Posted by Charlie on Tuesday, March 27, 2001 at 1:33AM :
In Reply to: Tire Pressure posted by StevePT50 on Monday, March 26, 2001 at 8:40AM :
Most bias ply 9.00-16s are rated at about 3030 lb @ 60 psi. My 9.00R16 Michelin XZLs are rated at 3750 lb @ 65 psi and 4660 @ 80 psi.
Anyways, the NDs should carry about 100 lb/psi in terms of axle load. The unladen rear axle load for an M37 is about 2700 lb. The rated cargo capacity is 2000 lb on the highway and 1500 offroad. That corresponds to laden weights on the rear axle of 4700 and 4200 lb respectively. Even with 2000 lb on the rear axle, 50 psi should be sufficient on the highway.
In these calculations I add 5 or even 10 psi for "high" speeds, over 60 mph. If speeds of 70-75 mph are feasible and SAFE (radial tires, disk brakes) then 40-45 psi is appropriate even unloaded. On the other hand if a truck is solely used on dirt roads under 45 mph then I think you could run 30-35 psi when empty to improve the ride and traction. When in doubt, a bit of overinflation is safer than underinflation at high speeds. Also when in doubt, feeling the sidewall's temperature right after stopping gives one an indication of whether a tire needs more air or not. If it's more than comfortably warm it probably needs more air.
Charlie
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