Installing a 39T chainring on a Brompton
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- Опубликовано: 29 июл 2024
- One of the questions we get frequently asked is ... how can I further reduce the gearing on my Brompton
The Brompton A Line B75 comes with a 44T chainring (and Brompton don't make a smaller one)
The Brompton C Line Explore (6 speed) comes as standard with a 50T chainring and an Urban (2 speed) comes as standard with 54T
This change can only be made to the "spider" crankset - not the older fixed crankset
To see the effects of changing Brompton gearing - check out the Brompton Gear Calculator
xldev.co.uk/bgc.html
The video consists of several parts
0:00 | Intro
2:15 | Removing your old chainring
4:33 | Installing the new chainring
5:47 | Shortening the chain
8:04 | Test ride
8:46 | Outtakes
The 39T SRAM chainring we used was:
brilliantbikes.co.uk/chainrin...
Chain ring tool:
brilliantbikes.co.uk/bike-too... 
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I have had a 39T chainring on my Bromptons for years. I have always thought that Bromptons are overgeared for anything other than short commutes in flat cities, even with the 44T option. Thye really should offer this as an option (with chainguard) instead of just messing about with different colours and pretending that this gives more choice.
I use a 54. I'm dead 'ard. For it is speed I need. A life time of racer's precludes reductions. Brommies can't descend a 12-20 km descent and I ride it as a single speed.
My Brompton had the 50t chainring, yuck for climbing up the hill back home. So I replaced it with 44t chainring, now thinking of dropping it down to the 39 teggies chainring as I'm sure that hill is getting steeper. (BCD) Bolt Circle Diameter of 130 mm. Thanks for this video and stick with the 50t if your legs are borrowed from Chris Boardman.,
Eight years ago when I got my Brompton it had a 50 tooth chain ring, a couple of years later I went to a 44 tooth, this year I put a 40 tooth chain ring on. My chain rings are getting younger and I'm getting older.
They're just losing their teeth!
My Brompton was a 2Sp, which I converted to 6sp, and subsequently replaced the dinner plate sized 54T chainring with a 39T one: This absolutely revolutionised the bike, and made it SO much more capable. It spins out on descents at about 45kph, but at any faster than that I'd rather be freewheeling anyway! I think the minimum size that can be fitted is 38T?
On the subject of the lack of the chainguard on the non-standard chainrings, one of my first 3D printer projects was to design one of these. It simply fits on with a set of M5 bolts that go through the middle of the chainring bolts themselves.
That is a great idea, I also have true the 39t and only reason of going back to 44 was the chain guard … but can you share the file of the 3D printed one that you made?
@KarlOnSea I would also love to have that 3D print file!
Since I have my S6L-X, I’ve changed the front chainring for a 39T. It’s a real game changer for those who live in hilly areas. I’ve done another great change: adding a third sprocket and converted my 6 speeds Brompton to a 9 speeds one. It’s even better now.
What 3 rear sprocket sizes do you now have?
@@SimonBrowneNZ 12-15-19T and it’s from TI Parts
Wow, well done. Whats your minimum gearing now?
I might do this. Even with a 44T chainring, I rarely use 3 high or 3 low.
Been using 39t for few years. Previously not really using the 3+ gearing when I was with 44t or 50t but now I am able to use 3+ to get 35-40km/h plus I am able to get up hilly road where I am staying ❤
I changed from the default 50T to the 44T back in the day when my Brompton was named M6L. I wanted to order with the 44 from the start but the vendor at the bike shop looked at me like I had just asked to be shot in the face or something, and somehow convinced me that lowering the gearing would "make me feel like a hamster on a spinning wheel". I listened to him because, why not? He's got the experience and I had never ridden a Brompton before. He was wrong of course. And the default 50T made me feel all kinds of discomfort. I'm a very short woman (I'm 5ft). With very short legs on top of that. And the 50T was completely inadequate for my type of cycling, my cadence, my fitness, EVERYTHING!! So much so, that I was NOT enjoying my bike rides at all, and kept wondering what was going on that felt so wrong 😓The 4th gearing always felt too loose and the 5th too hard. I didn't even try the 6th. Well. Maybe once. Just to see how it felt like.
Changing to the 44T has been THE BEST modification I made to my beloved Brompton. I use consistently ALL of the gears and my cadence improved a ton. Yes you lose some speed on your highest gear but, how fast do I want to ride anyway? Having a lower first is more important to me
You might even like to go lower with a 39T chainring.
Many thanks both for watching! So glad you made the change and you’re happy with it!
Great video. Love the way you use the fold mechanism to insert the chain into the tensioner. Until now I linked the chain under tension which is not great-
On my electric Brompton I put a larger chainring on as I was forever spinning out. My S6R has been kept at 50 tooth. I hadn’t realised that more modern bikes have a 52 tooth chainring. Thanks as always for your film.
I also find that my electric C-Line is too easy to pedal even with no battery/motor help. I live in a fairly flat area and rarely use anything other than 3+ or 3-. Would a larger chain wheel help and what size would you recommend?
Very helpful video. I am suprised there wern't more bloopers mind you! Love your channel 🙂
I changed to a Thorn 39T when I did the C2C a couple of years ago. 6 speed bike, so it helped. Still have a fairly hilly commute to work, so I've left it on.
Fitted a 39t in the summer to get around the Cotswolds. It makes a huge improvement. The 44t was seemingly for velodromes, and the 50t for Chris Hoy.
The 39t could possibly negate the six speed Bromptons...
To sad that Brompton doesn’t offer a chain guard for the 39T chainring. Nice presentation as always 💐
Thank you for watching!
First mod i did to my 6 spd brompton was to install an old nos durace crankset i'd had lying around for years.
Depending where im riding i manually switch between the large and small chainrings. Works a treat.
Congratulations. You are a great brompton mechanic
Thanks for watching!
I changed to 44t about 4 years ago (hilly area ) I left a review on the Brompton website and because it was the first, Brompton sent me two free inner tubes !!
I still use it but mainly level 1 assist on my e brommie theses days
Excellent video! Thank you for this. It’s very helpful.
Thank you for watching!
Very well explained! Thanks you
Very informative again.👍
Many thanks for watching!!
Very informative video .....thank you 😊
Thank you for watching!
sharing my implementation here, i've gone to the limit of 38T. the chain just comes into contact with the spider arms but I haven't had any problems. for the chain guard, I fashioned one out of a 2mm kitchen cutting board (kitchen boards are oil/acid resistant by design - available at my local $2 store). attached it on to the 4 chainring bolt hexagonal holes using "rubber mushroom plugs" (don't know the proper name). they attach snugly when the round tails (of mushroom plugs) are squeezed into the hexagonal allen bolt holes. been riding it so for a year, 2 bikes, haven't fallen off.
do you have a photo please?
Brilliant!
Thank you and thank you for watching!
Nice. Did this last week 😉 But because of the bad weather, I haven't been able to do a test drive on some of our local hills yet 🤷♂
Lefty Lucy is a new one to me, never heard that before. I'm getting old and I'm going to have to do this to my Brommie soon. Getting old sucks.
I’m running an H&H 40T chainring on a BWR six-speed, with rear sprockets of 13t and 18t. Lowest gear is 23.6 gear inches. The intervals between gears are not even, but you get used to that. I’ve had two dozen Bromptons since the 90s, and still can’t understand why Brompton over-gear their bikes so much.
I have that too and agree. For flat cities it might be OK on the low end, but a 50t on 3+ would be too quick for my taste.
Great timing, this has been on my to do list for over a year 😂 I can't believe how long the stock gearing is. Waaaay over the top for 99% of us.
I used a T39 (an old Shimano 105 chairing) during my last journey in England
I have a 39 tooth chainring on my Brompton. I use it around town and on the occasional bike camping trip. I have been tempted to file the ends of the spider just a bit so I could use a 38 tooth. After I put the 39 on, I had a bit of problem with the chain coming off. So I switched to a chainring with wide-narrow teeth and it has never come off after that
"Just do one!" 😂😂😂 Love it. 😂
Stronglight chainsets (£31 from Spa cycles) are a direct swap for older non spider bikes. I have a 44T and a 38T I use here in hilly Bradford. Much cheaper than Brompton OE.
Hi, can you talk about changing to a s-handle bars or straight bars from a h - handle bars, this is something I am looking to do, I know you have to change the stem also 👍🏾 great content as always 💯
I use a 53 / 39t dual front. The 39 is a backup ring for overseas for manually changing with my foot lol
I just did one!
This is great... nice video. 2 questions... what is the percentage reduction in gearing from 50->39T on a 6 speed and how did you know to remove 4 links from the chain?
Yes. A-Line has 44-15
B75 has 44/39 double and 25. Expedited 6 speed has 44/39 and std. P-Line has 46 and 21,19 first and second gear. I live at the top of the highest hill in town!
Wow that’s lots of modifications! What did you add for the double?
@@brilliantbikes
MTB crank with 39/44. It takes the gearing down a notch, my preferred gear is 2nd (direct drive) I normally select the chainring before setting off.
I did a video.
The other thing I don’t use any gear calculator I just count rotations on the hill between lamp posts.
Heresy! Sheldon Brown bicycle gear calculator is the go to calculator!
Sorry! I’ll make sure I link to him next!
Thanks for watching!!
As an owner of a 2019 SuperlightM6LXBrompton (Presently, below 9 kilo, original mudguards and still falling, with a little more work!) I did at first wonder for what use I had the low gears, of 6, till I met a steep serpentine road going up and I had to walk on top! I have seen a double chainring for being mounted in front, but honestly, I hardly think I have any use for more - low gears. Finn. Denmark
Thanks for watching! I have had the odd I need to walk moment!
@@brilliantbikes It was part of a road with crossing "cattle tubes" over the road, which I had to cross on foot, or through a gate to the side, up to a former Lighthouse on top!
And going down again, I was (very) scared that my brakes couldn't manage the braking of the small and high speed rotating wheels from - very high speeds to zero, many times before crossing the tubes on foot!
But my Brompton, and its brakes never let me down and made me reach the bottom again, safely!!!! Finn. Denmark 😃
Hello. Great video and the change seems straightforward. But I do have one question. You change from a 50t to a 39t and remove 4 links on the chain. How do you determine how many links to remove (or add) when changing to a smaller chainring (or larger)? I currently have the 50t and am thinking of trying the 44t.
Great question. For what my experience is worth you can measure this in chain links eg 106, 104 , 100 or in inches .
Count your teeth on front largest chain ring , and your largest cog on the cassette.
Then measure the length of the chain stay on your bike
so...
Once done there's an equation for length in inches which once measured you round up to the nearest link. (You can always shorten the chain if you break it too short)
The method is
(
(ChainRingTeeth/4) +
(CassetteTeeth/4) +
(ChainStayLength * 2) +
1.0)
* 2
= Chain length in inches.
Take a tape measure to your new or old chain and measure to the nearest breakable link and round up if unsure or on wide cassettes/tensioners. Eg SRAM Xx1 says to add two for the long derailleur arm on a 1 X chainring
So assume your Brompton is being set up for 38T front chainring , with 16 largest cassette ring and a 16" chain stay length.
38T = (38T/4 + 16T/4 + 16"CSL+1)*2 = 93L but round up to 94Links.
I hope this helps. It's great to have an outgoing chain to practice on then use a new chain once confident.
Great video, lovely and clear guidance. One question, what is the formula for working out how many links to remove from the chain?
It should be around a quarter of the change in the number of teeth on the ring, though since it has to be a whole number of links you obviously can't always be exact.
50T to 44T is a difference of six teeth. The chain touches half the circumference (or a bit more) of the chainring, so we need to shorten it by half (or a bit more) of 6 teeth - say 3-4 teeth. Each link spans two teeth, so divide by 2 again, and two links is the only practical option. Worked well for me.
50T to 39T is 11 teeth, so we should shorten the chain by 5½, 6 or 7 teeth, so I'd say three links. But four links clearly works fine, and Hannah is the expert!
I find with my 6 speed the gaps between gears are too big and even as a roadie I rarely use top gear as it’s too high
I would ignore the comment about not re-using quick links, I have re-used them dozens of times !
Many thanks for the comment and for watching!
Thank you for this. I have previously changed to a 44" but had to resort to trial and error for how much chain to remove. Is there a formula or a look-up chart you could share which shows how many links for how many teeth?
The difference between 44 and 39 teeth is 5 teeth, which corresponds to 5 chain links. However, as you have to remove an even number of chain links, you will remove 4 individual chain links.
From 50 teeth to 39, the difference is 11 teeth, so 10 chain links have to be removed.
6:25 4 links removed. The chain sits on half of the chain ring.
I'd say the maths is 25 - 19½ = 5½ links
6 would be closer,,,
But taking out 4 is a good first step rather than 6 and then maybe having to add 2 back in if it is too tight.
Great video. I love your videos and clear explanations!
I also changed mine to a 39T but did not shorten the chain. I don't see any problems for the moment. Is it really necessary to shorten the chain? Thanks!
Thanks for watching!
You should shorten the chain so it does not slap and it is more likely to fall off when you fold it. The chain tension is designed to keep it tight, but the chain being the correct length will help more
I love my new chainring ❤ I live on a very steep hill so this video was a godsend. Also looks sick! However, my chain slips when I back pedal - did I do something wrong there?
Does it slip on the chain ring? Did you shorten the chain?
Looks like the chain rubs the rear triangle when folded. I guess it doesn't do that with bigger ring? Anyway I would add some protection tape on the frame.
I replaced my old chainring bolts with Ti ones, as the old ones were rusting.
Nice video, really informative, thanks! I think I might do this or something similar for a hilly ride I'm planning. My only concern is the lack of a chain guard on the 39T. H&H makes a 40T chainring that has an integrated chain guard and that will fit the Brompton. I wonder if anyone has tried it? I doubt it'll be much different from the 39 T except for the chain guard.
Oh, and can anyone comment on what it's like to pedal on the flats with such a small chainring?
We have found the 39 quite good, and you’re right I can’t imagine much difference between the 39 and 40.
Thanks for watching!
That was quick! I think I'll be doing this myself. I just can't understand why Brompton overhear their bikes!
Thanks for watching! I generally find them OK but the smaller chain ring will help with the hills.
I think Bramptons are overgeared. If you’re used to a faster cadence the standard gearing doesn’t make sense.
Exactly what I’ve been thinking about doing! Do you sell the SRAM 39T chainring? Another alternative is the FSA
Thanks for watching!
Yes we still have it, link as follows:
brilliantbikes.co.uk/chainrings/6067-sram-chain-ring-road-39t-v2-130-alum-3mm-black.html
I’ve referred to your informative video to install the 39 tooth sprocket to my Brompton. Would you identify the tool that holds the shoulder nut on 4 of the five fasteners? It fits the slots on the recessed nut(?).
Thank you so much. Paul in Chicago
Many thanks for watching!!
It is a CNW-2
brilliantbikes.co.uk/bike-tools/66-chain-ring-nut-wrench-cnw-2-from-park-tool-usa.html
Hopefully you can buy it locally
Hi baby, thanks for this video.
Thanks for watching!
How did you know to take out 4 chain links? Is there some kind of link between the difference in teeth and the number of links removed?
1 chainring tooth plus/minus equals 1 chainlink plus/minus.
Giving rise to that well-known saying “I would watch her remove links from a bike chain”😂
Thank you so much for watching! We really appreciate it!
I went other direction, 54T chainring and swapped 13T to 12T sprocket on BWR hub. Would love to go even bigger chainring but all in the market seems very “aliexpress special”.
Boah, Chuck Norris himself!
Go stone. I have a 60t with them that goes on a 105 crank
Is there any way of changing to 39 from 44 on an old Brompton without changing the bottom bracket and going to a "spider"..? Thanks,,,I have the original non-spider type crank with the integrated crank/ring/chainguard.
I have a 38t on there, it does barely rub the spider so 39t is probably better
How do I calculate how many links need removing from a standard A Line 44T down to the 39T in your video? Thank you in anticipation.
We would remove 2 chain links when going from 44 to 39T
Have you consider changing to a dual chain ring 53T/33T without deraileur? I am happy to stay at 33T for most of the terrain if possible. I am on Brompton A series 3 speed internal hub. Can I add three sprocket to the back?
TBH I don’t like a front mech on any bike, so not really considered it for a Brompton. Thanks for watching!
would any chainring work as long as its 130 bcd and 5 holes? I see options of 39T from inner chainrings for 2by cranksets. Do those work aswell?
I still have the 50t installed but want to try 44 or even 39 since I almost never use the hardest gear event on flats in my commute but I have hills on my daily commute/rides.
The 44t brompton chainring is quite expensive here in my area so I wanted to try a 44T or 39T first (from cheaper brands) before I commit.
So there is no chain catcher to interfere with, right? Might be trickier with new P line.
Yes we agree as the chain catcher on the C line and the P line chain catcher does. Or adjust to that small a chain ring
Thanks for watching!
@brilliantbikes why don't you put a 17t sprocket on the rear to widen the ratio ?
Try them both and tell me which is easier?
@@SimonBrowneNZ on my brommie I have a two speed that had a 17t but I fitted a 19t to it an now the ratio is wide enough for real world riding. With a 54t in the front.
Han Solo, hey there, how does the 39 affect the higher gears when in use?
Thanx, Laurie
Hello! It does just reduce all the gearing, but rides nicely! The hub gear calculator is the best place to see the difference
xldev.co.uk/bgc.html
Thanks for watching!
Why no chain ring guard on the 39 tooth sprocket?
Many thanks for watching and for the question. It’s a non-Brompton chain ring and we could only find a smaller one with the correct BCD that did not have a chain ring guard
What does the p line come with? Annoyingly I feel like I need a bit more either side 😂😂
One of the reasons I’m still on 6speed with BWR, patiently waiting new for internal hub variant…
Trouser clips - not as good as a chain guard but definitely better than nothing!
Thanks for watching!
May i know the SRAM model/part number u used? Tnx!
Many thanks for watching and for the question, this is a link to the one we used
brilliantbikes.co.uk/chainrings/6067-sram-chain-ring-road-39t-v2-130-alum-3mm-black.html
if you were to add a double chainring (with manual shifting ofcourse), from H&H, I guess the chainring comes with 50-39 double, I guess you do not shorten the chain. So in that sense, can you live without shortening the chain even with a single 39 chainring? What are the disadvantages if any in retaining the longer chain (that comes standard with the 50 tooth chainring)?
The tensioner may not cope with the 39 and go too low and slack unless shortened; shorten the chain and the 50 may not cope and be too high and tight. Time for a bit of trial and error one link at a time. 50 is generally too big so a 46 and 39 combo might be better for pedalling and make the tensioner work better too with not so much difference in teeth.
@@SimonBrowneNZ thanks. I am not sure if I can get a 130 BCD dual chainring of 46 and 39 combo that fits the standard brompton BB.
Great video.
Since my chainring, sprockets and chain are all lining-up (due to wear) to be replaced together, I have to decide to go to T39 or back to T50. My favourite 'flat' cruising Gear Inches was 81.3 (second to last hardest). I do miss that cruising gear everyday with my T44. But, on the T39, seems like the hardest gear is close to it (78.0 gear inches).
Someone should 3D print a chain guard.
Has anyone 3D printed a chainguard for a 39T chainring?
Thanks for watching, not that we are aware of yet, let us know if you find one
I wish brompton 42T would be released
No need to change sprockets and chain?🤔
Nope not unless they are worn. You can just shorten the chain.
Thanks for watching!
Why not just add a charming on it make it 2by and install ah fd hanger and fd shifter then even the stock Chainring will never be change again just for hill climbing
I’d love to see this done on a pline. Maybe to 46?
It would be fine, you would just need to move the chain catcher.
Thanks for watching!
@@brilliantbikes no need to shorten chain?
It is interesting that the current-you is watching this comment about the video of your past-you talking to your past-current-you. Looking forward to the future-you click like to this comment.
😂 thanks for making me smile and for watching!
Single 39? I think the H&H 33/50 or 33/54 are better.
If you need speed, put on the bigger chain ring and for everything else the 33. Plus 1 ring that works with 1. Chain length that gives you 2 options. Oh and it got a ring guard as well for the clean ride.
Nearly a bike ,have a similar feeling regarding my humour = nearly a joke, thinking about hills wasn’t you going to do a comparison with the P - line against the six speed up that hill you have down other comparisons on ? People have often told me that I’m the missing link must be some kind of compliment, yes the song is here stop being impatient, song = Chain Reaction = Diana Ross.
39T is too slow for flat roads
Thanks for watching!
True
You will enjoy the next hill, though.
@@SimonBrowneNZ yes, I do understand that. I would prefer a 40+ chainring for balance between road and hill.
Love your channel, but “Climb hills easier”?!!! “More easily”, please🙄😊