PSI Rise In Track Tires
09-14-2009, 05:49 PM
#1
Rennlist Member
Thread Starter
PSI Rise In Track Tires
Okay, now that I am getting my brake cooling under control I wanted to throw out another little issue I've run into... psi rise in my slicks.
In all the years and all the cars I've had (none being as heavy or as powerful as the current 996 TT) the normal rise in tire pressure is somewhere in the 6 to 8, maybe, just maybe 10 psi on a hot day with long session. With the TT I've been seeing 14 to maybe as high as 16 no matter what starting psi I try and it's been confounding me. Now that I temp checked the rotors (1475 F) and find that the wheels almost non touchable with gloves on after 15 minutes, I am thinking that there just might be some heat radiation into the hollow spokes from whopping rotor temp that could explain some of this additional psi rise.
What say you?
In all the years and all the cars I've had (none being as heavy or as powerful as the current 996 TT) the normal rise in tire pressure is somewhere in the 6 to 8, maybe, just maybe 10 psi on a hot day with long session. With the TT I've been seeing 14 to maybe as high as 16 no matter what starting psi I try and it's been confounding me. Now that I temp checked the rotors (1475 F) and find that the wheels almost non touchable with gloves on after 15 minutes, I am thinking that there just might be some heat radiation into the hollow spokes from whopping rotor temp that could explain some of this additional psi rise.
What say you?
09-14-2009, 06:15 PM
#2
Still plays with cars.
Lifetime Rennlist
Member
My experience on a lighter GT3 driven at race speeds is similar to yours i.e., 8-10 lbs at air temps in the 60 to 85 degree range.
On the other hand, I am talking about R compound tires like the Hoosier R 6, Pirelli Corsa or Michelin Cup.
With an aggressive driver on new street tires or full tread R 888 I could imagine higher temps.
Your really high brake temps suggest that you really brake late and hard. Braking warms up tires fast which is why we brake like maniacs on the warm up lap of a race. Could your braking technique be the reason?
Best,
I also never see brake temps as high as yours
On the other hand, I am talking about R compound tires like the Hoosier R 6, Pirelli Corsa or Michelin Cup.
With an aggressive driver on new street tires or full tread R 888 I could imagine higher temps.
Your really high brake temps suggest that you really brake late and hard. Braking warms up tires fast which is why we brake like maniacs on the warm up lap of a race. Could your braking technique be the reason?
Best,
I also never see brake temps as high as yours
09-15-2009, 10:07 AM
#5
Rennlist Member
Thread Starter
Yes, excellent point because in contemplating this situation, I see the high rise in all four slicks, however, the cooling issue seems only with the front rotors. (I think) We did not take a rotor temp in the rear and now I wish I had done so.
09-15-2009, 10:12 AM
#6
Racer
Join Date: Jun 2007
Location: Atlanta area
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
Rotor temps are definitely too high. Bet caliper temps are too high also. With R6's and now the new Hoosier racing slicks I am seeing around 10 degress rise after 20 minutes.
Consider going to Nitrogen for less temp rise but perhaps you need to change your braking methods.
Consider going to Nitrogen for less temp rise but perhaps you need to change your braking methods.
09-15-2009, 10:25 AM
#7
Rennlist Member
Thread Starter
Trending Topics
09-17-2009, 09:56 PM
#9
Burning Brakes
I've heard the common fallacy that nitrogen has less pressure rise than air, (not true, dry air and dry nitrogen are the same- it's the moisture in either that get you)... but never that nitrogen is, in fact, cooler.
09-18-2009, 10:29 AM
#10
Rennlist Member
Thread Starter
09-18-2009, 05:50 PM
#11
Burning Brakes
09-18-2009, 08:16 PM
#13
Rennlist Member
Thread Starter
We're just goofing... racing applications are fine, I believe the Good Ol' Boys run nitrogen if I'm not mistaken, just for that reason -- predictable pressure management. It's the street cars we're laughing about... it's a joke. Dealers have now found a way to actually charge customers to maintain pressure in there tires and keep them coming to the dealership. I've actually seen posts where people have said, ready for this... that their car handles better with nitrogen in the tires. "One born every minute... "
09-19-2009, 01:23 AM
#14
Super Moderator
Needs More Cowbell
Lifetime Rennlist
Member
Needs More Cowbell
Lifetime Rennlist
Member
I wouldn't be so hasty to jump to your conclusion.
There is a true secondary benefit to running nitrogen (cheap dry gas) in street car tires which might not be so obvious....
One of the primary causes of TPMS failure is moisture impingment, which of course gets more likely as the temp and humidity increase....such as the case when you fill your tires on a hot/humid day and inject fairly significant amounts of water vapor into the tire, then proceed to heat it up due to road/tire friction.
Obviously this is much less likely if the tires are PURGED, then filled with N2.
N2 in the tires is preferred by manufacturers as long as the car is in the warranty period...of course once it's outside of warranty, they would prefer you fill the tires with water and buy TPMS sensors.
There is a true secondary benefit to running nitrogen (cheap dry gas) in street car tires which might not be so obvious....
One of the primary causes of TPMS failure is moisture impingment, which of course gets more likely as the temp and humidity increase....such as the case when you fill your tires on a hot/humid day and inject fairly significant amounts of water vapor into the tire, then proceed to heat it up due to road/tire friction.
Obviously this is much less likely if the tires are PURGED, then filled with N2.
N2 in the tires is preferred by manufacturers as long as the car is in the warranty period...of course once it's outside of warranty, they would prefer you fill the tires with water and buy TPMS sensors.
09-19-2009, 01:03 PM
#15
Burning Brakes
I wouldn't be so hasty to jump to your conclusion.
There is a true secondary benefit to running nitrogen (cheap dry gas) in street car tires which might not be so obvious....
One of the primary causes of TPMS failure is moisture impingment, which of course gets more likely as the temp and humidity increase....such as the case when you fill your tires on a hot/humid day and inject fairly significant amounts of water vapor into the tire, then proceed to heat it up due to road/tire friction.
Obviously this is much less likely if the tires are PURGED, then filled with N2.
N2 in the tires is preferred by manufacturers as long as the car is in the warranty period...of course once it's outside of warranty, they would prefer you fill the tires with water and buy TPMS sensors.
There is a true secondary benefit to running nitrogen (cheap dry gas) in street car tires which might not be so obvious....
One of the primary causes of TPMS failure is moisture impingment, which of course gets more likely as the temp and humidity increase....such as the case when you fill your tires on a hot/humid day and inject fairly significant amounts of water vapor into the tire, then proceed to heat it up due to road/tire friction.
Obviously this is much less likely if the tires are PURGED, then filled with N2.
N2 in the tires is preferred by manufacturers as long as the car is in the warranty period...of course once it's outside of warranty, they would prefer you fill the tires with water and buy TPMS sensors.
Why?
Yes, bottled, 99.998% 'technical pure' nitrogen is certified moisture free. Got it. That is what they use for jet aircraft, race cars.
The little nitrogen concentrators they use at tire stores are no more 'pure' in terms of moisture removal, that the air compressor sitting next to it.
It isn't the gas you put in that matters- it is the 'moisture free' nature of whatever gas you use.
A