One of the things I really like about these types of discussions is that it brings out the myths people have. I hope everyone realizes that I am pointing these things out so we can all be better informed. I've learned a lot of things in these forums, and tires happens to be my area of expertise. Please don't take this personally:
Originally Posted By: fsskier
H and V rated tires are often very poor in rain, some are just plain dangerous.
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Sorry, just the opposite - compared to S and T rated tires, H and V rated tires have much better wet traction - all other things being equal.
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Making H and V rated tires requires the use of low hysterisis rubber compounds that bend and distort very little - in order to remain cool at extremely high speeds.
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I just spent 15 minutes on the phone getting a short lesson on tread compounds:
Tread compounds that have low hysteresis have good rolling resistance. But you can't use hysteresis to characterize tread compounds that wear well against tread compounds that have good grip. They will have higher hysteresis than good RR compounds, but other than that, the correlation falls apart.
So if you had to characterize tread compounds on H and V rated tires, "low hysteresis" is not it.
Further, it is the construction that gives the tire its speed capability. H and higher speed rated tires have to have an overlay over the belt - commonly called a cap ply. The higher you go, the more overlay you need.
What the overlay does is reinforce the belt package. This resists the centrifugal forces, reducing the magnitude of the standing wave, and therefore not only reducing the running temperature but also reducing the stresses on the belt package.
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The downside of these hard compounds is inflexibility, and low traction when cold. Witness the Indy cars flying off the track at low speeds when behind the pace car.
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That is caused by the tire not being heated enough. When they get up to operating temperature, they grip just fine, thank you!
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Tire engineering articles often talk about this conflict, indeed Car and Driver writer Pat Bedard once noted that most people using V and H rated tires were increasing, not decreasing their risk.
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I think you've misinterpreted something Pat wrote. I'll bet that what Pat was trying to point out was that lower aspect ratio tires are more prone to hydroplaning - and that is true. It is also true that lower aspect ratio tires tend to have higher speed ratings.
One of the major problems in trying to sort this out is the "All other things being equal". There are so many permutations that it is hard to make generalizations from experience.
If we separate "wet traction" into 2 components - hydroplaning resistance and wet grip - you'll find that hydroplaning resistance to almost exclusively the tread pattern, while wet grip is a combination of tread pattern (mostly sipes) and tread compound.
As pointed out, there are compromises that have to be made and it is sometimes difficult to sort out what the compromise was unless you're the guy designing them.
OK, that's a first pass through. I'll let others comment before the next installment.