HPDE Tire Pressures.....
#1
HPDE Tire Pressures.....
I've just switched from 17-inch rims down to 15-inch rims with 195-55 Dunlop Sport Z1 Star Spec rubber and would like suggestions on tire pressure for a Track Day.
Around town I've been running 34 psi but would like suggestions from others running 15 inch rims on the track. My experience has been to start with a slightly lower cold temperature pressure for track days as the tires will really heat up providing the higher pressure. I'm just not sure how low to go with 15 inch rims.
Suggestions are greatly appreciated.
Around town I've been running 34 psi but would like suggestions from others running 15 inch rims on the track. My experience has been to start with a slightly lower cold temperature pressure for track days as the tires will really heat up providing the higher pressure. I'm just not sure how low to go with 15 inch rims.
Suggestions are greatly appreciated.
#2
I've just switched from 17-inch rims down to 15-inch rims with 195-55 Dunlop Sport Z1 Star Spec rubber and would like suggestions on tire pressure for a Track Day.
Around town I've been running 34 psi but would like suggestions from others running 15 inch rims on the track. My experience has been to start with a slightly lower cold temperature pressure for track days as the tires will really heat up providing the higher pressure. I'm just not sure how low to go with 15 inch rims.
Around town I've been running 34 psi but would like suggestions from others running 15 inch rims on the track. My experience has been to start with a slightly lower cold temperature pressure for track days as the tires will really heat up providing the higher pressure. I'm just not sure how low to go with 15 inch rims.
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#9
It's interesting that Alex @ Tire Rack recommended a much higher cold temp than anyone seems to be comfortable with, even slinger688, who I defer to on almost every track-tech question.
At a HPDE I asked an instructor the very same question and his answer was to get as close as you can get to the tire's maximum pressure (when hot). At another HPDE I got a very similar answer.
I'm not sure what the "correct" answer is, or if there is one, but I've been trying to up the pressure a little at every HPDE and have been very satisfied with the performance. Last week at Lime Rock I started at about 36 with my 16" Dunlop Direzzas. They heated up to about 46. The max pressure on the sidewall is listed at 51.
I hope others weigh in with their expertise and experience.
At a HPDE I asked an instructor the very same question and his answer was to get as close as you can get to the tire's maximum pressure (when hot). At another HPDE I got a very similar answer.
I'm not sure what the "correct" answer is, or if there is one, but I've been trying to up the pressure a little at every HPDE and have been very satisfied with the performance. Last week at Lime Rock I started at about 36 with my 16" Dunlop Direzzas. They heated up to about 46. The max pressure on the sidewall is listed at 51.
I hope others weigh in with their expertise and experience.
#10
.mmm
I'd have expected a pressure rise of 3-4 lbs from cold to hot, with slightly more increase at the front axle.
I start at 38/44, and bleed after each run for autocross. For HPDE, given that one cannot adjust after a lap or two, I'd start lower (35/42) to reach the target pressures.
I do run 15" rims with Star Specs (the 205).
So I can see where Alex is coming from.
I assume you are running stock camber? If so then chalking would be a good idea.
Every year when I get a new set (RS3, R1R, Star Spec for the last 3) I have found a safe area and tested for max lateral acceleration (GTech) by varying the front pressures while holding the rear at a constant 40 psi. Once I've found the best front pressure I then vary the rear to optimize the balance of the car, going higher to gain rotation or lower to avoid it.
Trying for optimum balance using this approach at relatively low speeds (e.g. 40 mph or so) can however lead to a solution that is a handful at track speed so I run less rear pressure (44 not 48) at the track.
FWIW,
Charlie
I'd have expected a pressure rise of 3-4 lbs from cold to hot, with slightly more increase at the front axle.
I start at 38/44, and bleed after each run for autocross. For HPDE, given that one cannot adjust after a lap or two, I'd start lower (35/42) to reach the target pressures.
I do run 15" rims with Star Specs (the 205).
So I can see where Alex is coming from.
I assume you are running stock camber? If so then chalking would be a good idea.
Every year when I get a new set (RS3, R1R, Star Spec for the last 3) I have found a safe area and tested for max lateral acceleration (GTech) by varying the front pressures while holding the rear at a constant 40 psi. Once I've found the best front pressure I then vary the rear to optimize the balance of the car, going higher to gain rotation or lower to avoid it.
Trying for optimum balance using this approach at relatively low speeds (e.g. 40 mph or so) can however lead to a solution that is a handful at track speed so I run less rear pressure (44 not 48) at the track.
FWIW,
Charlie
#11
Interesting. I may have to rethink my initial thoughts on lowering the pressures from street to track use. I had always been told that autocross guys raise the pressures as they aren’t out long enough to gain heat and track guys lower pressures since they are out long enough to build up heat and raise pressures.
Can someone either provide a link or explanation as to how the chalk marking works. I understand I’m trying to see how much the tire is rolling over, but where do I want it to stop? Also, do I mark the entire sidewall or just a few simple vertical marks?
My Mini should be a totally new car compared to the last time I was at the track. I’ve gone from bone stock with all season tires to : 15% pulley, CAI, Exhaust, Rear Sway Bar, Slotted Rotors, Hawk HPS pads, S.S. Brake Lines, Team Dynamics Rims and Star Spec rubber.
Can someone either provide a link or explanation as to how the chalk marking works. I understand I’m trying to see how much the tire is rolling over, but where do I want it to stop? Also, do I mark the entire sidewall or just a few simple vertical marks?
My Mini should be a totally new car compared to the last time I was at the track. I’ve gone from bone stock with all season tires to : 15% pulley, CAI, Exhaust, Rear Sway Bar, Slotted Rotors, Hawk HPS pads, S.S. Brake Lines, Team Dynamics Rims and Star Spec rubber.
#12
Using a probe style pyrometer, and adjusting to get even tire temps across the face of the tire would be the most accurate and effective way. You need a buddy to take the temps, the time you'd take to get out and probe them yourself will loose valueable temp data.
Once your dialed in after a gang of runs, park the car. The next morning take your pressure cold, and you will have the sweet spot exactrly where your cold pressure should be to achive the handeling you dialed in the day before.
Alex
Once your dialed in after a gang of runs, park the car. The next morning take your pressure cold, and you will have the sweet spot exactrly where your cold pressure should be to achive the handeling you dialed in the day before.
Alex
#13
Using a probe style pyrometer, and adjusting to get even tire temps across the face of the tire would be the most accurate and effective way. You need a buddy to take the temps, the time you'd take to get out and probe them yourself will loose valueable temp data.
Once your dialed in after a gang of runs, park the car. The next morning take your pressure cold, and you will have the sweet spot exactrly where your cold pressure should be to achive the handeling you dialed in the day before.
Alex
Once your dialed in after a gang of runs, park the car. The next morning take your pressure cold, and you will have the sweet spot exactrly where your cold pressure should be to achive the handeling you dialed in the day before.
Alex
Thanks!
#14
The pyrometer readings are not so easy to interpret.
#15
At my first HPDE (high in the mid 80's) I ran really close to the max pressure on the stock 175/65R15s on my MC. 49psi front and 46psi rear HOT. This was due to trying to keep the shoulders from rolling too much.
I lost my notes on the cold temp from the following morning, but IIRC they were around 39-40psi
I lost my notes on the cold temp from the following morning, but IIRC they were around 39-40psi
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