Setting tire pressure on a MH is not like on a passenger car, where you simply look at the info sheet on the door jam and do what it says. You need to actually weigh the thing. I’m afraid to ask how many class A motorhome owners have never weighed their rigs, but I fear it’s a considerable percentage. There are two reasons we need to weigh:
- To set the tire pressure properly
- To ensure you’re not over weight on the GVWR or either GAWR
Ideally you want corner weights (i.e., the weight on each of your 6 or 8 tires), but this is easier said than done. If you can hook up with the RV Weigh Mobile Weight Station company that specializes in corner weights for motorhomes, then go for it! This would be the best option, but we’ve never had our schedule overlap. The easiest option to use a Cat truck scale at a truck stop. Here is an excellent write up of the entire process: http://www.motorhome.com/rv-how-to/rv-tech-tips/weigh-to-go
Unfortunately some Cat scales have curbs on either side that preclude weighing one side only, so you’re stuck with just an axle weight. This is better than nothing. Since you don’t know the left/right proportion, add a little fudge factor of 10% into the axle weights.
For example, the first time we weighed our new MH the tow car was attached, so I couldn’t back up to get any reweighs and there was a line of trucks behind me that prevented going through a second time. Here is the weight slip:
Notice I was not able to differentiate the rear and tag axles as I was flat towing, which is less than ideal. But at least I can set the front axle weights. Our MH was fully loaded for a 1 month trip, had full diesel, all occupants aboard, 3/4 fresh water, and empty grey and black tanks.
The weight rating for my MH are:
Front GAWR: 14,600 lb
Rear GAWR: 20,000 lb
Tag GAWR: 10,000 lb
GVWR: 44,600 lb
GCVW: 54,600 lb
So I’m safely under all weights with the caveat I don’t know the split between the rear and tag axles. Given I’m 6140 lb under the total for both axles, it’s likely I’m not exceeding either. But this data is better than nothing for a newly purchased unit.
Taking the front axle weight, dividing by 2 and adding 10% yields 7320 lb per tire. The tire inflation chart for my tire (Michelin XRV 305/70R22.5L) yields 110 psi.
