In my experience that 26 psi low pressure can still be too high when starting out on a hot day. The track will be hotter than the OAT. It is also not uncommon that tire pressures will increase by 10+ psi while driving on the track. A lot of it depends on ones capability, alignment, session length, etc. In addition its not uncommon that F & R tire pressures increase at a different rate. Plus different tire brands respond differently to a starting psi setting.

 

Yes and no; maybe an oversimplification on my part. What you're describing is how the "summer vs winter tires", "loaded vs unloaded", and "comfort vs non-comfort work" options work. The circuit pressure option is different (and temporary); I'll elaborate below:

Your tires read whatever they read by the TPMS (which is often not what they read with an actual gauge). You select the option that says "these are the circuit pressures". Which really just amounts to saying "I'm okay with these pressures". If you try to select the option and the tires are below a certain hard-coded threshold it won't let you select it no matter what. I suppose in theory you'd come off the track while tires are hot, and then select the option as your "optimal pressures", however, the value is lost every time you turn off the ignition. So, it wouldn't do anything for you on subsequent sessions (assuming it actually does something different with the TPMS programming).

So, for all intents and purposes, it just functions as a "I'm okay with pressures this low" check box, and letting you operate at a lower psi threshold than typical. It also has this lovely "feature" where if you're within a psi or two of the hard-coded lower limit it "rounds down" to being too low. So, your TPMS might warn you that the tires are low; you'll see one tire listed at 26 psi (that you manually measured at 27.something psi), you go to select the the "circuit pressures" option and it'll say, "sorry can't select a circuit pressure below 25 psi".



TL,DR: It functions as I originally explained. You're not missing much on a Spyder.

 

thank you for all info.. but what melted actually means ? I assume that tires are too hot, so they are overloaded by driving style?

 

Just to chime in- the photo of the "melted" tire, it is actually pick up of rubber from the track that other drivers put down. Especially if you get off line due to error or to make a pass you can pick up a lot of rubber. That's what it looks like to me.

 

yeah there are rubber from track when i was running back to pits, but also there snall waves, which i think its from tire

 

Yep, the "small waves" are normal. It is from the surface of the tire getting hot and sliding against the pavement repeatedly (normal when driving on the track; not to be confused with "drifting"). That appearance by itself does not mean the tire was overheated.

 

When auto's are imported by ship they are "tied down" & then the tires are aired up to make them even tighter. Dealerships rarely reset the pressure before delivery.