I recently installed 2 Michelin Pilot sport 335/35/YR17 in the rear and the same 2 Michelin Pilot sport 275/40/YR17 on front.
Before this, I was running with a 5 year old set of tires (275/40 ZR 17 on all corners) with a very minimal tread left. Tires were General (a Continental brand).
I used a set of Zr1 wheels. (9.5" front and 11" rear).
Before the swap (needed) the car was handling fine, very responsive glued to the ground. The downside was only that in a sharp corner I was not able to use
additional throttle due to oversteering.
Now it seems I have in the rear 2 flat tires.
It seems I have 2 rear tires with very weak sidewalls. I have the feeling that I start to turn the steering wheel and the car reacts only 1 second later.
Slaloming is a very disaster...
Car is aligned perfectly and a second check confirmed that the car holds alignments specs.
During the turn the car seems better, but when I'm finishing the turn the car need an additional second to go straight.
I'm speaking of touring/city speed!! not autocross speeds! (I haven’t tried higher speeds... I'm afraid..).
Contact patch seems good even with higher than suggested inflation I can't spin rear tires!
I really don't know if it is a sidewall problem or a body roll problem. The only thing I know is that the only change made is the tire swap and a new alignment.
I tried every kind of pressure from 20 psi to 50 psi with the same feeling.
If I can rate the before and the after I can say that with a optimal rate of 10 before was 8 now is 1.
Can't be only a tire problem... It seems I have something disconnected or some mechanical part loose.
During the installation there is some dangerous operation that the tire man can have made? (broke something.. disconnected something...)
Checked the lug nut and they are in torque specs. Sway bar bushing seems ok, and it seems there is no end play on tires ( hub bearings).
I can’t believe to the theory of the smaller rim. Yes I’m using a 11” rim for a tire rated for a 11” to 13” rim. This can be a part of the problem but I think the BIG problem is
On a broken/disassembled/loose mechanical part (good before the swap and bad after the swap), or a defective tire set.
Please help me, where I have to see first, in order to find the reason of this??
Thanks and sorry to have re-posted this subject, but I really need your help.

 

Probably is the narrow rim, wide tire problem.
Do you have original tires and rims to test your theory of mechanical failure.
If not try and borrow some.
Good Luck

 

I have the old rims...
...not the old tires :mad
Help meee

 

so? you have 11 inch rim's with 13 inch tires?

If this is the case, I think you seriously need to buy a set a 13 inch rim's if you want to run those 13 tires on your car.

 

... and you have a 11" tire on a 9.5" rim??
(in the case you have the stock 275/40/ZR17 on the stock 9.5 rim..)

 

Im with Agent86, is there someone around who can loan you a set for a quick spin around the block, preferably with the 9.5 & 11 inch rims. You must rule out or confirm big tire / small rim situation.

 

I actually have 4 spare 275's in my step dad's garage, but I live in Canada...

I sure you could find a used set for cheep, and I mean "USED" since you just want to test it.

I would call the neighboring scrap wards.
Good luck!