SSinister11x

My 1996 SS M6 is pretty smooth driving under 55 mph but when I get up there in speed it starts to shake pretty bad and just isn't a comfortable ride. I know that some of the vibration is coming from the SS ram air hood ( I can see the hood shaking real bad in the wind) But the feel of the car just doesn't feel smooth like I would like it to be. I just replaced the wheels and tires with 15x7 (front) and 15x10 (rear) Weld draglites in Mickey Thompson Radial SR tires. Do narrow front wheels cause a car to ride bad at higher speeds? Thanks for any replies, always much appreciated.

TrybalRage

Wheel balance, driveshaft balance. That's where I would start, at least.

daytonablackZ28

I was a technician for Discount Tire for 5 years mounting tires on everything from Bentleys to Bobcats, and sounds to me its gotta be a tire balance issue. your stock SS wheels had wheel weights stuck on the outside lip of the wheel as well as on inside lip. (like 1.00 oz. wheel wieght hammered on the outside lip and a .75 oz wieght hammered on the inner lip).
thats how you get the best balance out of a tire and wheel combo. The weld draglights you got most likley if you look at them have wheel weights literally stuck on the inside flat of the wheel. (static balancing we called it). the skinnies I doubt has anything to do with the the shaking at 55 on up, but im suspecting since all four of your wheels have been balanced using that static method, thats the issue.
most tire shops by default will only balance drag style wheels like that (wheel weights taped on the inside hoop of the wheel) because well... Draglites dont have a lip on the wheel big enough to hold a wheel weight, so they stick a strip of square weights on the inside and call it a day.
Ive balanced plenty of wheels like that and most have been ok, a little shaking yea, but being your Draglites, well....necessary evil.

see where and how many wheel weights they used. if theres a crapload of em mounted on the inside loop of every wheel, thats prolly causin the shake and they need to rebalance em, and/or break loose the tire from the wheel and spin the tire around on the wheel to get the heavy part of the tire further away from the heavy part of the wheel. (i know, sounds complicated). check out where the wheel weights are (IF THEY EVEN USED ANY) and then go from there

mrmint69

Did the car run normal before the change of the wheels and tires? If so, you need to have them checked and hope the shop that did the work will figure it out for free. Check the latch and make sure its bolted down tightly. I have seen several where they didn't tighten the nuts or bolts and it did what you describe. I work at a body shop and we fix this stuff all the time and never charge. You could call around and check if you don't want to work on it yourself.

zmike

Like mentioned above, also check the driveshaft balance. Usually a vibration around 55-60 is a wheel/tire balance issue. I think the driveshaft balance issue comes in at a higher speed?

daytonablackZ28

Driveshats are generally much less prone to vibration issue simply by the nature if thier design, but don't rule it out if gets abused a lot. The weights on driveshafts are usually welded.on and.can come off. Don't forget driveshafts spin a lot faster? But then again since they are not bolted to a part of the car that the driver has a direct feel too makes a imbalances druveshaft usually hard to detect, even at high speed. Still easy to check em out anyways for missing weights, bent yoke, etc

SSinister11x

Thanks man, I'll definitely have that latch looked at. I'm not sure how the car ran with other wheels/tires. I bought er off ebay sittin in a field with wheels and tires that looked like they'd been pulled from the ocean. I trailered it to the house and put on the new welds/MTs

SSinister11x

Ugghh, doesn't sound fun but i'll press the tire shop to make em as good as possible. Thanx for the reply man.

Injuneer

The steel driveshafts on the 4th Gen LT1's are a major source of vibration, particularly when the rear gears are swapped to 3.73's or 4.10's. The problem is due to a critical frequency issue with the steel shaft. The problem was so widespread that GM issued a technical service bulletin, and would replace the steel driveshaft with the aluminum driveshaft used with the 1LE option.

That is why people are mentioning the driveshaft as a possible source, but with stock rear axle ration, it's generally not a problem at 50-60MPH.

daytonablackZ28

It's not that big of a deal really. I mean I was a tire tech for 7 years and I had guysrunning draglites and streetstars comback with vibration issues at times. I took care of it. You paid em to do a job, they outta do it.
I might suggest going to another tire place and see if they can make better on the balancing. I would definitely look inside your wheels and check to see if they used stick on wheel weights and if so how much weight is there in each wheel, especially the front wheels. Each liittle square you see is .25 ounces. There shouldn't be more than maybe 2 ounces.
Also see if they do NOT static balance the wheels (stick on weights on inside of rim only)
But rather use hammer- on type steel clip on weights on the rim lip instead. Discount tire co. Or Americas tire are a good places to take the car to get those wheels balanced out better. Or go to a speed shop and tell them your dilema. You got decent radial tires so the tires are most likely not the problem.
Don't forget to rule out the other stuff like the other guy said
(driveshaft out of balance, air turbulance under the hood, flywheel or ring gear bent stuff like that. If everything was ok with the old wheels and tires though, the culprit is just rebalancing.
Hope I helped you get it straight.

Injuneer

Balance weights are installed on the inside of the rim on drag wheels to avoid having them fly off the edge of the rim and become lethal objects. A couple of ounces of lead, hitting your head at high velocity can be fatal. All my drag wheels are balanced internally with tape-on weights, and I've never had a problem. In additiion to installing them in the inside of the rim, it's also a good idea to duct tape them.

Mickey Thompson recommends static balancing of bias-ply slicks:

Street use is a different situation.

daytonablackZ28

thats what we did, tape em on too. forgot bout that. most of the guys runnin 10 wides or DR's didnt care bout shakes at 55 mph because they would hit 55 mph in a nanosecond anyways. this guy on here has those Mickey Thompson SR radials in jegs and summit racing catalogs. bias ply slicks shake HARD at steady hiway speeds.

just curious but what size rims and tires are you NOW running on the car? you said you never drove the car with the stock wheels?? im assuming stock size on a 1996 SS was 275 40 17 all way around. Z28's were 245 50 16