lower tyre pressures
Pro
Joined: Oct 2005
Posts: 628
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From: Summerville SC
[QUOTE=dr bob;7730864]I have a very vintage direct contact pyrometer that's served me well. Fast-forward to modern tech, and the IR temp gun reads quite close to and a lot faster than the old tool. Just shoot from close in, maybe an inch or two. --Record your readings!!!--
I thought you were supposed to check the temp at about 1/8" inch into the tire for proper readings. The surface cools very quick when coming to a stop to check them and the tire pyrometers are set up to calculate and compensate for how much heat is removed when the metal spike is inserted. I think a good tire pyrometer is more complex than just a surface reading IR gun.
my .02
I thought you were supposed to check the temp at about 1/8" inch into the tire for proper readings. The surface cools very quick when coming to a stop to check them and the tire pyrometers are set up to calculate and compensate for how much heat is removed when the metal spike is inserted. I think a good tire pyrometer is more complex than just a surface reading IR gun.
my .02
Race Car
Joined: Dec 2003
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From: Atlanta, GA
There is a very big difference in optimal tire pressure between different tire sizes and profiles. I have noticed that the lower the profile, the lower the pressure I need to run because the construction of the tire itself is a lot stiffer to be able to handle that lower profile. I found that for 235/40-18 and 265/35-18 tires, 28psi front and 30psi rear cold readings are optimal for even tire wear. In contrast, 205/55-16 tires on the other car require at least 36psi cold.
Another thing that makes a large difference is the width of the wheel compared to the width of the tire. If the wheel is very wide compared to the tire (i.e. 265 tire on 10" wheel), the pressure should be set less than the same tire on a narrower wheel.
Dan
'91 928GT S/C
475hp/460lb.ft
Another thing that makes a large difference is the width of the wheel compared to the width of the tire. If the wheel is very wide compared to the tire (i.e. 265 tire on 10" wheel), the pressure should be set less than the same tire on a narrower wheel.
Dan
'91 928GT S/C
475hp/460lb.ft
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From: In a tizzy
Most of the Michelins, Bridgestone and Pirellis I've run street and autocross performed best at the Porsche recommended cold pressures so much so that I had stopped measuring temps. When I did a lot of temp measuring on these tires I found the 10% cold to hot rule was fairly nill as there was a very very wide pressure range the tires gained 10% pressure. My old skool mechanic told me the 10% rule when he gave me a very accurate tire gauge to use.
Because of the 10% pressure gain over such a wide range I called Bridgestone asking what pressures were best. They gave me their F1 tired guy. This was when they first came out with the Pole Position. He said with their modern radials it would take 3 psi in either direction to make any difference in handling and to get a temp gauge to test the heat across the tread and start with the 36 psi cold Porsche recommended. After a LOT of messing with tire pressures I found the stock pressures worked best.
This has worked well for me for years even with lower profile tires. That was UNTIL I got the Dunlop Direzza Sport Star Specs. They gained more than 10% pressure heating up and when I followed the pressures I'd been using ended up blistering the centers of the front tires. With a new set of front tires I started watching the temps across the tire again. To keep the centers within 10 degrees of the outside edges I had to drop the hot pressure to 30 psi. It took 3 runs before the pressures quit rising 2 to 3 psi a lap. Even though the tread temps stayed around 140F.
If the rim is too narrow for the tire width it will cause the tire to balloon and you will always have center tread wear.
Because of the 10% pressure gain over such a wide range I called Bridgestone asking what pressures were best. They gave me their F1 tired guy. This was when they first came out with the Pole Position. He said with their modern radials it would take 3 psi in either direction to make any difference in handling and to get a temp gauge to test the heat across the tread and start with the 36 psi cold Porsche recommended. After a LOT of messing with tire pressures I found the stock pressures worked best.
This has worked well for me for years even with lower profile tires. That was UNTIL I got the Dunlop Direzza Sport Star Specs. They gained more than 10% pressure heating up and when I followed the pressures I'd been using ended up blistering the centers of the front tires. With a new set of front tires I started watching the temps across the tire again. To keep the centers within 10 degrees of the outside edges I had to drop the hot pressure to 30 psi. It took 3 runs before the pressures quit rising 2 to 3 psi a lap. Even though the tread temps stayed around 140F.
If the rim is too narrow for the tire width it will cause the tire to balloon and you will always have center tread wear.
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From: Working the street corner for $$$
That was UNTIL I got the Dunlop Direzza Sport Star Specs. They gained more than 10% pressure heating up and when I followed the pressures I'd been using ended up blistering the centers of the front tires. With a new set of front tires I started watching the temps across the tire again. To keep the centers within 10 degrees of the outside edges I had to drop the hot pressure to 30 psi. It took 3 runs before the pressures quit rising 2 to 3 psi a lap. Even though the tread temps stayed around 140F.
I was wondering about your input: Are you happy with them on your 928? The 30 psi is a very interesting finding. Do the shoulders roll under at those low pressures? I run 36F/34R or else the shoulders get destroyed. Also, are they noisy? My car w/ Koni's, Hypercoil's, and solid aluminum rack mounts is VERY sensitive to tread design vs road noise.
Any opinions you have, I would love to hear. Thanks!
Chronic Tool Dropper
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From: Bend, Oregon
I thought you were supposed to check the temp at about 1/8" inch into the tire for proper readings. The surface cools very quick when coming to a stop to check them and the tire pyrometers are set up to calculate and compensate for how much heat is removed when the metal spike is inserted. I think a good tire pyrometer is more complex than just a surface reading IR gun.
my .02
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From: Working the street corner for $$$
34psi hot. There was a bit of "off the track and skewed re-entry" activity involved with this, so I don't think it was pressure-related. I cut off the offending bit, then did a couple dozen more laps.
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Racer
Joined: Feb 2005
Posts: 337
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From: Orlando, FL: Treasure Coast, FL
This is a great topic. We talked about hot and sticky, too much, tire wear, et al.
Inquiring on going max tire pressure on a 928. Say it is hotter the closer you get to the equator, so ok to use lower cold pressures for street use (real use). I have mostly used lower pressures as mostly were high performance cars in southeastern US. I will continue to keep pressures low seeking good traction in the heat. And now 928. Say Porsche says the 36, thats northen Europe. Fine.
Any direct experience on running maximum 928 tire pressure at a track requiring it. Any of you run at Daytona and how much pressure is essential?
Regards,
Inquiring on going max tire pressure on a 928. Say it is hotter the closer you get to the equator, so ok to use lower cold pressures for street use (real use). I have mostly used lower pressures as mostly were high performance cars in southeastern US. I will continue to keep pressures low seeking good traction in the heat. And now 928. Say Porsche says the 36, thats northen Europe. Fine.
Any direct experience on running maximum 928 tire pressure at a track requiring it. Any of you run at Daytona and how much pressure is essential?
Regards,
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Joe Kucinski
Race Car
Joined: Jan 2004
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From: Charlotte, NC
The tread separation that I go was when I was experimenting. I usually ran track hot pressure at 38-40, but was seeking to see if I could get more even wear with higher pressure. I recklessly started at 40, and after a couple of sessions developed a whump whump whump sound. Found the pressure had gotten over 50 and a couple sections of the tires developed a four to five inch "bubbled" tread area that brought the tire WAY out of round. Whoah. My experiment should have been a little more closely monitored. I don't ever recall pressures increasing that much with temperature. Usually I have to bleed out a pound or two a couple of times a day (morning into afternoon).
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From: In a tizzy
Erik, the only time I got shoulder roll was on a wet skid pad. It was obvious it was rolling as the fronts were skipping in extreme understeer. And that was only the fronts. Otherwise they don't show any scuffing past the tread edge triangle.
Everyone I talked to said the Direzza Star Specs were very sensitive to pressure. Probably because their heat so quickly.
Everyone I talked to said the Direzza Star Specs were very sensitive to pressure. Probably because their heat so quickly.
Three Wheelin'
Joined: Feb 2009
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From: Washington "Dc"
no, you dont want your tires anywhere near 40psi cold, UNLESS you want best fuel economy. I always tell the story of the NSX boys (about 5 of them) that were at our track day and they ALL were spinning out all over the track. when I interviewed one of the guys, who seemed to be the ring leader, ( wiping up dust from all over his car from an off road spin) I asked what pressures they were running. they replied that they were at 40psi cold. I told him to take temps afterward, but I would bet them to be in the 45psi range , min. he then told me that ALL of the guys were running the same pressure (would explain the similar performance of the group 
) anyway, I suggested 30psi cold. his jaw almost dropped on the ground. anyway, without too much coaxing, they alll dropped the pressure to 30psi and were all very happy with the handlng. 34-36psi on most all street tires is a good range to be at hot. not too many tires I know about, will be happy on the track at 40psi hot and neither will you.
Oh yeah, the rest of the day, not one NSX ever spun and made a big dust cloud again!
) anyway, I suggested 30psi cold. his jaw almost dropped on the ground. anyway, without too much coaxing, they alll dropped the pressure to 30psi and were all very happy with the handlng. 34-36psi on most all street tires is a good range to be at hot. not too many tires I know about, will be happy on the track at 40psi hot and neither will you.Oh yeah, the rest of the day, not one NSX ever spun and made a big dust cloud again!
Hey, as a racer do you think the 10% rule is a good rule (hot temps should be no more than 10% greater than cold temps? ) I was always told too low a cold pressure will cause overheating greasy tires..
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From: saratoga, ca
not really. generally, it depends on the tire, how old the tire is, and how good the driver is. a top driver (or really bad driver) can ge the temps up 35%. (i.e. 9psi rise on a 30psi starting point). that is determined by how much heat you get in the tire, and that depends on the conditions i started with above.
I usually get about 7-8psi rise on 28 to 30psi starting points, and on hoosiers A series, I start at 22psi and get them generally to around 30psi hot. so, lot of factors. with tires, its knowledge and adjustment factors and not rule of thumbs that work best. But I guess those could be rule of thumbs too
I usually get about 7-8psi rise on 28 to 30psi starting points, and on hoosiers A series, I start at 22psi and get them generally to around 30psi hot. so, lot of factors. with tires, its knowledge and adjustment factors and not rule of thumbs that work best. But I guess those could be rule of thumbs too
Instructor
Joined: Jul 2009
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SO - for the ave street guy (me), am I best served running at the porsche recommended psi or would I get better tread life running a bit lower? Would the tradeoffs be that significant? I'm running 18" RE050 poles.
Frank
Frank