Can someone help me with tire pressures on R-Compounds please?
06-07-2005, 09:35 AM
#16
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Originally Posted by RedlineMan
Nick;
Most R-tires like to be around 40 hot. This usually equates to a pyrometer reading that will show a tire in the right temp range to optimize the rubber compound for grip. Anything under 35 hot is obviously not putting the tire in that range.
This tells me that you are a novice-to-low-intermediate driver, and there is no personal judgement of you being made there.
As I offered previously, you can indeed run those types of numbers and not be in trouble. At the same time, this thread will plant in your mind that if you do get quicker, you should expect to make pressure changes like those discussed here to keep your tires healthy and yourself safe.
Again, I must stress the importance of the pressure increase from cold to hot. no matter where you are on the scale, this is of paramount concern. If you started at 26 to get your 32/35 hot, well, you are within a safe 10lb increase, but you also have some room left for improvement regarding getting to 40 hot where the tire works best. The only way you are going to hit the magic 40 is to get faster, but you will also have to keep pace of cold-to-hot pressure increases, and add air to maintain a healthy 10psi +/- margin.
The ideal would be to start at 30-32 and hit 40 hot. This would give you very well supported tires, and good and sticky too. If you go over a 10lb increase, they will overheat and get greasy. The first part (well supported tires) is why Mark offered what he did; a safe set of tires. My sense is that you are at the "feels better at lower pressures" stage, and that is fine. Now, when you get quicker, you'll be armed with the right info to stay safe too!
Most R-tires like to be around 40 hot. This usually equates to a pyrometer reading that will show a tire in the right temp range to optimize the rubber compound for grip. Anything under 35 hot is obviously not putting the tire in that range.
This tells me that you are a novice-to-low-intermediate driver, and there is no personal judgement of you being made there.
As I offered previously, you can indeed run those types of numbers and not be in trouble. At the same time, this thread will plant in your mind that if you do get quicker, you should expect to make pressure changes like those discussed here to keep your tires healthy and yourself safe.Again, I must stress the importance of the pressure increase from cold to hot. no matter where you are on the scale, this is of paramount concern. If you started at 26 to get your 32/35 hot, well, you are within a safe 10lb increase, but you also have some room left for improvement regarding getting to 40 hot where the tire works best. The only way you are going to hit the magic 40 is to get faster, but you will also have to keep pace of cold-to-hot pressure increases, and add air to maintain a healthy 10psi +/- margin.
The ideal would be to start at 30-32 and hit 40 hot. This would give you very well supported tires, and good and sticky too. If you go over a 10lb increase, they will overheat and get greasy. The first part (well supported tires) is why Mark offered what he did; a safe set of tires. My sense is that you are at the "feels better at lower pressures" stage, and that is fine. Now, when you get quicker, you'll be armed with the right info to stay safe too!
As far as my driver skills go, I'm actually an advanced driver and part-time instructor. I've been doing this for going on 8 years now. Granted I am no real race car driver and never plan to be but my skill level doesn't really have anything to do with the question I asked IMO.
My original question about tire pressure comes from not having the experience with my Porsche and R-Compounds. I've had R-Compounds on many other cars and even though I knew that they tire liked to be run at a certain pressure, I had hoped someone could give their experience to shorten my dial in time. I'm never afraid to ask a question if I don't know. Regardless of anyones skills, there is always the ability to learn more.
I appreciate everyones input and have bookmarked this thread for future reference.
06-07-2005, 09:48 AM
#17
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John - I do not disagree, typical starting pressures cold for the Corsa and Cup are in the 27-28 lbs range to reach hot pressures of 34 - 36. At 40 lbs the corsa showed sub-optimal temps (too cool) and I assume that explained the reduced grip. Track surface also matters, for example a couple of very smart guys run higher hot pressures at Lime Rock (over 40 lbs) so as always YMMV
06-07-2005, 10:26 AM
#18
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Nick, I'm a medium speed runner in the top DE group, so others will have different opinions, but the best information I have found on tire pressures is the Michelin Pilot Sport Cup PowerPoint presentation based on their systematic testing with various Porsches. It can be found at www.cb-racing.com or if you Google "michelin pilot sport cup presentation". Their recommendations are as follows for HOT PRESSURES:
Old 911's: F: 32-35 R: 32-35
Newer 911's including 964: F: 26-28 R: 32-35
944/944 T: F: 35-38 R: 26-30
996: F: 32-34 R: 37-40
They also recommend large wheel/small tire combinations for better turn in, less wiggle on exit, and better response to tire pressure tuning.
My experience with the above numbers has been very positive. I had been driving for years with amost equal pressures front and rear on my 951, but kept wearing out the middle third of my rear tires while the outsides were pristine. Michelin recommended an 8 to 9 psi difference front to rear for the 944/951, and I took the plunge. I start at 29/22 cold and 35/27 hot, and it works like a charm. Less understeer and even wear at the rear, with the tires turning over to the arrow indicators on the side.
For the 964, Michelin recommends 205-55/16 at the front and 225-50/16 at the rear, with the above hot pressure ranges. You will notice that they recommend 6 to 7 psi less pressure in the front than at the rear.
I've just finished reading "Moneyball" by Michael Lewis. It's an outstanding book about the difference between fact and fiction in baseball. The same principles apply to any sport. The geniuses at my tire shop told me a few years ago that my rear tires were wearing in the centre because my tire pressures in the rear at 35 psi were TOO LOW, that the wear was occuring because I has so much power that my tires were BALOONING ON THE STRAIGHTS. An interesting hypothesis, with the conclusions based no doubt on much systematic experimentation. As on old engineer once told me, believe none of what you hear and only half of what you see.
End of rant.
Old 911's: F: 32-35 R: 32-35
Newer 911's including 964: F: 26-28 R: 32-35
944/944 T: F: 35-38 R: 26-30
996: F: 32-34 R: 37-40
They also recommend large wheel/small tire combinations for better turn in, less wiggle on exit, and better response to tire pressure tuning.
My experience with the above numbers has been very positive. I had been driving for years with amost equal pressures front and rear on my 951, but kept wearing out the middle third of my rear tires while the outsides were pristine. Michelin recommended an 8 to 9 psi difference front to rear for the 944/951, and I took the plunge. I start at 29/22 cold and 35/27 hot, and it works like a charm. Less understeer and even wear at the rear, with the tires turning over to the arrow indicators on the side.
For the 964, Michelin recommends 205-55/16 at the front and 225-50/16 at the rear, with the above hot pressure ranges. You will notice that they recommend 6 to 7 psi less pressure in the front than at the rear.
I've just finished reading "Moneyball" by Michael Lewis. It's an outstanding book about the difference between fact and fiction in baseball. The same principles apply to any sport. The geniuses at my tire shop told me a few years ago that my rear tires were wearing in the centre because my tire pressures in the rear at 35 psi were TOO LOW, that the wear was occuring because I has so much power that my tires were BALOONING ON THE STRAIGHTS. An interesting hypothesis, with the conclusions based no doubt on much systematic experimentation. As on old engineer once told me, believe none of what you hear and only half of what you see.
End of rant.
06-07-2005, 10:39 AM
#19
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Originally Posted by RedlineMan
Gents;
Do not words like "most" and "usually" infer that I was not casting anything in stone here? OF COURSE it is down to each specific tire type and driver to come up with a pressure map that fits his equipment and driving style.
To say that an MPSC "gets greasy" at 40lbs tells us nothing. Was that because they don't like to be there, or that you overheated them? If you started at your 25 and hit 40, you DID overheat them! If you started at a more proper pressure that kept the increase to around 10psi, and they were greasy, then you may have proved a point. For the record, I started my MPSCs at 29/28/27/26 and hit the spec perfectly... which is 34-36 hot, by the by.
I have been trying for 10 years to explode the myth of underinflating performance tires because they "feel better." I have been trying in that time to give people a system whereby they can stay safe while they figure out how to PROPERLY fettle a set of track tires... and learn to drive.
Do not words like "most" and "usually" infer that I was not casting anything in stone here? OF COURSE it is down to each specific tire type and driver to come up with a pressure map that fits his equipment and driving style.To say that an MPSC "gets greasy" at 40lbs tells us nothing. Was that because they don't like to be there, or that you overheated them? If you started at your 25 and hit 40, you DID overheat them! If you started at a more proper pressure that kept the increase to around 10psi, and they were greasy, then you may have proved a point. For the record, I started my MPSCs at 29/28/27/26 and hit the spec perfectly... which is 34-36 hot, by the by.
I have been trying for 10 years to explode the myth of underinflating performance tires because they "feel better." I have been trying in that time to give people a system whereby they can stay safe while they figure out how to PROPERLY fettle a set of track tires... and learn to drive.
I agree, feel has nothing to do with it. Again, I don't think anyone said that. I use a pyrometer to determine the right pressures. Sometimes it "feels" wrong initially but that changes.
George
06-07-2005, 01:18 PM
#20
Race Car
Hi John,
I would like to learn some of your wisdom.... (please)
I have a stick pyro (tif brand) and did some racing a while back...
I did some tire temps when I started tracking my 1971 911, looking for even temps across tire. temps were in 170-190 range (as I rember), played with air press, (without changin camber or toe), and got the (front) outside and middle close at 26-27 (cold) insides were 10 degrees higher. (190) running 2 degrees negative camber, 1/16" toe in.
currently running 26/28 air cold. (think its 33-35 hot, best I remember).
running Toyo's ra1 and Kuhmo victor racers shaved. (225x15")
for my 2400# car, what would you suggest?
(your comment on 40 psi hot, has me questioning my processes)
thanks in advance!
I would like to learn some of your wisdom.... (please)
I have a stick pyro (tif brand) and did some racing a while back...
I did some tire temps when I started tracking my 1971 911, looking for even temps across tire. temps were in 170-190 range (as I rember), played with air press, (without changin camber or toe), and got the (front) outside and middle close at 26-27 (cold) insides were 10 degrees higher. (190) running 2 degrees negative camber, 1/16" toe in.
currently running 26/28 air cold. (think its 33-35 hot, best I remember).
running Toyo's ra1 and Kuhmo victor racers shaved. (225x15")
for my 2400# car, what would you suggest?
(your comment on 40 psi hot, has me questioning my processes)
thanks in advance!
06-07-2005, 02:19 PM
#21
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Originally Posted by George A
Are you sure you read my post? Don't make assumptions. I've started them at 32 cold just because I had fears (like most) of starting too low. Yes, I got them to 40 and they didn't "feel" bad, I was just not getting the optimal temps across (nor lap times).
Of course you are right, and I apologize... profusely. I would never want to be thought of as being indelicate, or wro^@#... wr%$(... less than perfect.MrBill -
My 944 is close to your car at 2500-and-change. I run RA1s at 29/29/27/26 and hit 40/39/37/35 or there abouts, depending on the track. I might need to bump up a pound in front. Mid Ohio saw me bleeding off from these starting pressures, where Watkins Glen needed more air to stop the tires from feeling mushy. You usually will not get the rear tires fully "up to temp" on most courses (944), and that's OK.
