Determining Tire Pressure
I have read that you should not pay much attention to the inflation psi marked on the tires, but rather go by the vehicle recommendation printed on the door edge. In other information I have found ch...
Forum Discussion
The vehicle placard is correct for the size and load range tires specified by the maker (as printed on the placard), generally assuming a fully loaded vehicle. For a class C motorhome, that's often fairly close to the truth, so these are a decent starting point.
Tire manufacturers do give tables of pressure based on load. A more accurate approach than using the placard is to weigh the axles with the motorhome fully loaded and ready to go (or preferably each corner, and use the higher end of the axle when there's a difference) and use the manufacturer's chart to determine the minimum inflation. Most would go a few pounds above this to provide a little cushion for extra loading. (Of course, one should not go over the tire's maximum pressure rating, nor the wheel's maximum pressure rating--which may be lower than the tire's maximum, particularly if tires of a different size or load rating than originally specified are used.)
The pressure stamped on the sidewall of the tire is the maximum pressure for the tire, and only applicable at or near the maximum rated load. Having too high a pressure for the loading can lead to abnormal tire wear, a harsh ride, worse traction and braking performance, and often poor vehicle handling. Underinflation can lead to much the same thing, and also causes the tires to heat up more which can cause them to fail.
To summarize: the best way is to weigh the loaded motorhome and look up in a table for the size and type of tire. (It does not need to be for the exact tire manufacturer or model; the sizes and load ratings are standardized.) A usually acceptable way is to go by the placard on the door. Putting the maximum rated pressure in all the tires, as stamped on the tire sidewall, is generally speaking not a good idea.
Tire manufacturers do give tables of pressure based on load. A more accurate approach than using the placard is to weigh the axles with the motorhome fully loaded and ready to go (or preferably each corner, and use the higher end of the axle when there's a difference) and use the manufacturer's chart to determine the minimum inflation. Most would go a few pounds above this to provide a little cushion for extra loading. (Of course, one should not go over the tire's maximum pressure rating, nor the wheel's maximum pressure rating--which may be lower than the tire's maximum, particularly if tires of a different size or load rating than originally specified are used.)
The pressure stamped on the sidewall of the tire is the maximum pressure for the tire, and only applicable at or near the maximum rated load. Having too high a pressure for the loading can lead to abnormal tire wear, a harsh ride, worse traction and braking performance, and often poor vehicle handling. Underinflation can lead to much the same thing, and also causes the tires to heat up more which can cause them to fail.
To summarize: the best way is to weigh the loaded motorhome and look up in a table for the size and type of tire. (It does not need to be for the exact tire manufacturer or model; the sizes and load ratings are standardized.) A usually acceptable way is to go by the placard on the door. Putting the maximum rated pressure in all the tires, as stamped on the tire sidewall, is generally speaking not a good idea.
