Hi Gary,
CCX33911 said:
With a lowered car (e.g. 4.25" ride height and 245/45-17=25.6" tires) the bump steer can be .2" at 2" suspension travel.
Yeah, getting optimal bump steer usually creates packaging or design modifications if it was not a priority from the onset. One would like to believe the original GT40 was optimised in this regard, however all the replicas have issues.
I'm interested to know if the toe change of .2 was in or out and in bump or droop. Bump steer gets "ugly" if it causes changes in the intended path of the car or makes the steering "nervous" and unpredictable.
My observation in driving the CAVs quite quickly on the track and carefull observation of steering feedback on the road, is that bump steer does not become an issue. It may not be optimal however it doesn't get "ugly".
About the toe change in bump: Say we were turning right - if it was a toe out number on the left front wheel the car would run wider than planned on a bump in a corner. If the inside wheel (in droop because of weight transfer)went toe in at the same time the two toe events would compound the sensation of understeer although the intended turn path would resume after the suspension damped the bump (assuming you're not in the kitty litter). If the inside wheel went toe out instead there would be some cancellation of the effect. There would be additional scrub and heating of the tires and loss of speed. Just an example to keep the grey matter going
In a strait line on level ground, if both wheels undergo bump or droop, even through larger angles, the the toe changes cancel each other out. It's one wheel bump steer adding to the turning radius that will bite you in the behind. This goes for rear end bump steer too. Some cars run sunstantial toe in at rest and dial more in to help drivers maintain the intended path through a corner. Very comendable in a mini van or family hauler, sports cars need to be predictable and stable without numbing the chassis responces.
And what if the bump steer is less than the slip angle of the tires or suspension deflection of the bushings? What about Ackerman? Oh my! I'm rambling again. Very interesting stuff though...
What is absolutely true is that the CAV chassis is stiff enough to tell you exactly what's going on with those four little contact patches of rubber on the road. It responds very well to proper alignment, shock valving and suspension upgrades that reduce friction and misalignment associated with the rubber bushes in the stock suspension.
So carry on Chuck, the car will only get better and better
Cheers