Lance 4c

I replace the the Contis with Sumis in November of 2011. Was very happy with the performance, and did not understand any of the bad reviews on this board. I recently replaced the rears as I had put about 9k on them with aggressive street driving, and the insides were to the limit. Sumitomo must have changed something, because now the car feels like it has mismatched tires. I feel like I am going 20% faster than indicated speed. Not stable at high speeds. I have replaced the rears with other brands over the years, and have not yet felt this. At first I thought they just needed to break in, but now I think not. Any others have this experience when replacing the worn rears with the same tires as existing fronts?

darth g-f

Well I did that a lot on my track Elise. But like the TT, it's always two sets of rears for one of fronts. So the car always felt planted, because worst case, was some understeer because of the heat cycled and hardening fronts.

I doubt Sumitomo changed their compound. But maybe they did. At first my Sumis were a bit greasy when new, but that didn't last long. You say it's not that, so the only thing that comes to mind is the tire pressure getting lower with the lower outside temps making the car less predictable.

James88

I had this same issue except l went from Pirellis to Michelin ps2, Pirellis had
a direct steering and the ps2 soft cushy feeling not very nice.

Kevinmacd

They may have increased the tread depth, if that is the case you may be feeling the tread moving until they wear down a bit.

thomapa1

I'm on my second set of Sumitomo rears, first set up front still. Overall, I thought an OK tire for around town driving.

First set of rears lasted 5k miles and had even wear (a few spirited mountain runs, a DE). I'm at about 6k on this set of rears and still have some life left (about 4 Autox events).

Car came with worn Sumis on the rear and PS2s up front - I quickly went to new Sumis all around, but I always had an 'unstable feeling' at speed, as in highway driving - lane changes. Seemed like I was always doing some steering corrections, had wandering/tramlining. Tweaked my suspension adjustments, no luck until I played with tire pressures.

I used to run 34f/42r cold. These tires heat up quite a bit when pushed. Eventually started measuring tire pressures hot and brought it down to 34f/35r hot which is about 31/32 cold. Made a huge difference in my stability. Not 100% better, but very much improved. Next switch is to go to PS2s to see if that solves everything.
Take a look at your tire pressures as a start.

rmc1148

I would drive them for awhile and let them wear in, I just put new contis on rear front were like new= same feeling

jeffbnnc

I just put a whole set of them on my ride last week. I don't drive it much or track the car. But, I'll report back on wear issues. Rides great to me. Handles really good as well with them.

Happy trails!

drh

I like my Sumis. Perhaps yours just need a good scrub in.
PS-2s were squishy and wore out way to fast
Pzeros were nice but got very loud after some use.

Lance 4c

Thanks for all of the advice. I was thinking the tread depth could be the issue, but didn't experience such a noticeable difference in past rear swaps. I will also try the 31/32 pressure and see how it drives. Like I said in my post, the first set felt awesome after a few miles of break-in. Now I have put over 500 miles, but still not feeling the love. Thanks again. I will report back with any changes.

Carlo_Carrera

Sounds like the new rears just need a few heat cycles to firm up. Most tires need this.

brad@tirerack.com

How worn are the fronts? Half worn fronts that are heat cycled harder will feel different when combined with new tread-depth rears. It's possible there could be some mold release still in the new rears as well, making them slide just a bit. This feeling is a complaint I get once in awhile, but I don't see as many instances of it from the Z IIII as I do with Hankook V12's. Give them several hundred miles to break in and re-evaluate the condition. It's a difficult condition sometimes to put your finger on or resolve, and you may have to break down buy a set of new fronts in order to truly get expected performance back. At least they are cheap.

As far as we know Sumitomo has not made any changes to the tire.

Lance 4c

Thanks Damon. I have over 700 miles on them. I know the greasy feeling when they are new, but this isn't what I am feeling. What do recommend for air pressure? The feeling is more like a sway at high speed. The car feels unstable at high speeds, like what I felt on a previous Porsche I owned when it had mis-matched tires. I was thinking the tread depth changed the rake...Theoretically speaking, 100 feels like 130, and so on. Speeds under 80 feel normal.

383hq

Don't shoot me for stating the obvious, but it's also worth checking the tyre pressures with a good gauge once back from the shop.

Macster

Assuming the tire inflation pressure is ok, if the tire is unidirectional it is mounted in the right direction, and the car's alignment is within spec, it reads like the tires do not have the sidewall stiffness or perhaps some other parameter is incompatible with the car's tire needs.

Often owners of these cars operate on the assumption that as long as the tire fits that all that matters.

But just because a tire fits does not mean it is suitable for use on the car.

Lance 4c

Macster. As I posted, I was very happy with the original 4. I am questioning why the car doesn't handle as it did after replacing the rears with new same tire. Your statement below does not apply:

"Often owners of these cars operate on the assumption that as long as the tire fits that all that matters.
But just because a tire fits does not mean it is suitable for use on the car."