Tire fitment question

[Michael Bulriss]

To add to this discussion, my aluminum wheels are stamped 7250 lbs at 120 psi. The 12R22.5 tires are labeled 7390 lbs at 120 psi for single wheel use.

More importantly the tire charts specify that the duals have a minimum 13.2" spacing with the12R and minimum of 13.8" with 315s. Measuring the current rear spacing on the 8.25 wheels with 12R tires shows them barely at the 13.2 minimum spacing, so I am concerned how people are mounting 315s.

FWIW, one Michelin chart shows the 315 tire max load at 8000 lbs on 8.25 wheels versus the 9090 with 9.0 rims. Seemed like a dramatic change.

Decisions, decisions. Having a head time deciding next step since I am just updating the steers currently and moving those tires to the tag. I had thought the slightly wider 315 would make a difference on the steers, because even when i changed from 7.5 to 8.25 wheels on the 83PT and stayed with 11R tires, it made a big improvement in driving feel by widening the tire cross section out. FWIW.

Mike Bulriss

1991 WB40 "Texas Minivan"

San Antonio, TX

Sent from my iPhone

On Mar 15, 2013, at 12:43 AM, "Don Bradner" <"bluethunder@arcatapet.com"> wrote:

Is that your Wide Body with that 7000 lb rating?



Clearly, Alcoa has made a lot of different rims at 8.25 inches over the years. I wish I had a WB sitting in front of me so I could look, but I do know that mine were not below the '90's 14,600 front axle rating, which a 7,000 lb would have been. In the current Alcoa book they list several different 8.25 22.5-inch wheels, with ratings as high as 8050 lbs, but none lower than 7300.



At 110PSI, the 12R is rated for 6870 lbs in a single tire configuration, which would be underinflated for any of the 90s wide bodies. They all needed a full 120PSI to carry the full weight. I'm surprised an 88WB wouldn't weigh that much.



The ride difference between a 12R at 120 and a 315 at 100 IS noticeable.



The rubbing when suspension-dumped with steering turned had nothing to do with pressure. It is a phenomenon on most, if not all, of the wide-bodies at any pressure.



On 3/15/2013 at 5:23 AM tulipvendor50 wrote:



>Don stated:

>"Alcoa documents list 8.25-inch rims variously as 7400 lbs"

>

>Bill:

>There is a coach right next to me with 8.25 inch rims and it clearly

>states "7000lbs"

>

>Don stated:

>"As far as the fenders I had the older rubber ones, and the tires would

>hit when dumped-while-turned even with 12R - the extra half-inch of tread

>on the 315 made no difference. I did NOT put 315s on the drivers because

>of the potential rubbing issues. Those that have done so (Shane comes to

>mind) run their drivers at higher pressure than needed for the load, which

>negates the ride improvement. "

>

>Bill:

>I run my tires at 110lbs pressure and have had no problem with the

>rubbing. I doubt very much if one could really feel the difference in

>ride with the higher or lower pressure.

>

>

>

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