Years and years ago, i switched the front sway bar to 32 mm, installed poly lower control arm bushing and put in 275/40's on a 9.5 inch rim.
I did these all at once and the change was dramatic considering the springs and shocks are stock.
The thing that bothers me about it is the twichyness and lack of straight line stability. Any little bump will try to send me 10 degree's off course and requires constant correction when driving on the majority of roads around here.
I never evaluated each variable independantly and was wondering which of these options would most improve tracking without throwing away too much grip.
1. My first chioce is going from a 275/40-17 to a 255/45-17 to gain an extra 1/2 inch on the sidewall to absorb shock.
2. Getting a new set of front lower control arms with rubber bushings. This i am pretty sure will allow alot more deflection and steering wheel comfort. I don't really need to clip apex's at 140 any time soon, so i think the harshness vs. road feel can soften up back to stock.
3. Cheapest option is throwing the original Z/28 front sway bar back on.
My uneducated guess would be
1. 20% improvement
2. 30-40% improvment
3. 10% improvement
Let me know which you noticed increased harshness the most if you have a similar singlly added mod.
BTW rim offset was custom settup for f body. As i recall the added width was added on the inside and the outside. Would the slightly wider track throw off geometry that much? Subframe connectors and a 2 pt tower brace were done at the same time. Bar is a lingenfelter's as well as recommended alignment spec's. Any input so i can drive with just one hand for a change?

 

Keven: I have found the same "twitchyness" when using the 275s. With no other changes, going back to a 245 tire (not as wide) cures the problem completely.

I think its less complicated - more tread feels/grips more of teh road and pulls the car more.

This is probably part of the reason the C5 vette utilizes a 245/285 front/rear combo - keeps the ride nice and smooth.

Ryan

 

Yep, wider front tires have this effect. They tend to follow irregularities in the road surface more. I am no suspension/car setup expert by any means, but I bet if the front suspension and steering were fully adjustable that a lot of this could be "tuned" out. But to some extent, it's a price you pay for wider tires.


Up till this year I was using a stock front tire size and switched to 275/40/17's. BIG difference, as with yours, the car now wants to steer itself and requires a lot more correction. Anyone know if there are alignment or other changes to minimize this effect?

Rich Krause

 

It's the wider tire. On my 95 when I put the ZR1 wheels on I noticed this. I tried running 245/45ZR17s on the front and the "twitchieness" went back to stock levels. Personally, though, I really don't mind more twitchiness to gain the extra grip of the 275. Also, having a good alignment can make a difference with this too. The amount of "toe" on the alignment can help with this, but I don't remember exactly which way to go on it.

 

Just replaced my tie rod ends at 60k miles at the advice of another board member all I can say is, if haven't yet, do so. There isn't any way to tell they're bad while on the car. The inner joints can fool one into thinking the outers are tight. To my surprise both nuts were to hold them in were not at the right torque. Once you get them out and compare them to the new ones you'll see why they wear out. They are puny.

 

My car has the same problem but it doesn't sound as bad as your describing. I have bilstein shocks, hotchkis springs, and a hotchkis sway bar, on 275's in the front.

I'm not convinced its all in the tires though
My sister has a ws6 which comes with stock 275's and her car tracks perfectly.

Not sure whats that adds up too but maybe it sheds some light on the sucject

Mike

 

I agree with the width comments. My '91 C4 had 275s up front and followed the grooves in the road quite bit. That's one thing I like about the 245s, my Z tracks perfectly.

Along these lines, I thought it was really interesting that a new Ferrari 360 had 215s up front. When I was at the Panoz Track Day on Friday, there was a new 360, and I was surprised that it had those skinny tires on the front. Probably since the Ferrari is much lighter up front, being a mid-engine car, but I had always associated 7 inchers with subcompacts, not supercars.

It would be interesting to see how a sticky 245 compares to a moderate 275. I suspect a sticky 245 would probably do just as well or better.

 

If you want to have more straight ahead stability get the GW upper control arms and set your front alignment to max caster. The difference is quite suprising with 245s or 275s

 

You can tell if the rod ends are bad by having somebody crank the steering wheel back and forth while you look at them with a flashlight.

 

I ordered new lower control arms that i'll have on next week.
I have nitto 315's in back and saw they don't make 555r's in 255/45-17 but they do in standard 555's. I'll give them a try after the control arms if they don't do much good.
Got a link on them there upper control arms?
Thanks for the replies and i will post the results as i get em.
Keven

 

Before you try these options, try a performance oriented alignment. Its inexpensive and a little negative camber and you may find the handling to improve tremendously w/o changing-out many parts. You didn't mention anything about an alignment since you've installed these parts.

Steve

 

lil toe in will help, but for autox you want a lil toe out