Why Lowering Your Car Can Result In MORE Body Roll
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- Опубликовано: 11 мар 2024
- Lowering your car can result in MORE body roll rather than less because the suspension roll centers are lowered. Even though the center of gravity is also lowered, there will likely still be more body roll. This video explains why that is true.
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Suspensions Explained
Huibert Mees
This is actually a really important clarification, and illuminates why in racing, it's still useful to have the car be very low, even if production-based. Spring forces can be compensated with stiffer springs, though not ideal, and contact patch loss from geometry can be compensated with aggressive alignment. Meanwhile weight transfer, and so the tires' place on it's load sensitivity curve is only determined by CG. So for minimal weight transfer the CG should be low, and contact patch should be well-managed.
You can't align around a bad suspension, and stiffer springs are just limiting its effect. I guess the old "Any suspension works if you don't let it" adage applies here, but is seldom optimal.
A too-low or too-high roll center can't be compensated by springs, it is a leverage issue. Increasing spring stiffness reduces weight transfer, thereby traction. Intuitive? Not exactly.
@@nobodynoone2500
It sorta becomes intuitive after many a miles spent behind the wheel trying to go fast.
Its why my first car was super low while all my current cars are kept at their oem heights, even after some mods regarding damping or basic geometry.
@@nobodynoone2500Weight transfer actually happens regardless of spring stiffness, spring stiffness controls body motion and of course the tire's contact with the ground. Gokarts experience weight transfer despite not having suspension at all. The reason many passenger cars setup for racing have large amounts of negative camber is to compensate for body roll and the resulting camber loss, that's what I mean by alignment. So yes in essence you can align around a bad suspension. It's not ideal, but it will be faster than running a factory ride height and alignment. In fact most cars can go faster around a track with just a more aggressive alignment (generally more camber, maybe some toe out) but of course suffer increased tire wear in normal driving. What I mean by the roll center being compensated with stiff spring is that as is described in the video, the forces generated by the roll moment are transferred into the springs rather than suspension components, so by stiffening those springs (including sway bars) the actual body motion can be reduced. Of course at the cost of a stiffer ride which will suffer on uneven surfaces, but often not an issue on a race track.
Hello, I'm a team member of an FSAE team from India and you have no idea how much your videos have helped me!
I just wanted to thank you and also to request help with your expertise in automobiles to improve the FSAE community.
You should come to Formula Bharat or Supra SAE India as a judge, would love to chat more with you!
I like the TR6 model as a demonstrator, the king of lift off camber change that puts hairs on your chest.
I remember seeing a TransAm cornering very fast once during the late 1970's. The front of the car's suspension seemed to lift the car higher off the pavement, but I saw very little roll and the car maintained traction during the event. I attributed most of this effect to the car's having a very large stabilizer bar on the front suspension.
Was I correct, and can you give us a video, or a series of videos, on the effect of stabilizer bars when placed on the rear of vehicles like mini trucks (older Toyota pickups, for example), and what happens to traction in curves and cornering with added rear stabilizer bars. Your videos are very educational. Thanks.
I hope you earn all the money in the world with this channel so that your format doesn't change. Just love it. Thanks for all your videos. A fan from BraSil.
Good stuff!
Huibert you are my goat
Clear and crisp explanation
Please explain how manufacturers choose a tire diameter (OD) in the design phase for a new car. Is it simply dependent on what looks good on the car?
Great video as always!! I have been thinking a lot about air springs lately, and since I know they were used on the Model S, I figured you would know something about them. I would love to see a video in the future about the differences between air and coil springs.
Thanks!
Great explanation as always and straight to the point. For those who are interested in this issue, I strongly recommend reading the correspondence on SAE forum about Jacking forces. A person under the nickname Z, as well as the author of the channel, gives a comprehensive explanation of how the virtual swing arm, roll center, and jacking work.
Thank you. I cover those topics as well in my 2 part video on roll centers. Hopefully Z and I are saying the same things!
Fantastic explanation.
Are there any books you would recommend covering suspension geometry topics such as this?
How to Make Your Car Handle by Fred Puhn is a free pdf. Old, so doesn’t cover the last 4 decades, but a great basic primer with easy pictures and explanations. I find it a great companion to these videos
Thanks for making this playlist, please do an entire playlist where one can design a suspension for an vehicle from scratch including all the formulas and software used in the suspension design.
I'm planning to do a pretty radical suspension setup for my car.
Total:1520kg~ 55% F/45% R
I'm looking to get:
6kgf/mm front springs (165mm max, 130mm working compression travel)
35kgf/mm Antiroll Bar Front
5kgf/mm rear springs (170mm max, 130mm working compression travel)
27kgf/mm Antiroll Bar rear
I plan to have around 60mm of available working suspension travel for dynamic compression forces. 70mm will be taken by car's static weight and preload.
Clarify my understanding of anti roll bars, they link the L and R suspension and based on it's stiffness will be how much the suspension are linked by?
In my application, would the front and rears be roughly linked by 85%~? (35:6 and 27:5)
So lets say a 1g lateral force, my outside front tires would be exposed to 420kg of static and an additional 420kg of dynamic force. With my 130mm of working travel 70mm is for static, so normally that would mean my 60mm remaining travel would not be enough, as I would need another 10mm. But due to my ridiculous 85% link, I can use 85% of the other suspension resulting in a total dynamic spring rate of 11kgf/mm and only 39mm of travel after the static drop of 70mm.
Is this sound theory? If not, I'll just run the basic suspension setup. I'm looking for comfortable highway rides, but also a cornering animal.
A few questions:
1) since electric vehicles have a much lower center of gravity due to their batteries, would they experience less body roll assuming the same geometry and lowering distance?
2) how does a swaybar work and is it a reasonable way of offsetting the impact of lowering your vehicle?
3) in a previous video you covered wheel spacers. Is there any compounding or offsetting impact of both lowering the vehicle and adding wheel spacers?
Love your videos! Thanks so much for the informative content!
EV's do have much lower centers of gravity and so will roll less, all other things being equal. What an EV does for you is give you the opportunity to make the anti-roll bars much smaller, or even get rid of them (especially the rear one) which give much better ride. That gets to your second question. Anti-roll bars could be used to compensate for the additional roll a lowered car might have, but that would hurt ride. That's true for stiffer springs as well.
Lastly, wheel spacers increase the track width so they would reduce the weight transfer during cornering. They do nothing for body roll, however.
This goes a long way to explaining jacking on some suspensions. I imagine a load path from the centre of the contact patch to the roll centre, the horizontal component is roll, the vertical component is jacking force extending (in most cases) the suspension.
I've a related question regarding the roll axis (which you already commented on) but in relation to roll frequency and the rear axle 'seeing' the turn later than the front axle. Does the ideal roll axis change for applications ie fwd / rwd, front engine / rear engine, consumer / race / rally?
Lots of cars run trailing arm which would have a suboptimal roll axis but seem to perform OK.
The roll axis plays its part in the whole understeer/oversteer picture and since FWD/RWD/front engine/rear engined cars all have different inherent understeer characteristics, the balance of the roll axis with bump steer/bushing compliance/spring rates/anti-roll bar stiffnesses will be different.
BTW, I talk about jacking in my 2 part video on roll centers.
@@suspensionsexplained thanks I hadn't seen it.
All other things being equal, a vehicle with a lower center of gravity should have better traction than a vehicle with a high center of gravity, correct? Considering the slip angle.
Yes, with all else being equal. I think it's easier to think of weight transfer and body roll as two separate outcomes from the cornering force acting on the center of gravity/mass. Weight transfer is dependent primarily on the cornering force, and the CoG height. Body roll is dependent on the same things, but with the addition of the suspension geometry, and will affect how the wheels are aligned when cornering forces are applied. Body roll can therefore affect how well the tire contact patch is being used, which will affect how much cornering force gets applied in the first place. If body roll means you get too much camber gain, then more roll stiffness, or a higher roll center will allow you to use less negative camber to achieve similar cornering forces.
I assume you mean cornering traction, but, yes, a lower CG will give you better cornering traction because the inside and outside tires are doing more equal work generating cornering force. The more weight transfer you get, the lower the overall cornering power of the combined inner and outer tires will be. This is because of the non-linear behavior of tires. Their cornering capability does not increase linearly with increased vertical load.
Thank you, Huibert! Between your Autopian articles, these videos, and How To Make Your Car Handle (free basic primer by Fred Puhn: check out the pdf, people!), I now have a decent idea of what goes on when I throw my car at corners-and why that slammed POS was so freaking darty over bumps 🫣