help with understeer and body roll - please:)

[Steve]

Hi,

I have been having a problem with understeer, specifically I get it when I go into a corner hard - then when I accellerate, the turn in is sudden and sharp. This is telling me that too much weight is coming off the front inner wheel, then when I accellerate the weight shift is causing the inner wheel to bite.

I have a modded R33 skyline, sus mods are ohlins coilovers, 8kg springs front, 3(ish -not sure) kg springs rear. Cradle (rear subframe) bushes - both polly and harmount. Front adjustable castor rods, front camber arms (-2deg), ride height is 345mm from center of wheel to guard front and rear. 1/2cage fitted. And front and rear whiteline adjustable swaybars - both set to the hardest adjustment.

The fixes (that I think may work) are to:

Lighten off the front say bar - I dont want to do this, as I am scared it will increase body roll, or

Increase the size of my rear sway bar - but AFAIK there isnt a larger one available???

does anybody know of any other ways around this?

I was thinking of fitting wheel spacers to try and widen the track a little.

I cant really afford to lower my car anymore, as I dont want the attention that will surely follow from the law. (Here in SA, I have already lowered my car 15mm lower than min legal ride height for R33)

Also, I havent locked the hicas yet - could this be having much of a bearing on the problem?


Thanks heaps for any help

Steve

[Steve]

Gee, it gets quiet in here:rolleyes:

[Jakub]

Hi Steve,

Apologies for the delayed reply. Im not exacly sure which model R33 you have, so i'll just stick with general vehicle dynamics.

The understeering nature can be cured by moving more of the roll resistance "proportion" towards the rear, like either stiffening the rear or softening the front end (springs/dampers[turn in]/anti-roll bars). I would try softening the front bar (and also because your currently maxed out on both) than stiffening the rear, because from the information your given it seems the car has already a very high roll resistance, and your front camber is at a highish -2 degrees, which should be able to handle a little bit of roll.
Other choices in trying to reduce the understeer can be reducing front tyre pressure, widening the front track, increase the front tyre widths and even to raise the rear height a little.

In regards to the HICAS, we have tested skylines with and without (locked rear rack, or rack replaced with rigid link) and have found lap time reductions of 1 sec. which is a big improvement!
4WS is very handy to have around town, although at the race track and during real hard driving, its non-linear nature sometimes makes it unpredictable. The input for 4WS is usually speed and front steering angle, however in some cases inputs such as vehicle yaw rate are also included ( I beleive Nissan introduced this in some R33's), all this leads to unpredictablilty in the rear end, especially if the car becomes unsettled and needs correcting - it can lead to oscilating behaviour.

Regards
Jakub

[Steve]

Thanks for the reply Jakub, looks like softening the front swaybar is the go then.

with the camber, I was actually thinking of increasing it to around -3 at the front? Apart from tyre wear, can you see any major drawbacks?

Also, do you know of any local manufacturers that do hicas lock bars?

Nearly forgot, my R33 is a GTSt, series 1.

Thanks again

Steve

[Jakub]

Hi Steve,

From race tyre (slick) data in terms of cornering force generation, it is advantageous to run higher camber values. Another thing to perhaps think about is the reduction in your track width at you increase your camber, as the contact patches are now towards the inside of the tyre instead of the middle, this is hard to calculate without tyre data, easiest is to test and feel. The camber will most probably outweight the reduced track.
However I must emphisize that this could lead to accelerated tyre wear.
Additionally you may want to reduce toe in slightly on the fronts (apply a little toe out), as -ve camber will have a slight effect like toe in.

Yes, here at Whiteline we are currently developing and testing HICAS rigid links and locking links, if you are interested please contact me off list (email).

Regards
Jakub Zawada B.E. (Mech)
jakub@whiteline.com.au