The Kumho tires are quiet but squirmy

[MikenOH]

Tire compounds harden with age. What you have now is a newer tire in the front with rubber as soft as it gets from the factory and tire on the rear which has probably hardened over the years. Not very conducive to balanced handling, besides the differences in how the tires are designed.

I understand everybody's financial situation is different, but mixing tires, in my experience, isn't going to get you where you want to go with the Boxster.

[Dale_K]

The rear tires are part of a matched set of very inexpensive ($300 for all 4) Sumitomo tires the previous owner put on in July 2010. I understand the risk vs reward question about mismatched tires and was willing to accept it. The new tires are listed as "grand touring" tires rather than max performance and I was willing to accept that too. The most I'm out if I junk them is $230 so it's not the end of the world.

Seeing as how I'm not getting much tire pressure advice I'll try out some different pressures and report back. I like the nice quiet ride and the ablility to rotate tires from side to side. No so good for responsiveness though.

[Topless]

Originally Posted by Dale_K

The rear tires are part of a matched set of very inexpensive ($300 for all 4) Sumitomo tires the previous owner put on in July 2010. I understand the risk vs reward question about mismatched tires and was willing to accept it. The new tires are listed as "grand touring" tires rather than max performance and I was willing to accept that too. The most I'm out if I junk them is $230 so it's not the end of the world.

Seeing as how I'm not getting much tire pressure advice I'll try out some different pressures and report back. I like the nice quiet ride and the ablility to rotate tires from side to side. No so good for responsiveness though.

Dale,
I am sad to say that tire pressure advice wont fix this. Grand Touring All season tires are just far too different from Max performance Sumis to ever be a good match. Your car will feel like it is on banana peels until you resolve this. If you like the Grand Touring A/S tires, put em on all four corners. You will get a nice quiet comfortable ride good in all weather conditions and sacrifice some grip. Maybe a good tradeoff depending on your driving style.

[thstone]

I think that you're not getting much tire pressure advice because adjusting tire pressures can't possibly solve the problems that you have described.

Here is a guarenteed solution to every problem you mentioned:

Step 1: Throw away all four of the cheap Grand Touring tires.

Step 2: Go buy a set of four Michelin PS2's and have them installed at a reputable tire installer. You simply cannot go wrong with these tires.

Step 3: If you want to reduce a little of the inherrent understeer that is designed into the Boxster, then go slightly wider and slightly lower in profile in the front (245/35/18) to get a little better front bite. You need to lower the profile (while increasing the width) to keep the overall diameter nearly the same as the stock tire to avoid problems with your speedo and ABS. Stay stock in the rear (if you increase width in the front and rear then you won't address any of the stock understeer).

Case closed. Problems solved.

[chris97boxster]

My 2 cents
when I put new rubber on the rear (M-pilots)
I messed with the tire pressures for about the next week
Why? A 2 pound difference makes a large enough difference
to the way a tire carcass behave...that u should not ignore the/feedback
that the tire is giving you....this goes for any brand of tire
I started @ 31 psi then 33 then 35 (rear)
noteable diffence in how the tire behaved (rolling over/ sidewall flex/ or too harsh/stiff)
and what.sound it was making (tire squeal/chirp)
pick the same road/turn (cloverleaf) & drive it a few times with different tire pressures

I settled @ 34 in the rear
and 33 in the front
your results will b different BUT TRY IT
I've heard good things about the tire ur using
But the person telling me about this tire was using it on a 240Z
and loved how it made the car handle and behave when pushed

Establishing the right tire pressure helps u get the max out
of the tire which means u get the car to handle like it should
And to me, handling is the utmost important aspect of this car
especially when I tackle cloverleafs & on/off ramps.

I remember someone on this forum stating that anyone can go fast
in a straight line, but turns make drivers better (something like that)
Ok...my 4 cents
Chris

[Dale_K]

Thanks for laying out how you experimented with the pressures. I'm running 29/36 at the moment and I'll try going up a few pounds on the front (new Kuhmo) tires.

The PS2's are too expensive for me. I might go with Hankook Ventus, which is what i have on my Corvette, if I decide the Kuhmos aren't gong to cut it after trying some different pressures. The Ventus tires really work well on the C6 but I have to carry an air compressor and tire plugs since they're not run flats. Good trade off for a better ride though.