Help! My C4 is horrible over bumps - Updated and FIXED!
 

See page #4 for update!



Hi all! I love my C4 but it really has some serious issues going over bumps. I live in WI and the roads are not great. We get lots of heaved pavment. Basically the car rides good on smoothish road, but when you hit a bump or a heave, the steering wheel gets really light and the car darts one way or the other in the lane. It doesn't give you that "holding the road" feeling at all!

My car is a 91. All stock except for 2000 wheels. 18" rear, 17" front. Has a used, but good, set of bilsteins on it. Suspension seems tight, nothing worn out that I can tell. What can I do make the car not so volitale over bumps? Driven daily, not raced. I was considering a camber brace but need input.

Thanks for the help!

I have the same problem and also live in WI. Any help is appreciated.

what size front tires??????

245/45/17 front
275/40/18 rear

I have a similar problem with my 84. It's much improved with the new rear Edelbrock shocks, but I'm sure the cause is old/worn bushings in the rear end.

There are no more rubber bushings from any suppliers either - at least none I've found so far. There is a seller on E-bay who has a few full sets of NOS rear control arms (with rubber bushings) for $300, but I think they only have them for the early cars.

If what I read is true, the 84s had much stiffer suspensions then the following years. People complained so much it only took 1 year for GM to respond and soften them up a bit...WW

I had the same problem with my 86. I also put on 2001 wheels and tires.You go over bumps like railroad tracks, and you have to find the lane you used to be in.
I put on different tires, and wow what a change!!!
I went to the Dunlop Direzza 101 tires, and the car glides over rail road tracks, and greases over bumps. The 265/40/17 are the same dimensions as the 245/45/17.
I went with the 265's, and saved $30 per tire.
Too bad Dunlop doesn't make tires in that style big enough for the rears.
Oh, well, you can't rotate them anyway, so why have the tread match?
I went with the Sumitomos because I couldn't find matching tires. I figure If they are inexpensive, I had time to look around for different rears by the time they wear out, but they seem to be holding up very well.The rears don't seem to be soft enough for mega-traction, but I can't really complain about the ride from them, just not enough stiction.
the fronts are great. They really fixed things with the bumps.
If you guys are crashing over bumps, try the Dunlops. They have a wear rating of 300.

We are talking tires....something you normally change occasionally, not like I mentioned painting your car lime green

Live with it. It's the nature of the beast. C4s ride like trucks. GM was on drugs when they designed the C4. I replaced Bilsteins with KYBs on my '92. Helped slightly. It's the transverse leaf springs. The worst is the '84 then get's better as each year goes. GM engineers made the spring thinner and thinner. Be thankful you don't have an '84. You don't know stiff. I'm considering getting Kuhmo Exta ASC tires. Softer side walls.

C4s don't brake very well either. My '84 had new slotted and drilled rotors and calipers. Could hardly stop it. My '92 has new calipers and rotors / pads can hardly stop it. Rough ride bad breaking is the nature of the beast with C4s.

I have C5 front brakes on my 86. Now it stops way better than the factory stuff ever let it...........
Now I can make my ABS function whenever I hit the brake pedal really really hard.
Never got it to work before the brake change.

None of that is true for a properly operating C4. :crazy:

To the OP; I believe that the root of the problem is the flexible frame and too-stiff springs. I believe that you need to either stiffen the frame, or soften the suspension...or some of both.

Wider tires are even worse, I have a camber brace, cross bar brace/,X frame brace. They all help.

Lower rebound damping in the front can help to eliminate this issue (but is by no means the only possible way to handle it). It is not due to the springs (unless they're too stiff, which would be an issue with coil springs too).

Which suspension RPO do you have?

How many miles are on it ? I have everything new , Bearings , balljoints U joints , rodends.
Any play make the bumps even more harsh .Car isnt too bad now .
Where in WS are you ?


Got rid of the 16 " wheels to a 17 & Khumo esta. Big improvement

Check your wheel bearings and all suspension bushings. I had bad rear wheel bearings and the rear would change directions on bumps and hard cornering.

How old are the tires?

Thanks for the help...I'll try to answer everyone's questions, let me know if I miss any.
1) Tires are date coded 2003. They are goodyear something. 26psi all around
2) 120K on the car. Nothing loose in the suspension.
3) Wheel bearings seem tight when car is on a jack. Will double check.
4) Suspension bushings...I should doublecheck but again, suspension was tight when car was on the jack and I tried to move the wheel around.
5) Suspension RPO - No clue. I will check
6) In located just west of Menomonee Falls.

What would be more beneficial...camber brace or the cross brace? I'm thinking of starting with tires first but still hoping to hear some other thoughts from people.

We drive Corvettes and the C4 is known to drive like a bumpy car. A C4 Corvette is not going to drive nice throughout speed bumps, pot holes or bumps.

If anyone would like a nice motion movement while you drive throughout those mentioned above, buy a Lexus.

Nothing (tires, shocks or bushings) is going to soften your monospring spring suspension and wider or bigger tires makes it "worst".

I have to make a video and show you guys how my LT1 Vette rides with the VBP sports suspension and HD Bilstein or my LT4 Vette with coilovers.

The reason why Wider/bigger tires make it worse isn't b/c the the tires are bigger. IOW, bigger tires aren't necessarily condemed to ridign worse. People get wider tires, but continue to run the same tire pressure. :crazy: The larger the tire, the less pressure you need to carry the same load. A 275 tire doesn't need nearly as much pressure, to carry the wieght of the 3300 lb Corvette, as the 245 tires does on my 3900 lb CTS-V. Teh more pressure you run, the "harder" the tire is, and the less compliant.

I have a BASE '92 with C5 Z06 wheels (275 front/295 rear). I run about 24 lbs up front and 22 lbs rear. Aside from the frame shake/shudder, the car rides O.K. Sharp-edged bumps still upset the car, but I believe that is due to the frame more than the suspension.

22 lbs of air do not meet my speed demands.