Anal about tire PSI?

[SEXY-BEAST]

So I'm wondering how uniform (i.e. anal) people are about keeping their air pressure in all 4 tires?

I recently had to put more air in my tires after my TPM went off in the cold weather. I tried to get 32 psi on all 4 wheels, but noticed my pressure varied from 34 to 31 PSI-- and those would even change throughout my drive. Right now, my left front is 34; right front 33 and my two rears are 32.

[SherM4n]

You weren't expecting the pressure to change non-uniformly when you're driving?

[Suds]

Yep your tire pressure will vary for lots of reasons.
First off the TPMS isn't as accurate as a good pressure gauge.
If you are stopped a lot your exhaust will heat some tires hotter than others and build more pressure.
Driving into turns will build more temperature into your outside tires.

When I overpressure my cold tires, then bleed them with a good pressure gauge, I can control the tire pressures within 1/2 psi or better. The TPMS shows closer tracking but measured tire pressure may show 1 to 2 psi offset from the handheld gauge to the TPMS.

For daily driving I try to keep the tires within 2 psi, for the track or AutoX, I try for 1/2 psi.

[SEXY-BEAST]

Originally Posted by SherM4n

You weren't expecting the pressure to change non-uniformly when you're driving?

[SEXY-BEAST]

Originally Posted by Suds

Yep your tire pressure will vary for lots of reasons.
First off the TPMS isn't as accurate as a good pressure gauge.
If you are stopped a lot your exhaust will heat some tires hotter than others and build more pressure.
Driving into turns will build more temperature into your outside tires.

When I overpressure my cold tires, then bleed them with a good pressure gauge, I can control the tire pressures within 1/2 psi or better. The TPMS shows closer tracking but measured tire pressure may show 1 to 2 psi offset from the handheld gauge to the TPMS.

For daily driving I try to keep the tires within 2 psi, for the track or about-x, I try for 1/2 psi.

Thanks for the breakdown!

[seis-speed]

I am anal about tire PSI, but it can vary greatly. Just parking my car where one side is getting sunlight and the other side is not can make the PSI dramatically different. I like more PSI than 32, I generally like 34 for some reason it rides better to my judgement.

I am not anal about other things, I have a rock chip and some sand in the trunk, the car could use a good detailing, but PSI management and not revving a cold engine are two areas that I am pretty diligent in.

[gatorfast]

Agree that the psi on the tpms varies greatly and should be more relied upon to see if a tire is materially low vs an accurate psi reading. I use a digital gauge and measure/add air 1-2 times a month.

[SD ///M4]

Originally Posted by SEXY-BEAST

So I'm wondering how uniform (i.e. anal) people are about keeping their air pressure in all 4 tires?

I recently had to put more air in my tires after my TPM went off in the cold weather. I tried to get 32 psi on all 4 wheels, but noticed my pressure varied from 34 to 31 PSI-- and those would even change throughout my drive. Right now, my left front is 34; right front 33 and my two rears are 32.

You didn't mention how you put air in your tires. If you did it at a gas station using the pressure gauge built into their air hose, it won't be accurate.

First of all, to properly inflate your tires you need a decent tire pressure gauge. The most accurate are known as "racing" tire pressure gauges, such as this one from Amazon: https://www.homedepot.com/p/Porter-C...2002/203162815. This one has a bleeder valve, allowing you to let air out of your tires. My wife and I have two of these, one in each of our trunks.

It's also nice to have a decent portable air compressor, similar to this one at Home Depot: https://www.homedepot.com/p/Porter-C...2002/203162815. Another option would be the VIAIR 85P Portable Air Compressor: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1. You can keep this one in your trunk along with a plug kit and just get rid of the BMW M Mobility Kit. We also each have one in our trunks.

Start the compressor and wait until it gets over 50 psi. Then start adding air to your tires and checking with the gauge until your tire reads about 40 psi, then bleed off the air slowly until it comes down to the psi that's indicated on your door jamb, usually 32 psi for the F8x M3/M4.

After you've inflated your tires to the recommended setting, reset the TPMS using iDrive. Press "Reset" and then drive off. It will calibrate the TPMS automatically. General consensus is that you should check the air in your tires monthly.

[SD ///M4]

Originally Posted by PureModelsOnly

Fun fact: you can easily top off the tires a few PSI with a bicycle tire pump. It's not physically hard at all. No need for an expensive air compressor or those crappy portable ones that crap out after a few uses.

A bicycle tire pump. That's adorable...

In the 20+ years I've tracked my cars I've never seen anyone inflate their tires at the track with a tire pump. Most of us use "those crappy portable ones that crap out after a few uses" for years.

I guess this is truly "Different strokes for different folks".

[gatorfast]

Originally Posted by PureModelsOnly

Mmm I've had like 3 portable tire compressors crap out, they're slow loud and annoying. I don't like turning the car on just to use the cigarette lighter jack either. Like I said this is for like filling 1-2 PSI not a flat tire. And I don't track my car. Im not a BMWCCA member. I'm just a typical BMW leaser.

You do not have to turn on the M3/4 for the 12v outlet to work which is great.

[Harpinc]

The only time my tire pressures are spot on is at the track. Otherwise they are very close on TPMS

[SD ///M4]

Originally Posted by gatorfast

You do not have to turn on the M3/4 for the 12v outlet to work which is great.

The 12V power ports in the M3/M4 are not "always on", like the 12V port in the console of my Z4 M Roadster. You need to turn the ignition on (one push of the Start/Stop button) to get power to the 12V ports. Once on, they will "time out" and lose power after about 10 minutes if the car is locked, longer if it's left unlocked. I actually tested this and posted my results in a thread probably in the summer/fall of 2016 but I can't find it.

I have the VIAIR 85P portable air compressor and the instructions explicitly state that the engine needs to be on before switching on the compressor.

[dim635csi]

F8x cars have secondary engine cooling radiator at the front left tire. You can check tire temps in iDrive, this tire is always getting hotter on the run. 10F difference makes it about 1 psi.

@SD ///M4 - I'm seeing a lot of manual bicycle tire pumps at autocross events, too.

I use battery powered inflator instead. While it cannot inflate a flat tire, 10-20 psi back and forth is what you need most.

[gatorfast]

Originally Posted by SD ///M4

The 12V power ports in the M3/M4 are not "always on", like the 12V port in the console of my Z4 M Roadster. You need to turn the ignition on (one push of the Start/Stop button) to get power to the 12V ports. Once on, they will "time out" and lose power after about 10 minutes if the car is locked, longer if it's left unlocked. I actually tested this and posted my results in a thread probably in the summer/fall of 2016 but I can't find it.

I have the VIAIR 85P portable air compressor and the instructions explicitly state that the engine needs to be on before switching on the compressor.

That's odd and not the case in my car. I do not need to turn the ignition on to have the 12v outlet work. I simply plug in the air pump and it works without the engine or ignition being on.

My wife's car however (a GMC) does require the ignition to be on in order to get 12v power.