Tire Pressure Quandry

Harvey51 wrote:
Our E350 sticker says 65 front, 60 rear. The Michelin chart says much lower. I tried going 10 lower on both and finally settled on 60 front and 55 rear which seems to make it easier to steer than 5 higher or lower. Oh, I put an extra 2 psi on the passenger side front wheel as recommended by an old truck driver who said it helps compensate for the highway slope away from center.

That would probably be okay if you were driving the Ford cab and chassis with no box on it. I think you are asking for a blowout/tire wear/poor gas millage with that low a rear tire pressure. Go by the house sticker not by the chassis sticker until you get to a truck stop and weigh it when it's loaded and gassed up. Then take those weights and go by the tire manufacturer's chart for that exact size and model tire.

Our E350 sticker says 65 front, 60 rear. The Michelin chart says much lower. I tried going 10 lower on both and finally settled on 60 front and 55 rear which seems to make it easier to steer than 5 higher or lower. Oh, I put an extra 2 psi on the passenger side front wheel as recommended by an old truck driver who said it helps compensate for the highway slope away from center.

Yes by some magic the tires are rated the same at same pressure.

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

I would be a 65/80 unless there was some issue to resolve.
Might even go 70 in front and see how it rolls.

Remember the RV has many components that play into the quality and safety of the ride.

There are the springs, the shocks, the sway bars, and the tires. All contribute to the suspension. If tire pressure was not a factor in the ride, you could just get solid rubber tires.

Too little air for the weight causes tire wear and if way too little could cause overheating and tire failure. Too much air for the weight causes a harsh ride for the occupants and for the rest of the unit (shakes it to pieces).

Many people overthink this. Use Ford's recommendations for this chassis, 80 rear, 65 front. Even a 24' is heavy enough that 80 psi is not too much pressure. Could you get away with 72-75? Sure, but it's better to err on the side of a little too much pressure than not enough as long as you don't exceed the tire's capacity.

Using Michelin's chart:
225/75/16E

65 PSI Single (Front) equates to the GAWR of the 4600# front axle E450 used through 2007 (chassis year)
and
75PSI works out to GAWR of the 5000# axle used from 2008 up.

80 PSI = MAX. Most likely over inflated for most needs.

ALL "E" load class tires are certified by DOT for the same load rating at PSI.
To get the exact PSI for your vehicle ypu need a 4 corner weight the consult the charts.

You can also call the tire manufacturers with the 4 corner weight and they will give you the PSI that you should be running.

Another answer that may be correct for some of us with a 24' Class C is to go ahead and use the tire pressures recommended by the coach manufacturer even if these pressures seem on the high side for the size of the RV.

Winnebago recommends 65 PSI front, 80 PSI rear, on our E450 24' Itasca and that's what I use. These are the tire pressures for the maximum 14,050 lbs. that it's E450 chassis is rated for.

I use those pressures and get these affects:

1. I get great one-hand easy stirring and tracking when going down the road.

2. I get less tire sidewall heating on all six tires due to less sidewall flexing due to the more rigid tire sidewalls that result from high pressures.

3. I get no worries about "overloading our tire pressures" with any loads below chassis maximum - either as loaded when we start out or with increasing loads as we rockhound during the trip ( ;) ).

4. I get great lateral stability on curves, with passing big rigs, and in high cross winds due to the rigid tire sidewalls.

5. I get heavy vertical pounding in the rear from highway cracks due to the combined affects of the stiff E450 rear leaf springs and the more rigid rear dually tire sidewalls.

6. So far for about 10 years of us owning our Class C we have always gotten even tire tread wear - no baldness of any kind showing up in the centers of the treads.

I prefer use of higher than load-mandated tire pressures - IF AND ONLY IF - one does not get unevern tire wear from this and if one can put up with the stiff(er) ride.

eddard49 wrote:
There should be weight rating/recommended pressures printed right on the tire sidewalls.....at least there is on mine.

No, there's not! There's a MAXIMUM, but the tire manufacturer has no idea what vehicle those tires were going to go on, so they can NOT make a recommendation.

My KINGDOM for a STICKY on this! Ford and Fleetwood applied stickers that cover the maximum weight designed into the unit (chassis for Ford, coach for Fleetwood). Highly unlikely that you can get near that loading in a 24-foot coach unless your camping trips include delivery of watermelons or car batteries.

Which is why we need a sticky. The correct answer to all this is to weigh your coach, configured, loaded, fueled, populated, for actual RV travel and use. If you have access to a scale that you can get the four corners onto individually, so much the better. But it's more than adequate to use the CAT Scale found at just about every Travel Center... Pilot/FlyingJ, Love's, T/A and all those. If you tow a vehicle or trailer, have it hitched up too. For $10 you get a legal- for-trade weight slip showing Steer, Drive (rear of your coach) and Trailer.
Take a tire pressure chart such as Michelin's and adjust the pressure of the pair of fronts, and all four rears, to the numbers in the chart. You can use Michelin for other brands because the specs are industry standard. Notice the first two sizes are the ones discussed here and they ARE the same as Phil noted.
If your tires are hot by the time you get to the CAT scale, I suggest you use the charted numbers plus 05-PSI. Then adjust to what the chart says when the tires are cool and shaded the next day.
Which Chassis do you have, E350 or E450?

There should be weight rating/recommended pressures printed right on the tire sidewalls.....at least there is on mine.