Comments on: Roll Centre and Roll Moment

By: Suspension Secrets

Suspension Secrets — Fri, 22 Jan 2021 09:37:55 +0000

In reply to Xinyu Luo. HI Xinyu, thanks for the comment. When we talk about roll in this article we are assuming that the excessive roll (present in a passenger car) as already been removed. Once excessive roll has been eliminated, you can begin offsetting the roll stiffnesses between the front and rear axle to have end softer than the other. Lateral load transfer is the movement of load to the outer wheels during cornering. The stiffer end of a car will always have more LLT than if it were softer (unless it has excessive roll which we have removed). If you look at an image of a F1 car cornering hard you will see that the rear rolls more than the front due to this. F1 cars are a difficult example for this though due to the high amounts of aero being used which alters dynamics completely. Low aero or non aero circuit cars benefit more form these rules due to relying much more heavily upon geometry.

By: Xinyu Luo

Xinyu Luo — Tue, 19 Jan 2021 21:43:08 +0000

Hi,
I don’t really understand this sentence:
“For a front wheel drive car, the front roll centre will generally be lower down than the rear roll centre. Also, for a rear wheel drive car the rear roll centre will often be lower than the front roll centre. This gives the driven wheels more roll and therefore more grip through the corner. ”
Why more roll means more grip through the corners? I think more roll means more lateral weight transfer, and this reduces the overall grip. For example, F1 cars have very little body roll during cornering. Whereas passenger cars have significant body roll during cornering. The logic behind should be, although the outer wheel gets more weight through lateral weight transfer, the gain of grip from this weight increase is less than the loss of grip on the inner wheel, therefore the sum is less. Am I right?
I know that all I care about here is lateral weight transfer, nothing else. Therefore in real life, camber change during body roll could also affect grip, but still, as a general rule, should more roll means more grip or less griop?

By: Suspension Secrets

Suspension Secrets — Wed, 06 Jan 2021 11:08:47 +0000

In reply to John Sheer. Hi John, thanks for the comment. Yes you are correct. Roll centers will be affected on the front and rear wheels when a car is lowered and ideally all 4 corners should be corrected. It is a more common issue on lowered FWD cars due to the effects being more pronounced and the understeer being dramatically worse on a FWD platform once lowered. However, roll centres do still need correcting at the rear wheels, particularly on lowered RWD cars as it will affect the dynamics of the car still. Thanks

By: John Sheer

John Sheer — Sat, 26 Sep 2020 06:52:09 +0000

Super useful article, thanks for putting this information out there. I see a lot of roll center correction kits on the market for FWD cars and they all are for the front suspension, which perplexes me. I expect raising the roll center in the rear would benefit a FWD car more (all other things being equal) than the front since, I think, this would combat their natural tendency to understeer. These kits are marketed specifically for lowered cars. With suspension drop being equal in the front and rear, would it not be beneficial to adjust roll center all around? What am I missing here?

By: Suspension Secrets

Suspension Secrets — Tue, 28 Apr 2020 14:47:09 +0000

In reply to Richard Greenup. Hi Richard, thanks for your comment. Yes for RWD it is beneficial to run a lower roll centre on the rear to increase the roll moment at the rear axle as this will reduce LLT and increase grip on the driven wheels. A stiffer roll moment is very similar to running a stiffer anti-roll bar.

By: Richard Greenup

Richard Greenup — Sun, 26 Apr 2020 09:35:14 +0000

For a dedicated mid sized club circuit race RWD modified production car 56/44 weight distribution with front Mac struts and rear multilink, what roll centres would you recommend? I was under the impression that the front should be lower than the rear, particularly for turn in, but your info above says otherwise

Thanks, great site, it’s my go to from now on, cheers.

By: Suspension Secrets

Suspension Secrets — Fri, 28 Jun 2019 08:37:02 +0000

In reply to Mohamed Anwar. Hi, For multilink Suspension you choose the upper and lower suspension arms and trace their lines as you would with a wishbone. The angle they are at is the angle so trace the lines to intersection.

By: Mohamed Anwar

Mohamed Anwar — Thu, 27 Jun 2019 21:03:02 +0000

How can I locate the Roll canter of a Multi-link suspension? its akin to Double wishbone, but the “wish bones” are inclinded differently. Its the same case if a rear double wishbone has some anti-squat built into it, i mean the wishbone is inclined when viewed from the side.

so what to do in this situation?