fatbillybob

For you guys racing in the rain with dedicated rain race tires like the hoosier dot sports car rains, if you were buying a second set of wheels would you buy and run the same size wheel and tire you would in the dry? In the snow on streets a narrower tire often outperformed a wider tire. What happens in the rain? Narrower still better?

Thanks!

Larry Herman

I run my Hoosiers on the same size wheels because #1 it is what Hoosier recommends and #2 it is what I have. I am limited to the same overall tire sizes due to availability. I do not know if pinching the tire on a somewhat narrower rim will have any measureable affect on it's contact width.

SundayDriver

Narrower is better with a lot of water. My Goodyear rains - same labeled size as the slicks - are narrower at the tread. The challenge you get with real rains is as the track dries - the rains are a very soft compound (at least full-on racing rain tires) and will not last when heated on a dry track. In that situation, wider helps keep the temps down.

I would guess an inch or two narrower at the tread is good but much more is a problem. Because of the deep grooves (and pattern) along with a very soft compound, true rain tires have amazing grip in the wet.

Gary R.

I had a set of 16" rims that came with my car that were 1" smaller diameter than the 18" wheels my R6's are mounted on. I run 225/255 Wets on them vs. 245/275 Dry R6's. Seems to work well.

pat056

Bob Woodman from Woodman Tire recommended I go with a narrower tire for rains, the theory being they would move more water away from under the tire quicker.
My Hoosier Tires sizes:
Dry- Front 245 Rear 275
Wet- Front 225 rear 245
I amazed at how well my car sticks in the rain.

Sean F

+1

ltc

^ +1, at least in karting.
You will also adjust tire pressure depending on how much water is on the track.

fatbillybob

oh, I didn't even think about tire pressures. Any comments on you you find that sweet spot? Do you still use a pyrometer or manufacturer settings? It is hard to get rain experience.

SundayDriver

Pyrometers are pretty worthless for rain tires, at least at our levels. I start with a higher cold pressure - usually about half way between normal cold and desired hot. Part of the strategy is that you won't get as much heat. The other part is you want good separation of the tread that comes with higher pressures.

ltc

Sorry I have no experience with rain tires/pressures on my Cup car....haven't driven in 2 years and may never drive it again.....

On karts (Bridgestone YKP tires FWIW), the pressure difference can be almost 2:1.
25psi in absolute full wet/torrential conditions, 15psi in wet/damp conditions.

As mentioned, it has to do with heat/pressure rise and also contact patch.

Another curious thing about karting (my son LOVES karting in the rain, odd kid I know) is the gearing changes and wheel changes. (I'll skip the chassis changes, seat position changes, alignment changes, yadayada.....it's amazing how much stuff you have to change in 15 minutes if they declare a wet race)

We will almost always go up 3-4 teeth in the rear (compensates for lower cornering speeds/lower RPMs) and some people will switch from magnesium rims (almost always used with slicks) to aluminum rims...the theory being aluminum holds the heat better than magnesium.

sleder

+1 on size being slightly narrower- +1 - 17 " wheel dia. vs dry @ 18" and +1 on higher pressures.

stownsen914

Judging from what the pros use as rain tires, width must depend on the aggressiveness of the tread pattern. Look at how wide the rain tires are on pro cars (ALMS, Grand Am, etc). They seem to use full width or very close to it. But their rains also have very aggressive tread patterns (wide and deep channelling to flow lots of water). I would think that narrower treaded tires outperforming wideer ones probably happens when the tread patterns are more like "standard" road tires.

Scott