Appropriate Tire Pressure?

[rvnetter]

I have a 25' Class B+ motorhome. It has 16", Load E tires rated at 80psi cold. Is it safe to run them anywhere between 65psi - 80psi cold? I currently have them inflated at 70 psi, we have an average load, with 2 adults.

Thanks for your input

[4x4van]

time2roll wrote:

j-d wrote:
Whatever the Chassis manufacturer (Ford? Chevy?) sticker in the door jamb says, is THE MAX. That is almost certainly less than the 80 PSI on the sidewall of a Load Range E tire.

I respectfully disagree. The tire sidewall is the max always. The door sticker is the manufacturer's recommendation for ride, safety, handling and comfort with the expectation the user stays within the weight ratings.

I prefer mine a bit firm so I would be running 5 to 10 psi over the door sticker not to exceed the tire sidewall max.

Tire manufacturers have no idea what vehicle their tires are going to be installed on; none. The number on the tire is for the TIRE's max load, and will most times be significantly higher than a particular RV will ever require. That's why load charts exist.

The RV manufacturer on the other hand knows exactly what the maximum GVWR on their vehicle is, and lists (on the doorjamb) the pressure required for that weight. Since the rig should never be loaded above that, any increase in pressure is not necessary, and will not improve ride, safety, handling, etc. Depending on the actual weight of the rig, the door tag numbers may be higher than necessary, but never lower.

[JaxDad]

The whole subject of tire pressure is one I find amusing, the part about ‘4 corner weighing’ hilarious!

Tire pressures are of course best taken when the tires are cold. However, as a tire starts to roll that little flat spot at the bottom, and the 2 little bulges in each sidewall, move along the circumference of the tire to stay in contact with the road. This flexing and relaxing cause heat. An average size tire turns about 750 times to cover a mile, so at 60mph those tires turn 750 rpm. After just a half an hour the tire temperature can rise 50 deg’s. Tire pressure increases by about 1 degree per 10 deg increase in tire temperature.

From the time you check tire pressure at say 9am and find then at say 60 deg’s, to a sunny hot afternoon of 90 deg’s and 6 hours of highway driving the tire pressure could have easily changed by 10 psi.

Oh, but on a snowbird dash south on a cold rainy early winter day, they may have only increased by 3 or 4 degrees.


So much for precise pressure settings ………

[time2roll]

j-d wrote:
Whatever the Chassis manufacturer (Ford? Chevy?) sticker in the door jamb says, is THE MAX. That is almost certainly less than the 80 PSI on the sidewall of a Load Range E tire.

I respectfully disagree. The tire sidewall is the max always. The door sticker is the manufacturer's recommendation for ride, safety, handling and comfort with the expectation the user stays within the weight ratings.

I prefer mine a bit firm so I would be running 5 to 10 psi over the door sticker not to exceed the tire sidewall max.

[Grit_dog]

OP, dont' get bogged down with 4 corner weights and being accurate to the pound.
Moreso, don't worry about it at all until you have it loaded to camp again.
Get a quick weight of each axle at a closed DOT scale or a transfer station or somewhere, free. Farm country?, grain elevators typically have scales.
Then you know.

You could be fine with 30 psi (not likely) or need 80 psi.
If it drives reasonably well like it is and the tires aren't bulging, it's not grossly over or under as it sits.

Cheers!

[Harvard]

F1bNorm wrote:
... my 24' B+ wanders all over the highway...

POPULAR MECHANICS MAY 1973:
START QUOTE:
If too little caster exists, the car will wander and weave,
thus necessitating constant corrections in steering.
END QUOTE:

[F1bNorm]

Here's what the Michelin Truck Tire chart looks like. https://www.rvsafety.com/images/pdf/michelinloadandinflationrvtruck.pdfhttps://www.rvsafety.com/images/pdf/michelinloadandinflationrvtruck.pdf

Weigh your MH and find the chart for your brand, model and size tires. At max pressure, my 24' B+ wanders all over the highway, much better handling at the corrected pressure.

[cvk]

Here’s how I weighed all four corners at empty truck scales. Weigh front axel, then rear axel, back up and weigh passenger front tire then passenger rear. Simply subtract the one front weight from the total front and do the same with rear. Easy peazy alll done.

[j-d]

loggenrock wrote:
Cat or recycle/moving/gravel scales are fine, but won't give you a side-to-side balance weight.

Correct, and CAT even mentions in "How to Weigh Motorhome" that they cannot provide side to side (or maybe they say corner) weights.

But PLEASE - Let's get off the dime here and go to a nearby CAT scale. Pony up $10 and get enough information for a good start.

[loggenrock]

Cat or recycle/moving/gravel scales are fine, but won't give you a side-to-side balance weight. Organizations such as the RV Safety and Education Foundation www.rvsafety.com will do 4-corner weights - cost $60 when I did it - and will give you the recommended tire inflation pressures for whatever tire you are running based on the weight they are carrying. ST

[Dennis_M_M]

All good advice. Here is a link to the Cat Scale website explaining how to weigh. There is also a link there to find a scale near you.

https://catscale.com/how-to-weigh/

[NewmarJeff]

rvnetter wrote:
I have a 25' Class B+ motorhome. It has 16", Load E tires rated at 80psi cold. Is it safe to run them anywhere between 65psi - 80psi cold? I currently have them inflated at 70 psi, we have an average load, with 2 adults.

Thanks for your input

To be safe, I would contact the Motorhome manufacturer for what they recommend and double check with the tire manufacturer.

[j-d]

Whatever the Chassis manufacturer (Ford? Chevy?) sticker in the door jamb says, is THE MAX. That is almost certainly less than the 80 PSI on the sidewall of a Load Range E tire.

Weighing your coach, as ready for travel (people, supplies, stuff all on board) at a truck stop or other scale is best. Than adjust pressure according to a Load/Pressure chart. Adjust again once the tires are cold. Michelin's chart is easy to find. You can use that chart for Michelin or other brands, as long as the specs of the tires are the same.

If you tow a car, have it behind you at the truck stop CAT scale. It'll give your Front Axle as "Steer", Rear Axle as "Drive" and Car as "Trailer."

[Cobra21]

We have a 21' C. Probably the same tire size as yours. Max on tires is 80.
The door jamb from camper company states 55 all the way around. We run 60 on all
and seems to be fine.
Brian

[KD4UPL]

Weight at a truck stop, quarry, landfill, feed mill, etc.
Use the manufacturer's load inflation table for your tires to determine the proper inflation pressure for the weight they are carrying. That's really the only way to do it.