I have a question, It might be stupid but when Im driving my 02 Z06 on the highway at 55 or above, if I hit a dip in the road or small pothole the car veers in either direction, Is there something wrong with the suspension or is it the large tires?

 

Mine does it too, I think it has to be because of the stiff suspension. BTW, mine is a coupe with the soft F45 suspension.

 

thanx, I thought something could possibly be wrong with my car.

 

Sounds like a vette to me.

 

The term is "bump steer" and it's caused by the tires. If you put new tires on it won't do it for awhile but it does come back. I think all Vettes do it to one extent or another.

 

 

So.....what does a bump-steer kit do? or just a myth?

 

Sorry, never heard of it. Is that like getting a bucket of "prop wash" in the Air Force? Or sending the little leaguer for a bucket of foul *****?

Sorry! I wasn't making fun but I think "bump steer" is just something us Vette owners learn to live with.

 

Bump steer has nothing to do with tires. It has everything to do with the geometry of the front suspension. Bump steer is what when the suspension moves up through its travel, it will steer itself left or right because the geometry can not be completely correct to prevent this. Think about the fact that the upper and lower control arms are not the same length. So as the wheel moves up the steering arm is not drawing a consistent arch because the upper ball joint and lower ball joint are not moving inboard at the same rate. The tie rod can only swing in a consistent arc.

 

I know what you are saying, but you are not completely correct. The tires are a part of your suspension. The first portion of any impact that the car receives is the tires. With the run-flat tires the stiff sidewall restricts some of the flex and subsequently transfers more of the impact up thru the shocks to the control arms in the front and thru the mono-leaf in the rear.

The worst bump steer that most C5 owners deal with is the "hop" when a bump is hit with the rear wheels while turning. This will actually cause the back end to hop counter to the direction you are turning feeling like an over-steer at the front wheels. At speed this can be unsettling until you are used to it.

To the original poster, the C5 is a sports car and as such has a rigid frame and stiff suspension. The very same components that prevent body roll and tighten handling will contribute to bump steer.

 

thanks everyone for clearing that up, just wanted to make sure my car was okay. Other cars Ive owned including Mastangs and Camaros never did this.

 

Very well put Paul!

 

This is a bump steer kit:
http://baer.com/cgi-bin/htmlos.exe/0...9144800004867?

 

The reason you didn't see it on any of your other cars is because Vettes have leaf springs that go across the car. No other cars (that I know of) do.

Because of these tranverse springs, when more downward pressure is put on the spring, as would happen at the point when your car is coming up out of a dip, the downward pressure cause the springs to flatten out of their normally arced position, thereby extending their overall length at that moment, which in turn causes the wheels to tilt.

With downward pressure the top of the wheels tilt inward by design, which is one of the reasons Vettes handle so good around corners ON FLAT OR EVEN SURFACES. Think about it - when you turn hard right, the centrifugal force places most pressure on your left front wheel, and in other cars that transfers to pressure on the outer left edge of that left tire. If you put more force in the corner, you can actually see the top of other cars' left front wheels tilt OUTWARD, or with enough pressure, their wheels will actually flex outward.

Conversely, when you turn hard right in a Vette, the downward pressure of the spring actually serves to tilt the top of the left tire INWARD, and if it wasn't for the the centrifugal force pushing that tire straight back up again, you would notice that you would be riding on the inner right edge on that left tire. So, this combination of pressures puts the Vette's tire more upright and therefore more tread stays on flat on the ground when cornering ON FLAT OR EVEN SURFACES.

On the other hand, if you turn into a corner, and it doesn't have to be a hard corner, when that downward pressure is released, as would be the case if you hit a patch of uneven asphalt, like a dip, rut, hole, or whatever, the spring momentarily returns to its normally arced shape, thereby changing the tilt angle of that wheel for that brief moment, which changes the pressure on the tire tread. When that wheel resumes its pressure on the road, the tire is then at a different angle than it was originally, but then quickly resumes the original angle. This quick change of angles is what causes the bump steer. And, there's nothing you can do about it.

You can try changing shocks, tires, special alignments, swaybars, ride height, or whatever, but that fact is that as long as those transverse leaf springs are in the car, you will NEVER eliminate bump steer.

Of course, you could go get a different car, and lose the advantage of those transverse leaf spring in the FLAT OR EVEN CORNERS, and also spend the rest of your life looking out the window of that other car at Vettes, because no matter what that other car is, and no matter what shortcomings Vettes have (and they have many), that other car will never be a Chevrolet Corvette!

Now, if you experience what often feels like excessive "shimmying" in the steering wheel and the car itself when hitting uneven pavement while driving straight, your steering may be shot. That is a common problem in Vettes that are driven hard or are subject to harsh road conditions on a regular basis. Now, that doesn't necessarily mean that you are careless or thrash your Vette. For example, normal freeway speeds in Los Angeles is about 85 at 90 mph. Unfortunately, some freeways have bad sections of road joins, patches, etc. But, if you tried to slow down to accomodate for those bad spots on the freeways, you can easily be plowed by the rest of the L.A. freeway traffic running like wild Wildebeast over the plains in the African Serengetti, so you are forced to just drive right over those car-ruining L.A. Freeway monstrosities, and over time your steering gets beat HARD.

 

I have the standard suspension and stock springs on My 98. I put on ZO6 sway bars and noticed a little bit better cornering. (No bump steer) I just put on 2004 ZO6 shocks and it made quite a difference in ride and the way the car corners. "Excellent" feel and still no bump steer. I just went thru Orlando on the I-4 bump track at 90MPH and car was very stable. Actually, it felt great.
My question is: If I install the ZO6 front & rear springs would I then have a bump stear problem? Do you think it is worth the Mod? I drove a 2004 ZO6 and I really liked the way it felt but I decided to keep My 98 coupe and upgrade the suspension and do a few other improvements. I would like to know if this is worth doing. My stock springs are just the soft standard springs that came on a 1998.

 

You DO have bump steer, but you just may not notice it, or maybe aren't as sensitive to it as others are, or you may be one of those people that actually prefer a stiffer ride and bump steer is inherent with a stiff ride. And, if you like the stiffer ride, bump steer will be of little consequence to you, especially since you already mentioned that you feel your car has none. Not that anything's wrong with liking a stiff ride.

As far as the Z06 springs are concerned, I would think you would definitely notice a difference. The ride will be stiffer, but if handling is what you're after, there will be a significant improvement, simply because the springs are stiffer.

FWIW, I previously had a C4 with stock Bilsteins, and I had bump steer. I sent the shocks down to Bilstein twice to have them custom worked for better ride and handling, not to try to elimintate bump steer. While ride and handling did indeed improve with each modification by Bilstein, the bump steer was still there. Later I changed front shocks altogether, and there was still bump steer.

Today, I have a C5 with F45 adjustable suspension. While the bump steer is still a characteristic of the 5th generation Vettes, I do notice the bump steer makes itself apparent in different ways depending upon which setting I use. Supposedly, on F45 suspension systems the lowest setting is softer than a base suspension system, the middle setting is between the the base and Z51, and the highest setting is stiffer than the Z51.

But, the bump steer is never completely gone. Like I said in my previous post, the design of the suspension itself lends itself to producing bump steer. But, who cares if it makes the car a little less sure-footed at times, nothing beats having a Vette, bump steer and all!

As a matter of fact, yesterday my son and I were going somewhere in my C5. We were approaching an intersection where a Mercedes SLR McLaren had just approached the intersection from the left and turned right. Now he was in my opposing traffic. Turns out that the driver was apparently test driving the car. What blew my mind was that as he approached, I could see he was looking at my car. He wasn't looking at me, I watched his eyes, and there was no doubt that he was looking at my car. As we passed each other, he continued to actually crane his neck to check out my car as thoroughly as possible. What a trip! Here was a guy test driving a $450,000 car, and he was checking out my cheap American sports car! Goes to show there's no substitute for American Muscle, bump steer and all!

Here's a link to the Mercedes the guy was driving: http://www.rsportscars.com/eng/cars/m_slrmclaren.asp

 

There is nothing at all like a "CORVETTE" (NOTHING) There are Corvettes and there are other sports cars. I would not trade My 98 Corvette for anything except another Corvette. Well, I could not even do that because I like this 98 coupe to much.

I might have Bump steer but I guess it just does not bother me as much as a car that just does not feel like it is stuck to the road like my car feels now. The car feels planted now. Before it felt like it wanted to jump into the next lane on a bumpy curve at high speed.
I'll probably go for the springs, If I dont like them I can always take them off and sell them. Now my only problem is spending the $$$$$ I don't have to buy them.
Ronnie

 

that was the first time i have actually been able to fully understand what the heck someone was trying to tell me about bump steer. i get it now. i lowered my tire pressure to see if it was the thick runflats side walls and it seemed to change allitle. same corner, same speed, same bump. but i cant run around underinflated always. thanks for spending the time to post those responses

 

You're welcome. And, BTW, don't believe anyone who tells you that going to regular tires will eliminate the bump steer...it won't. I ran the best non-runflat tires on my C4, Goodyear Eagle GS D3s, and while those tires are, in a word, AWESOME, they won't eliminate bump steer. Admittedly, while those tires on a C5 would dramatically improve the ride on a C5 as well, they won't eliminate bump steer. Further, non runflats have a softer sidewall, so you'd probably experience a little sidewall flex when pushing corners hard. And, you still have to consider getting stranded somewhere far, far away if you get a hole in the tire. Yikes!

 

Correct. This kit is to correct the geometry. Tires hopping across the pavement is another. And by the way I agree the real problem that we feel is the tires hopping across the pavement. The tire will absorb most of the Geometry induced bump steer until you lower the car and change its geometry. This is why a good front end shop will make sure the car is at proper ride height before adjusting anything. I adjust bump steer on Race cars all the time and even use it to tune the suspension to some degree.
http://www.ioportracing.com/instructions/bumpsteer.htm
http://www.irvansmith.com/tech9.htm