Class A tire Air pressure

It all depends on how much weight the tires are carrying. Have you had your coach weighed. All four corners is best but front and rear axle is better than nothing. The weight your tires are carrying, when cold, will give you the inflation pressure to start your trip. Do not worry about a temperature change when you are driving for that day.

The ONLY definitive way to say how much pressure to maintain in your tires is to:

1. Have the motorhome weighed. Weigh each corner separately - this is very important.

2. Find the inflation chart for YOUR tires and compare the weight of your heaviest side of each axle with chart and see how much pressure the tire manufacturer recommends.

That is the pressure you should maintain. Rules of thumb don't apply to tire pressure.

The mfg knows the tires will gain air pressure while being driven - all tires do it. They want to make sure you don't exceed a certain pressure when cold before starting your trip.

Excessive loads can also damage tires, part of it by generating excess heat. This is why they label the tires with the maximum load.

If they were worried about how much the tire will gain during operation, they would also put a maximum HOT air pressure rating on there.

As long as you follow the max cold air pressure and the max load capacity, the warm or hot tire pressure is taken care of.

Bill

Somewhere in your rig is a document glued to a wall that shows Gross Axle Weight Ratings and the suggested tire pressures for the front and rear wheels. Set your pressures to this when tires have not been used for several hours. Then at the next opportunity do as others have suggested and go get it weighed and adjust pressures if desired.

Do be careful to make sure that both tires on the same side of a dually axle are at the same pressure. (I know this isn't exactly related to your question, but it's kind of important anyhow.) If they're at different pressures, one of the two will have a slightly larger diameter, and one or both will be forced to slip a little as you drive and they will wear relatively quickly. I aim for within 1/2 psi of each other.

It's not nearly so important that the tires on opposite sides of the vehicle be precisely equal in pressure, though of course that's generally the intent.

DrewE wrote:
Do be careful to make sure that both tires on the same side of a dually axle are at the same pressure. (I know this isn't exactly related to your question, but it's kind of important anyhow.) If they're at different pressures, one of the two will have a slightly larger diameter, and one or both will be forced to slip a little as you drive and they will wear relatively quickly. I aim for within 1/2 psi of each other.

It's not nearly so important that the tires on opposite sides of the vehicle be precisely equal in pressure, though of course that's generally the intent.

That is a good point and they do make filling hoses that allow you to tie both duels together so that they are both filled to the exact same air pressure. I use the Psiclops XL180 but there are other brands out there.

You have to know the weight of each corner of your RV before you can even guestamate the correct pressure. Once weighted, you find the chart for your tire and air them to the proper pressure.

OK. I appreciate everybody's feedback. I will definitely do my best to find a place to weigh my RV on all 4 corners. However, the SF bay area doesn't exactly have weigh stations down the street. It is not a trucking area. I know I will run into something on HWY 5 and I know there is a truck stop with a weigh station about an hour away in Gilroy off HWY 101 but not sure if it is just for trucks.
Now in the meantime, and without making the assumption that everybody has immediate access to weigh stations, while I prepare for my trip and head South towards a weigh station should I air up closer to the 120lbs max or be under at 110lbs or what?

Thanks again!

With my 2005 Diplomat and Michelin XZA2 tires, I run 95 PSI on the rear and 105 PSI on the front. After running for 30 minutes, my TPMS will usually show about 112 PSI rear and 122 PSI front. My Michelins are rated for 130 PSI cold.

You should gain about ten to twenty PSI when warm, depending upon ambient temperature. Your 105 and 109 PSI are slightly high, but should be fine for this coach. Your tires are rated for 120 PSI cold. I am slightly heavier on the rear axle than you are because we have the PAQ.

Yes, I agree that a four corner weight is the best solution.

frankiebIII wrote:
OK. I appreciate everybody's feedback. I will definitely do my best to find a place to weigh my RV on all 4 corners. However, the SF bay area doesn't exactly have weigh stations down the street. It is not a trucking area. I know I will run into something on HWY 5 and I know there is a truck stop with a weigh station about an hour away in Gilroy off HWY 101 but not sure if it is just for trucks.
Now in the meantime, and without making the assumption that everybody has immediate access to weigh stations, while I prepare for my trip and head South towards a weigh station should I air up closer to the 120lbs max or be under at 110lbs or what?

Thanks again!

Somewhere in your coach, or on a plaque attached to a closet wall, etc will be a spec sheet that shows the maximum axle weight, front and rear, that your coach chassis is designed for. It may be something like 10,000 pounds max front axle weight and 15,000 pounds max rear axle weight, as an EXAMPLE. Then you go to your tire chart and set the air pressure to handle that maximum weight on both the front and rear axle. That should give you a little cushion in your tire air pressure until you get an accurate weight.