First, I'm well aware that a difference in rear tire pressure between left and right can cause the car to veer on accel and deceleration but I'm puzzled at my situation.

I'm running Prodrive GC-06D 17x7.5" +48 w/ 225/45/17 and 17x8.5" +54 offset with 255/40/17. At high speed (which amplifies the effect), the car would veer to the left on slight acceleration (from cruising) and then veer to the right if I lift just a bit. I tend to believe it's from the rear suspension because when I correct with steering input to keep the car going straight, I feel like both the front and rear are steering in the same direction making the car "walking" sideways. I checked tire pressure and even tried swapping left and right wheels with no difference.

Then, I tend to think it's a problem with suspension bushings or hub bearing. I checked and tightened all rear suspension and subframe bolts. I wiggled the rear wheels and there wasn't any slack. I even removed the spring/shock assembly and wiggled the suspenion at about normal ride height thinking maybe the spring preloading the bushings may hide the problem but I still couldn't find any slack. I even tried having my brother simulate standing start but with the ebrakes pulled while I observe the rear wheels from the outside. Again I didn't see any movement in the rear suspension.

What surprised me is that last nite I swapped back on my factory 16" with all-seasons for the winter and the "mysterious veering" seems to be gone! What makes me puzzle is that when I first got the car with the 16", I had the problem though not to the extent with the Prodrive. Now it feels like the problem is suddenly gone. Would the 11mm offset difference (+54 vs +65) be enough to reveal a problem that would be hidden by the stock wheels? Anybody else running lower offset wheels got similar encounter? I would imagine people running even lower offset wheels would be the ones to report first?

 

Lower profile tires make tramlining more prevalent than with the 16's. The other possibility is you have a defective tire causing the pull.

Moving to the wheel/tire forum.

 

Offsets are not your problem here. Seems like an alignment problem to me. Your symptoms would be indicative of having more toe-in on the left than right. As weight transfers to the rear under acceleration, the left rear wheel steers the rear end to the right. It could also be a toe-out condition on the right rear. I'd have a competent shop check out all your alignment settings pronto!

Other possibilities, but maybe only if you're not the original owner, or if you have a set of coilovers or something... are springs or damping rates. If you have don't have your ride height set equally left to right, you can get strange tendencies on accel/decel. If your springs are not identical left and right, same thing.

Let us know what you find.

 

If it was an alignment setting the problem wouldn't change with a diffferent set of tires.

 

Thanks for the suggestions.

I tend to think the problem is not due to a defective tire. I swapped left and right tires and one would think the car would veer the other way but it didn't. Same as before the swap.

I also tend to think it's not the alignment (or at least not the alignment alone) because the problem doesn't occur with the 16"s. Before I had the last proper alignment done, I deliberately set different amount of rear toe and rear camber from side to side for testing but the "mysterious-veering-against-throttle" stayed the same. Only difference was an added constant pull to one side.

That's why I tend to think that it's a problem with my suspension/alignment which can only be amplified by the different-than-stock offset wheels (torquing on the hub from the moment-arm effect).

I'm not the original owner but the car is stock and at the last alignment change (on brand new tires), ride-height from side to side (both front and rear) were the same (before ballast with the driver).

I may have to wait til next spring when I put on new rubber for the 17" to see how things go. And I prefer to do an alignment on brand new tires. At this point, I'll have to wait til the snow is gone and I put back the 17"s to do any further testing. Any suggestions are still welcome though.

 

Sure it would.

Different tires have different sidewall stiffnesses which could certainly change the feeling of a misalignment! Even going from my all-seasons to summer tires, I can feel much more bump steer when riding on the summer tires.

 

I'm stumped but you might try posting this problem in the racing and competition forum, those guys have a wealth of suspension experience on this car and have seen just about every hinky thing you can think of. Good luck!
Mike

 

Had these wheels and same symptoms on the street especially when pavement is uneven or crowns. Did well at the track though. Reason could be that these wheels are lugcentric not hubcentric. Switch to hubcentric wheels and you'll notice the difference.

 

Bringing back this old thread because I just got some new tires for the 17"...

A little recap on the problem...
- car veered to left on increasing throttle (and right on decreasing) while highway cruising on both 16" (all-seasons) and 17" (summer).
- swapped left/right sides with the 17", same result
- put back 16" for winter and problem totally gone.

The weather has been nice these 2 weeks and I decided it's time to re-visit the problem. I snapped back on my 17s and the problem showed up again! I tried swapping left/right tires again. Unlike last time, the behavior did a mirror-image flip -- veer right on increasing throttle and left on decreasing! Yay! I concluded that my 17" tires are the culprit so I accelerated my plan to order new summer tires from Tirerack. Mounted the tires friday and immediately the problem is entirely gone! Some pics here.

Not only that, the front/rear balance on cornering is much better because my old 255/40 Hankook K102 was narrower than the new 245/40 Kumho SPT while the 225/45 Hankook was just a bit wider than the 215/45 Kumho. Also, because of new rubber, soft sidewall and deep tread to yield a bit of rubberband effect, the backend doesn't like to wander like before any more. With 1/4" toe-in, it's supposed to be a -ve feedback mechanism to reduce backend wander. But with the old Hankook, it's like each rear tire was fighting for its own direction of travel. On bumpy road and varying throttle, the backend would wander into directions depending on which rear tire had more instant traction. You can imagine what it's like on hard-cornering (or check out this video going thru' turn 1 at high speed).

With better planted backend now, I revised my alignment setting once again with a little bit less rear camber and toe-in. The backend feels best ever but I'll need more time to scrub-in the tires before I know for sure if the problem will come back or not. Thanks guys for your suggestions.