Roll Centres

[Jwb]

Theoretical Question.

I have a double wishbone suspension system with a front roll centre height of 2". The wishbone pickups are optimised to reduce roll centre movement under roll. The car is balanced in respect to under / oversteer.

Now if I raise the roll centre to for example 3" or 4" again with pickups optimised to reduce roll centre movement under roll and all other things the same, what will be the real effects when driving.

Thanks

John

[Sam_68]

I'm quite surprised to see you posting a question like this, John! I'd have thought you were as well qualified to answer it as anyone on this forum!

To kick off the discussion, though:

* Impossible to easily quantify the effects on camber gain, etc., 'cos it is too dependent on specific geometry... chassis pick-up positions, upright design etc.

* Body roll would be reduced, for given spring stiffness.

* There would be an obvious effect on diagonal weight transfer, leading to simple changes in understeer/oversteer balance and potentially much more complex changes in 'skewed roll' as the car negotiates a corner... again impossible to quantify without a full analysis of both ends of the car, including spring rates, roll stiffness' and gemoetry.

* There would be an increase in jacking effect (unless droop was limited, which might create complex side effects in terms of diagonal weight transfer).

I'm curious... why do you ask!?

[Jwb]

I am aware of the theoretical differences, such as an increase in camber gain and more jacking but wondered how those differences would feel to the driver. I have only ever designed one suspension set up and know how that feels to me behind the wheel. Also when I designed that all I did was pick some roll centre positions, make the lower wishbone level and as long as possible. The RC height determined the top wishbone angle and all I did was play with top wishbone length to give minimal RC movement. I then accepted everything else. I chose springs as soft as possible and used the front bar to balance the car….simple eh? I didn’t get too deep into the theory behind RC`s. A friend asked me the question and I couldn’t properly answer, my books are not with me and it is a few years since I was deep into the suspension.

Maybe I should re phrase the question and instead of just increasing the front RC by 3”, increase both front and rear by 3”.

So the answer is pretty much that it will alter the understeer / oversteer balance which can be balanced out with ARB. The overall grip may reduce but would an amateur driver notice that?


John