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      07-27-2016, 02:00 PM   #1
reala
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M235i tire pressure

Ive been wondering why bmw recommeds 5 psi more in thr back. I thougt that its just for safety. So
Ive been driving with even tire pressure and its resulting in more body roll and no feel right. I just put 3 psi more in the back and feels alot better. 34 37 cold.
I dont know its becuas i got all season rfy tires or not. This car is very sensitive to the pressure
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      07-27-2016, 03:02 PM   #2
15GT-TO-M235
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to maintain understeer built in.
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      07-27-2016, 09:58 PM   #3
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Quote:
Originally Posted by 15GT-TO-M235 View Post
to maintain understeer built in.
Higher pressures in the rear will (generally) neutralise a bit of understeer.
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      07-27-2016, 10:08 PM   #4
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Quote:
Originally Posted by DanielGr View Post
Higher pressures in the rear will (generally) neutralise a bit of understeer.
no... it's the other way around... high pressure in the front will neutralize understeer

http://www.tirerack.com/tires/tirete....jsp?techid=58
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      07-27-2016, 10:25 PM   #5
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I can quote sites that back up my argument too...
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      07-28-2016, 08:33 AM   #6
reala
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From my experience with this car higher in thr back rotates rear easier inducing more oversteer with less traction. Jusy like bmw recommends.
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      07-28-2016, 07:57 PM   #7
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Quote:
Originally Posted by DanielGr View Post
I can quote sites that back up my argument too...
like which?

tire grip is like a pyramid .... there is an optimal pressure where you will get the most grip.... to either side you will start loosing grip....

the thing is that usually the optimal pressure is fairly high say 38-40 psi.... so in most cases the you are on the left of the peak which means that if you lower the pressure you will be losing grip...

now if you are at 40 psi and you push it to 45 psi now you are going the other way and you will also lose grip cause you will be reducing the contact patch...
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      07-28-2016, 08:31 PM   #8
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Can we say we're both right and wrong? There is no hard and fast answer to 'do x to get x' when it comes to tyre pressures as it will depend heavily on the car, type of tyre, where your pressures currently are etc...

Using your pyramid, if you're on the underinflated side of it on your fronts (i.e. under the peak grip), increasing them increases their grip relative to the rear i.e. cancelling out understeer/possibly to the point of inducing oversteer.

Other way still stands. Assume your fronts are at peak grip, overinflating your rears to reduce grip and suddenly you have a oversteering car.

As for those sites...

https://www.facebook.com/notes/ultra...0134442380550/

http://www.trackdayguru.com/tyre-management.html
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      07-28-2016, 08:56 PM   #9
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Quote:
Originally Posted by DanielGr View Post
Can we say we're both right and wrong? There is no hard and fast answer to 'do x to get x' when it comes to tyre pressures as it will depend heavily on the car, type of tyre, where your pressures currently are etc...

Using your pyramid, if you're on the underinflated side of it on your fronts (i.e. under the peak grip), increasing them increases their grip relative to the rear i.e. cancelling out understeer/possibly to the point of inducing oversteer.

Other way still stands. Assume your fronts are at peak grip, overinflating your rears to reduce grip and suddenly you have a oversteering car.

As for those sites...

https://www.facebook.com/notes/ultra...0134442380550/

http://www.trackdayguru.com/tyre-management.html
Yes, that's what I'm saying.... there is not an absolute right option... but in most cases increasing tire pressure in the front will lead to less understeer in the case you are below the optimal pressure...

Also increasing tire pressure, will increase your spring rate which will lead to understeer... so there are more factors than just grip but usually spring rate doesn't make such difference as the grip from the tire

even the 2nd site you posted shows...

Symptom Pressure Adjustment
Understeer Increase Front or reduce Rear 2 psi *
Oversteer Increase Rear or reduce Front 2 psi *

as for the facebook guy... I think he is just wrong
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      07-29-2016, 10:17 AM   #10
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Quote:
Originally Posted by pikcachu View Post
Yes, that's what I'm saying.... there is not an absolute right option... but in most cases increasing tire pressure in the front will lead to less understeer in the case you are below the optimal pressure...

Also increasing tire pressure, will increase your spring rate which will lead to understeer... so there are more factors than just grip but usually spring rate doesn't make such difference as the grip from the tire

even the 2nd site you posted shows...

Symptom Pressure Adjustment
Understeer Increase Front or reduce Rear 2 psi *
Oversteer Increase Rear or reduce Front 2 psi *

as for the facebook guy... I think he is just wrong
Here's another source to back up your argument,which I agree with 100%

http://store.uucmotorwerks.com/artic...ybar_setup.htm
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      07-29-2016, 02:02 PM   #11
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I am happy with 44 - 47 setting now but going to try 47 - 44 over the weekend.
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      07-29-2016, 02:03 PM   #12
reala
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Btw mine is xdrive with stock p7 tires
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      07-29-2016, 03:32 PM   #13
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Quote:
Originally Posted by pikcachu View Post
like which?

tire grip is like a pyramid .... there is an optimal pressure where you will get the most grip.... to either side you will start loosing grip....

the thing is that usually the optimal pressure is fairly high say 38-40 psi.... so in most cases the you are on the left of the peak which means that if you lower the pressure you will be losing grip...

now if you are at 40 psi and you push it to 45 psi now you are going the other way and you will also lose grip cause you will be reducing the contact patch...
Mind sharing your tire pressure specs?

I run 235 and 265 staggered. 38F and 40R cold
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      07-29-2016, 03:48 PM   #14
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Quote:
Originally Posted by ocN55
Quote:
Originally Posted by pikcachu View Post
like which?

tire grip is like a pyramid .... there is an optimal pressure where you will get the most grip.... to either side you will start loosing grip....

the thing is that usually the optimal pressure is fairly high say 38-40 psi.... so in most cases the you are on the left of the peak which means that if you lower the pressure you will be losing grip...

now if you are at 40 psi and you push it to 45 psi now you are going the other way and you will also lose grip cause you will be reducing the contact patch...
Mind sharing your tire pressure specs?

I run 235 and 265 staggered. 38F and 40R cold
I have the stock 225 245 and I'm at 35-37 cold on PSS

PSS are fairly soft sidewalls so they will roll over if not inflated well
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      07-29-2016, 07:51 PM   #15
reala
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Quote:
Originally Posted by pikcachu View Post
I have the stock 225 245 and I'm at 35-37 cold on PSS

PSS are fairly soft sidewalls so they will roll over if not inflated well
I thought you said more pressure in front
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      07-29-2016, 07:54 PM   #16
pikcachu
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Quote:
Originally Posted by reala
Quote:
Originally Posted by pikcachu View Post
I have the stock 225 245 and I'm at 35-37 cold on PSS

PSS are fairly soft sidewalls so they will roll over if not inflated well
I thought you said more pressure in front
Stock pressure is 32-38.

So I do have more pressure in the front than stock
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      07-29-2016, 08:20 PM   #17
reala
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Quote:
Originally Posted by pikcachu View Post
Stock pressure is 32-38.

So I do have more pressure in the front than stock
No i mean more pressure in front than back.
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      07-29-2016, 08:47 PM   #18
pikcachu
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Quote:
Originally Posted by reala
Quote:
Originally Posted by pikcachu View Post
Stock pressure is 32-38.

So I do have more pressure in the front than stock
No i mean more pressure in front than back.
You can do that if you want even more oversteer.

When it says more it means more pressure than before, not necessarily more pressure than the rear.

But for the track I would run 33F-31R if you have a decent track tire
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      07-12-2019, 07:23 PM   #19
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… my head hurts.
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