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Lap Dog
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Discussion Starter · #1 ·
I am taking my 325i to the track with its new Michelin PS2 tires in a couple of weeks and I was wondering if anyone has had enough track experience with the PS2s to recommend tire pressure. The tires are 235/40/17 all around. 2 degrees neg camber all around. With the 3 or so other street sets that I've had the car on the track before, 38f/37r seemed to work best for neutral feel. Before the camber plates, I needed more like 4 psi more in the front to reduce understeer but with camber, the car feels neutral with similar pressure front and rear.

I've read that the PS2 perform better with relatively low pressure - can anyone confirm this?
 

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Notwithstanding what The Hack said, I answered this question for myself by using a tire thermometer on a race track. What you need is to make the full tire width to work hard for your driving style and track conditions. In general, underinflated tires abuse the edges and do not engage the center; overinflated ones bulge in the center and do the opposite.

I was looking for even temperatures across each tire (from the outer edge, through the center to the inner edge). For my PS2s (225, 18" front, 245 18" back) HOT tires the answer was 40 psi for the front and 37 for the rear.

Take the numbers with a grain of salt, since they are to change not only for a diferent car and tire size, but also for different driving conditions.
 

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Lap Dog
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Discussion Starter · #3 ·
EZ said:
Notwithstanding what The Hack said, I answered this question for myself by using a tire thermometer on a race track. What you need is to make the full tire width to work hard for your driving style and track conditions. In general, underinflated tires abuse the edges and do not engage the center; overinflated ones bulge in the center and do the opposite.

I was looking for even temperatures across each tire (from the outer edge, through the center to the inner edge). For my PS2s (225, 18" front, 245 18" back) HOT tires the answer was 40 psi for the front and 37 for the rear.

Take the numbers with a grain of salt, since they are to change not only for a diferent car and tire size, but also for different driving conditions.
Thanks for being specific. We are all adults here (I think :D ). That was my guess too - somewhere in the 37-40 psi range. I wish I had a pyrometer too but I am too cheap to spend $120 on it. I do watch the triangles at the beginning of the sidewalls and usually chalk up the tires too but it sure is nice to start in the ballpark so I can get to the fine-tuning part faster. Another indicator that I watch is how much pressure I pick up in each corner. If I pick up about the same all around, that's a good sign and I work off of that. Thanks again!
 

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I've run the PS2s on track a couple of times and after playing with the pressures, I was extremely impressed once I had them dialed in. I found them, pressure-wise, to be much like the SO3 Pole Positions, only better. Anything over 37 HOT and they felt greasy to me. I found 35-36 HOT to be a good setting for the PS2s.

My car is a heavy weight E36 M3 with 245/40-17s (when I run street tires), semi-stiff suspension, -3.5 degrees camber in the front and -2.0 in the rear.

Hope that helps. It's easier to bleed air accurately than to add, so I'd suggest starting from a point you might let air out from. I go more by how my car feels than by tire temps, however, so take it for what it's worth.
 

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Be careful if using a tire temperature guage. I was at an autox event last year when I was bleeding off pressure, and another (well respected) autocrosser came up with a guage, and proceeded to help me adjust, based on temp.

I got thru 3 gates, and 2 cones of a slalom before I spun. I rarely spin, and it was definitely due to the pressure. I finished the rather greasy feeling run, and checked pressure again.. it was different left to right and front to rear, with a front right and left rear bias.

Not saying that using the temp guage is a bad thing, but be judicious with it.
 

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LarryN said:
Be careful if using a tire temperature guage. I was at an autox event last year when I was bleeding off pressure, and another (well respected) autocrosser came up with a guage, and proceeded to help me adjust, based on temp.

I got thru 3 gates, and 2 cones of a slalom before I spun. I rarely spin, and it was definitely due to the pressure. I finished the rather greasy feeling run, and checked pressure again.. it was different left to right and front to rear, with a front right and left rear bias.

Not saying that using the temp guage is a bad thing, but be judicious with it.
I can't see how one can set the right tire pressure on one temperature reading. The way it is done is by measuring both the pressure an temperature on hot tires right after a run and making small adjustments. And then repeating the measurements and adjustments after the next run until you are satisfied with the results.

The fact that you tire pressures after that run were all over the board suggests that the tires had not been set correctly. It is possible though that the spin off contributed to the uneven pressures too.
 

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This side up.
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SergioK said:
You can blame the tires for a spin... or you can blame the driver??? :dunno:
:stickpoke
I'm sure some readers might be wondering the same thing... :angel:
 

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SergioK said:
You can blame the tires for a spin... or you can blame the driver??? :dunno:
:tsk:

Did the OP ask for people to take swipes at constructive feedback to his question? No. Move along.
 

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Lap Dog
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Discussion Starter · #10 ·
At driving schools, I've been taught that pyrometers are really useful for setting up the car for each track. The idea is to measure the inner, middle, and outer sections of the tire to see where it's getting a workout. Ideally, temperature should be the same in all sections. It's more of fine-tuning the suspension and out of my reach for each track, though...

FWIW, LarryN is one of the very best autoXers in the Boston chapter. He won his competitive class both last seasons. Hopefully we'll finally stop his run this year :bigpimp:
 

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Donkeybike?
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liuk3 said:
:stickpoke
I'm sure some readers might be wondering the same thing... :angel:
Well, I can always make excuses for a spin... like the time when I picked up some FOD (nail or bolt of some kind) and my tire exploded mid-turn. Oh wait, I didn't spin although a certain 'fester got one hell of a ride at Cal Speedway. :D
 

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Donkeybike?
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bluetree211 said:
:tsk:

Did the OP ask for people to take swipes at constructive feedback to his question? No. Move along.
Are you offended by the insinuation that the driver is ultimately responsible for what happens to the vehicle? Or do you just find comfort in blaming external factors for what a driver does?
 

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SergioK said:
Are you offended by the insinuation that the driver is ultimately responsible for what happens to the vehicle? Or do you just find comfort in blaming external factors for what a driver does?
I was ultimately responsible. It was my fault for letting that person mess with my tire pressures. Having the opposite corners with almost 10 pounds more than the tire next to it caused the spin. I don't dally around out there, and I know the car's limitations. I trusted that the person knew what they were doing with the meter and I was wrong. I was simply telling the OP to not be over compensating on the tire pressures, as I did.
 

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I agree with this. If you have an adjustable suspension and you plan on spending the practice session setting your car up for a sprint or endurance race, by all means... break out the pyrometer. Otherwise, however, it's overkill IMHO. Especially at a driving school.

On the subject of excuses for spins... haha! My favorite of all time is someone who blamed a strong cross wind for a spin in T8 at WSIR. That was one of the best stories I've heard. :rofl:

brave1heart said:
At driving schools, I've been taught that pyrometers are really useful for setting up the car for each track. The idea is to measure the inner, middle, and outer sections of the tire to see where it's getting a workout. Ideally, temperature should be the same in all sections. It's more of fine-tuning the suspension and out of my reach for each track, though...
:
 

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Interlocker said:
On the subject of excuses for spins... haha! My favorite of all time is someone who blamed a strong cross wind for a spin in T8 at WSIR. That was one of the best stories I've heard. :rofl:
I've had cross-winds at Turn 8 at WS shove my car a couple of feet to the left, but blaming them for a spin... :tsk:
 

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Interlocker said:
On the subject of excuses for spins... haha! My favorite of all time is someone who blamed a strong cross wind for a spin in T8 at WSIR. That was one of the best stories I've heard. :rofl:
The best T8 excuse I've heard is, "The steering wheel broke." Though in that case, it really did. :yikes:

Lee
 

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Donkeybike?
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Lee said:
The best T8 excuse I've heard is, "The steering wheel broke." Though in that case, it really did. :yikes:

Lee
Wasn't that not just a spin, but a roll (or multiple rolls) as well?
 

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SergioK said:
Wasn't that not just a spin, but a roll (or multiple rolls) as well?
Yup, Greg Ross's car which Carl McGinn was co-driving at the enduro. Amazingly, even after the roll, they were able to fix the car and won their class. :wow:
 

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Raffi said:
Yup, Greg Ross's car which Carl McGinn was co-driving at the enduro. Amazingly, even after the roll, they were able to fix the car and won their class. :wow:
AND as a certain unnamed poster to this forum (not me, of course. :eeps: ) was inside cleaning out some of the dirt and climbing though the cage, his knee may have somehow triggered the fire suppression system. :rofl:

Hey, wait... wasn't this supposed to be about tire pressures or something? ;)
 
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