Toyo recommends no lower than 18lbs starting cold pressure for RA1s to potentially achieve 200 deg tread operating temp, hot pressure 41-43lbs. Granted this is with at least 2.5 neg camber to -5 deg.

I wonder if in a 20 min session, starting at mid 30s pressure is just too much, with select portions of the tread heating up and sticking well before heat is evenly distributed across the tread.

Just something to think about.

If this is a wrong supposition, I wonder how much faster KMS could have gone at SOWs if the Kumhos he had didn't start with 17.5/22.5 pressures.

Let's see... PV=nRT. Was that Kelvin or Celsius... trying to figure pressures given a corresponding increase in a starting temp. Would a hot temp of 200 deg F with a starting pressure of 35 psi at 75 deg result in 41 psi? Or should we not even be concerned with these things?

 

I have started off with mid 30s (cold) and ended up with overheated/greasy tires during 20 minutes runs. I start with lower pressures now.

 

A lot of it seems to depend upon starting ambient temps, but I have found tires come up to temp in ten minutes or so. Found the pressure gain from cold to hot on Kumhos may only be 6-8 pounds with moderate temps but 8-12 gain with cold tires. So I would still start at 30 and come in for a quick check in the hot pit lane after 10-12 minutes to see where you are (for both temp and pressure).

 

I think if the pressures are right, the tread temp will basically be right. So if you're checking pressures when hot, it doesn't matter what they started out at.

I never know what my cold pressures are (i.e. what they were at the start of a session) until I check them the next day. Sometimes they're in the teens or low 20s, sometimes much higher. Just depends on the conditions at the track that day.

 

How much the tire pressure rise depends largely on how much water vapor is in the air in your tires, which you can't really control. This is largely why race teams inflate with nitrogen - to enable more consistent and predictable pressure response patterns.

 

Absolute temp (Kelvin or Rankine).

 

This year it seemed like I was getting major changes from Cold to hot PSI

Last week I drained the tank on my compressor on my garage, it about a qt of water drained out

Maybe I should check that more often?

 

cold psi is a joke. only hot psi matters.

you need to check your tires immediately at the end of each session.

 

Check your temperatures at three points across each tire (inside, middle and outside). If your middle is significantly hotter than the edges, your running to much pressure, and vice versa. This is assuming that you aren't suffering from any camber, castor or any other suspension mis alignments.

 

And/or get a water trap for your pressurized hose.