Pittsburgh Bureau of Fire

[Roto-Ray]

Yep, Joel hit it on the head.  Generally, once you get above about 31,500 pounds (IIRC) on the rear axle, the only option is to go with the a larger tire and wheel combination, and steel wheels aren't available to use.  I haven't seen any of the Alcoa's with a high rating either.

 

Most departments would simply go to a tandem axle setup from the beginning to keep their individual axle ratings down, but there could be a length issue that would prevent the use of a tandem axle design.