I Need A Physics Lesson... - BMW Forum - BimmerWerkz.com
3-Series (E36) Chat relating to the BMW 3-Series from 1992-1999. Autodoodad Specific models include: BMW 316i, BMW 318i, BMW 318iS/ti, BMW 320, BMW 323, BMW 320, BMW 324, BMW 325, BMW 328.

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#1 (permalink) Old 04-04-2005, 11:42 PM
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I was looking at the handling adjustment tips on BavAuto, and it says to increase oversteer, lower the pressure in the rear tires and increase pressure in the front.

My thinking is that this would do the opposite because there will be more grip on the rear tires (bigger contact patch) and less grip on the front. So what gives?

Thanks...i'm here to learn!

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#2 (permalink) Old 04-05-2005, 12:24 AM
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I think they have it backwards as well.

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#3 (permalink) Old 04-05-2005, 12:30 AM
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Quote:
Originally posted by umdbandit@Apr 4 2005, 07:42 PM
I was looking at the handling adjustment tips on BavAuto, and it says to increase oversteer, lower the pressure in the rear tires and increase pressure in the front.

My thinking is that this would do the opposite because there will be more grip on the rear tires (bigger contact patch) and less grip on the front. So what gives?

Thanks...i'm here to learn!
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Hahaha, nice catch man, I agree they got it mixed up like I get theories mixed up in physics

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#4 (permalink) Old 04-05-2005, 12:43 AM
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no, actually they are correct, oversteer is when the front end is gripping(to some extent) and the back end is very lose so it swings around... they do not have it backwards
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#5 (permalink) Old 04-05-2005, 01:43 AM
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Cool

When you take a turn too fast and the front end hits the guardrail first, thats Understeer. When the back end hits first, thats Oversteer...

If deflating your tires increases traction, then why do so many autocross drivers overinflate their tires to 40 PSI, 45 PSI or more?

Hmmm...

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#6 (permalink) Old 04-05-2005, 09:49 AM
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Quote:
Originally posted by docrobot@Apr 4 2005, 11:43 PM
When you take a turn too fast and the front end hits the guardrail first, thats Understeer. When the back end hits first, thats Oversteer...

If deflating your tires increases traction, then why do so many autocross drivers overinflate their tires to 40 PSI, 45 PSI or more?

Hmmm...

used
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I've heard that they do that to keep the tires from rolling over on the sidewall and damaging their rims.

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#7 (permalink) Old 04-05-2005, 10:10 AM
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Quote:
Originally posted by xsperf@Apr 4 2005, 09:43 PM
no, actually they are correct, oversteer is when the front end is gripping(to some extent) and the back end is very lose so it swings around... they do not have it backwards
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Right, but if the back tires have less pressure, they will be gripping more than the front ones. I also believe they have it wrong.

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#8 (permalink) Old 04-05-2005, 10:28 AM
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It's not just BavAuto actually. I have seen it on other sites as well. I just did a search on google and found a few more. I guess i'll just have to run an experiment one of these weekends to see if it is true.

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#9 (permalink) Old 04-05-2005, 10:37 AM
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They have it right.

Properly inflated tires grip better than underinflated in a corner. The sidewall roll is what you don't want for traction.

It seems counterintuitive if you've never had a RWD car with a leaky back tire.

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#10 (permalink) Old 04-05-2005, 02:31 PM
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Quote:
Originally posted by umdbandit@Apr 5 2005, 05:42 AM
I was looking at the handling adjustment tips on BavAuto, and it says to increase oversteer, lower the pressure in the rear tires and increase pressure in the front.

My thinking is that this would do the opposite because there will be more grip on the rear tires (bigger contact patch) and less grip on the front.* So what gives?

Thanks...i'm here to learn!
[snapback]325721[/snapback]
They are 100 % correct. If you want to go a step further than tire pressure, to increase oversteer;

you'll have to also mount a wider tire up front, norrower in the rear

more negative camber up front, more positive camber in the rear

softer springs front, stiffer in the rear

softer front stabilizer, stiffer rear.

Of course you don't need all this if it's minimal. These suggestions are for racing and also dependant on track conditions and your tires.

You get all this tuned to the car and you get a BMW with the characteristics of a Porsche 911.

The best way is to experiment. In small increments. 2 psi will make a world of a difference in the way a car handles especially in the corners. I know my race track is the German Autobahn. :P
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#11 (permalink) Old 04-05-2005, 07:35 PM
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i may be wrong but in terms of traction I think that pro drag cars release pressure on their slicks a little so that their is more surface area on their tires for the traction of the big motor. I don't know how this applies to understeer or oversteer but thought i might contribute.

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#12 (permalink) Old 04-05-2005, 09:46 PM
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Quote:
Originally posted by spieluhr@Apr 5 2005, 05:35 PM
i may be wrong but in terms of traction I think that pro drag cars release pressure on their slicks a little so that their is more surface area on their tires for the traction of the big motor. I don't know how this applies to understeer or oversteer but thought i might contribute.
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I too thought it was the other way! Damn s what is a good tire pressur? Right now I have 36 in the rears and 40 in the fronts. BTW I have staggered tires 235 front 255 rear what should I use for best handling?

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#13 (permalink) Old 04-05-2005, 10:13 PM
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lol, there's a mod over on bimmerforums called silverstreak. Thought that was you. Anyway, sorry for the interruption. Back on topic.

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#14 (permalink) Old 04-05-2005, 11:32 PM
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Quote:
Originally posted by spieluhr@Apr 5 2005, 07:35 PM
i may be wrong but in terms of traction I think that pro drag cars release pressure on their slicks a little so that their is more surface area on their tires for the traction of the big motor. I don't know how this applies to understeer or oversteer but thought i might contribute.
[snapback]326225[/snapback]
I was waiting for someone to bring this up.

Drag racing, and going straight traction (or hook, as people call it) is different than sticking in a corner.

I run 32 psi in all four tires when I run my Mustang on the street, and would autocross at about 35. When I run it at the 1/4, I run 40 up front and 20 in the back.

When you are going straigt, the car will squat and give more surface area, so a little less pressure is good. When you corner, the lateral acceleration would cause the tire to roll onto the sidewall and slide at the same pressure. That's bad.

That is also why people don't run drag radials in an autocross. The sidewalls are too flexible.

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#15 (permalink) Old 04-06-2005, 12:19 AM
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whatever guys, the main point is that bav auto is not stupid enough to make a mistake on their website.. if they had the tip up there, they would make sure its correct before putting it up
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