SoDiezl350

I'm posting in this forum because you guys seem to have the best understanding and technical knowledge.

I recently switched the oem thin spoke wheels on my C5 with a set of HRE 540s. Ever since I made the switch, the handling at freeway speeds has become darty and hard to control. To better describe it, when I'm going straight the car feels fine. When I enter a turn however, the smallest steering inputs seem to upset the car and cause it to dart off to the side.

The original wheels and tires that were on there were Toyo T1Rs in 245/45/17 and 275/40/18. The stock thin spokes are 17x8.5 and 18x9.5

The wheels that I put on are HRE 540s in 18x9 and 19x10. The tires in the front are half worn Pirelli P Zero Assimetrico in 255/40/18. The rears are brand new Hankook V12s in 285/35/19.
I had all 4 wheels balanced. Since the Pirellis are non directional, I've tried switching them from left to right to see if they have been "broken in" in one direction. This did not fix the problem.

One thing I'm wondering about is whether the increased overall diameter in the front has now created a slight front rake which is causing the car to lift and reduce traction. It seems to me though that such small changes shouldn't produce such drastic effects.


I'm somewhat reluctant to buy new tires up front as these seem to grip well and still have life left in them. I'm not entirely convinced that this would solve the problem either.

Any help would be appreciated.

cleanerPA

First off- you should never run different tires on the car- always run the same make and model of tire on all 4 wheels. I can see running drag radials on the rear for drag racing only, but otherwise, this is a bad idea.

You will have different levels of grip front and rear with different tires- this is a bad idea and can lead to unexpected under/oversteer depending on which axle has more grip.

Uneven wear on the worn front tires may contribute to an alignment issue- have you checked the alignment of the car?

You will have a "sharper" turn-in feel, in general, when going to a lower profile tire. You will also feel a change in the suspension and how it works if you change the unsprung weight- significantly heavier wheels and tires will cause the suspension to not work as well.

I don't think that you will find much in the way of aero issues at speeds under 100mph, although others will chime in that can speak to changes in rake- this will affect handling.

froggy47

You went to lower profile & wider footprint tires although not by much. This could very well result in more tendency to tram line or trolly track.

I would get a GOOD alignment, not one of those quicky "close enough" ones.

MARK the alignment bolts.

SoDiezl350

The alignment was done about 3000 miles ago. Car drove fine before new wheels and tires were installed. The used front tires came with the wheels, but the tires I took off the car all wore evenly.

Car is currently on PFADT Featherlight coilovers, swaybars, poly bushings, and camber kit.

froggy47

I've changed rim sizes, run mis matched tires, old/new never had any issue with trolly track except if my toe was out instead of 0 deg. I still vote align & especially toe, then caster. All I got so far.

fatbillybob

Too many things can go on to cause your problem. Get new tires have westend alignment do the job in gardena. He is the best if you have no gear to DIY. Then join in on Corvette challenge 2013 and learn even more about your car. A good cheap tire to start is the nitto Nt05. Old high profile tires mask alignment problems. You go to the low profile wider Bling-bling for that twitchy performance. You hope to get some of that.

cleanerPA

Amen to that.

Get rid of those crappy tires and get some fresh rubber. Hankook EvoV12 are fine for a BMW 5 series, but really have no place on a sports car- they don't have enough dry grip. Great in the rain, though and they do not have silly treadwear.

SoDiezl350

So I installed new tires on the front. I did go with Hankook V12s, but whatever the downfalls of these tires may be, the symptoms are not indicative of under-performing tires.

Due to the cold weather, my poly bushings have began making a bit of noise lately and I am beginning to wonder whether they may be the cause of this problem.

cleanerPA

Did the new tires in the front fix the problem?

Poly bushings won't make your handling get strange- with stiffer bushings, your suspension will react more quickly to any inputs you make, but it will not make the car feel unstable. However, poly bushings will exacerbate any alignment issues that you already may have.

SoDiezl350

Unfortunately no, the problem remains :-/

The reason I'm suspecting the bushings is because they recently began making noise and I'm wondering if they need to be re-lubricated.

froggy47

I don't think it's poly bushings.

SoDiezl350

Lemme guess... alignment?

Gonna be a busy xmas break!

froggy47

How are the wheel bearings? Ball joints? Rod ends? Basic stuff but still. Steering box?

braknl8

Is this always the case when you give steering input or unpredictable throughout the turn....for example, are there times that it turns in ok but all of a sudden "catches" and darts in the direction of the wheel?

Was ride height adjusted by any suspension component means (spring bolts/coilovers) to "fit" the new wheels better (fill in the gaps, etc)?

Also, still got the old wheels/tires? If not find a buddy that does. One sure way to determine if the new ones are the culprit and not something else going on. Sounds too simple but I've read back through the thread and didn't see it mentioned yet. Could be chasing your tail for a while w/ out narrowing this down.

froggy47

Can you sense/feel whether it's the front or the back that get's antsy (referring back to post #1) sometimes it's a little hard to tell.

cleanerPA

No, poly bushings making noise will not affect your handling- the lubrication is only to prevent noise.

VetteDrmr

Actually poly bushings start binding (which affects handling) before you start hearing them, that's their biggest downfall. Solve that problem by lubing them when they start making noise by taking them apart, or do what I did on my Miata and install zerk fittings and squirt them twice a year.

To the OP, you went to wider, lower profile tires. That aggravates tramlining (or rut hunting, wandering, whatever you want to call it) and enhances turn-in response (which is your original concern).

I see two options for you: one, adapt to the increased responsiveness/sensitivity in your driving style, or two, get the car realigned increasing toe in in the front towards the upper limits of stock C5 recommended settings, and add a small amount of toe in to the rear to calm down the rear slightly. You also have to watch the tire wear when you start adding toe (toe in, outer edge, toe out, inner edge), but it will numb the response somewhat.

HTH, and have a good one,
Mike

blackdak318

Sorry but absolutely disagree with that. They're a good daily drivable summer tire and there are tons of reviews by others corvette owners on here that will back that up. They're not an R comp or even a 100 or 200 wear rating tire but they're not advertised as that. I personally have them on my Z06 and they're a good bang for the buck tire. I would bet money that the new Hankook tires are not this guys problem.

cleanerPA

Thank you for chiming in Mike- I didn't know that poly starts binding- I thought that the lube was only to quiet them as they are naturally quite noisy.

cleanerPA

I guess we have a difference of opinion on what makes for a good street tire, then.

My opinion of the Hankook V12 Evo is also based on personal experience, but not on a Corvette. I chose them for my Volvo based on good reviews and the fact that they were $85/each after a significant rebate. They're comfortable, quiet and very good in the rain, which makes for a good tire for a luxury car. However, they definitely fall short in dry cornering and braking. I formerly had Michelin PS2 on the same Volvo, which was much better- just as quiet and good in the rain, but significantly better handling and braking. The downside to the PS2 was the wear rate- they lasted only about 18k miles on a daily driven car. I hope the V12 Evos last a bit longer but I would not buy them again.

I've used a bunch of other performance tires and for Corvette applications, I would choose Michelin Pilot Super Sport, Bridgestone RE-11 or Yokohama AD-08 if the size is applicable to your car. My C6 has RE-11s on it right now and they are way better than the stock Goodyear F1 Supercar- great in the dry, great in the wet (I've done 90 in a heavy, driving rain without any issues). My choice for replacement would be Michelin Pilot Super Sport.

Now these tires are nowhere near the price of the Hankooks, but I can't say that the V12 Evos are fitting of a Corvette. The sidewalls are not stiff enough and the dry grip is lacking- it gets worse as they wear in, as I felt that the dry grip was better when the tires were new. Don't you have traction issues with a Z06?

When it came to the OP's problem, the main thing was not that the tires were no good, but rather that you put a sticky Pirelli P Zero in the front and a much harder Hankook V12 Evo in the back, you're going to end up with a fair bit of oversteer, which would be solved by using the same tires front and rear.

I've driven cars with Bridgestone RE-01R, RE-11, S-02, S-03, RE070, Dunlop Z1 Star Spec, SP Sport Maxx, Michelin PS, PS2, PSS, Conti Sport Contact 2 and 3, Pirelli P Zero Rosso, P Zero Nero and a whole lot of older tires as well.