. Vittoria Corsa 25mm
Takes me back to first year uni, breaking up force vectors into their components. Nice video and circle :)
If you'd taken ten minutes, you could have weighed in at 48kgs, Emma.
Emma is a top notch presenter! You could sense the nerves when she started, but shes all ready Si-level pro as far as I'm concerned.
I could listen to physics lectures from those two all day long...
So the bottles are being used as finish posts!
#science
I never heard a word you said.....love your spirit and accent Emma.
I got lost with the math quiz, when you drew a circle. Is it Venus or Mars with clouds ?
Rough ground, aka, the British road network :(
grandad1982 most sections of road in the UK give carrefour de l'abre a run for its money.
come to the netherlands then! all roads smooth af. (:
How can you pump this wheelset to 8.2 Bar, when Vision recommend 7 Bar maximum?🤷🏻♂
Great video. I'm big, If I tried 29psi my tire would get off and walk and I would be riding on rims. I like the outtakes at the end, more please. Cheers.
sbdstudent Glad you enjoyed the video!
Science humour clarity - love you GCN team
I've been telling people for years to try less pressure. No one listens.
Maybe here's your ammunition?
What?
I love this video, definitely superb explanation on force vectors on a bicycle wheel. I should use this as an example on a class project.
Great video again Emma. You doing great at gcn .👍
Thanks Mark
This brings me back to high school physics. Great video, excellent explanation, and very clear. Now I know all I'd ever need to know about tire pressures. Thanks!
Si science means wearing nurdy glasses. Emma's science means using charts and using complex words. My copy of 'Bicycling Science' by Wilson/Papadopoulos say's Emma's doing it right and Si isn't.... :.)
I have gravitated towards bigger volume tyres and the condition of the roads I ride is just one reason - the smallest tyre I ride is 700x28 and they go all the way up to a set of Schwalbe Super Motos (2.4") that I managed to get working tubeless on my HT 29er and damned nice they are to at just 40psi on tarmac.
I tried buying “A Brief History of Bicycling” by Stephen Hawking on Amazon and they haven't got it - disgusting - not even a Kindle copy.
Good science communication isn't about using complex charts and words. It's about getting across the concept.
Nigel: Wow, that's high! With about 105-110 kg system weight (bike and me with pack), I run the 2,25" tubeless tires on my 29er HT with no more than 32 psi on the roads... That's as harsh as I want to feel those bumps!
I love where this is all heading. It's great to have Emma on GCN.
I really dig this.
Thanks A C
I know that there are 3 new presenters but are Dan and Simon not doing any practical fieldwork videos anymore...? :(
I'm actually surprised this is the first tire pressure gcn does science video. That's great Emma!
What an awsome piece of engeneering!!! Loved every bit! Congrats.
Hi, interesting video, but I think you really are missing a piece of the physics. When you roll onto a bump, yes, it slows you down. But when you roll off the bump you should get that energy back again, unless there is more going on - and there is. There is some explanation here: janheine.wordpress.com/2016/08/08/the-missing-piece-suspension-losses/
Basically, the energy from the vibration of the road ends up being absorbed by all the parts of your body that can jiggle about, ultimately resulting in energy loss in your muscles through friction.
How can we relate this to what happens when we go over a bump? I.e. why does rolling off the bump not give all your energy back? The answer is that when you hit the bump, the impact has lifts the bike and rider higher off the road. The weight applied by the bike on the bump on the way down is therefore lower than it was on the way up, because the bike has been lifted. If you draw the vectors, this means that the horizontal component of the force is less on the way down the bump, so you don't get all the energy back.You can imagine this getting more extreme until the bike is lifted fully off the ground and you have no help from the bump at all on the way down.
The benefit of the softer tyre pressure is, therefore, that it reduces the motion of the bike, and your body up and down. This means the force on the bump is closer to equal on the way up and the way down, therefore resulting in lower suspension loss.
Thanks Emma, and yes, that is an exceptionally good circle!
International roughness index? Who knew?
Very good video, but tire rolling resistance results from asymmetrical distribution of the vertical force across the contact patch (as explained, for example, in en.wikipedia.org/wiki/Rolling_resistance), rather than from the bulging of the tire.
GCN how do I relieve horrific arse pain after a long road bike ride? Please help my buttocks are in agony
HazardousFromage do you have padded cycling shorts??
HazardousFromage Butt secs
sound like you have bike fit issues
See rule #5
Squats. More cushion for the pushing 🤣
Well done! Jan Heine of Bicycle Quarterly advocates 30 psi and 35+ mm tires for randonneur riding. Seems like ideal experiment would be on a variety of tire sizes, each run at “minimum no-pinch-flats” pressure. (Sounds complicated!)
More physics with Professor Pooley
What else would you like Emma to look at?
I ride for pleasure only, mainly on canal and river towpaths which are often compacted gravel or cinder tracks, but far from smooth. I have what a few years ago was a top spec full susser mountain bike but was initially surprised how little the suspension did to smooth the ride; it really helped with serious imperfections on the track but made zero difference to the jiggling and vibration caused by surface roughness. So I played around a little and found that dropping the tyre pressure from around 50psi to 25psi made a huge difference and suddenly it was like riding a magic carpet; anything much over 25psi brought the vibration back. My initial thought was that this would require more effort from me to maintain the same speed, but (admittedly) subjectively the opposite seems true. My entirely empirical conclusion is that the suspension will deal with big hits, but that the tyre is responsible for dealing with the lower amplitude and higher frequency of vertical movements caused by small surface imperfections. In effect, I have two independent suspension systems working together. I'm going to make a guess that a hard tyre has little give and therefore a 1cm stone will cause the bike to move vertically up by nearly the same distance, meaning that as I'm pedalling, a portion of my effort goes into raising my entire weight (plus bike) up and down all the time, and with a poor ride as a side effect; a soft tyre may have more rolling resistance on a dead smooth surface, but on the towpath, that same 1cm stone will merely cause the tyre to deform which means that only the mass of a small area of tyre now has to be raised rather than the whole bike. A better ride is a bonus. The jury is out on my susceptibility to punctures though.
I can't do any more physics My brain hurts
🤓
Hi Emma, can you do one about crank length comparison as well please? Like most short female riders, we are in between 170-165, even 160 at times. Just wonder how do you make a decision on a crank length that suits your need? Thanks! We love you, Emma!
But more tyre pressure means easier broken wheel
I don't usually ride a road bike on such bad surfaces, and even when I don't have option to avoid it, I slow down to give myself enough time to avoid potholes, cracks and other pleasures.
When road surface gets reasonably smooth, then I return to my usual speeds. So for me and my style of riding, higher pressure is better option.
And yes, we do have enough of bad roads here in Croatia.
100 psi 👍
👍
Oh my, there are times when I forget that GCN has other presenters. Cracken good job Dr. Emma! I wonder why some tires have both a maximum and a minimum pressure. That minimum would certainly keep me from going to 2 bar since my tyre has a minimum pressure of 7 bar.
Glad you enjoyed the video
Can we unanimously agree to stop using BAR as measurement!! it's just inferior to psi
Theodore Kincaid Agree, its the obsession with making everything metric when there's nothing wrong with using imperial.
True I'm a metric guy out ease of use, but bar is just annoying to use for low pressure stuff like tires...
pretty much exactly that! I mean what's the point of using decimals if you don't have to, might as well use the more precise increments in relation to what were adressing. Similar reasoning to not using inches for bike sizes and miles for ride length...
Theodore Kincaid
Why not speak of mbar then?
Why not use kilopascals. Most other metric pressures are in kPa. 80psi is 550kPa
This video is brilliant and informative!! Well done Emma and team 👍🏻
İ dont understand you pls result table added. Because my English is very bad. 😒
Suggestions for GCN does science that might be interesting:
- Average power to maintain constant speed for an aero bike (frame, cockpit, helmet, wheels) vs traditional road bike in 1st wheel, 2nd wheel, 3rd wheel, 4th wheel.
- Average power to maintain constant speed for an aero bike (frame, cockpit, helmet) vs traditional road bike (same wheels) at 0, 5, 10, 15 degrees yaw angle.
This would be more enlightening than the data for a solo effort in 0 degrees wind provided by bike and component manufacturers.
Too many people on here kissing Emma’s ass just because she’s female. That test was substandard but a good try anyway.
CARDIOMACHINE1 Its not because shes female, its her presenter style and smarts that make good.
And you are salty because.......
+John Schaffer bravo
Well said Mr Schaffer.
She's articulate and brings a different approach than the others. It's refreshing. Cheer up, mate
Thanks Emma...... I love your detail in how you dig into something nice job👍
Great video! Do the same for cyclocross bike and a 75 kg person.
nice to see emma go into detail and teach people a bit of science :)
woolfel Cheers
Emma, I'm not sure how important the vertical and horizontal component of the pebble impact are, but I'm quite sure the essential question is which part of the impact the tyre takes, and which part is given towards the wheel, frame and rider.
At medium pressure, the deflection is almost entirely absorbed by the tyre and because the tyre is elastic, most "spring"-energy is given back afterwards when the pebble is "through". For a hard tyre, the rider takes most, and as Jan Heine points out, we absorb this energy very effectively as heat in our body (ca. 20-100W under normal road conditions and speeds, but people driving tanks have been found to absorb as much as 2000W).
However, at very low pressure, the tyre contacting the road is deflecting too much, almost exponentially increasing the rolling resistance with decreasing pressure (in line with the roller experiments in the lab).
Silca has a very nice blog where they have published quite an amount of theory and measurements, where you can see how these two effects merge (tyre adsorption -or casing losses- dominating at very low pressures and body absorption -or suspension losses- at higher pressures). They did this for several tyre widths, and also for nylon vs cotton threads.
My personal favorite is an app called Berto Tire Pressure, based on the work of Frank Berto, and on the algorithms of Philip Williamson. It gives good advice for tyre pressure for any weight and tyre size. It has a number of pre-programmed frame geometries for weight distribution, but can also be used to enter your own measurements of weight on front and backwheel. It works well for normal roads, for gravel and bad roads one could adapt "on the go"
please come back to GCN .You are the best GCN presenter