Non-RFT pressures

[Busterboo]

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.

Yep.

[Lazza]

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.

Yep.

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]

If your road tyres perform as well as you want, Lazza, then I'm pleased for you. :thumbsup

[Busterboo]

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.

"Laden" here refers not only to stuff in the boot, but also to 'loading' on the tyre caused by acceleration and speed.

[Tinker15]

Are you making this stuff up as you go along? 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.

[Phoenixboy]

Are you making this stuff up as you go along? 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.

[Busterboo]

Are you making this stuff up as you go along? 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.

No, I'm not making it up. Rotational Loading and, for example, the Shear Effect are two of the forces that tyre designers and manufacturers have to consider.

As for acceleration & speed, I'm talking about 0-62mph in 4.8s & 155mph.

[mr wilks]

Are you making this stuff up as you go along? 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.

No, I'm not making it up. Rotational Loading and, for example, the Shear Effect are two of the forces that tyre designers and manufacturers have to consider.

Of course they do but when a tyre company speaks of tyre pressures laden / unladen i would lather myself in custard & shuffle into town on my hands & knees if they were asking car owners to consider acceleration when inflating their tyres

[Tinker15]

Are you making this stuff up as you go along? 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.

No, I'm not making it up. Rotational Loading and, for example, the Shear Effect are two of the forces that tyre designers and manufacturers have to consider.

As for acceleration & speed, I'm talking about 0-62mph in 4.8s & 155mph.

I know I’m p&£*”#ng in the wind but I’m a glutton for punishment. So you set your tyre pressures for all the times on our wonderful roads that you do 0-62mph in 4.8 and 155mph? Me thinks you are grasping at straws now!

[Busterboo]

So you set your tyre pressures for all the times on our wonderful roads that you do 0-62mph in 4.8 and 155mph?

No, of course not. But I do drive quick quite often and quick enough for tyres to need to perform well.

You're not going to tell me you stay below the speed limit all the time, are you?

[Tinker15]

So you set your tyre pressures for all the times on our wonderful roads that you do 0-62mph in 4.8 and 155mph?

No, of course not. But I do drive quick quite often and quick enough for tyres to need to perform well.

You're not going to tell me you stay below the speed limit all the time, are you?

Well I have been known to occasionally exceed the limit! However, there aren’t many places round here where you can do 155mph! And my car (automatic) will only make 0-62mph in a leisurely 6.1 seconds. Therefore, if you don’t mind, I’ll be passing on the nearly 44psi rear tyre pressure suggestion.

[Busterboo]

Speed apart, using BMW's B-pillar sticker figures + regular wheel alignment gives excellent tyre wear. Not just longevity, but consistency.

So, a pair of Pirelli P Zero rears @ 44psi lasted 23k and still had 2.6mm left across the tread when I changed them.

[Lazza]

My Mazda MX5 has non RF tyres and the recommended pressures are 26psi all round. The car weighs 1280kg. Weight balance 52/48 which i believe is similar to Z4. Around 145bhp which is half of what I have now of course but standard has higher profile tyres (195/50/15 or 205/45/16 or 205/40/17).
Why would the Z4 need an additional 18psi?

[road warrior]

What a fascinating discussion that is turning your to be, all offerings make sense but completely disagreeing often. I know there is a way of arriving at the ultimate answer, and that is to visit a weighbridge and get the weight on each tyre corner and work it out from that. I think there are one or two tyre sites that will do the maths for you and convert into tyre pressure. . And please.. Don't go down the.. How much fuel and how fat is your passenger line.. Just.. Get some numbers.. Hmm?

[road warrior]

And.. Just to put a spoke in science corner.. I have dropped my pressures down to 32/34.. Just for comfort...