Bump Steer

[aromocki]

I am new to the Panoz experience and when I drove my Panoz for the first time I thought it was quite twitchy on the straights compared to my Porsche. It corners amazing though. I had a pro driver drive my car and he then looked at the suspension geometry and stated there was a quite a bit of bump steer in the car. We then compared it to another, not so heavily modified Panoz and found the same thing. Just wondering if anyone has done some engineering to fix this problem or am I the only one experiencing it?

I beleive the solution is to simply machine or shim the lower steering arms until the bump steer is gone.

Thanks,

Andrew

[panozracing]

twitchyness at speed is usually toe in my experience. Check and see what your toe is set to. you should have 1/8" of toe out.

Use Panoz's manual to get you to a basic setup which is a great place to start.

[NZGTRA17]

I agree with Brian. I have found my car to be quite sensitive to toe settings regards straightline stability. I like to have reasonable straight line stability so I am careful about how much toe out I use.

I would also check the bumpsteer curves (by removing the shocks and through using toe boards, check toe change with varying bump and droop heights). I usually do this over a range of +1.5" to -1.5". You can make up a set of toe borads at home very easily out of some MDF or plywood with a couple of sets of hinges and some long wood screws.

Plotting the toe change at the varying heights will give you a "toe curve". If excessive toe change exists, you would then shim and recheck and plot your new curves. This is not hard to do and is a very worthwhile exercise regards improving the handling of your car if bump steer is an issue.

It may well be that you have 2 issues to correct so I would check both the bump steer as well as the toe settings.

Kel.

[aromocki]

OK thanks for the info. We checked the toe and it was about 1/8" toe out and I think we even changed that to zero and the car didnt handle any better. We are planning on doing the toe "plot" and seeingt if it changes under suspension load. Thanks for your help!

[Werling]

Pictures Please of car

[aromocki]

Ok it looks kind of ugly now as I had to replace all the broken parts a few weeks ago as a Jetta spun in front of me as I was pittin and I t-boned it. I will paint it the Gulf GT-40 colours. Baby Blue and Orange in the off season.

[boothkc]

Bump steer is pretty minimal depending on ride height and alignment. We have rock solid straight line stability, no bump steer, and good cornering etc. Have had some "dartiness" under very heavy braking that was related to bad (worn out) Penske shocks that was resolved with rebuild. The biggest thing I notice when comparing the Panoz to the GT3 is that the Porsche brakes are MUCH better, but the ass is heavier.........

I think you need to start with a proper corner weighted alignment before you start grinding and cutting. The stock geometry solution is pretty good. Perhaps your ride height is too low to (looks that way in the pics).

Some reading for you: http://www.longacreracing.com/articles/art.asp?artid=13

http://panozgtra.com/documents/Align...s_-_GTS_RA.pdf

Have fun.

Kevin
GTS and GTRA

[NZGTRA17]

Another factor that may be exacerbating any alignment or steering geometry issues is the wider track of the car.

I tried to do some googling around wheel spacing and bump steer but did not find any quality articles. Seems to be general consensus though that widening the track via wheel spacers or greater wheel offset will impact on bumpsteer tendencies and many other alignment facets.

Kel.

[aromocki]

I think that both yoru points are valid as the car is wider and it is lower as well. My mechanic builds Transam cars from scratch and says that he can eliminate it over the winter and that its a bit of a tedious process but can be done no problem.

Thanks for your input.

[NZGTRA17]

Andrew, a non bumpsteer question for you...........what heads does your engine have fitted?

Is the inlet manifold a Victor Junior or a Super Victor? If a Super Victor, at what rpm does the engine start to pull well (i.e. can you pull it out of slower corners in say 2nd from 2500 - 3000rpm)?

Kel.

[Cobra4B]

That car is going to look rad in gulf oil livery.

[aromocki]

I dont know that much about North American Engines so I thought I would attach the build sheet.

4th gear will do 160 mph at 7000 rpm. The clutch grenaded during a race and I was stuck in 4th and I could do the entire track COMPETITIVELY in fourth gear as the engine has that much torque. You can put it in 4th and start the car from a dead stop no problem. I had a 4 speed dog box and I use first gear as its good for 70 mph and the car just pulls like crazy even if you are short shifting.

Hope that helps. If you need more info I can ask my mechanic.