Tyre pressure on non-run flats 224 wheels

Panta Rhei · Post by **Panta Rhei** » Tue Feb 12, 2019 1:35 pm

Hello

My car: 3.0si roadster.
I have bought styling 224 alloys and tyres with non-M sizes meaning 225/40 and 255/35.
Question is, after searching through this forum and zpost, WHAT TYRE PRESSURE is way to go?
Someone said: 'Pressure stays the same even after switching to non-run flats', the other one: 'Use Z4M model tyre pressure'.
What would you do?

For now I have - 33 psi/230 kPa front and 38 psi/260 kPa rear - as manual recommendation.
Z4M on the other hand - 30 psi/210 kPa and 32 psi/220 kPa.
I know Z4M has got higher profile, but it should not affect a pressure in that matter- physics, more compressed gas.

brillomaster · Post by **brillomaster** » Tue Feb 12, 2019 2:13 pm

I think the taller profiles of the Z4M sized tyres mean it can run lower pressures - personally I'd stick with pressures recommended in the manual for 225/40 and 255/35 tyres.

the physics of pressures in tyres isn't a perfect model, theres a lot of consideration regarding the size and shape of the contact patch, the influence of low profile tyres, the stiffness of the sidewalls, and how much the tyres should deform under load

but by all means try a lower pressure - at the end of the day its what you feel comfortable with!

Marlon · Post by **Marlon** » Tue Feb 12, 2019 2:18 pm

I keep it simple: 34 psi all round

flimper · Post by **flimper** » Tue Feb 12, 2019 2:25 pm

32 front, 34 rear works well for me

Phoenixboy · Post by **Phoenixboy** » Tue Feb 12, 2019 2:40 pm

buster will be along shortly to confirm

noiseboy72 · Post by **noiseboy72** » Tue Feb 12, 2019 9:47 pm

I find that 30PSI all around works well. It reduces the tramlining and bump steer and leaves the car feeling more planted.

Busterboo · Post by **Busterboo** » Thu Feb 28, 2019 7:01 pm

Just follow BMW's recommendations on the label on the B pillar.

john-e89 · Post by **john-e89** » Thu Feb 28, 2019 7:17 pm

Busterboo wrote: ↑Thu Feb 28, 2019 7:01 pm Just follow BMW's recommendations on the label on the B pillar.

That figure is for run flats on non 224 wheels on a 3.0si.

Busterboo · Post by **Busterboo** » Sun Mar 03, 2019 2:32 am

Marlon wrote: ↑Tue Feb 12, 2019 2:18 pm I keep it simple: 34 psi all round

That seems surprising, insofar as the work the rears do.

Smartbear · Post by **Smartbear** » Sun Mar 03, 2019 8:08 am

Busterboo wrote: ↑Sun Mar 03, 2019 2:32 am
Marlon wrote: ↑Tue Feb 12, 2019 2:18 pm I keep it simple: 34 psi all round
That seems surprising, insofar as the work the rears do.

Don’t forget cars can stop faster than they can accelerate, so braking force is stronger than drive force.
The fronts exert more braking force than the rears also, I’d say the fronts have more work to do than the rears?

Rob

Busterboo · Post by **Busterboo** » Sun Mar 03, 2019 10:41 am

Morning, Rob.

In the RWD E89, significantly higher pressures are stipulated for the rear than for the front.

Z4-forum.com

Z4-forum.com