Tire pressure in the rain question...

makaio · 11-07-2002, 10:25 AM

With next weekends track event at Thunderhill on the horizon, I'm trying to prepare my car for possibly a wet track day.

If it is raining or the track is wet, should I alter my regular tire pressure? If so, would it be up or down? I've never driven on a track in the rain, and I'm hoping that the Porsche gods will part the skies for this event

makaio · 11-07-2002, 07:24 PM

BUMP

I know you folks in the PNW can answer this one.

pwd72s · 11-07-2002, 07:57 PM

Wet or dry, I didn't bother, back in the old days, to change pressure for a track event because of the wet. But you did say track event, right? If the rain is fresh, a LOT of spilled oil is going to come floating up to the top...making things slippery as cat barf. If the rain has gone on long enough to wash the floating oil away, things are less slippery. Matt, have you ever driven in snow? If the rain is fresh, with standing water, drive as if it were snow, then build speed up if things don't get too loose...in other words, ease into it..

makaio · 11-07-2002, 08:09 PM

THanks for the tips Paul. When I first became a Fire Engine Operator, they put us through a "skid pan" training in old CHP cars. It's a 1/3 mile concrete track, painted with an oil based paint, and sprinklers to wet it down. Boy was that fun. Much like driving on ice with slicks.

The oils from T-hill should be lifted and washed away by Saturday the 16th, since it has been raining pretty good here, and it's not suppose to let up much in the next 7-8 days.

pwd72s · 11-07-2002, 08:19 PM

Just ease into it Matt...you'll get the feel as you go. But avoid being near other traffic, especially those who didn't just ease into it. Dig? Your fire truck skid training will serve you well here...

Don Wohlfarth · 11-08-2002, 05:20 AM

There's no secret, it's slick. Back it down.
If it's raining not only is it slick, you can't see but it may be slightly easier to drive as you will probably have standing water and you should at least be aware of that. There is a good chance of hydro planning.
You want to run a narrow tire with tred if possible. Raise the tire pressure 4# as this will help the tire move the water from under the tred.
If there is no standing water and the track is only wet you will be surprised as to how much grip is available, but it is still different from a dry track.
Paul's analogy of driving in snow is a good one.

Randy W · Randy W's Garage

There are two schools of thought regarding tire pressures in the rain: 1) raise pressure a few pounds to prevent hydroplaning, and 2) lower pressures a couple of pounds to prolong breakaway and improve traction in the slick conditions. Either is probably right, depending on the tire's tread design, the amount of speed you are carrying, and the number of turns you have to make.

David Bahr · 11-08-2002, 07:04 AM

After waiting to see what the experts would say, I would add this: the theory as I understand it is as there is less available grip, your cornering Gs go down, so you use a softer suspension setting, including lower tire pressures. Of course, if it's raining ambient temperatures are probably lower, so cold pressures need to be higher. I bet variance in circumstances prevent a good rule of thumb.

I think Thuderhill is asphalt so less standing water. Concrete tracks seem to get more standing water as the concrete sections settle differently. Either way, I seldom have experienced hydro-planing at the track in turns, only on the straights where speeds are higher. That's even on DOT R tires with no tread.

Good luck, ease up to speed, and keep the shiny side up. You will learn a lot more driving in the wet than in the dry.

Also, on wet days I keep a towel stuffed under the passenger seat so I can dry off the soles of my shoes after I get in the car. Wet shoes can slip off brake pedals. Not fun (don't ask how I know!).

makaio · 11-08-2002, 07:09 AM

David, thanks for the tip on the towel. That's a great idea.