Tyre pressures

[s5tuart]

So, I took my CLS Shooting Brake in for a free health check to my local dealer.
Apart from everything else they have adjusted the tyre pressures for me.
Recommended pressures are 2.3 bar front and 2.5 rear with just me driving.
With such low profiles I have been running them at 2.2 and 2.4 to try to add a bit more give to the sidewalls for more comfort.
The dealer has inflated all 4 (Dunlop Sportmaxx 2) to 2.5 and the difference is making me scratch my head?
The ride is more supple and compliant than before and road noise is diminished by a lot too?
The profiles are 35 front and 30 rear.
Can anyone give me a layman's terms explanation as to why this is please?

Also of note is that with the lower pressures I've been using the tread is wearing more in the centre of the tyres.
All the above goes completely against what I've believed for years

 

[s5tuart]

Recommended...

 

[sl500amgsport]

I am still experimenting with the Michelins, like you in the past used lower pressure but Kwik Fit set to cap pressures and the ride is a little harsh.

I am lowering it gradually until it feels right..

Mercedes SL500 R231

 

[s5tuart]

I am still experimenting with the Michelins, like you in the past used lower pressure but Kwik Fit set to cap pressures and the ride is a little harsh.

I am lowering it gradually until it feels right..

Mercedes SL500 R231

That's what I find odd, that higher pressures are giving me a softer and quieter ride.

 

[rorywquin]

So, I took my CLS Shooting Brake in for a free health check to my local dealer.
Apart from everything else they have adjusted the tyre pressures for me.
Recommended pressures are 2.3 bar front and 2.5 rear with just me driving.
With such low profiles I have been running them at 2.2 and 2.4 to try to add a bit more give to the sidewalls for more comfort.
The dealer has inflated all 4 (Dunlop Sportmaxx 2) to 2.5 and the difference is making me scratch my head?
The ride is more supple and compliant than before and road noise is diminished by a lot too?
The profiles are 35 front and 30 rear.
Can anyone give me a layman's terms explanation as to why this is please?

Also of note is that with the lower pressures I've been using the tread is wearing more in the centre of the tyres.
All the above goes completely against what I've believed for years

What temperature are the tyres when you adjust the pressure...........

 

[s5tuart]

What temperature are the tyres when you adjust the pressure...........

Cold, around 3-5 degrees. Outside temp. They were adjusted in the MB workshop.
im just taking the readings from the TPS but have also checked with a gauge.

 

[s5tuart]

 

[malcolm E53 AMG]

I’m running the MB estate at 36psi (245 35) front and 46psi (265 30) rear on 18in wheels and find the car drives much better with higher pressures - I used to run it at 34psi all round. It seems to me that wide section tyres need the extra inflation to sit correctly on the road by lifting the sidewalls, handling improves with better turn in and there is less road noise.

The BMW is the opposite, running 32psi (225 40) front and 32psi (255 35) rear on 19in wheels the ride is very firm even on non runflats.

The MB is airmatic so the extra inflation really does make a difference and the firm ride no doubt less noticeable but it is sitting on 18in wheels

 

[rorywquin]

Cold, around 3-5 degrees.

I've stuck with the recommended (tank flap) pressures and 17,000 miles on still have nice even wear and still have a lot of miles in them. Always adjusted when cold. The profiles are the same as yours.

I've never given ride comfort much thought, my thinking is that, "it is what it is" and a couple of PSI + or - is not going to make a noticeable difference! Or does it?

 

[s5tuart]

I’m running the MB estate at 36psi (245 35) front and 46psi (265 30) rear on 18in wheels and find the car drives much better with higher pressures - I used to run it at 34psi all round. It seems to me that wide section tyres need the extra inflation to sit correctly on the road by lifting the sidewalls, handling improves with better turn in and there is less road noise.

The BMW is the opposite, running 32psi (225 40) front and 32psi (255 35) rear on 19in wheels the ride is very firm even on non runflats.

The MB is airmatic so the extra inflation really does make a difference and the firm ride no doubt less noticeable but it is sitting on 18in wheels

I'm glad I'm not going dopey! I can buy in to the sidewall theory and I think you may have satisfied my curiosity.
it just seemed to go against everything I was ever told.
your theory also explains the centres of the tyres wearing more than the outsides. I need to get my head around it though.

 

[s5tuart]

I've stuck with the recommended (tank flap) pressures and 17,000 miles on still have nice even wear and still have a lot of miles in them. Always adjusted when cold. The profiles are the same as yours.

I've never given ride comfort much thought, my thinking is that, "it is what it is" and a couple of PSI + or - is not going to make a noticeable difference! Or does it?

It may be worth trying Rory
Give them a bit more pressure and try it.

 

[RhodieBill]

I always put +.2 Bar than the recommended. ie. 2.3(F 225/45Y17) 2.5(R 245/40W17).

 

[s5tuart]

One thing I haven't factored in is that the SportMaxx 2 are not OEM.
Therefore I almost certainly have different compounds, tread block and sidewall hardness etc.
I think I'm right in saying that the recommended pressures are exclusively for the OEM tyres and if one fits other brands the pressures don't necessarily transfer.
I will closely monitor fuel consumption now because less noise indicates less rolling resistance. Hopefully I'll get closer to some of the better MPG that many here are experiencing!

 

[RhodieBill]

I think I'm right in saying that the recommended pressures are exclusively for the OEM tyres and if one fits other brands the pressures don't necessarily transfer.

I'm afraid you're wrong, (with the exception of Winter Tyres). Just as long as they, (the Tyres) are the same Size the Pressures are correct.

 

[s5tuart]

I'm afraid you're wrong, (with the exception of Winter Tyres). Just as long as they, (the Tyres) are the same Size the Pressures are correct.

Ok. I thought that the different compounds in different brands might make a difference. Clearly not.

 

[M80]

I check tread wear regularly at 3 points on each tyre. My simplistic view is that if the wear is even my pressures are correct.
I'm using the usual view that more wear to outer means pressures are too low, too much wear in centre and it's too high.

All that goes out the window as the tyres become worn below around 5mm as I've often experienced uneven wear then.
Most of the time It's just me in the car with a similar weight set up, I can adjust some if that changes.

 

[Christian7]

So, I took my CLS Shooting Brake in for a free health check to my local dealer.
Apart from everything else they have adjusted the tyre pressures for me.
Recommended pressures are 2.3 bar front and 2.5 rear with just me driving.
With such low profiles I have been running them at 2.2 and 2.4 to try to add a bit more give to the sidewalls for more comfort.
The dealer has inflated all 4 (Dunlop Sportmaxx 2) to 2.5 and the difference is making me scratch my head?
The ride is more supple and compliant than before and road noise is diminished by a lot too?
The profiles are 35 front and 30 rear.
Can anyone give me a layman's terms explanation as to why this is please?

Also of note is that with the lower pressures I've been using the tread is wearing more in the centre of the tyres.
All the above goes completely against what I've believed for years

I run my SB close to the manufacturers recommended - 33/36 in winter and 34/37 in summer (given the tyres are generally warmer and therefore a little softer/cushier but that may be just my imagination). I’ve done this with all my Mercedes and seems to be the optimum for daily driving having tried both lower and higher pressures. If the car is full for a trip I do increase the pressures by 4-5psi but when it is unloaded it feels too firm. I‘ve been getting 40-50k miles from the rear tyres and more from the front (there’s a lot of motorway miles in there) so I take that as a sign that the manufacturer recommendations are pretty spot-on. Might try the higher front-end pressures based on your experience to see if I find the same effect.

 

[s5tuart]

I run my SB close to the manufacturers recommended - 33/36 in winter and 34/37 in summer (given the tyres are generally warmer and therefore a little softer/cushier but that may be just my imagination). I’ve done this with all my Mercedes and seems to be the optimum for daily driving having tried both lower and higher pressures. If the car is full for a trip I do increase the pressures by 4-5psi but when it is unloaded it feels too firm. I‘ve been getting 40-50k miles from the rear tyres and more from the front (there’s a lot of motorway miles in there) so I take that as a sign that the manufacturer recommendations are pretty spot-on. Might try the higher front-end pressures based on your experience to see if I find the same effect.

If you do try the higher pressures let me know the result please. Maybe the Dunlop's just gel better with the Airmatic at slightly higher pressures but it certainly produced a significant difference for me. My old normal was 2.2 front and 2.4 rear and now I have 2.5 all round.

 

[Christian7]

If you do try the higher pressures let me know the result please. Maybe the Dunlop's just gel better with the Airmatic at slightly higher pressures but it certainly produced a significant difference for me. My old normal was 2.2 front and 2.4 rear and now I have 2.5 all round.

Will do. If it stops raining(!) I might give it a go this weekend. I have MO Pirelli’s on mine so may not have quite the same impact. But a good excuse for going for a drive

 

[JBell]

I find this strange!!!

Excess wear in the middle of a tyre usually means it has been over inflated.

I run my tyres at the correct psi on the front and 2psi below recommended on the rear and they wear evenly, if I put the extra 2psi in the rear they wear in the middle indicating overinflation BUT only on the rear