My new C6 Z51 paddle shift is not modded but this is a performance question. It seems unsettled on any fast turns especially with some bumps. Is this what is called bump steer, I thing the steering moves when the car loads and unlaods the suspension. Any cures? Sway bars? Thanks.

 

It's not "bump steer", just a result of going too fast on an irregular surface.

The best suspension in the world won't keep you in contact when you hit a bump or are on a washboard surface.

Best advice is to take turns slower and at a safe speed, before you see your own tail in front of you

 

bump steer is a suspension term that describes the amount of "toe" change when the suspension moves up and down.

There are tons of suspension upgrades, some including a simple alignment. Is it understeering (front pushing) or oversteering (feels like the rear is going to come around)?

 

I am thinking maybe this post is from someone who wants to sell suspension products...................

 

The Corvette chassis engineers designed out bump steer. What you are experiencing on a uneven surface is pull due an effective camber change. This is exaggerated by the wide tires.

 

No, this is not a suspension ad. Just asking you all about hadling.

 

If you had bump steer you would feel it in the steering wheel and as you go over the bumps your steering wheel would move back and forth from right to left. (not a good feeling)
It is a result of the steering geometry being off in relationship to your suspension. That would not be the case in a C6. You were just going fast over bumps and the only thing you can do there is slow down

 

C5's have bump steer...C6's don't in my experience (and I have the Z51 also).

 

If you lowered it you would get bump steer more likely, it feels like darting left or right when going straight. I lowered mine and get bump steer. I got bumpsteer kits from Zip. I am putting on next week will let you know my results.

 

i believe the described effect is a result of the 'stiffer' suspension of the z51. the stiffer the suspension the more you will feel these types of events.

just out of curiosity, what tire pressure are you running ?

 

I've noticed minimal "bump" steer in my C6, and I am sensitive to it from my C5.

 

I thought bump steer was a factor of the front suspension maxed out and swerves front first.

I had the rear of my car skip once. I figured it was a result of going too fast through a turn on a concrete road (~135mph). I hit an irregularity and the back popped out and fishtailed twice before I regained control.

 

Here you go, from Longacre

Bump Steer is when your wheels steer themselves without input from the steering wheel. The undesirable steering is caused by bumps in the track interacting with improper length or angle of your suspension and steering linkages.

Most car builders design their cars so that the effects of bump steer are minimal. However, you must still take care to bolt on your suspension carefully so as not to create unwanted bump steer. Make sure that you are always using the correct components for a particular car. Bump steer must be designed into the car and cannot be adjusted out if improper parts are used or if pivot points are moved without considering bump steer design principles.

In order to accomplish zero bump the tie rod must fall between an imaginary line that runs from the upper ball joint through the lower ball joint and an imaginary line that runs through the upper a-arm pivot and the lower control arm pivot. In addition, the centerline of the tie rod must intersect with the instant center created by the upper a-arm and the lower control arm (See diagram below).

The instant center is an imaginary point that is created by drawing a line from the upper a-arm ball joint through the a-arm pivot where it is intersected by an imaginary line that extends from the lower ball joint through the inner control arm pivot. Where the two imaginary lines intersect is the instant center.

Sounds complicated? Really it is very simple. To achieve zero bump the front end must be designed correctly. The tie rod must travel on the same arc as the suspension when the car goes through travel. Simply matching lengths and arcs to prevent any unwanted steering of the front tires.

To exaggerate, if the tie rod were only 10" long and the suspension were 20" long then when the suspension traveled the tie rod angle would shorten much quicker than the suspension arc. In this scenario the tie rod would shorten much quicker through travel than the suspension and the car would toe in drastically over bumps. The shorter arc of the tie rod would pull on the spindle and toe it in through travel.

Bump Simplified - When designing a car, if the centerline of the outer tie rod lines up with the centerline of the lower ball joint, and the inter tie rod lines up with the lower pivot point then the length and angle of the tie rod and suspension will be the same resulting in zero bump. Most car builders design their cars in this fashion.

 

Let me explain what are kits do now that you have read the defintion.
They do not magically remove bumpsteer, nobodies bumpsteer kits do that. They give you the ability to adjust the bumpsteer, you can either dial some in or remove it, but you have to know how to do it. I include instructions with my kit to explain bumpsteer, and how to measure bumpsteer and then to set the bumpsteer kits. It is something you will need a good day to do accomplish. You can build your own bumpsteer gage or you can purchase one from longacre.

I believe we are the only company that also offers the complete rear bumpsteer kit and not like some who are just using the front in the rear of the car, we replace the inner joint also. Now to make this easy on someone who just wants to lower a car and not spend hours setting the bumpsteer here is what you can do. Before you do anything with the car sitting on the ground at ride height, use a angle finder to find the stock angle of the tie rod shaft. Once you have this go ahead and lower the car and install the bumpsteer kits. Once everything is back together and aligned, drive the car around the block to settle the suspension. Now using the angle finder measure the tie rod tube again. Unbolt the tie rod heim joint and add or subtract shims until you have the same angle before you lowered the car. Now you will have the same suspension geometery as when the car was stock. This does not mean you have 0 bumpsteer now, but it will be the same as what GM put in the car.
Thanks
Justin

 

Correct.

Bump steer is the tendency of a vehicle to suddenly veer or swerve to one side when hitting a bump or dip in the road. The condition is caused by uneven toe changes that occur as a result of the steering linkage or rack not being parallel with the road surface. This causes the wheels to change toe unevenly as the suspension undergoes jounce and rebound.

The C6 DOES NOT have bump steer. The chassis guys designed the suspension so that there is no bump steer, assuming the Z height and alignment are correct.

 

I disagree, are you listening to Chevrolet Engineers tell you this, because they also said the car could not be improved. Every car has bumpsteer, now the Corvette was designed not have any, but getting your alignment changed can create a small amount. If you lower the car you are changing the geometry. If you hit a large bump, that is not bumpsteer. Bumpsteer does not mean Bump=Steer. It is similar in what is does, but when you hit a large bump and the entire car moves you are changing angles in the chassis in its relationship to the road. This is like the gators on a race track, by getting the car at an angle it can turn sharper, but this is not bumpsteer. Look at the definition above from Longacre.

 

My C5 had serious bump steer coming up to 2 stop signs in town where the asphalt was deformed like waves by stopping traffic. The problem was nearly gone when I switched to Firestone RF's on front.
With the C6 there is minimal bump steer at these same stop signs.

 

 

Going around a turn with bumps, fast, will surely cause the car to jump sideways a bit and reduce control... normal for any car with a "performance" suspension. If this feels unsettling to you, then you do need to simply slow down in such conditions.

I also have a Z51 and find it to be just fine... excellent in fact. I would not change a thing about it. I believe however that the F55 option would react "better" in the condition you describe, the wheels would be a bit less eager to bounce on a bumpy or washboard surface.

I guess you could reduce this "problem" a hair by downsizing to weaker anti-sway bars... but then you'll increase body roll which is a negative thing if you are interested in taking curves fast.

The stock Z51 is fine... no need to modify anything. You just need to take it easy on bumpy curves, that's the solution.

 

Yup, I was thinking COILOVERS