Proper Tire Pressure for Increased (+5) aspect

taibanl · 04-14-2011, 07:45 PM

All,

I am running +5 greater aspect than oem (225/45/18 vs 225/40/18 and 255/40/18 vs 255/35/18)

The tire pressures for the above "standard" fitments would be:
35 front and 41 rear

I have them at 34/38. what do you think?

cb4 · 04-14-2011, 08:03 PM

Sounds about right to me. I run 245/40/18 square. I do 35psi up front and 36 for the back.

VMRWheels · 04-15-2011, 01:19 PM

225/45 and 255/40 are tall sizes. I do not recommend running these sizes since it may cause rubbing issues during compression or a full cabin.

Im a bit confused on what the additional tire pressure would do if the wheels are 5% over the recommended rolling diameter.

-Charles@VMRWheels

taibanl · 04-15-2011, 02:06 PM

I am running them at slightly lower pressure than the next size down

Thanks for the input though

mycoupe · 04-15-2011, 03:52 PM

The tires volume has nothing to do with the psi. Psi is psi. Running 32 psi for example will be the same, it'll just take more air to get it to that psi on a larger aspect ratio tire.

taibanl · 04-15-2011, 05:03 PM

Yes we all know that. The question was what psi is appropriate. The book has a whole chart of various options depending on tire.

ceb · 04-15-2011, 08:25 PM

You do know that changing the overall rolling diameter of the tire can be considered odometer fraud.

Odometer fraud is one of the few things that will void your entire warranty and may cause your title to be branded as "true odometer reading unknown."

taibanl · 04-15-2011, 09:37 PM

No. Not aware of that. I'll look into it

John_01 · 04-15-2011, 09:54 PM

The higher aspect ratio tyre will typically have a higher load rating. This makes it possible to lower the tyre pressure to improve the comfort, but there's a trade off in ultimate performance as the tyre deforms more under high loads. As far as performance and handling are concerned, I think you should keep the same pressure as you would have for a lower aspect ratio tyre.

kevon · 04-17-2011, 12:18 PM

I have done quite a few searches and this is the only thread I can find on tire pressure on an 18" rim. So please excuse my "thread jacking".

I just purchased some NON runflat tires. G-Force tires for somer. So far I love them but have that ongoing fear of getting a flat in the back of my head. The same day I had them put on the TPS light came on twice. We reset it both times and checked the pressure. All was fine. Hasnt came on in over 400 miles, so I'm assuming since I have the ABS type, the computer needed to learn the new tires?

Also what air pressure should I have in these tires? Tire place said 33/35 because thats what the car says, but I feel it may need higher due to the softer sidewall. What do you guys run?

chris328i · 04-17-2011, 02:12 PM

Tire pressure really has no impact on if you will get a flat or not unless the tire is severely under inflated. It's acceptable to slightly increase tire pressures above the std. pressures. For sustained high speed driving on the autobahns in Germany they typically increase pressures 5 psi to reduce heat build up. A slight increase in pressure may improve steering response in some tires.

04-14-2011, 07:45 PM	#1
taibanl Brigadier General 281 Rep 4,121 Posts Drives: BMW Join Date: Sep 2010 Location: NA iTrader: (4)	Proper Tire Pressure for Increased (+5) aspect All, I am running +5 greater aspect than oem (225/45/18 vs 225/40/18 and 255/40/18 vs 255/35/18) The tire pressures for the above "standard" fitments would be: 35 front and 41 rear I have them at 34/38. what do you think?
	Appreciate 0 Tweet Quote

04-14-2011, 08:03 PM	#2
cb4 Captain 60 Rep 910 Posts Drives: 2008 335xi Join Date: Jul 2009 Location: Massachusetts iTrader: (1)	Sounds about right to me. I run 245/40/18 square. I do 35psi up front and 36 for the back.
	Appreciate 0 Quote

04-15-2011, 01:19 PM	#3
VMRWheels BimmerPost Supporting Vendor 2042 Rep 25,989 Posts Drives: BMW Join Date: Jun 2007 Location: Anaheim, CA iTrader: (4) Garage List 2013 BMW M3 [10.00] 2015 BMW M4 [0.00] 2013 BMW F30 [0.00] 2014 BMW F22 [0.00] 2013 BMW F06 [0.00]	225/45 and 255/40 are tall sizes. I do not recommend running these sizes since it may cause rubbing issues during compression or a full cabin. Im a bit confused on what the additional tire pressure would do if the wheels are 5% over the recommended rolling diameter. -Charles@VMRWheels __________________ VMR\|Wheels \| 714.442.7916 \| sales@velocitymotoring.com \| www.velocitymotoring.com \| facebook \| flickr \| Instagram
	Appreciate 0 Quote

04-15-2011, 02:06 PM	#4
taibanl Brigadier General 281 Rep 4,121 Posts Drives: BMW Join Date: Sep 2010 Location: NA iTrader: (4)	I am running them at slightly lower pressure than the next size down Thanks for the input though
	Appreciate 0 Quote

04-15-2011, 03:52 PM	#5
mycoupe Banned 55 Rep 1,495 Posts Drives: 07 335i coupe 6spd Join Date: Dec 2009 Location: cincinnati, Ohio iTrader: (5)	The tires volume has nothing to do with the psi. Psi is psi. Running 32 psi for example will be the same, it'll just take more air to get it to that psi on a larger aspect ratio tire.
	Appreciate 0 Quote

04-15-2011, 05:03 PM	#6
taibanl Brigadier General 281 Rep 4,121 Posts Drives: BMW Join Date: Sep 2010 Location: NA iTrader: (4)	Yes we all know that. The question was what psi is appropriate. The book has a whole chart of various options depending on tire.
	Appreciate 0 Quote

04-15-2011, 08:25 PM	#7
ceb NHTSA Nazi 28 Rep 1,983 Posts Drives: 335ix Join Date: Aug 2009 Location: MD iTrader: (1)	You do know that changing the overall rolling diameter of the tire can be considered odometer fraud. Odometer fraud is one of the few things that will void your entire warranty and may cause your title to be branded as "true odometer reading unknown."
	Appreciate 0 Quote

04-15-2011, 09:37 PM	#8
taibanl Brigadier General 281 Rep 4,121 Posts Drives: BMW Join Date: Sep 2010 Location: NA iTrader: (4)	No. Not aware of that. I'll look into it
	Appreciate 0 Quote

04-15-2011, 09:54 PM	#9
John_01 Colonel 232 Rep 2,643 Posts Drives: E90 325i, E82 135i Join Date: Mar 2009 Location: Sydney, Australia iTrader: (0)	The higher aspect ratio tyre will typically have a higher load rating. This makes it possible to lower the tyre pressure to improve the comfort, but there's a trade off in ultimate performance as the tyre deforms more under high loads. As far as performance and handling are concerned, I think you should keep the same pressure as you would have for a lower aspect ratio tyre.
	Appreciate 0 Quote

04-17-2011, 12:18 PM	#10
kevon Converted 0 Rep 18 Posts Drives: 2007 335i Join Date: Jun 2010 Location: SE Michigan iTrader: (0)	I have done quite a few searches and this is the only thread I can find on tire pressure on an 18" rim. So please excuse my "thread jacking". I just purchased some NON runflat tires. G-Force tires for somer. So far I love them but have that ongoing fear of getting a flat in the back of my head. The same day I had them put on the TPS light came on twice. We reset it both times and checked the pressure. All was fine. Hasnt came on in over 400 miles, so I'm assuming since I have the ABS type, the computer needed to learn the new tires? Also what air pressure should I have in these tires? Tire place said 33/35 because thats what the car says, but I feel it may need higher due to the softer sidewall. What do you guys run? __________________ '07 335i e90
	Appreciate 0 Quote

04-17-2011, 02:12 PM	#11
chris328i Private First Class 3 Rep 111 Posts Drives: 328i Join Date: Mar 2011 Location: Ohio iTrader: (0)	Tire pressure really has no impact on if you will get a flat or not unless the tire is severely under inflated. It's acceptable to slightly increase tire pressures above the std. pressures. For sustained high speed driving on the autobahns in Germany they typically increase pressures 5 psi to reduce heat build up. A slight increase in pressure may improve steering response in some tires.
	Appreciate 0 Quote