[UnluckySaxon]

Originally Posted by Charlie (Wessex)

When you enter all your details, there is a box saying "VIEW SIZE DETAILS" with a downward arrow. Click on that and it will expand.

Here's a link to my car/tyres... https://www.michelin.co.uk/auto/brow...owDetails=true

If only...

[Charlie (Wessex)]

Ah the site seems to have crashed.

[ramparts]

Here's todays recommended "fully loaded"

[ramparts]

Comfort

[ramparts]

And eco

[ramparts]

I've brought mine down now to 40 all round, I'll round in a few days if it's any different

[Charlie (Wessex)]

Originally Posted by davidoff86

Here's todays recommended "fully loaded"

Sure - the same as mine. Now go look at your tyres and see what the max pressure is.

Do you go for BMW recco of 51psi, or the tyre manufacturers max of 50psi??

Serious question, as if you follow BMW advice (not that you are) you are exceeding the max pressures as determined by the manufacturer. Dangerous and seemingly BMW are happy with that given my star marked F1s are official, and max out at 50psi.

[ramparts]

Originally Posted by Charlie (Wessex)

Sure - the same as mine. Now go look at your tyres and see what the max pressure is.

Do you go for BMW recco of 51psi, or the tyre manufacturers max of 50psi??

Serious question, as if you follow BMW advice (not that you are) you are exceeding the max pressures as determined by the manufacturer. Dangerous and seemingly BMW are happy with that given my star marked F1s are official, and max out at 50psi.

Yeah I'd never run them that high it's madness.

I wonder if the manufactures max pressure is at a certain ambient temperature, if so it's still "in line". but yes, very very high none the less.

[ramparts]

More tyre pressure bingo, which goes to show the difference temperature makes!
All Tyres are at 36 psi this morning, down 4PSI since the ambient temp has dropped from 21 to 8.

[andbrads]

My M340i is on Goodyear Eagle F1, I will be changing to Michelin as soon as they are worn down. The car says I need 41 psi but I don’t like the feeling that high. The car is more understeery and the ride crashier, so I run them at 39 psi.

[Bc2005]

I have an M340i with 19” square 225/40r19 Pirelli run-flats, and for about the first 10 months iDrive recommended 38/41 psi. About a month ago it switched to 37/42. I already thought these were pretty high pressures, and they make the ride rougher, but 51 psi seems really crazy.

Is iDrive screwed up and recommending incorrect pressures?

[HighlandPete]

Originally Posted by Charlie (Wessex)

Sure - the same as mine. Now go look at your tyres and see what the max pressure is.

Do you go for BMW recco of 51psi, or the tyre manufacturers max of 50psi??

Serious question, as if you follow BMW advice (not that you are) you are exceeding the max pressures as determined by the manufacturer. Dangerous and seemingly BMW are happy with that given my star marked F1s are official, and max out at 50psi.

The recommended figure is a working pressure, not the setting pressure. Maximum pressure rating is for a cold tyre.

[HighlandPete]

Originally Posted by davidoff86

Yeah I'd never run them that high it's madness.

I wonder if the manufactures max pressure is at a certain ambient temperature, if so it's still "in line". but yes, very very high none the less.

I'm sure you follow that the iDrive is not recommending setting the tyres to that high pressure, it simply showing what is best at the selected loading and tyre temperature.

Before we had these readouts hardly anyone had any clue what pressure they were running with hot tyres. Comments like "I run at 35psi", is simply a cold setting pressure. Most would be in fact running a 38 - 40psi working pressure. A rear tyre at a cold setting of say 38psi, (typical BMW setting) will run near the mid 40's when hot and driving hard.

[srbs73]

Thanks for this. This question came into my head today and I've been running my PS4S' at 40 PSI.

Michelin's site says that it should be 39 for normal use and 46 for highway. I do mainly normal use so think 40 is probably a reasonable compromise.

[peelerec]

Originally Posted by srbs73

Thanks for this. This question came into my head today and I've been running my PS4S' at 40 PSI.

Michelin's site says that it should be 39 for normal use and 46 for highway. I do mainly normal use so think 40 is probably a reasonable compromise.

On the track I run them 35-36 HOT MAX. Any more and they tend to eat up the outsides even more. I think even 46 is too high for highway cruising. 38-40 max for daily highway cruising.

[Z_Victor1]

This Tyre Pressure conversation is interesting....I too was thinking these pressures seem far too high.

I used to think that filling tyres with Nitrogen mitigated the increase in pressure due to increasing temperature, but I'm wrong on that.
Gay-Lussac's Law (I think) covers all gasses.

A lot of info here:-
https://www.getnitrogen.org/sub.php?...eratureeffects

The other factor is the moisture content of air which also adds to the pressure increase.
And N2 eliminates moisture found in air...all open to discussion.

Still a faff getting it done though....

[andbrads]

I’ve just fitted PS4Ss coming off Bridgestone RFT or whatever the standard fitment RFT is for an M340i.

Controversially, I am slightly disappointed. I can’t feel any difference, or very very minor. I haven’t had the opportunity to drive the car with some intent yet so should perhaps reserve judgment but in my previous M240i, when I changed from the standard RFT to Michelin Pilot Sport (not S) it was a dramatic difference which was perceptible driving just 20 feet. The car felt lighter, I immediately had way more steering feel, the ride was better and the front end bite in a different league. I didn’t get any of these first impressions this time around.

I reduced the pressures down to 37 psi all around.

[NLJ]

The benefit of the PS4s is only realized at 7/10th and up!

[andbrads]

Originally Posted by NLJ

The benefit of the PS4s is only realized at 7/10th and up!

Damn, I might have made an expensive mistake then, I was toying with the PS5. Maybe once they bed in and I can drive them with some gusto I will appreciate them more. The main thing I expected, but am missing, is the upgrade in steering tactility that I felt in the switch on the M240i. Or maybe the RFTs I was coming off in the M340i had improved significantly.

[Fox530]

My M340i was on Bridgestone run flats when I collected it. By the time I got the car home I was worried I'd made a mistake in buying it - the ride quality was just unacceptable.

I immediately replaced all 4 with Pilot Sport 4S and the difference has, in my view, changed the car. I'm now really happy with it. The difference was clear to me immediately with no time required to wear them in.

[HighlandPete]

Originally Posted by andbrads

I’ve just fitted PS4Ss coming off Bridgestone RFT or whatever the standard fitment RFT is for an M340i.

Controversially, I am slightly disappointed. I can’t feel any difference, or very very minor. I haven’t had the opportunity to drive the car with some intent yet so should perhaps reserve judgment but in my previous M240i, when I changed from the standard RFT to Michelin Pilot Sport (not S) it was a dramatic difference which was perceptible driving just 20 feet. The car felt lighter, I immediately had way more steering feel, the ride was better and the front end bite in a different league. I didn’t get any of these first impressions this time around.

I reduced the pressures down to 37 psi all around.

In my experience the difference (if it's there) will be felt in the first drive, just like your first experience.

I've also felt that instant change in feeling, moving from one performance tyre to another in the past, not run-flat related.

My own take on this, years back moving from RFTs was dramatic, like in my E91 days. Today many more users find little difference, as RFTs are not as stiff as the early generations, plus suspensions are improved to accommodate the RFT much better.

I see you've adjusted the pressures, so that shouldn't be an issue.

[andbrads]

Originally Posted by HighlandPete

In my experience the difference (if it's there) will be felt in the first drive, just like your first experience.

I've also felt that instant change in feeling, moving from one performance tyre to another in the past, not run-flat related.

My own take on this, years back moving from RFTs was dramatic, like in my E91 days. Today many more users find little difference, as RFTs are not as stiff as the early generations, plus suspensions are improved to accommodate the RFT much better.

I see you've adjusted the pressures, so that shouldn't be an issue.

Thanks, I am hoping it’s the improvement on the RFT that’s making the difference so marginal, rather than the PS4S being inferior to the PS4, which very few say it is.

It’s such a shame tyres cannot be test driven.