Following on from yesterday's thread on my fitting Grabber AT3's to my L320 last night I checked the tyre pressures. The garage had set the pressures at about 3.3 bar (48 PSI). Checking the label inside the driver's door it advises 2.3 bar (33 PSI) front and 2.5 bar (36 PSI) rear. Hence I adjusted to these pressures using my reliable tyre pressure gauge once the tyres were cold.

Now the tyres look very low. See image below. I have even checked the pressures again with a different gauge to see if there was any error in readings.

Anyone else running Grabber AT3's in 275/40/ R20 or similar running higher than normal tyre pressures?



 There is no replacement for displacement - W O Bentley

MY2013 5.0 Supercharged HSE L320

I think ATs do look like they're low pressure because of all of the lumps on the sidewall compared to the smooth sidewalls of road tyres.

I run my AT tyres a couple of psi higher than the recommended i.e. 35f and 38r. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Thank you RRSTDV8 - I will adjust to (or possibly just above) 35 and 38 PSI tonight. I was worried about the slight side wall bulge out too. Hope the extra few PSI will sort this. There is no replacement for displacement - W O Bentley

MY2013 5.0 Supercharged HSE L320

Yep I run 36F 38R (habit - it's what the BMW likes, too) and the fronts do always look a bit 'flat' to me.. slowly getting used to it and not reaching for the compressor every time now!  2014 BMW 530d Touring, 2006 BMW 650i, 2018 Mini Cooper S

i've always ran with 45 - 48 psi on fronts. 50psi on the rears.
never had any trouble with wearing or traction.

anything less than 40pis and the tyres are soft looking and much higher rolling resistance. feels wrong on steering also. 2007 TDV6 RRS HSE..now gone
2012 3.0 SDV6 RRS HSE

It looks like 38-40 PSI might be a good call. If I never tow, carry heavy luggage, etc is there any reason to run higher pressures in rear tyres anyway (I would have thought more weight in front of an L320 than rear)? Therefore, now thinking of experimenting at 38-40 PSI for both front and rear equally. There is no replacement for displacement - W O Bentley

MY2013 5.0 Supercharged HSE L320

MGO wrote:

i've always ran with 45 - 48 psi on fronts. 50psi on the rears.
never had any trouble with wearing or traction.

anything less than 40pis and the tyres are soft looking and much higher rolling resistance. feels wrong on steering also.

Wow.

Just wow.

 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Silverstone wrote:

It looks like 38-40 PSI might be a good call. If I never tow, carry heavy luggage, etc is there any reason to run higher pressures in rear tyres anyway (I would have thought more weight in front of an L320 than rear)? Therefore, now thinking of experimenting at 38-40 PSI for both front and rear equally.

As an experiment tonight I've increased front and rear to 45 PSI and might then lower the fronts slightly if appropriate. There is no replacement for displacement - W O Bentley

MY2013 5.0 Supercharged HSE L320

45psi is ridiculous, frankly. But hey, they're your tyres and suspension bushes... 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

MGO wrote:

i've always ran with 45 - 48 psi on fronts. 50psi on the rears.
never had any trouble with wearing or traction.

anything less than 40pis and the tyres are soft looking and much higher rolling resistance. feels wrong on steering also.

Surely running at those kind off pressures you might as well have solid tyres, or at least buy a neck and back brace.

Cheers
Col

like i said.
it hasnt been a problem for me.
been running RRS for over 10 years and i wouldnt have it any other way.
winter tyres on these days and usually run at 45.

anything below 40 and the tyres are way too soft in my opinion.
certainly not good enough for the rears when towing. 2007 TDV6 RRS HSE..now gone
2012 3.0 SDV6 RRS HSE

RRSTDV8 wrote:

MGO wrote:

i've always ran with 45 - 48 psi on fronts. 50psi on the rears.
never had any trouble with wearing or traction.

anything less than 40pis and the tyres are soft looking and much higher rolling resistance. feels wrong on steering also.

Wow.

Just wow.

horses for courses as you say  2007 TDV6 RRS HSE..now gone
2012 3.0 SDV6 RRS HSE

MGO wrote:

like i said.
it hasnt been a problem for me.
been running RRS for over 10 years and i wouldnt have it any other way.
winter tyres on these days and usually run at 45.

anything below 40 and the tyres are way too soft in my opinion.
certainly not good enough for the rears when towing.

periodically towing 12' itwin axle for williams with near enough 3 tons overall.
nose weight shouldnt be over the 150kg as the trailer is well balanced.

never tried towing less than 48psi on the rears.
not dismissing your view on it. i'm sure would be perfectly fine towing at 40.

i just never experienced any downside with the higher pressures.
tyre wear is good. i get good milage out of the tyres. they wear perfectly even.
on over 300000 km with the previous RRS, i only had to change the front outer balljoints once and the rear upper wishbone. So not seeing any impact on suspension either. 2007 TDV6 RRS HSE..now gone
2012 3.0 SDV6 RRS HSE