325ci Tire Pressure Question

[BeastonMW]

Hi everyone,

As some of you may know I purchased my first BMW yesterday ('04 325ci) with 133K miles. She is a gem! I was looking at the owners manual and it has various tire pressure recommendations depending on the tire size. What I found interesting is BMW calls for more in the rear than the fronts. I am wondering what other people are running on there 325ci's? Looks like mine should be 30 psi in the front and 35 psi in the rear.

[jadatis]

Tire-pressure advice is all based on weight on tires and speed, and is to prevent any part of the rubber of tire to get above a sertain temp at wich it hardens ireversible, so it crackes every next bendig by the deflections a bit further until the tire blows , with the missery that goes with it, up to death people.

You can also influence under- and over-stear with the tirepressure .

But in your case the higher rear is because nowadays they only give advice for axles loaded to their maximum allowed and for towing even higher.
Its a matter of responcibility of the car-maker, so that if someone overloads or pressure drops or is read inacuratly to high , it still wont lead to lawsuts.

Before 2000 the European carmakers used for normal use - advice, the axleweights determined by the car maker for 3 persons and a little load , and this was mostly front higher then rear.
Nowadays normal advice is for GAWR's ( that maximum allowed axleweight by law) and for up to maximum technical car speed, wich is probably pretty high for a BMW.
To my conclusions, the Ford/Firestone- affaire that played in America around 2000 , had a large impact on how car- and tire-makers handled pressure-advice.
In that affaire lot of roll-over accidents , often because of blowing rear tire, that courced more then 100 death.
So you will realise how serious this matter is.

In 2006 American TRA stepped over to the better calculation for tirepressure , that European ETRTO used since decades, and still uses, but only for P-tires in SL and XL.
But this was to my opinion not the cource of the to low adviced pressure for the Ford Explorer of 26 psi, because it was repaired by lowering the P tires by 10% in maximum load, before calculating.
To my conclusions it was because the ofroad-looking tires had profile blocks that cover a part of sidewall , wich made it lesser sidewall to flex, or better, more heatproduction at the same deflection.

So it is still possible to use lower pressure on front then on rear, when you are only driver and a little load in the car, still more weight on front then on rear axle.
But if you want to go off the advice of the car-maker, they cant be held responcible if something goes wrong, so then you yourselfes are responcible.
So then you have to determine the needed pressure using as accurate as possible data.
Especially determining the real weights on seperate tires is the hardest part in it.
I can help you with that , but you cant hold me responcibe too.

Greatings from a "Dutch Pigheaded Selfdeclared Tirepressure-Specialist"
Peter

[dhurley34]

I've tried every combination of tire pressures and the following combinations work for me:

30/35 Summer
32/37 Fall/Spring/Winter

The reason for the differential between the seasons is the amount of pressure buildup from heat from normal driving. Summer = More pressure buildup so the pressure can be set low and it will grow by as much as 5psi from normal driving. If you set it too high when cold, the ride can become very harsh after driving several miles.

In winter and transitional seasons, its not as hot so pressure won't grow as much so the tires can be set higher initially.

Set it cold with a digital air gauge and check it often.

I may be a bit anal but coming from a racing background, don't set it if the sun is shining on one side of the car and not the other. It will cause the pressure to not be accurate by as much as 1.5psi.

[All2kool]

I have BMW Style 286 Staggered with 235/45/17 93V tires; my tire pressures are 32 front, 36 rear.

[BeastonMW]

Talked to a local shop today who only does alignments and I was pleasantly surprised to hear he does in fact use weights when doing BMW alignments. He said I would never do one without using them. He seemed to be quite knowledgeable of the car and told me $79 for the alignment. LOVE IT!!

I did however have something weird happen since I bought the car. I bought the car last Saturday. Drove it home, popped off all 4 wheels to inspect everything and then rotated the tires cross directionally. Immediately after doing that, the car pulled to the right. I checked all pressures and everything checked out. Last night, I put the tires back to the way they were when I bought the car on Saturday and she drives in a straight line. No more pulling to the right.

Do BMW's not like to be rotated? Is it standard to just run the rear tires down. Then move the fronts to the back and put new on the front? This is my first RWD. It's been all FWD or AWD prior to this.

[ItsGibson]

I would make sure that all the tires are the same size. I have wider tires on the back and rotating tires with different sizes could cause some issues

[dhurley34]

BMW advises to not rotate tires. Once they all begin to wear, they do so differently. Camber/shoulder wear is the chief reason rears shouldn't be rotated to the front.

[BeastonMW]

All 4 tires are the same size. And I can see why BMW advises not to rotate them. Car drives great. Tires have around 13K miles on them and look good.

What is the average tire life on a well aligned 325ci?

[MarcoZandrini]

The average tire life? Doesn't exist. Tire life is dependent upon many factors such as tire inflation, driving practices, road surface composition, road surface temperatures, etc.

[BeastonMW]

The average tire life? Doesn't exist. Tire life is dependent upon many factors such as tire inflation, driving practices, road surface composition, road surface temperatures, etc.

What are some people on here getting miles wise on there tires?

[dhurley34]

7/32nd left after 20,000 miles on Firestone Wide Oval Indy 500 here. New, they only had 9/32.

[BeastonMW]

7/32nd left after 20,000 miles on Firestone Wide Oval Indy 500 here. New, they only had 9/32.

Doing well. I don't plan on hot dogging the car and will run 35 psi in all 4 tires. Hoping to get good tire wear.