Run Flat vs Non tyre pressures?
Discussion
My 330D has non runflats on, obviously the recommended pressures on the door shut are for the original run flats.
What's the suggested difference for tyre pressures? I would have expected to put put slightly more pressure in them, but the empty pressure seems pretty high anyway?
Cheers
What's the suggested difference for tyre pressures? I would have expected to put put slightly more pressure in them, but the empty pressure seems pretty high anyway?
Cheers
Swervin_Mervin said:
Just fill as per on the plate on the driver's side door pillar.
I agree with Mervin, use the same pressures as per the plate on the door pillar. Pressure is related to the size of the contact patch and the load carried by the wheel, not by the run-flat feature of the tyre.I have a 3 series efficient dynamics which came from the factory with non run-flat tyres. I can take a look at the plate tomorrow if you want to compare the pressures.
Locknut said:
I agree with Mervin, use the same pressures as per the plate on the door pillar. Pressure is related to the size of the contact patch and the load carried by the wheel, not by the run-flat feature of the tyre.
I have a 3 series efficient dynamics which came from the factory with non run-flat tyres. I can take a look at the plate tomorrow if you want to compare the pressures.
If you wouldn't mind that would be great thanks, mostly out of interest if they're the same.I have a 3 series efficient dynamics which came from the factory with non run-flat tyres. I can take a look at the plate tomorrow if you want to compare the pressures.
255/35r18 and 225/40r18 are my sizes if they're listed on yours?
Cheers
I have had a look at the plate on the door pillar and I don't think it will be any help to Phil. As I mentioned before, this is the "efficient dynamics" version of the car and it is fitted with 205/60/16 tyres. This is obviously for economy. The plate only shows pressuress for the fitted tyre size and those pressures are very high, probably another economy measure.The other surprising thing is that it also lists pressures for M+S (mud and snow) tyres and these are lower. Here are the pressures in Bars:
M+S Tyres:
Up to 3 people: Front: 2.2 Rear 2.4
Full load: Front 2.7 Rear 2.9
Conventional Tyres.
Up to 3 people: Front 2.7 Rear 2.9
Full load: Front 2.7 Rear 2.9
I consider those pressures to be too high for comfort so I use the M+S settings which translate roughly to 32/36 PSI in old money.
M+S Tyres:
Up to 3 people: Front: 2.2 Rear 2.4
Full load: Front 2.7 Rear 2.9
Conventional Tyres.
Up to 3 people: Front 2.7 Rear 2.9
Full load: Front 2.7 Rear 2.9
I consider those pressures to be too high for comfort so I use the M+S settings which translate roughly to 32/36 PSI in old money.
I have an X3 with NRF fitted, when I bought the car the tyres were at 37-38psi against a door plate pressure of 32psi. In my ignorance and a quest for a softer ride I dropped the pressure to 32psi. After 5,000 miles and a safety check from BMW they reported uneven tyre wear on all four tyres that was symptomatic with under inflated tyres. They wouldn’t commit to what pressure they should be running at but I have now pumped them up to 35psi. I have invested in a digital tyre tread depth gauge and will remeasure after the next 5,000 miles. What I can say is the inside and the outside of the tyre tread had worn more than the centre of the tyre by a good 1-1.5mm. Clear indication of under inflation and this was evident on all four wheels.
So in my opinion I would increase the pressure by around 10% but that is only my experience with the tyre fitted to my x-drive X3
So in my opinion I would increase the pressure by around 10% but that is only my experience with the tyre fitted to my x-drive X3
Locknut said:
I have had a look at the plate on the door pillar and I don't think it will be any help to Phil. As I mentioned before, this is the "efficient dynamics" version of the car and it is fitted with 205/60/16 tyres. This is obviously for economy. The plate only shows pressuress for the fitted tyre size and those pressures are very high, probably another economy measure.The other surprising thing is that it also lists pressures for M+S (mud and snow) tyres and these are lower. Here are the pressures in Bars:
M+S Tyres:
Up to 3 people: Front: 2.2 Rear 2.4
Full load: Front 2.7 Rear 2.9
Conventional Tyres.
Up to 3 people: Front 2.7 Rear 2.9
Full load: Front 2.7 Rear 2.9
I consider those pressures to be too high for comfort so I use the M+S settings which translate roughly to 32/36 PSI in old money.
Thanks a lot for checking.M+S Tyres:
Up to 3 people: Front: 2.2 Rear 2.4
Full load: Front 2.7 Rear 2.9
Conventional Tyres.
Up to 3 people: Front 2.7 Rear 2.9
Full load: Front 2.7 Rear 2.9
I consider those pressures to be too high for comfort so I use the M+S settings which translate roughly to 32/36 PSI in old money.
I'll stick with the standard pressures and keep an eye on wear.
Comfort & handling is all good.
If it were me, I'd start with stock pressures and then bump them up 3 PSI all over if case there is a wear issue.
Another would be to get an IR gun ; they're cheap on eBay these days. With that, check the temperature of the tyre across the tread with it, if you are still on the RFs with even wear present. Try and replicate a similar temperature difference on the non-runflats.
I had to do the above on my M3 when I went to track tyres ; there were many stories about what I should go with With the IR gun I actually got some very nice results from the handling; I was surprised. It did take a little trial and error but I did get there
. For once, some online guides did come in handy .
Another would be to get an IR gun ; they're cheap on eBay these days. With that, check the temperature of the tyre across the tread with it, if you are still on the RFs with even wear present. Try and replicate a similar temperature difference on the non-runflats.
I had to do the above on my M3 when I went to track tyres ; there were many stories about what I should go with With the IR gun I actually got some very nice results from the handling; I was surprised. It did take a little trial and error but I did get there
. For once, some online guides did come in handy .It is easy to work out the correct tyre pressure, if you can be bothered, as it it a bit long winded.
Set you tyres to where you think they should be, when cold.
Drive for an hour to get them up to temperature and then test the pressures again, they should have increased no more than 4psi over the cold pressure.
If you have a bigger gain than that you have them too low to start with.
It really is that simple.
The reason too low a pressure is dangerous is they produce too much heat and that is when you can have a blow out, so makes sense to use the 4psi rule.
Set you tyres to where you think they should be, when cold.
Drive for an hour to get them up to temperature and then test the pressures again, they should have increased no more than 4psi over the cold pressure.
If you have a bigger gain than that you have them too low to start with.
It really is that simple.
The reason too low a pressure is dangerous is they produce too much heat and that is when you can have a blow out, so makes sense to use the 4psi rule.
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