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      11-16-2011, 08:54 PM   #23
disapr
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Quote:
Originally Posted by dbarnes View Post
to deal with oversteer you could increase R pressure OR decrease front pressure.
I'll try again - Can you explain why this would correct oversteer?

Oversteer to my understanding is a traction bias to the front, meaning that the front tires have more grip than the rear at the moment of oversteer.

If you increase the rear pressure wouldn't this reduce the rear traction and magnify the oversteer tendencies?
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      11-16-2011, 09:33 PM   #24
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Quote:
Originally Posted by disapr View Post
I'll try again - Can you explain why this would correct oversteer?

Oversteer to my understanding is a traction bias to the front, meaning that the front tires have more grip than the rear at the moment of oversteer.

If you increase the rear pressure wouldn't this reduce the rear traction and magnify the oversteer tendencies?
Quote:
Originally Posted by dbarnes View Post
You can do "either" not both. For example, to deal with oversteer you could increase R pressure OR decrease front pressure. However, let's say you increased rear but then under braking your rear starts to dance then you'd go back and drop the R pressure back to what it was before you raised it and then lower the F to get rid of the oversteer.

Please note, we are assuming all other varables are not being adjusted otherwise things can get complicated fast!

I think he meant to say Correct UNDERSTEER. Otherwise I'm confused also!
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      11-16-2011, 10:08 PM   #25
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Originally Posted by dapopa9 View Post
ahh ok I follow you now!
Sorry for the confusion

Spoke too soon...It looks like you are still confused?
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      11-16-2011, 10:28 PM   #26
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Quote:
Originally Posted by dapopa9 View Post
I think he meant to say Correct UNDERSTEER. Otherwise I'm confused also!
No, I stated it correctly - this would correct OVERSTEER on a front engine, rear wheel drive car. Although the way a tire generates lateral grip is complicated, however, simplistically speaking... if you remember from high school physics frictional forces are related to a normal force times the coefficient of friction (f = mu * N) so if you increase the pressure you will increase the effective normal force acting on the contact patch and, thus, assuming the tire has a constant coefficient of static friction (i.e., not sliding yet; if sliding then it becomes the kinetic friction coefficient) the lateral grip (frictional force) increases. Does this help?

On Roger Kraus Racing's website I found a table (standard table) describing how to adjust a setup to deal with oversteer and understeer - just click on "Understeer-Oversteer" to see the table:
http://rogerkrausracing.com/CompatSite/information.html

Please look in the oversteer column and tell me how you would adjust rear tire pressure to deal with oversteer?

Last edited by M3SQRD; 11-16-2011 at 10:42 PM.
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      11-16-2011, 10:38 PM   #27
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Quote:
Originally Posted by dbarnes View Post
No, I stated it correctly - this would correct OVERSTEER on a front engine, rear wheel drive car. Although the way a tire generates lateral grip is complicated, however, simplistically speaking... if you remember from high school physics frictional forces are related to a normal force times the coefficient of friction (f = mu * N) so if you increase the pressure you will increase the effective normal force acting on the contact patch and, thus, assuming the tire has a constant coefficient of static friction (i.e., not sliding yet; if sliding then it becomes the kinetic friction coefficient) the lateral grip (frictional force) increases. Does this help?
Hmmm...the article from TireRack and Michelin http://www.tirerack.com/tires/tirete...nd_Feeding.pdf says to do the opposite of what you are saying.

It Says on page 17 "To Decrease Oversteer higher the Front Tire Pressure or Lower the Rear Tire Pressure"
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      11-16-2011, 10:48 PM   #28
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Quote:
Originally Posted by dapopa9 View Post
Hmmm...the article from TireRack and Michelin http://www.tirerack.com/tires/tirete...nd_Feeding.pdf says to do the opposite of what you are saying.

It Says on page 17 "To Decrease Oversteer higher the Front Tire Pressure or Lower the Rear Tire Pressure"
Well, then I must not know what I'm talking about
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      11-16-2011, 10:56 PM   #29
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I must say I don't have much experience with this so I wouldn't bet too much that I'm correct either. haha! But that is kinda how I interpreted the article and it does make sense to me also.
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      11-16-2011, 11:10 PM   #30
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Quote:
Originally Posted by dapopa9 View Post
I must say I don't have much experience with this so I wouldn't bet too much that I'm correct either. haha! But that is kinda how I interpreted the article and it does make sense to me also.
To be honest with you there is no "right" answer - did you check out the link I had posted a few minutes ago? BTW, I'm speaking from 20+ years of practical track experience, mostly with BMWs, so that's how I handle tire pressure adjustments. Do you even know if that table is for a front engine, rear drive car?

I'm done discussing the subject and sorry for confusing everyone
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      11-16-2011, 11:41 PM   #31
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Quote:
Originally Posted by dbarnes View Post
To be honest with you there is no "right" answer - did you check out the link I had posted a few minutes ago? BTW, I'm speaking from 20+ years of practical track experience, mostly with BMWs, so that's how I handle tire pressure adjustments. Do you even know if that table is for a front engine, rear drive car?

I'm done discussing the subject and sorry for confusing everyone

Yeah they article you posted http://www.turnfast.com/tech_handlin...ling_pressure3 also suggested the same as the Michelin article to lower front PSI to reduce understeer:

"If the tires felt very slippery, especially if they got worse on every lap, then the tire pressure is too high. Take each tire pressure and write it down. If only the front or rear tires felt slippery (the front was slippery if the car understeered and wouldn't respond to more steering input, the back was slippery if the car wanted to oversteer and spin), then lower the pressure of just that pair by 4 psig while they're still hot. Try this setting for the next session."
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      11-17-2011, 04:26 AM   #32
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Quote:
Originally Posted by disapr View Post
I have the standard pilot cup tire, not the + version.

TobiasMUC - Are you running the same pressure all around?

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      11-17-2011, 04:43 AM   #33
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Quote:
Originally Posted by dbarnes View Post
Then it sounds like your starting pressures are OK once you adjusted them down. However, if you consistently run better lap times on a hot day then you should adjust your cold pressures up a couple of psi on cold days so hot pressures are always at 40 psi.

BTW, sorry to read about the nut job
Yeah he's crazy...I did the mature thing and let it go, but now he thinks he's almighty and 'won'
real PITA


is 40psi hot too much on a hot day?

I always thought running about 38 hot would be ideal?

I haven't tracked on the RS3s yet...but I've heard they're sensitive to temps on the track more so than other street tires
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      11-17-2011, 05:31 AM   #34
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Quote:
Originally Posted by dapopa9 View Post
Yeah they article you posted http://www.turnfast.com/tech_handlin...ling_pressure3 also suggested the same as the Michelin article to lower front PSI to reduce understeer:

"If the tires felt very slippery, especially if they got worse on every lap, then the tire pressure is too high. Take each tire pressure and write it down. If only the front or rear tires felt slippery (the front was slippery if the car understeered and wouldn't respond to more steering input, the back was slippery if the car wanted to oversteer and spin), then lower the pressure of just that pair by 4 psig while they're still hot. Try this setting for the next session."
That's not the same thing. If a tire's pressure is too high then, yes, you must reduce the pressure in the tire. Tires have a pressure, actually temp, range they like to work in and if you exceed that pressure/temp limit the tires will start to feel greasy. This is a case of abusing the tires and having to reduce pressure to keep a tire in its operating range which is not the same as fine tuning the handling balance of your car - your cold pressure was too high and resulted in overheating the tire. Obviousy there's a limit to how much pressure you can use because the tire will start to balloon too much. Clearly, there's a minimum pressure setting, too.

Here's an example for you...if you set your the pressure of a tire at 20 psi and then 50 psi, assuming the tire doesn't get greasy (extreme example), which tire pressure setting will have more grip - the one at 20 or 50 psi?
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      11-17-2011, 05:44 AM   #35
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Quote:
Originally Posted by persian54 View Post
Yeah he's crazy...I did the mature thing and let it go, but now he thinks he's almighty and 'won'
real PITA


is 40psi hot too much on a hot day?

I always thought running about 38 hot would be ideal?

I haven't tracked on the RS3s yet...but I've heard they're sensitive to temps on the track more so than other street tires
Glad to hear it's over. It was smart to distance yourself from someone who is clearly not mentally stable!

38 or 40 psi - it all depends on the tire, as well as the track surface. Try both, or even a third setting, on a given day and see which one works better. No two track days will be identical - that's why you'll hear a lot of race teams say they aren't able to use a setup from a previous year, or even a recent test, at the same track. Experiment with different setting - that's part of the fun! Everything I've stated is based on experience.

Just to really confuse things...why is it that you have to run a stiff front sway bar, relative to the rear, on an e46 M3 to reduce understeer (not a typo)?
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      11-17-2011, 07:06 AM   #36
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Here's the last link I'm going to provide on the topic of adjusting tire pressures for driving on race tracks, not autox circuits:
http://www.summitpoint-raceway.com/i...atid=38&id=174

My own personal experience with e30 M3s, e36 M3s, e46 M3s and e92 M3s follow the tire pressure tips, as well as all other suspension tuning tips, in the links I've provided. Clearly I'm in the minority on how tire pressures should be adjusted to FINE TUNE handling characteristics, although it appears I'm also one of the few with a lot of practical experience, so please ignore all of my comments and go figure things out on your own.
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      11-17-2011, 10:03 AM   #37
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Quote:
Originally Posted by dbarnes View Post
Here's the last link I'm going to provide on the topic of adjusting tire pressures for driving on race tracks, not autox circuits:
http://www.summitpoint-raceway.com/i...atid=38&id=174

My own personal experience with e30 M3s, e36 M3s, e46 M3s and e92 M3s follow the tire pressure tips, as well as all other suspension tuning tips, in the links I've provided. Clearly I'm in the minority on how tire pressures should be adjusted to FINE TUNE handling characteristics, although it appears I'm also one of the few with a lot of practical experience, so please ignore all of my comments and go figure things out on your own.
Thanks for sharing your experience and the links - I'm here to learn the correct way to manage tires and handling characteristics so I will definitely give this a try.
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      11-17-2011, 01:05 PM   #38
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Quote:
Originally Posted by disapr View Post
Thanks for sharing your experience and the links - I'm here to learn the correct way to manage tires and handling characteristics so I will definitely give this a try.
+1

I'm grateful for all the info on here

A friend of mine cored his almost new PSS after 2.5 track days and 2k miles.
I don't want to be cording any tires...

to prevent cording, alignment yes, but tire pressure plays a big roll too right?


If the outside edge of the tires are wearing too much, that means too much pressure right?
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      11-17-2011, 01:12 PM   #39
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Quote:
Originally Posted by persian54 View Post
If the outside edge of the tires are wearing too much, that means too much pressure right?
I haven't read the second link (yet) but the first link really describes a good way to solidify a working tire pressure. I'm shopping for a pyro right now and will use this method to dial it in.
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