Tire fitment question

[Don Bradner]

Alcoa documents list 8.25-inch rims variously as 7400 lbs and as 3550KG (which
would be over 7800 lbs), but I don't see any at 7000. I don't have a coach at
the moment to look at the wheels, but at 7000 most Birds from 1988 on would be
overweight on the front wheels and I don't think they were. Likewise if a 12R
was only rated to 6780 that would be a big problem, but that is actually the
"less than" - it is for duals. For singles, the 12R is rated 7390.

That isn't actually the point, though. The point is that a 12R, to handle a
14,600 lb steer axle, needs 120PSI, the max on a 120PSI rated tire. Using a 315
only requires 100PSI on a 130PSI rated tire. It is a whole lot easier to inflate
to 100 than it is to 120, particularly if using coach-supplited pressure, and
the reduced pressure is also a better ride. I made the switch in 2008, and was
very happy with the result.

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.
I'm actually in the process of buying a coach that has had the drivers switched
to 315s, and I'm going to have to give those tires a good look.

Don Bradner
90 PT40 "Blue Thunder" (sold)
My location: http://www.bbirdmaps.com/user2.cfm?user=1

On 3/14/2013 at 9:26 AM Wilhelmus Schreurs wrote:

>Mike:
>Here are some facts:
>8.25 inch rims - 7000 lb rating
>9.00 inch rims - 9000 lb rating
>
>12R tire rating - 6780 lb rating - less for doubles
>315 tire rating - 9090 lb rating - less for doubles
>
>We went from the 8.25 to 9 inch rims as well as changed to the larger 315
>tire due to the allowable weight rating, all increased to the 9000 lb
>rating.
>We have not experienced any problem with the tires scrapping either aired
>up or down, with the exception if the front tires are not straight on the
>aired down position.
>
>With the weight facts listed above, why would anyone put a 315 tire on a
>8.25 rim, they have done nothing to increase the weight rate value because
>the weakest point now is the rim at 7000 lbs
>
>Bill
>1988 40WB XXV "Anniversary Special Edition"
>Kitimat, B.C. Canada eh