Quote:
Originally Posted by renfield90
(Post 2523199)
It's a less a question of skill - I'm not a pro, but on certain tires I can detect a change in the balance of the car caused by 1-2psi - and more one of magnitude. Your average street tire is going to want pressures in the 30-45psi range, vs. true slicks which want their pressures around 20psi or sometimes even lower. Longacre will sell you 0-60, 0-30, and even 0-15psi gauges as a result.
When pressure is lower, 0.5psi is suddenly a much larger adjustment in terms of percentage. If you had some hypothetical tire that was inflated to 1psi and you adjusted by 0.5 psi, that's a massive 50% change.
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I never implied that the difference couldn't be felt by an amateur (I know I've felt happy about 1/4 psi adjustments before) but rather that it's of minimal value in the amateur HPDE world vs. other settings that can be manipulated such as camber, toe, spring rate, sway bar, damping, etc. Being "in the ballpark" is usually as good as you need to be.
Quote:
Originally Posted by Toyarzee
(Post 2523209)
That's my concern. Even if I'm militant about finding a routine where I can get as close as consistent as possible, I'm worried that this elusive issue will cause data collected to be less accurate and useful. Plus at Buttonwillow and some other tracks, a cool down lap and 5 mph lap around the garages will drastically alter my temp readings and I'll find myself only getting good pressure readings.
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And that's why people who are good at setting up cars make the big bucks. I always look at it like a divining rod "My current data shows I'm here, I want to go there" i.e. if my fronts are hotter than the rears by 10 degrees I can interpret that as understeer and make adjustments, maybe the next data set the tires are 20 degrees hotter overall and the delta increased to 15 degrees, whatever I did didn't work (or maybe the driver is doing poorly i.e. overworking the fronts under braking, or maybe it did work but other factors contributed to the increase) and you use your divining rod to adjust from there.
Yup some snapshots are dark, some are light, some are hot some are cold, some are 20 feet from the track exit some are 200 feet, the car is the same and so is the driver, if the metaphorical camera is in the same position you can make steps to bring the image into focus.
Quote:
Originally Posted by Toyarzee
(Post 2523215)
Also, what spurce do you guys reference when citing optimal pressure and temperature ranges for different tires? Or is it mostly guess and check, and other drivers input?
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I never found anything other than random forum posts, for instance, contrary to renfields post above from what I've seen the current crop of street tires on an 86 or similar lightweight vehicle like to be sub 30 psi ambient, low 30's when hot, some people have claimed as high as 34 but I find those setups seem to have a big split between tire pressures indicating to me that they're band-aiding a handling problem elsewhere. By the end of last year I was setting my tires at 27 psi in the morning and leaving it alone the rest of the day as the other variables (namely camber and driving) were more valuable to track and tweak for me.
Experimentation (read: guess and check) will always win out in motorsports, build intuition, write down adjustments and results, and use that to guide future guesses. It was a valuable piece of advice as a kid that if you always follow the guidance of someone you will always be a few steps behind them, something unacceptable if you're competing with the guy.
:cheers:
:burnrubber: