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[tomasis]

hello

my car is E91 325i.

I want to check regarding tire pressure. I feel driving summer wheels is too lively after switching from winter wheels. I got an idea of what is neutral driving as winter wheels are the default size, nothing strange.

Summer wheels are fairly stretched in front.

The front rims are 19"x9.5 wide. The tires are 235x35.

The rear rims are 19"x9.5". The tires are 265x30.

The BMW manual says 35psi /39psi for a typical 19" set 225 resp 255.

I did try 32/38psi front/rear but it is still too lively. How much can I reduce in the front wheels before it is dangerously low?

many thanks in advance!

[jadatis]

My made rimmwidt calculator, made after contact with a tiremaker, and using the rimmwidth ratio's of ETRTO, gives for 235/35 a widest rimm of 9.5 inch, measure rimm (is ideal) 8.5 inch width.
For the 265/30, widest 10 inch, measure rimm 9.5 inch.

For low aspect ratio ( hight width division is your 30 and 35) a wider rimm is needed then for fi AR 80.

Once read about trucktire on to small rimm, for wich Michelin made new pressure/loadcapacity list, with lower maxload and 120 psi instead of the 130 psi standard. Even lower maxload then expected for 120 psi. That to small rimm gave tears where sidewall goes over to treath.

A totally different tire, but gives an idea of what is important. If we pull this trough to your tire, wich most likely has higher maxload/loadindex then the OEM tires. Its still within the ranges of allowed.
But extra important to determine the axleloads acurately, and dont use a higher pressure then needed, for your maximum used speed.
Your tires are most likely XL/reinforced/extraload, most low AR tires are, and those are calculated in maxload for referencespeed of 160kmph/99mph, and reference pressure of 42psi/ 2.9 bar.
So dont fill to maxcold given on sidewall of 51psi mayby or sometimes XL 60 psi.

[tomasis]

yes my tires are XL (Hankook Ventus S1 Evo 3)

8.5x19 and 9.5x19 are common for BMW cars. I prob try to change to a bigger front tire once the current one wears out as I will able to fit with new M3 arms later.

I got an idea of how to make good pressure in tires by using a thermal camera. I have Infray P2. I made readings today. Pretty consistent readings, not overinflated or underinflated. Usually warmest from the inside then it goes down linearly to the outside of the tire surface.

Got the idea from the video. Currently, my tire pressure is 32psi /37psi front/rear. I need to experiment a bit as I think the difference between front and rear needs to be larger. Like 30/37 or 32/39 hm. My question would be what psi difference should it be for the 235mm tire on both different rims 9.5" vs 8.5"