Q: “I did a track day at NCM in the rain – not damp, but RAIN. Rain, as in standing water many inches deep against curbs, little rivers flowing, no visibility when following… you get the picture. Years ago, I thought you would lower your hot (coming off track) tire pressure to soften/make more compliant tires as you do for sway bars, shock settings, etc. However, a pro who’s name I won’t mention (but he’s won a “few” races in BMWs), suggested that lower pressure was flat wrong. He said you should increase your hot pressure significantly to help pump the water from under the contact patch. Since then, I’ve tried raising a couple of psi a few times and it didn’t hurt, but it wasn’t obviously better either. What’s your take? Raise pressures, lower pressures or the same in the rain?”
A: “Raise pressures, lower pressures or the same in the rain?” Yes.
I’m kinda joking there, but kinda not. Here’s my experience and very general guidelines: If the track is wet but without water building up, then lower pressures can help, as it “softens the car”; if there is water building up (as in puddles and rivers), then higher pressures to get that crown on the tread so the tire will cut through the water will help. Of course, there are always exceptions to the rule, and knowing when water is building up on the track surface is not easy (and it can change from lap to lap).
I’ve had great success with higher pressures. And it’s not a matter of raising them 1 or 2 psi – they need to be raised a lot. I’ve taken a race rain tire that usually ran with 25 psi up to 40 psi – it was fantastic in the heavy rain. It was not so good when the track began drying!