Tire tempreatures
08-17-2007, 08:37 PM
#1
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Tire tempreatures
I was at the track tonite, checking it out, i will be running on the 5th of September.
These are night track times, three 20 minute sessions.
Tonite, the temp was 32-35C and everyone was pushing their car(s) on the track.
Now, those tires get dang hot, but i want to know what is the limit of street tire temperatures on the track.
I run 36psi all round on my 86 951 with 16" Fuchs, just like the manual.
If one was to increase or decrease pressure, does it lower the temp? what is the max tire temp. before one should get nervous and how to cool them down quickly?
These are night track times, three 20 minute sessions.
Tonite, the temp was 32-35C and everyone was pushing their car(s) on the track.
Now, those tires get dang hot, but i want to know what is the limit of street tire temperatures on the track.
I run 36psi all round on my 86 951 with 16" Fuchs, just like the manual.
If one was to increase or decrease pressure, does it lower the temp? what is the max tire temp. before one should get nervous and how to cool them down quickly?
08-17-2007, 10:23 PM
#3
Race Car
The factory recommendations are for street use, not track. You'd want to run 6-10 pounds lower than that, initially. Even then, I'd use the tire company's track pressure recommendations over the generic ones Porsche made about some specific tires manufactured 21 years ago.
Ambient or track surface temperatures aren't the biggest factor in tire temps. You can make tires feel greasy by overinflating them and you can make them hot and greasy by underinflating them. Again, the manufacturers have specific temperature ranges that are considered optimal, and you adjust your pressures and suspension settings based on that.
What tires are you running? In a pinch, I'd start at 28-30 psi cold, all around, and adjust from there. But that's a wild guess, since I don't know if you're running street or track tires.
Ambient or track surface temperatures aren't the biggest factor in tire temps. You can make tires feel greasy by overinflating them and you can make them hot and greasy by underinflating them. Again, the manufacturers have specific temperature ranges that are considered optimal, and you adjust your pressures and suspension settings based on that.
What tires are you running? In a pinch, I'd start at 28-30 psi cold, all around, and adjust from there. But that's a wild guess, since I don't know if you're running street or track tires.
08-17-2007, 10:51 PM
#4
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I am running street tires, in stock 205/55/16 front and 225/50/16 rear.
Currently 36psi all round, the tires are rates AA temp, what does that mean and at what temp should i be concerned (with infrared thermometer).
Currently 36psi all round, the tires are rates AA temp, what does that mean and at what temp should i be concerned (with infrared thermometer).
08-18-2007, 07:58 AM
#5
Hosrom-
On the street you measure tire pressures cold i.e before you start driving.
On the track you measure your pressures hot, as soon as you can after you pit. Therefore, most people start out with pressures that are considerably lower than they would use on the street and run relatively slowly on the track for a couple of laps to bring the tires up to pressure / temp.
Like said above, depending on the ambient conditions and brand of tire most people start around 28-30PSI with a goal of having the tires read between 36-38PSI when hot. Once again this is very tire & track dependent but it sounds like you should start at a lower pressure than what you have been.
On the street you measure tire pressures cold i.e before you start driving.
On the track you measure your pressures hot, as soon as you can after you pit. Therefore, most people start out with pressures that are considerably lower than they would use on the street and run relatively slowly on the track for a couple of laps to bring the tires up to pressure / temp.
Like said above, depending on the ambient conditions and brand of tire most people start around 28-30PSI with a goal of having the tires read between 36-38PSI when hot. Once again this is very tire & track dependent but it sounds like you should start at a lower pressure than what you have been.
08-18-2007, 04:08 PM
#6
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Okay, so i will start with 30psi all round on the track.
Then, after the first session, 20 minutes, i will measure the pressure, i should see no more than 40psi.
If i see higher than 40-psi, i need to add air?
Sorry guys, but i need to know the basics here, i dont want to blow up the tires on the track.
Then, after the first session, 20 minutes, i will measure the pressure, i should see no more than 40psi.
If i see higher than 40-psi, i need to add air?
Sorry guys, but i need to know the basics here, i dont want to blow up the tires on the track.
08-18-2007, 04:29 PM
#7
Race Car
Yes, bleed off the air above 36-38 psi when you check them after a session. Keep checking after each session out. You'll heat them up more as the day goes on, and when the tire gets hotter, the pressure will increase.
Re-check your lug nuts after the first session, and check them again mid-day. Don't tighten them too much (if you have a torque wrench, tighten them to between 75-95 foot-pounds), but the heat can cause them to come loose.
As the day goes on, you'll see some rubber gumming up on the tires. Some of it will be what you pick up off the track and some of it will be from the heat in your own tires causing the rubber to form globs. Don't worry too much about this -- a little street driving will wear it off. But also visually check for cracks, blisters or evidence of tread separation during the day. Some tracks are very hard on tires.
And while I'm at it, pay attention to your brakes, too. If you can, flush the system before the event and have high temp fluid (like ATE Blue) put in. Pay attention to the feel of the pedal changing while you're out on the track. Brakes can heat up to the point where the fluid near the calipers boils, which can introduce air bubbles into the system, which can cause a soft pedal or complete brake failure. It's called 'brake fade' and it's more likely to happen as the day goes on. You should pull in at the first sign of it. If you lose your brakes (meaning the pedal goes to the floor), pump the pedal repeatedly to try to get some pressure back.
Re-check your lug nuts after the first session, and check them again mid-day. Don't tighten them too much (if you have a torque wrench, tighten them to between 75-95 foot-pounds), but the heat can cause them to come loose.
As the day goes on, you'll see some rubber gumming up on the tires. Some of it will be what you pick up off the track and some of it will be from the heat in your own tires causing the rubber to form globs. Don't worry too much about this -- a little street driving will wear it off. But also visually check for cracks, blisters or evidence of tread separation during the day. Some tracks are very hard on tires.
And while I'm at it, pay attention to your brakes, too. If you can, flush the system before the event and have high temp fluid (like ATE Blue) put in. Pay attention to the feel of the pedal changing while you're out on the track. Brakes can heat up to the point where the fluid near the calipers boils, which can introduce air bubbles into the system, which can cause a soft pedal or complete brake failure. It's called 'brake fade' and it's more likely to happen as the day goes on. You should pull in at the first sign of it. If you lose your brakes (meaning the pedal goes to the floor), pump the pedal repeatedly to try to get some pressure back.
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08-18-2007, 06:29 PM
#8
Originally Posted by hosrom_951
If i see higher than 40-psi, i need to add air?
.
NO, you need to let air out to what ever your target hot tire pressures should be (36-38?)
As the day progresses you may have to do that several times.
The next morning if you are running again check your tire pressures, they may be as low as 26 - 30 and this is what you should start out next time if everything is the same.
08-18-2007, 08:21 PM
#9
Be carefull checking cold tire preasure. The sun on one side of the car can add up to 2 lbs of preasure from the sun heating the tires. In your neck of the woods it could even be more.
08-18-2007, 09:08 PM
#10
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Thanks guys, my response:
Yes, okay, i will start off witha cold 30psi, then at the track, i will bleed off anything over 38psi. Yes, i do have ATE Blue in the car, and a can of it now. I was planing on changing it anyways, since it is past 2 years since i replaced the fluid.
Yes, i will pay attention to the lug nuts and pads, i do have the torque wrench and i always set the lug nuts to 94-96ft/lbs as the manual, and will check. As for the pads, i was planing on getting an extra set just in case the current ones wear off.
Okay, got it, thanks.
It is a night session, still the weather is in the low to mid 90'sF, no sun though and the car will be parked in the shade all day till the last minute and have the pressure set to 30psi all round before driving to the track.
For the record, on the street, i drive my car with a complete tool box (where i can do everything except remove the engine and change the rear bearings, it is that complete), 1 liter coolant bottle, 1 liter engine oil, and air compressor, battery charger, jumper cables and a toe cable. At the track, a buddy of mine (944 NA) will be using his car as a "garage" to carry all the tools and stuff, so my car would be as light as possible just for the track (even the spare tire is coming off).
One last thing, is there a certain tire TEMPERATURE i should watch out for? i have the infrared thermometer.
Originally Posted by JackOlsen
Yes, bleed off the air above 36-38 psi when you check them after a session. Keep checking after each session out. You'll heat them up more as the day goes on, and when the tire gets hotter, the pressure will increase.
Re-check your lug nuts after the first session, and check them again mid-day. Don't tighten them too much (if you have a torque wrench, tighten them to between 75-95 foot-pounds), but the heat can cause them to come loose.
As the day goes on, you'll see some rubber gumming up on the tires. Some of it will be what you pick up off the track and some of it will be from the heat in your own tires causing the rubber to form globs. Don't worry too much about this -- a little street driving will wear it off. But also visually check for cracks, blisters or evidence of tread separation during the day. Some tracks are very hard on tires.
And while I'm at it, pay attention to your brakes, too. If you can, flush the system before the event and have high temp fluid (like ATE Blue) put in. Pay attention to the feel of the pedal changing while you're out on the track. Brakes can heat up to the point where the fluid near the calipers boils, which can introduce air bubbles into the system, which can cause a soft pedal or complete brake failure. It's called 'brake fade' and it's more likely to happen as the day goes on. You should pull in at the first sign of it. If you lose your brakes (meaning the pedal goes to the floor), pump the pedal repeatedly to try to get some pressure back.
Re-check your lug nuts after the first session, and check them again mid-day. Don't tighten them too much (if you have a torque wrench, tighten them to between 75-95 foot-pounds), but the heat can cause them to come loose.
As the day goes on, you'll see some rubber gumming up on the tires. Some of it will be what you pick up off the track and some of it will be from the heat in your own tires causing the rubber to form globs. Don't worry too much about this -- a little street driving will wear it off. But also visually check for cracks, blisters or evidence of tread separation during the day. Some tracks are very hard on tires.
And while I'm at it, pay attention to your brakes, too. If you can, flush the system before the event and have high temp fluid (like ATE Blue) put in. Pay attention to the feel of the pedal changing while you're out on the track. Brakes can heat up to the point where the fluid near the calipers boils, which can introduce air bubbles into the system, which can cause a soft pedal or complete brake failure. It's called 'brake fade' and it's more likely to happen as the day goes on. You should pull in at the first sign of it. If you lose your brakes (meaning the pedal goes to the floor), pump the pedal repeatedly to try to get some pressure back.
Yes, i will pay attention to the lug nuts and pads, i do have the torque wrench and i always set the lug nuts to 94-96ft/lbs as the manual, and will check. As for the pads, i was planing on getting an extra set just in case the current ones wear off.
Originally Posted by smlporsche
NO, you need to let air out to what ever your target hot tire pressures should be (36-38?)
As the day progresses you may have to do that several times.
The next morning if you are running again check your tire pressures, they may be as low as 26 - 30 and this is what you should start out next time if everything is the same.
As the day progresses you may have to do that several times.
The next morning if you are running again check your tire pressures, they may be as low as 26 - 30 and this is what you should start out next time if everything is the same.
Originally Posted by beab951
Be carefull checking cold tire preasure. The sun on one side of the car can add up to 2 lbs of preasure from the sun heating the tires. In your neck of the woods it could even be more.
For the record, on the street, i drive my car with a complete tool box (where i can do everything except remove the engine and change the rear bearings, it is that complete), 1 liter coolant bottle, 1 liter engine oil, and air compressor, battery charger, jumper cables and a toe cable. At the track, a buddy of mine (944 NA) will be using his car as a "garage" to carry all the tools and stuff, so my car would be as light as possible just for the track (even the spare tire is coming off).
One last thing, is there a certain tire TEMPERATURE i should watch out for? i have the infrared thermometer.
08-18-2007, 09:36 PM
#11
I think what you have done is enough prep and if you stay with the tire preasure stated above you will be fine. You are not going to run at the limit the first time so tire temp shouldn't be an issue. You can get too wound up in car prep and forget to prep the driver. Relax, have some fun.
08-18-2007, 10:46 PM
#12
Burning Brakes
An infrared thermometer will not be very accurate for evaluating tire tread temps, as it measures only the surface temps of the tire. After a cool down lap, and driving down the pits to where you are parked, the surface temps will be different than what they were out on the track. Since you are just starting out, and on street tires, I would suggest you concentrate on getting accurate pressures. They will reflect what the general tire temps are. Specific tread area temps will have to be taken with a probe type pryrometer.
08-19-2007, 12:21 AM
#13
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As an addition to what Jack said about lug nuts, do not tighten aluminum lug nuts when they are hot.....they can snap off. 
Either wait until they cool or, better yet, switch to open top steel lug nuts for track use.
Marc
Either wait until they cool or, better yet, switch to open top steel lug nuts for track use.
Marc
08-19-2007, 08:17 AM
#14
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Tire Temps
Using a tire temp probe, not the infrared surface variety, and as soon as you get off the track, assign a pal to take you tire temps immediately when you get off the track....if they are over 225 F, that is too hot. Most tires can't take heat over 225...or so I have been told. I am NOT an engineer.
The temperatures across the tire can tell you a lot about your tire pressures, alignment, etc. Research tire temps and alignment.
The temperatures across the tire can tell you a lot about your tire pressures, alignment, etc. Research tire temps and alignment.
