Tire Pressures

[rivrduk]

I guess all can tell that i am new to the Motorhome world by all the questions that i have already asked, and guess what i have another. The tires on my Motorhome are 255/80R 22.5XRV. On the sidewall of the tires it says to inflate to 90 lbs when tires are cold, however the man i purchased the Motorhome from said there was an update on the amount of air to put in the tires. I have the update and it calls for 100 lbs in the front tires and 90 lbs in the rear tires, it states that the GVWR is 26,350 lbs. Does this sound right for the air pressure in tires since it calls for 90 on the sidewalls. This update came from freightliner corporation. Thanks in advance, Rivrduk

[InPursuit]

26,350/6 (real rough approach) = 4391lbs per wheel

somewhere on the side wall for your tire will be its WEIGHT rating at Xlbs (psi)
lets say it was 95psi and 3900lbs

take that as a model and stick your numbers into it

3900 = 88.8% of your 4391
95psi x88.8% = 84psi

(there are other factors which apply, but...) that tire can handle that weight at 84psi

follow?

[RVDude]

InPursuit gives completely invalid advice as did the man you bought the rig from.

Here's the one and only tire manufacturer recommended approach for determining tire pressure
1) weigh your rig loaded and fueled at least axle by axle on a local truck stop scale
2) go to the tire manufacturers inflation tables for your specific tire and size and see what they say to inflate at the given weights - (tables at the tire manufacturers web sites)
3) do not pass go, do not collect $200, do not alter this, do not complicate it.
4) it really is that simple

[Rocky Larson]

BTW, in the past I went to a local brick and concrete business and was able to make several passes over the scales to get each corner weighed. Charged me $6. A truck stop scale was only able to do by axle because of fencing. Local scrape metal yard said no charge to run over scale (axles only) but no documentation provided. I just used an unattended selfserve CAT scale. It has three platforms so I was able to get each axle and the toad weight. Looking back, if I wasn't towing and could have backed up (no other traffic waiting) I might have been able to approach the scale from first the right side and then the left side and got each wheel position weight. It takes credit cards and was $9 for the first pass and $1 for a second pass.
Yep, I am getting heavier, and it is in all the wrong places. Fortunately I can move things around.
I check the tire chart for my tires, configuration and weight for the proper cold pressure inflation.

[RickO]

RVDude has it right. That's the way to determine your proper inflation pressures and it needs to be repeated periodically because we all gain weight as we grow older.

[historyljc]

I agree with RVDude and Rick. Don't overlook weighing your rig at a nearby DOT scale. Try to pick one that's not on a busy interstate but an old US highway. The one I use is on US 90 in route to a couple of our campgrounds. They're about like the old Magtag repairman, the loneliest person in town, they're glad to have business. No charge and if asked will give you a printout.

[Gary RVRoamer]

The pressure shown on the tire sidewall is what is needed to carry the maximum load on the tire. It is not the 'recommended' pressure. Go with the pressures shown in the tire tables for your brand and size of tire, if available. Goodtear, Michelin, Bridgestone, etc. will be online. Others may not.