Tire width or compound? (NOT a "which tire should I buy thread)

[Hornung418]

I've got 235 Kumho XS mounted on 8.5s. Killer in the dry. Tragic in the wet.

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[M0nk3y]

BP,

One thing I may note is that he may have pushed the limit of the tires and overdriven the tire to cause it to chunk. It may be his driving style that cause the tires to excessively chunk. He bought the PSS when they were first introduced in 2011 and there were barely any real information on them except they were a bi-compound tire with a harder compound in the middle and a softer compound on the outer edge. I believe he was driving it like it was a Bridgestone RE11 and that may have cause the tires to reach it's limit far faster than it was capable of handling.

As for rain,
I've tried my 255/35/18 RE11s, 245/40/17 StarSpec1s in the rain and its definitely not bad in regular rain. However if there is a lot of standing water, I would be more concern with it. The treadwear 200 tires are definitely aren't extremely terrible in the rain, just not as great as some regular summer tires. If I ever switch to R compounds in competitive racing, I'm sure the RE11 or Starspecs would be my intermediate tires.

Personally I would try the PSS even at the cost. It comes with a 6yr 30k warranty if it is same tire size all around. I definitely expect the PSS to outperform the S04 and DW on the track. Since my usual cost for tires is roughly $1200 for the RE11 on the 18s, $900 non-mounted isn't too bad.

Actually, DWs are superior in the wet over Star Specs, RS3s...etc. Many people on autox run small tires (around 225-235 on a 9" wheel) during rain events

[derbo]

Would that appy to track days too? Everyone I encounter had used star specs in the rain but it's not in heavy rain.


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[LivesNearCostco]

In theory, tire width shouldn't matter for lateral grip. Friction is F*A*k, or Force (downward force per area unit) * Area * friction constant (tire compound grippiness). If your tire is twice as wide, it has 1/2 the downward force per area--assuming car weight stays the same. If your tire is half the width, A is halved but F per area is doubled so again theoretical friction is the same. But in reality this isn't true because friction does not go up linearly with downward force. Double the downward force per area = less than double the friction per area, so wider tires usually have more grip in the dry and lighter cars normally corner better than heavier cars -- if all else is equal.

Several things also mess up the equation, mostly heat and water. Tires have an optimum heat range so the friction constant "k" increases then decreases as the tires warm up. Narrower tires heat up faster than wider tires. So if you have a light car in cold weather, narrower tires might get into the best temp range sooner. A heavy car in hot weather might like wider tires to prevent overheating. And in rain a narrower tire might cut through the water better to get more surface area onto the ground.

Back from my tangent... all else equal, for dry track I would get 9" wide wheels and 255mm tires in the best compound I could afford (where "best" is some combination of dry grip, wet grip, and ability to handle heat). Since I already have 8.5" wheels, maybe 245mm.

[az3579]

Back from my tangent... all else equal, for dry track I would get 9" wide wheels and 255mm tires in the best compound I could afford (where "best" is some combination of dry grip, wet grip, and ability to handle heat). Since I already have 8.5" wheels, maybe 245mm.

You know, you can fit 255's on a 8.5" wheel. That is the stock setup.


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[LivesNearCostco]

You're absolutely right, and my street tires are 255mm rear on the stock 8.5" rim. I did run 255mm Hankooks on my 8.5" track wheels, then went to 245 ExtremeDW, then 235 Conti/Hoosier takeoffs (which are really like 245mm). There's lots of online debate about which is the best tire width on 8.5" rims--many say the 255mm is better in the dry. I'm not good enough of a driver to say for sure whether 245mm has better turn-in and steering feel, especially since I've never tired the same tires twice in different widths.

I signed up for driving school with local Porsche club next weekend. Was assuming it would be my last event on the Conti/Hoosier slicks, but rain is forecast, so maybe I will be driving the staggered PSS (OEM rims) instead.

[tkundhi]

BP,

I know you are considering a 255 tire but let me share my experience. I recently went with PSS in 245/35 all around on the ZHP. Cheaper than the 255 but not by that much ($206/tire). FWIW, there is a $70 rebate till month end. These tires will be 85% street and 15% track. I mounted them Wed and immediately drove 900 miles to COTA and then put 250 track miles on them this past weekend. Last year I ran the Dunlop Direzza ZII in 255 on an E36 M3. The ZHP is heavier than the M3. The PSS definitely have more grip. So I think compound in more important than width.

Note width will vary based upon manufacturer. Sometimes even within manufacturer. Michelin makes two versions of the PSS in the 245/35 18. One is an OE spec tire for the European M135, the other is the regular version. Both are available here. The OE Spec tire has a wider tread width and is over 1 lb lighter. It's also more expensive by $30/tire. I went for the cheaper version.

FWIW I had no problems running with a 332ti on Hankook (r-comps) and an E34 M5 that was on Hoosier/Contis. I didn't think I would stay with those cars on their sticky tires. But I did. Overall I very impressed with the ZHP on PSS.

Since much of your driving will be street use, do you end up keeping the tires until the are completely worn? With cheaper tires I found myself replacing them sooner. Wet performance went down and noise went up as they wore.

t.

[az3579]

T,
That is some good insight. At this point I have no doubt in my mind that the PSS's performance is top notch. This is why I'm considering them as my next set of track wheels when they wear out, probably in 245 size as well.

Going forward I'm going to consider the tire's performance over its size based on the logical answers I see in this thread.


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