MPSC tire failures - Help!
06-26-2005, 12:18 PM
#16
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Dr Jupeman,
Several things to consider for your particular setup, in order of importance:
The 295 is too wide for the 10 inch wheel, period. You need at least an 11 inch wheel for this tire. Really a ten inch wheel should take a 265, which really isn't big enough for the back of a Turbo. The narrow wheel/wide tire situation makes tire temp data useless. Do what you have to do to get the right wheels. Cheaper in the long run.
Pressure. I would experiment with much higher pressures. I would take your current starting cold pressure and add 2 psi and try it. Keep doing this session after session until you really feel the rear end not sticking or feeling weird. Tires flex an amazing amount, and when you have construction problems you need to look at reducing the flex.
Camber is dependent on roll stiffness. 964's need a good amount of rear camber because they roll the camber out pretty significantly. 3.0 degrees should be pretty close unless your suspension is really soft. I would shoot for a 30 degree spread across the tire, with inside hotter, unless it is the inner sidewall giving you trouble.
Balance. I think you need to look for a little understeer so you are getting the max out of the front tires. You need a monster rear tire for this car, and since you don't have it, you have to make sure you are not overloading the tires you do have.
As lwilkins pointed out, you have a junky 'preload only' LSD. If it is not currently causing problems it soon will. However, the bad LSD should only wear the inside of the tires and can't really cause sidewall problems.
Rotation on the rims just plain shouldn't happen. There is something wrong with the wheels if it does. I can't see how they could be damaged during mounting, but I am sure it is possible.
Chris Cervelli
Premier Motorsports
Several things to consider for your particular setup, in order of importance:
The 295 is too wide for the 10 inch wheel, period. You need at least an 11 inch wheel for this tire. Really a ten inch wheel should take a 265, which really isn't big enough for the back of a Turbo. The narrow wheel/wide tire situation makes tire temp data useless. Do what you have to do to get the right wheels. Cheaper in the long run.
Pressure. I would experiment with much higher pressures. I would take your current starting cold pressure and add 2 psi and try it. Keep doing this session after session until you really feel the rear end not sticking or feeling weird. Tires flex an amazing amount, and when you have construction problems you need to look at reducing the flex.
Camber is dependent on roll stiffness. 964's need a good amount of rear camber because they roll the camber out pretty significantly. 3.0 degrees should be pretty close unless your suspension is really soft. I would shoot for a 30 degree spread across the tire, with inside hotter, unless it is the inner sidewall giving you trouble.
Balance. I think you need to look for a little understeer so you are getting the max out of the front tires. You need a monster rear tire for this car, and since you don't have it, you have to make sure you are not overloading the tires you do have.
As lwilkins pointed out, you have a junky 'preload only' LSD. If it is not currently causing problems it soon will. However, the bad LSD should only wear the inside of the tires and can't really cause sidewall problems.
Rotation on the rims just plain shouldn't happen. There is something wrong with the wheels if it does. I can't see how they could be damaged during mounting, but I am sure it is possible.
Chris Cervelli
Premier Motorsports
06-26-2005, 12:26 PM
#17
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Charlie,
In your original post you said that your "tires' failed was this 1 or both rears? The failure pattern you're describing certainly sounds like like a low air pressure failure. If it was 1 tire that failed I would (will) want to look at the rim and valve assembly very carefully. The tire failures I had on my 964 turbo were all 285s I thought 295s were the cure. I did have 3 failures out of 5 at LRP which I attributed to the extremely bumpy ( ****ty) track conditions. Anyway call me
Dan Jacobs
PS: Hey Lynn
In your original post you said that your "tires' failed was this 1 or both rears? The failure pattern you're describing certainly sounds like like a low air pressure failure. If it was 1 tire that failed I would (will) want to look at the rim and valve assembly very carefully. The tire failures I had on my 964 turbo were all 285s I thought 295s were the cure. I did have 3 failures out of 5 at LRP which I attributed to the extremely bumpy ( ****ty) track conditions. Anyway call me
Dan Jacobs
PS: Hey Lynn
06-26-2005, 12:29 PM
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your solution may be as simple as running a higher rear pressure. I use 36 at Summit on the rear, but slightly higher at LRP.
Please see page 44 of the ppt presentation below. Although your car is not a 996, your tire size is the same and your car is in the same weight ball park and making plenty more torque.
http://www.pcaucr.org/pcaucr/forum/post.jsp?postid=1365
Please see page 44 of the ppt presentation below. Although your car is not a 996, your tire size is the same and your car is in the same weight ball park and making plenty more torque.
http://www.pcaucr.org/pcaucr/forum/post.jsp?postid=1365
06-26-2005, 12:31 PM
#19
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Dan, I was planning on calling you tomorrow... 
Each time only one of the rears, the left rear. I also had a DSSR (285) fail at Lime Rock in the same way in April. I had a 285 MPSC fail at the Glen (Tracquest a month ago). All left rear, but different wheels each time. Note that I rotate my wheels/tires from side to side. The tire that failed at Lime Rock yesterday was on the right side at Watkins Glen for the race (only ran in warmup, qualifying, and the sprint race there).
Ever since my GT3 Cup tire delamination "event" I have been extraordinarily cautious about tires and tire pressures. I know we have talked about these failures being caused by air pressure before but I check before/after each run and if anything I'm bleeding the pressure down (usually set once and it is spot on the rest of the day).
Time for custom offset 11" wheels? I can stay in C with 11's at least...
Each time only one of the rears, the left rear. I also had a DSSR (285) fail at Lime Rock in the same way in April. I had a 285 MPSC fail at the Glen (Tracquest a month ago). All left rear, but different wheels each time. Note that I rotate my wheels/tires from side to side. The tire that failed at Lime Rock yesterday was on the right side at Watkins Glen for the race (only ran in warmup, qualifying, and the sprint race there).
Ever since my GT3 Cup tire delamination "event" I have been extraordinarily cautious about tires and tire pressures. I know we have talked about these failures being caused by air pressure before but I check before/after each run and if anything I'm bleeding the pressure down (usually set once and it is spot on the rest of the day).
Time for custom offset 11" wheels? I can stay in C with 11's at least...
06-26-2005, 12:47 PM
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I think reviewing the situation with Dan is your best and safest advice given his personal experience and extreme expertise. Dan was the one who encouraged me to go higher on my rear pressures when i first used these MPSC, I took his advice , and have never had a problem.
Chris, I must say, that although the tire rotation I get on the rim of a GT3 street car with these tires is only a few mm or a couple cm each session (if any), many of rears that have come off either GT3 cup cars(2) or a GT3RS I used to drive have rotated anywhere from several mm, to many cm. Most of these were mounted by Dunlop tire changers. I also had some rear tire rotation on a low horsepower H class 911 with Hoosiers. This activity spanned over likely 40 different rear wheels, and multiple tire changers over the driving span of these 4 vehicles.
Have you never seen this? I would think with the level you drive your cars I would certainly expect it.
Dan can certainly vouch for some of these rotations as he was the chief on my first cup car and all of my GT3RS grand Am experiences.
Hi dan!
Chris, I must say, that although the tire rotation I get on the rim of a GT3 street car with these tires is only a few mm or a couple cm each session (if any), many of rears that have come off either GT3 cup cars(2) or a GT3RS I used to drive have rotated anywhere from several mm, to many cm. Most of these were mounted by Dunlop tire changers. I also had some rear tire rotation on a low horsepower H class 911 with Hoosiers. This activity spanned over likely 40 different rear wheels, and multiple tire changers over the driving span of these 4 vehicles.
Have you never seen this? I would think with the level you drive your cars I would certainly expect it.
Dan can certainly vouch for some of these rotations as he was the chief on my first cup car and all of my GT3RS grand Am experiences.
Hi dan!
Last edited by ldw; 06-26-2005 at 01:35 PM.
06-26-2005, 02:15 PM
#22
Nordschleife Master
Originally Posted by Dan Jacobs
The tire failures I had on my 964 turbo were all 285s I thought 295s were the cure.
Jupe & I have talked lots about his and are baffled. My car does have less torque (332 vs. 384) and weighs less (3000 vs. 3274), but that's about it.
I told you to get a 3.3 C2T
06-26-2005, 10:59 PM
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Charlie - I read that the sidewalls failed. That rules out camber and such - camber or toe problems show up as tread wear.
My guess is somebody got a new machine for mounting tires and broke the bead when installing. This happened to a friend of mine - nine flats in one event. Talk to whomever mounted the tires to the rims. This could also explain failure on two different types of tires.
Rgds,
My guess is somebody got a new machine for mounting tires and broke the bead when installing. This happened to a friend of mine - nine flats in one event. Talk to whomever mounted the tires to the rims. This could also explain failure on two different types of tires.
Rgds,
06-26-2005, 11:14 PM
#27
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Originally Posted by Bob Rouleau
Charlie - I read that the sidewalls failed. That rules out camber and such - camber or toe problems show up as tread wear.
My guess is somebody got a new machine for mounting tires and broke the bead when installing. This happened to a friend of mine - nine flats in one event. Talk to whomever mounted the tires to the rims. This could also explain failure on two different types of tires.
Rgds,
My guess is somebody got a new machine for mounting tires and broke the bead when installing. This happened to a friend of mine - nine flats in one event. Talk to whomever mounted the tires to the rims. This could also explain failure on two different types of tires.
Rgds,
06-26-2005, 11:22 PM
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Dr. J,
I just forwarded your pictures and description of your setup to my buddy at Michelin. Most of his work is with the setup of their slicks on GT3 RSR's and Ferrari's in ALMS and GT3 Cups in the IMSA Porsche Cup. He may be able to offer insight with the MPSC's too, or at least know someone in the Motorsports division who can. I'll let you know.
Mike
I just forwarded your pictures and description of your setup to my buddy at Michelin. Most of his work is with the setup of their slicks on GT3 RSR's and Ferrari's in ALMS and GT3 Cups in the IMSA Porsche Cup. He may be able to offer insight with the MPSC's too, or at least know someone in the Motorsports division who can. I'll let you know.
Mike
06-26-2005, 11:36 PM
#30
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Originally Posted by Mike Buck
Dr. J,
I just forwarded your pictures and description of your setup to my buddy at Michelin. Most of his work is with the setup of their slicks on GT3 RSR's and Ferrari's in ALMS and GT3 Cups in the IMSA Porsche Cup. He may be able to offer insight with the MPSC's too, or at least know someone in the Motorsports division who can. I'll let you know.
Mike
I just forwarded your pictures and description of your setup to my buddy at Michelin. Most of his work is with the setup of their slicks on GT3 RSR's and Ferrari's in ALMS and GT3 Cups in the IMSA Porsche Cup. He may be able to offer insight with the MPSC's too, or at least know someone in the Motorsports division who can. I'll let you know.
Mike