| Author | Message | ||
     Skully |
Back in October, I had a set up at our local track that worked quite well. I have Pirelli SC2 Supercorsa Pros, and the ambient temperature topped out around 80dF. Our first race in the CMRA will be in February. Typically, the day starts out around freezing and them warms into the 50s. Any suggestions about what tire pressures I should run based on your experiences with similar tires and temperatures? Thanks, Keith CMRA 211 | ||
| Slaughter |
You need more to measure the pressures HOT - read them as close to coming off the track as possible. 32/28 coming off the track would be a decent start. Maybe 31 in front... depends on how it's feeling. For cold pressure, the first guess would be about 4 psi lower... starting 28/24 If you have warmers, it gets dicey since you're probably going to be cooler at the end of 8-10 laps than coming off the warmers... so have your pit mate at the hot pit wall with a pressure gage - or better yet, go right to the Pirelli vendor trackside and have him measure the pressures hot. | ||
| Froggy |
Couldn't you run nitrogen to prevent the tire pressures from changing? | ||
| Slaughter |
Nitrogen ONLY helps because it is "dry" - no water in it (where compressed air has whatever water was in the air that day) - water expands HUGE compared to a gas. Because Sunny and I are scuba divers, we use scuba air for tires. It's free for us (she gets it because she's a scuba instructor) and is thoroughly dry and we have all the hoses, regulators and adapters as part of our scuba rigs. You are still going to get 4 to 4.5 psi difference between cold and hot pressure even with a totally dry gas. The "hot" pressure is really what counts - that is what your handling is based on and the ONLY way to get those numbers are to measure them coming off the track. The track-side vendors are an AWESOME resource for this information... but cold weather racing is a problem since you can LOSE a lot of heat in your tires just in the ride from your pit out to the track. Another really good thing to realize is that you might also want to drop another half to pound pressure just to compensate for the stiffer rubber due to the cold temperature. I run 32/28 (hot) pretty much year-round but drop almost a full pound when it's freaking COLD... and adjust AFTER my first session out. But again, my MAIN goal is just to finish a year without wadding up myself or my bike again and I just try to get points because I'm actually FINISHING - and not missing months-worth of points while saving up $$$ for repairs - or missing a couple months with bones healing... so I'm not pushing it as hard as a "real" racer. | ||
| Skully |
Steve, You and I have "talked" about this in some detail and what you say above makes sense. But at the end of the day, what is it we are really looking for? Is it constant pressure or constant temperature? I realize the REAL goal is grip, but what is the best method for predicting what the grip will be with the crude tools that I have (IR temp gauge and a pressure gauge)? I suppose that in a closed system, they are basically the same. Thanks, Keith | ||
| Slaughter |
This is from my age-faded memory of a few conversations with CT Racing (Pirelli distributor for West coast) It seems to be a couple things - heat for stickiness but in order to get the same "handling response" out of the carcass, you really have to have about the same pressure when the tire is up to working temperature - so you get the same amount of flex. The working temperature obviously varies a LOT. If the day starts out at 35 degrees (pretty likely here in 2 weeks) - I'll likely run HOT pressures of 30-31 front and 27 rear running SC1/SC2 - (Blue/Green) Pirelli - super soft front and soft rear. Measuring tire temps will be on the order of barely 120F when I get to the pits. Most of the rest of the year, I'll run SC3/SC3 (yellow/yellow) medium/medium and when HOT 32/28 the temps have read as high as 170. Again, the tires DO cool pretty fast coming off the track. Handy to have the "pit boss" right there coming off the track to measure temps (or leave your IR sensor with the Pirelli guys and ask them to be ready for you when you pull off) I guess, it's still a fuzzy "art" - and I keep the notebook handy. For the freaking cold days (Jan and Feb at Willow) - I'll get settings on the first practice session and make adjustments based on feel during the day... and sometimes feel that I'm chasing my tail. Again, I'm NOT a fast guy, this is just what has worked OK for me on the Pirelli slicks - same rubber compounds as the Pirelli DOTs (Message edited by slaughter on January 04, 2010) |
