Tyre pressures and wear.

[Pinger]

Rotated my tyres (as per the handbook) today - a first for me. The reason I did was because the rears have worn more than the fronts and as mine is a RWD 2500 Suburban and winter is approaching, an extra mm on the driven axle could be the difference between getting off my driveway or slithering to the bottom.
What has me confused though is that the rear tyres aren't only more worn than the fronts they are more worn in the centre. This would suggest over-inflation but they've been run (for 5700 miles) at 50psi - which is the 'comfort' pressure as per the door jamb sticker. The fronts have been run at around 45 psi and show even wear.
So, could it be that the different size (265/65. 17) require different pressures to the stock (245/75. 16) tyres? And, should I run lower than 50psi at the rear (for more even tyre wear)?

 

[RichLo]

What load range are they? and whats the max pressure on the sidewall?

If they are lower load range and sidewall pressure say's 35psi then yea they are over-inflated.

If they are 51psi or 80psi sidewall pressure then just run them at whatever the door jam says. Slightly over worn in the center may just be a cost of running them. 45 PSI would help but if the door jam says 50 minimum then just run 50.

 

[OutlawDrifter]

If they are a 10-ply LT rated tire, you could try 45-48psi and see if that corrects the issue. Sounds to me like the fronts are telling you where its at.

You can also take a piece of chalk and "color" a section across the top of the tire, drive a few revolutions and see where it is wearing the most, adjust tire pressure until you are happy with the chalk markings.

 

[Pinger]

What load range are they? and whats the max pressure on the sidewall?

If they are lower load range and sidewall pressure say's 35psi then yea they are over-inflated.

If they are 51psi or 80psi sidewall pressure then just run them at whatever the door jam says. Slightly over worn in the center may just be a cost of running them. 45 PSI would help but if the door jam says 50 minimum then just run 50.

112T, max load 1120kg, max pressure 44psi is what's on the sidewall.
Door jamb sticker for 'comfort' is 35psi front, 50psi rear (max load, 8 passengers and 200lb luggage).

If they are a 10-ply LT rated tire, you could try 45-48psi and see if that corrects the issue. Sounds to me like the fronts are telling you where its at.

Inclined to agree - that the fronts are telling me where it's at. But I'm wary going lower than GM 'comfort' 50psi on the rear. And it's the rears that wore unevenly.
Also, I suspect going much lower will kill my fuel mileage. I lost 1 mpg (from 13 to 12) which I think was due to the one of the fronts leaking down to 37.5psi (leaky valve stem - sorted now but haven't driven to know). Looking like it's a choice between fuel mileage and tyre life...

 

[someotherguy]

Wait.. so you're running the rears at higher than the sidewall-indicated max pressure? Or did I read that wrong? If it is indeed the case, then it sounds like you have tires on it not rated for the vehicle. That considered, may be time for a tire upgrade, but in the meantime you should lower the pressure so you're not exceeding max inflation indicated on sidewall.

Richard

 

[df2x4]

^ X2.

I ran passenger tires on my Suburban for a while (mistake, the door sticker calls for load range C LT tires) and I couldn't run them at what the door sticker called for. IIRC I was running around 35-40PSI in all four. Everything improved massively when I went back to LT tires.

 

[Pinger]

Wait.. so you're running the rears at higher than the sidewall-indicated max pressure?

Yes. When I got them, the 44psi max pressure confused me but...

Or did I read that wrong? If it is indeed the case, then it sounds like you have tires on it not rated for the vehicle. That considered, may be time for a tire upgrade,

... they are the correct load rating.

but in the meantime you should lower the pressure so you're not exceeding max inflation indicated on sidewall.

Richard

I hear you but I'm wary and, there's got to be a margin above the 44si that is safe - surely?

^ X2.

I ran passenger tires on my Suburban for a while (mistake, the door sticker calls for load range C LT tires) and I couldn't run them at what the door sticker called for. IIRC I was running around 35-40PSI in all four. Everything improved massively when I went back to LT tires.

I can't remember what I cross-referenced to obtain the load rating but I'm 100% certain I got it right. The tyres that were on it when I got it were at 50 and 80psi front and rear. I immediately dropped them to 45 and 50psi (for the sake of the ride quality). But I'm still wary of lower pressures on such a heavy vehicle (I ran 30psi on my 730kg (1600lb) smart). You reckon 35 and 40psi is feasible/desirable?

 

[df2x4]

You reckon 35 and 40psi is feasible/desirable?

Yes, I'd try it. At least that way you're back down below the max pressure listed on the sidewalls.

 

[someotherguy]

Pretty sure a 2500 Suburban requires a load range "E" tire. That's about a 3K lb rating per tire, max inflation 80 psi. Even a 1500 Suburban should be running XL tires which are a little over 2K lb per tire, max inflation 50 psi. That's why I'm saying the 44 psi max inflation on your sidewall is telling me the tires aren't chosen correctly for your truck.

There's some slightly conflicting information based on standards vs. how a particular manufacturer may have made a tire - it might exceed the standards, so the max inflation listed for a particular tire might be higher than what the standard calls for. Here's some more info though: https://www.tirerack.com/upgrade-garage/what-are-load-ranges-ply-ratings

What's the load range on your sidewall?

Richard

 

[Pinger]

Yes, I'd try it. At least that way you're back down below the max pressure listed on the sidewalls.

Do you consider it dangerous to run at 50psi when the max is supposedly 44psi? I've been running the rears at that for a while now (I thought they were at 45psi but it transpires my gauge under-reads by 5psi).
The reason I want to continue with 50psi for now at least is to see if the tyre dropping to 37psi was the cause of my worsened fuel mileage. If it wasn't, then there's something amiss somewhere else (that will need attention).