old motorhead

Well....You're going from a rear tire that's too short to one that's too tall. If you keep the 265/35 18's in front, the 305/30 19's are a much better match.

racerxrick

To the OP what was the final outcome on this???

I just experienced the same thing and typically run my PSS at 28-30 psi cold. Was on a 9 day road trip down to Tail of the Dragon and most of the other local roads. Car handled and drove great and was pushed hard..however on a lonely two lane under max boost (700+whp) she started wobbling in the back...was really unnerving. I chalked it up to uneven road surface.

Then...on the interstate (in mexico) a modded car tried to pick on me and she was smooth as butter to 165...HOWEVER next day same scenario and the back wobbled hard, was really disconcerting. My travel partner in his supercharged GS could even see the wobble.

Fairly new 345/285 combo PSS Michelins...I keep hearing this only happens with Michelin. I'd like it to never happen again!

CMY SIX

who say's the roads "clean" enuff to go fast on? if it's covered in small gravel what would you expect?

racerxrick

Still hoping to hear from the OP on his outcome.

HOWEVER i MADE TWO CHANGES (THOUGH SHOULD HAVE DONE ONE AT A TIME).

1. had Discount Tire check balance, one rear wheel had lost all weights and was out 2.5oz. They stated that they couldn't road force balance the 345's because they were too big. The fronts were within a .25 oz.

2. Increased air pressure to 35 rear and 32 front.

RESULT: no wobble though low end traction was very compromised. Made more than a half dozen pulls with no issue.

NEXT: will lower pressures AND car is going on the lift for a thorough inspection tomorrow plus hitting the alignment machine.

Details to follow...

mikeCsix

You should stay close to the tire pressures the manufacturer lists on the door sill of 30/30 cold. My Michelin PSS's are very stable at high speeds and grip well as they warm up on the track.

HOXXOH

That's assuming you have the same size tires as OEM. Although the total square inches of footprint will remain nearly the same with any size tire, the shape will change. The only way to control the shape is either adjusting the car weight or adjusting the air pressure.

racerxrick

Yeah that's what I've been running them at and I am impressed with the traction (acceleration and lateral). I've also driven through a number of rain storms on road trips recently and just ran the roads on Tail of the Dragon and surrounding.

Upsized currently to 345/285 combo

PA_BLUE_C6

I am going to put my almost new set of oem size tires on to see if a little wobble I thought was my bad driving is really this too wide tire syndrome.

2008 Z51 manual coupe

mikeCsix

They are even more impressive when you get them up to track temperatures.

racerxrick

I'm sure of that Mike, though i haven't tracked it we just returned from Tail of the Dragon and the tires did heat up..

ssmike56

Does anyone know if this is an issue with just the PSS? I have Pilot Sport Z/P Plus run flats on my base '06. Should I be concerned? I haven't gotten it up to high speed but I don't want to encounter the dreaded wobble when I do!

racerxrick

I am starting to catalog this issue and saving links to threads...THIS IS NOT JUST A CORVETTE ISSUE! I have found threads on GT500 and even BMW forums with just a little research. Michelin was kind enough to swap my rears out for $96 (sarcasm implied) and I still have the issue.

I posted the following to another thread today:

I have been following threads like this on multiple forums (it's not just a Corvette problem) and the issue is ALWAYS the same and ALWAYS related to Michelin tires! 100% of the time after reading through a typical thread eventually it comes out the owner with the "wobble" has Michelin's. To be clear not all owners with Michelins experience this.

Me: (702whp 2010 GS) I have been fighting this and I have two other sets of rims (drag pack and DR's on spare 19" rears)...with these other rears there is NO WOBBLE! Switch back to the Michelin PSS and under hard 3rd and 4th accel the rear end wobbles and it is VERY scary!

Michelin "exchanged" my rears and denied ever hearing of this problem (despite others reporting the issue and a friend reporting the issue directly to a race engineer at COTA). And yes I have another friend locally with his 675whp GS experiencing the EXACT same issue on his low mileage car.

BTW, I was charged $96 to exchange the rears for another set.

What really sucks is I love the wet/dry traction (lateral and straight line) but cannot trust these at high speeds as under accel the car "at times" will wag it's tail like a dog with a bone!!!!!!!!!!!

Going back to Discount this week to work on exchanging for another brand.