> You offer no source for "the 6% safety margin"
> you say is required .... There's no
> mention of the additional 6% here:
> http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=70

As per U.S. Department of Transportation, Part 571.110, Subpart B...

S2.Application.This standard applies to motor vehicles with a gross vehicle
weight rating (GVWR or 4,536 kilograms (10,000 pounds) or less, except for
motorcycles, and to non-pneumatic spare tire assemblies for those vehicles.
Tire selection and rims and motor home/recreation vehicle trailer load
carrying capacity information for motor vehicles with a GVWR of 4,536
kilograms (10,000 pounds) or less.

S4.2.2.2 When passenger car tires are installed on an MPV, truck, bus, or
trailer, each tire's load rating is reduced by dividing it by 1.10 before
determining, under S4.2.2.1, the sum of the maximum load ratings of the
tires fitted to an axle.

S4.2.2.3 (a) For vehicles, except trailers with no designated seating
positions, equipped with passenger car tires, the vehicle normal load on the
tire shall be no greater than 94 percent of the derated load rating at the
vehicle manufacturer's recommended cold inflation pressure for that tire.

(b) For vehicles, except trailers with no designated seating positions,
equipped with LT tires, the vehicle normal load on the tire shall be no
greater than 94 percent of the load rating at the vehicle manufacturer's
recommended cold inflation pressure for that tire.

- Ron Salmon
  The Bus Depot, Inc.
  www.busdepot.com
  (215)  234-VWVW

_____________________________________________
Toll-Free for Orders by PART # :  1-866-BUS-DEPOT