Race Rain Tires
Today I want to talk about race rain tires. My experience has been with non-DOT Hankook W50 190/570-15 wets but I imagine much of it will apply to Hoosier H2O and even more will apply to Hoosier Dirt Stockers, should anyone still have any.
Phenomenal Initial Grip
The first time I ran the Hankooks, the car felt very close to operating in dry conditions despite the weather being a steady light rain.
Rubber on race slicks and street tires is too hard to really grip wet pavement. Due to water film on top of pavement the pavement does not bite into the tire as hard as when it is dry, resulting in a loss of grip. Worse, because the grip is already partially lost the difference between maximum grip and zero grip (e.g., tire hydroplaning over water) is smaller. Race rains have a very soft tread compound - similar to snow/ice tires - which deflects a lot more than dry tire compound, and is able to stick better to wet pavement. When people talk about rain tires "inspiring confidence", they are referring to the much bigger difference between "grip" and "no grip" of race rains vs dry tires, as well as the driver feeling the race rains losing grip partially (tire lifts over water but does not completely detach from pavement) whereas slicks especially are more like on/off switches going over water.
In the event in which I ran the Hankooks for the first time I started the day in the novice group and was promoted to the intermediate group for the second session and advanced group for the third session. I was quite literally running circles around most of the remaining cars on the track.
And Then They Sit
The fact is, it does not rain that much here in Northeast. If you do few events per year you might get unlucky and have rain on, say, 2 out of 5 weekends. With more events, the percentage that are held in rain rapidly decreases.
Full rain tires have compounds that are too soft for dry conditions. These compounds are intended to be cooled by the water on the track. When driven on dry pavement, which could be as much as a dry line on a largely wet but drying track, the tires overheat and literally melt.
Add the time and effort it takes to change from dry to wet tires, and even when I had rains mounted I only really used them in steady rain conditions. If it rains slightly, or might rain, I often stay on dry tires until the car hydroplanes, and only change to rains for the following session.
The result is the tires sit unused for much of the season.
There are two parts to wet tires: tread pattern that evacuates water and soft compound that conforms to the road surface better. As the tires sit, rubber ages and hardens. The result is that old race tires do not stick to pavement very well.
An important observation here is that a slick tire in light rain does not actually hydroplane most of the time. In a moist or lightly wet scenario, a soft slick can still get through the moisture to the pavement. And being soft, the tire will still grip. In lightly wet conditions a soft slick can outperform a hardened with age rain tire.
I've owned my race rains for about 3 years. In this time they froze in the bed of my truck for at least one winter.
By last summer, I only ever ran the rains in downpours. I got some Hoosier A6 mid season and used those in moist, wet and even rainy conditions. In fact, only when the car started positively going off track I began to contemplate changing to rains.
Toward the end of 2013 I bought a set of Bridgestone RE-11 street tires. I intended to run these in wet conditions where I would have run the race rains previously. Street tires are not going to be as good initially but they should not fall off drastically over their lifetime either. Plus, because they are pretty hard, I can use them in drying conditions, when rain is forecast but before it happens, and in cold weather if I want to use them up for whatever reason.
The last event of 2013 at VIR it did, in fact, rain and I ran RE-11s. They were ok - not mindblowing, but not bad either. I did not set any lap records but the tires felt solid.
Street tires are definitely not magical and need care when driving over lakes and rivers. But they should have a long and productive life.
Tagged: rain driving