Hi folks,
While testing IR temp sensors, I noticed that the center of my tires are cooler than the shoulders during high speed corners. This seems to suggest my tire pressures are too low for the load placed on the tires, is that correct?
https://www.youtube.com/watch?v=SWKnXWSbeNM
The pressures I'm running now (31 psi hot, -4 camber, 295/30/r18 RE71RS on 10.7" wheel, 3500lb rwd car), seems to be what most folks recommend on this platform, and what I've had good luck with in previous years. Could it be the aero platform causing an increase in load, and thus making the tire underinflated relative non/low aero cars?
Basing on ride height changes at speed (8 hz laser distance sensor), and cornering speed increases, I would estimate the car's making 20% of its weight in downforce at 100mph (will be tested in a tunnel). Should I increase my tire pressure based on the cornering time weighted average weight accounting for aero?
It seems my front left contact patch would be 690 cm^2 without aero, and 820 cm^2 with aero at 100mph. Is this increase causing the center of the tread to buckle in under cornering loads? Pyro suggests things are okay (linear temp delta from inside shoulder to outside), but I think the temp is normalizing across the width of the tire on the straights.
At the end of the day, what matters is not what the sensors or the theory says...it's what is fastest (if that's your bag) or what produces the best wear (if that matters more). Period.
Sensors are data used to give a *possible* direction for improvement. Give it go, back-to-back, and meaure any performance change.
The guy who wins the competition is the one who goes the quickest...not the one with the "theoretcically best" sensor or pyro readings.
I've done plenty of testing where the empirical results did not match what theory predicted.
In reply to Andy Hollis :
Thanks Andy, I'll play with a pressure sweep next time on track. But before I do something dumb, do you think a 3500 lb car with ~700 lbs of downforce running 38 PSI for 295/35/r18 RE71RS would be a bad idea that shouldn't even be tested? I've seen a few rough numbers tossed around the forum here, and I think the highest number I've seen you give was ~34 PSI.
Came here to try and direct you toward some relevant articles, but it looks like the pro himself Andy has it handled.
For more datapoints, RE71RS will drop off in terms of grip when over 150f surface temp (gSum vs surface temp plot)
In reply to Andy Hollis :
Id be concerned that if you are running non optimal pressures you are compensating for another part of your setup you should look into. Tire pressures are a tuning tool but its a sign there is more speed elsewhere.
In reply to theruleslawyer :
Let me relate a story. It involves drag racing in a very specific rule set (stock appearing Buick Grand Nationals). 900-1000hp engines with stock heads and intake manifolds and stock appearing turbos that have 90-100psi exhaust manifold pressure to make 30 pounds of boost. It's crazy what they can do.
Anyway. An engine builder was commenting on a regular class winner using a much smaller cam than the other competitors. "How much faster would be be if he had a bigger cam?"
Maybe he's faster because he didn't go too big on the cam?
Faster is faster, no matter what the theoretical numbers are.
Pete. (l33t FS) said:
In reply to theruleslawyer :
Let me relate a story. It involves drag racing in a very specific rule set (stock appearing Buick Grand Nationals). 900-1000hp engines with stock heads and intake manifolds and stock appearing turbos that have 90-100psi exhaust manifold pressure to make 30 pounds of boost. It's crazy what they can do.
Anyway. An engine builder was commenting on a regular class winner using a much smaller cam than the other competitors. "How much faster would be be if he had a bigger cam?"
Maybe he's faster because he didn't go too big on the cam?
Faster is faster, no matter what the theoretical numbers are.
I guess if you are satisfied with that answer and your curiosity ends there. Sure.
What kind of sensors are you using to gather the data? I was just looking at IR sensors from IZZE I think, but they were pretty spendy for 4. Tried looking other places but they seemed even more expensive...
garudathree said:
In reply to Andy Hollis :
Thanks Andy, I'll play with a pressure sweep next time on track. But before I do something dumb, do you think a 3500 lb car with ~700 lbs of downforce running 38 PSI for 295/35/r18 RE71RS would be a bad idea that shouldn't even be tested? I've seen a few rough numbers tossed around the forum here, and I think the highest number I've seen you give was ~34 PSI.
Back when we did skid pad pressure sweeps, we'd typically go as high as 40 and as low as 22. But we also stopped going up or down when the lap times got worse.
You certainly won't hurt anything running that high.
