Non-RFT pressures

L

Lazza

Member
 Wokingham
Ok, without wanting to start a new bun-fight, I’m going to ask “that” question :rofl:

What is the recommended tyre pressure for non-RFT on my E89 35i? The RF pressures seem way too high so I was thinking around F34 R36. This is on Uniroyal Rainsport 3. Does that seem about right?
 
tyre presure is load dependant as your not altering the loading just changing the tyre use the guide on your door pillar
 
Lazza said:
Ok, without wanting to start a new bun-fight, I’m going to ask “that” question :rofl:

What is the recommended tyre pressure for non-RFT on my E89 35i? The RF pressures seem way too high so I was thinking around F34 R36. This is on Uniroyal Rainsport 3. Does that seem about right?
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Id say bang on perfection with those numbers whether 18inch or 19inch , may vary a little depending on tyre brand / kind of driving you mainly do & also Re Se , Mpsort or aftermarket springs but i would expect F34 R36 to satisfy 99% of Z owners 99% of the time .
you could play around from there up or down but not by much
 
Thanks Mr Wilks. A good place to start then. I’m happy to tweak them to find my own personal sweet spot, I just wanted a good starting point :thumbsup:

montymog said:
tyre presure is load dependant as your not altering the loading just changing the tyre use the guide on your door pillar
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While this is true, run-flats have different characteristics and requirements from standard tyres. No car the size of a Z4 should need over 40psi in non RFs!
 
mr wilks said:
... i would expect F34 R36 to satisfy 99% of Z owners 99% of the time ...
you could play around from there up or down but not by much.
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F34 is a couple of pounds too low, but R36 is more than 7 out!

Don't believe me? Then ask Michelin: https://www.michelin.co.uk/tyres/car-tyres#type=type_2&brand=BMW&range=z4&model=(e89)%20z4%20roadster&engine=sdrive35is%20(3.0%20l%20340)&year=2009&selectedFitment=225-40-18-88-W&selectedFilter=winter&fronthighwaypressure=36.26&frontnormalpressure=36.26&rearhighwaypressure=43.51&rearnormalpressure=39.16&frontDimension=225-40-18-88-W&rearDimension=255-35-18-90-W&retainFitment=225-40-18-88-W
 
Busterboo said:
mr wilks said:
... i would expect F34 R36 to satisfy 99% of Z owners 99% of the time ...
you could play around from there up or down but not by much.
Click to expand...

F34 is a couple of pounds too low, but R36 is more than 7 out!

Don't believe me? Then ask Michelin: https://www.michelin.co.uk/tyres/car-tyres#type=type_2&brand=BMW&range=z4&model=(e89)%20z4%20roadster&engine=sdrive35is%20(3.0%20l%20340)&year=2009&selectedFitment=225-40-18-88-W&selectedFilter=winter&fronthighwaypressure=36.26&frontnormalpressure=36.26&rearhighwaypressure=43.51&rearnormalpressure=39.16&frontDimension=225-40-18-88-W&rearDimension=255-35-18-90-W&retainFitment=225-40-18-88-W
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I might be being thick but if you follow the link it says FRONT 36.26 (36.26)PSI and REAR 39.16 (43.51)PSI. So is it 39 or 43?
 
If you click on the arrows, you'll see Michelin's figures are unladen and laden. They're the same front and higher rear, of course.

Unladen or not, however, they're significantly higher than recommendations in this thread.

The bottom line is that most people drive round on tyres that are too soft.
 
The cross/arrows don’t work on an iPad. Checking on my MacBook it actually says ‘normal use’ which with the limited ability to carry massive amounts of luggage is probably what most people would use. I agree it is higher than some have mentioned on this thread but not as high as that recommended for run flats.
 
Many people's logic seems to be, 'I've ditched the horrible & hard runflats. Now I can run 'normal' tyres at lower pressures.' And they then often run them too soft - 32 & 34 or 34 & 36 are quite common.

All I'm suggesting is to follow tyre manufacturers' or BMW's guidelines.
 
Busterboo said:
Many people's logic seems to be, 'I've ditched the horrible & hard runflats. Now I can run 'normal' tyres at lower pressures.' And they then often run them too soft - 32 & 34 or 34 & 36 are quite common.

All I'm suggesting is to follow tyre manufacturers' or BMW's guidelines.
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so your suggesting running the same pressures on non runflats as runflats.
the info on the door pillar is for runflats, which I assume if you follow bmw guidelines, will also be for runflats, as they are unlikely to offer advise on tyres they don't fit to the car.
 
Phoenixboy said:
so your suggesting running the same pressures on non runflats as runflats.
the info on the door pillar is for runflats, which I assume if you follow bmw guidelines, will also be for runflats, as they are unlikely to offer advise on tyres they don't fit to the car.
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Yep. :)
 
Busterboo said:
Phoenixboy said:
so your suggesting running the same pressures on non runflats as runflats.
the info on the door pillar is for runflats, which I assume if you follow bmw guidelines, will also be for runflats, as they are unlikely to offer advise on tyres they don't fit to the car.
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Yep. :)
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You can do that if you like. I’ll run mine with the pressures I can feel are “right”. The fitters put them all at around 39psi (actually something like 36/38 front and 39/40 rear). The car felt like it was skating on ice. I dropped them to 34/36 and it was an instant improvement. I will probably tweak the pressures as I get used to it to suit me but I doubt they will end up far from where they are. 10 years of driving an MX5 on track means I have a fairly good feel for these things.
 
Busterboo said:
If you click on the arrows, you'll see Michelin's figures are unladen and laden. They're the same front and higher rear, of course.
Click to expand...

"Laden" here refers not only to stuff in the boot, but also to 'loading' on the tyre caused by acceleration and speed.
 
Are you making this stuff up as you go along? :roll: On the website it doesn’t say laden and unladen it says normal and laden. One would assume that normal would mean exactly that I.e. normal. There is no mention that acceleration is forbidden or you can’t drive up to the speed limit.
 
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