I have been told that when racing with R-compounds (treaded I assume) in the rain, it's best to lower the tire pressure. Now this is contrary to street tires where you would raise the psi for wet conditions on the street.

Why would you lower the psi? Would you do the same to a performance street tire on the track?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RacerZook &raquo;</TD></TR><TR><TD CLASS="quote">Why would you lower the psi? </TD></TR></TABLE>

Theory is to allow more tread squirm thus creating heat allowing the rubber to become stickier. I rains here all the time and we have yet to really figure out whether lower or higher pressures make much of a difference.

Driving smoothly seems to be most important.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RacerZook &raquo;</TD></TR><TR><TD CLASS="quote">Would you do the same to a performance street tire on the track?</TD></TR></TABLE>

I wouldn't have a clue and have no need to know.

Rick

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turfer &raquo;</TD></TR><TR><TD CLASS="quote">
I rains here all the time and we have yet to really figure out whether lower or higher pressures make much of a difference. </TD></TR></TABLE>

I think that's because it depends on the specific tire you are talking about. Running higher pressures can also cause the tire to slip and create more heat. I don't think any generalization can be made about all tires.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
Driving smoothly seems to be most important.

</TD></TR></TABLE>

Okay, I stand corrected. THAT is a good generalization.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RacerZook &raquo;</TD></TR><TR><TD CLASS="quote">Why would you lower the psi?</TD></TR></TABLE>

To try soften up the car (same reason you'd disconnect the sway bar or adjust your shocks). Not sure to what extent it would work and I want to say that I have run w/ higher and lower pressures and I can't say right now if I recall a difference.

 

I run both Hoosiers and Michelin Sport Cups. I do not know the official Hoosier recommendation for rain pressure changes, but Michelin recommend raising the pressure by 5-6 psi for the rain to help raise the temperature. They also recommend cutting groves into the tires for any more water than just a "wet" track. I was also running Yokohama 032R-Soft compound as a wet tire this year and that worked very well, as they came up to temperature much better than those others and the grooves seemed to clear the water quite well. I have not seen any official rain recomendation for the Yokohamas either. So in the case of the Michelin's, you stiffen the tire as the temperature gain it gives you in the rain is more important for grip (those are low grip tires when cold, but great when hot), and then soften the suspension to reduce the 'sharpness" of the car's response.

 

I would think that you would want higher pressures. In the rain you constantly have the H2O on the tire, cooling it. You aren't going to have the increase in pressure that you would in the dry. So I could see a higher starting pressure with a target "hot" pressure that is lower than dry pressures.

Or just be smooth

 

There are a lot of trains of thought out there, but here's mine.

If it's raining hard and a lot of standing water has developed, I run higher pressures. This makes the tire more round (balloons the tire) and it has a better chance of cutting through standing water before aqua planning.

If the track is just wet with few, if any, standing water areas I would run normal or maybe even slightly lower cold pressures than usual because:
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turfer &raquo;</TD></TR><TR><TD CLASS="quote">Theory is to allow more tread squirm thus creating heat allowing the rubber to become stickier.</TD></TR></TABLE>

Why I don't believe you would do this with street tires is because street tire compound does not benefit you with significantly more grip (if any) once they are heated up, as R compound tires do, so there is no reason why you might want to heat them up faster. The only thing I would try if it's raining hard would be to start them off at higher pressures to create a tire that's more round to cut through water slightly more effectively.

 

I agree with Hracer.

In rain, and on a track with standing water, you want to run higher pressures; 5 or 6 psi more. Because this overinflates the center section and helps in water evacuation. I tried this at Laguna Seca in the rain, using ao32r tires; when I ran them 5 psi higher than normal, the car felt better overall than running the reccomended pressures for a dry session or even lower pressures than normal.

On a damp track or in cold weather, I usually run 1 - 2 psi more pressure to help the tire heat up.