Since I bought the car in september Ive been bitching about the rear end being to stiff on the bumps, and not gripping on the turns. I blamed it on me being spoiled because the camaro replaced a very sweet 944 that was stolen.

The car has the SLP 17" rims with 275/40/17 Comp TAs.

Last weekend I put the factory salad rims on with the original Goodyears on the rear, and a used pair of pirelli 600s 225/55/16 on the front for an autocross this weekend.

I noticed the same noise and vibration in the pirellis that made me swear i would never buy new pirellis (thats another story that almost cost me the sale of my Legend Coupe when i put the pirellis from my brothers BMW on the car and gave him the new michelins) and made me wonder how BMW and Mercedes could put these disasters on their cars.

Now here is the important part, the rear end is much more civilized with the 16" goodyears. Much better behaved on road irregularities, and bumps, and it seems the 245 goodyears are gripping turns better than the 275 BFGs.

Before I try to trade the chrome SLPs with near new TAs for a set of 16" rims, is it the tire or the size of the rim? ths suspension modifications done by the PO are listed in the signature.

TIA

 

It could be any number of things, but in general the 16" wheels/tires will ride better than 17" wheels/tires due to the 16" setup having 1" more sidewall in the tires. This allows the tires to give a better ride. This could also help handling on rough surfaces if your rear shocks/springs are too stiff. On a good surface though, the wider wheel/tire combo is always going to handle better. Personally, I can tell you that my Firehawk with the Level II suspension (now sold as Level I) rides as good or better than a stock fourth gen, and handles much better. And this on is over some of the worst roads I've ever driven. It's just a guess, but I'd wonder if the rear springs you have may be too stiff, or if the shocks aren't really matched to them. If you've got the actual SLP Eibachs, then I'd tentatively point the finger at the rear shocks and suggest you try one of the following (in order of preference):
Koni SAs
3rd gen Bilsteins
4th gen Bilsteins
SLP Bilsteins
stock 4th gen rears
I don't know why the previous owner would have gone with DRM shocks as DRM specializes in Vettes, not f-bodies. Yes, they do sell f-body parts, but you're the first person I've ever heard of that's used their f-body Bilsteins. I'm sure their are others out there who have them, but I've never heard any feedback on them in 8 years of being around f-bodies.

 

Thats what i wanted to ask Rippie when i called his place to find out some specifics about his revalving. he seemed a little pissed that i wasnt happy with his product.

Im know the difference in ride could be attributeable to the difference is sidewall, but handling too. the added roll from the sidewalls seems negligable compared to the increased traction. what am i missing here? when I went from 16 to 17 in rims in the porsche the ride barely compromised. here it is like night and day.

 

That's why I'm really thinking it may be the shocks. In my 95 Formula, I went from stock 16" wheels/tries to 17" wheels with 275/40s in the front and 315/35s in the rear and the ride quality changed very little. This was with stock springs and shocks. In my 00 TA I went from stock springs/shocks to Eibach springs w/ stock shocks and from the stock 16" wheels/tires to 17" wheels with 275s all around and noticed zero ride sacrifice. As a matter of fact, I think it rode better than stock.

One other thing that I didn't think of early is the wheel weight. You say the previous owner put on SLP chrome rims, I'm guessing you mean the 5 spoke SS style wheels? If so, are they genuine GM rims that have been chromed, or an aftermarket chromed wheel? Either way, the point I'm getting to is the weight. The more the wheel weighs, the more it will affect ride and handling. It's only been fairly recently that the wheel manufacturers have started making the chromed SS/ZR1 style wheels in a decent weight. The original ones would usually weigh around 5-10lbs more per a wheel if I remember correctly. That's a huge difference in unsprung weight and could be contributing to the problem.

 

It's all in the correct combination of parts.

I use 17x9.5 with 275's on the street (Pirelli P7000's) and have NO trouble. I use 17x11's with 315 Hoosiers on the track and have no trouble. I use 120# springs in the rear and Bilstein HD's, 500# front with Koni SA's and my car rides better than stock if you ask me.

Call Sam and talk to him, it'll be the best phone call you can make, you won't be sorry.

 

Evan,
funny you should ask if the rims are genuine GM. when i bought the car i asked the PO, and he said he bought the wheels and tires from for $1800, and emphatically stated they were genuine SLP.

when i took them off last week i noticed two rims had the gm logo on them and two didnt. I heard the SLP rims made for gm had peeling problems but the others didnt.

 

You might want to try weighing each wheel/tire to determine if any are heavier. Also, the fact that they are chrome means they are heavier than an equivalent painted wheel (usually only 1 or 2lbs though). The 16" wheels will definitely be a lot lighter than the 17s. I'm not sure the wheel weight is the culprit, but it's at least something to look at.

 

What about the tire themselves? How old are they? I've noticed a significant drop-off in the stick of my BFG KD's over 3 summers.

 

the tires are practically new. the PO put about 2000 miles on the car in the last two years. thats why it seems so odd that they ride so poorly.

 

The taller sidewalls on the 16" tires are simply more forgiving. I noticed this big time after setting up my suspension with the factory wheels then installing my 18" wheels. Too much roll stiffness in the back.

A simple test would be to try your car without the rear sway bar in place, and then try the factory bar instead.

As for the pirellis, I've avoided them after a friend could not get them balanced on his ford probe.

DaveH