Run-flat & non-run-flat tyre pressures

[Busterboo]

Just phoned Sytner BMW Leicester. Spoke to the Chief Technician, said that I'd switched from Bridgestone to Pirelli, from run-flat to non-run flat, and asked which pressures I should use.

His answer was (the same as Bridgestone's): "If it's the same tyre size, it's the same pressure."

 

[Ducklakeview]

Just phoned Sytner BMW Leicester. Spoke to the Chief Technician, said that I'd switched from Bridgestone to Pirelli, from run-flat to non-run flat, and asked which pressures I should use.

His answer was (the same as Bridgestone's): "If it's the same tyre size, it's the same pressure."

Somewhere to avoid taking your car then...

Seriously, just do what you want, but make sure you post some pics after you have wrapped the rear end of your 35is around a tree, so we can all say "told you so" but I'm sure your knowledgeable BMW dealer will apologise and pay for the damage... Not!

Mike

 

[bmwaddict]

Mate, don't do it, everyone is clearly advising you against it.
I work in the tyre industry and I don't care what bmw says, putting 45psi in a normal tyre of the type we use on our zeds (low profile, wide sporty tyres) will surely compromise the grip and therefore safety of your car if you ever push it and drive spiritedly.
I do mine 33 front 36 rear, and although it's not an e89 you must see from what everyone is saying that it's not a good idea to put loaded ford transit type psi in a tyre of a 1400kg sports car.

 

[Steve84N]

One thing I have noticed is that higher profile tyres tend to run lower pressures. This can be seen on something like a 3 series where the door sticker has pressures listed for different wheel/tyre options. Therefore, the M might be a little low as they run a higher profile. This is consistent with what most people settled with as being a bit above M but below standard RFT.

 

[Busterboo]

Have just phoned 4 tyre manufacturers and asked each one the same question:
"Are run-flat and non-run-flat tyre pressures the same?"
Their answers were:

Michelin: "The same."
Goodyear/Dunlop: "The same."
Bridgestone: "Tyre pressures depend on the vehicle."
Pirelli: "We do not give tyre pressures. Follow your car maker's advice."

 

[Busterboo]

Have just phoned 4 tyre manufacturers and asked each one the same question:
"Are run-flat and non-run-flat tyre pressures the same?"
Their answers were:

Michelin: "The same."
Goodyear/Dunlop: "The same."
Bridgestone: "Tyre pressures depend on the vehicle."
Pirelli: "We do not give tyre pressures. Follow your car maker's advice."

The BMW figures for the E89 35is are 2.6 bar/37.7 psi front and 3.1 bar/44.96 psi rear.

These are, however, for (a) 2 passengers & luggage and make no mention of (b) speed.

I can find no figures for 1 passenger & no luggage or for high speed.

 

[Nictrix]

Just to throw something else into the mix, our X6 that has runflat tyres and the rears are 315 x 20 and front 275 x 20 are 2.0 bar front and back.
Our 23i Z is 2.5 bar front and 3.0 bar rear on 18" with the rears being 235s.
Why is the pressures lower for a much heavier car?
And we have been running the Z4 with standard pressures with non runflats for almost 3 years with no problems and no loss of grip for the driving that we do.

 

[Busterboo]

Just to throw something else into the mix, our X6 that has runflat tyres and the rears are 315 x 20 and front 275 x 20 are 2.0 bar front and back.
Our 23i Z is 2.5 bar front and 3.0 bar rear on 18" with the rears being 235s.
Why is the pressures lower for a much heavier car?
And we have been running the Z4 with standard pressures with non runflats for almost 3 years with no problems and no loss of grip for the driving that we do.

Your E89 23i's pressures, recommended by BMW (and confirmed by the major tyre manufacturers to be for both run-flats and non-run-flats) are, as you say, 2.5 bar front and 3.0 bar rear. In old money, that's 36.25 psi and 43.5 psi.

You say, however, "for the driving that we do", you've been running your non-run-flats at "standard pressures" - presumably in the low 30s - "with no problems".

Good, I'm glad. The 'driving that I do' can make my 35is's 335 bhp & 370 ft/lbs of torque a bit of a handful sometimes and I envy you your 23i.

For my part, however, I want to drive my car at the recommended pressures because, when I push it hard, I need all the help the tyres can give me.

(As for your X6, like any car, don't the tyre size, profile, laden weight & speed of use dictate the pressures?)

 

[Nictrix]

You say, however, "for the driving that we do", you've been running your non-run-flats at "standard pressures" - presumably in the low 30s - "with no problems".

You have grabbed the wrong end of the stick, the Z4 is run at standard pressures ie. 2.5 bar front 3.0 bar rear with no problems.
You seem to have pulled low 30s from nowhere as I mentioned nothing about this.
I was on your side with this discussion.
I do believe you have a point in wanting to know what pressures you should put in whether or not lower than the manufacturer states.
Just because you are being told these pressures are too high by people on the internet does not mean that they are correct.
This same argument goes on with bike forums as well as nowadays it is fairly normal for the rear on a bike to be 42psi which a lot of people say this is 6 psi too high.

 

[Busterboo]

You're right. I misinterpreted "standard pressures".

But now I'm very glad you're 'on my side'.