Tire Inflation pressures

[Travelin2]

I just installed a set of Borg valve stems today and am getting my tire pressures figured out on this new to me 2004 Coachmen Concord 235 SO. It's on an E450 chassis so it has a huge CCC. I weighed it yesterday on certified scales.....Front axle with both of us in the driving seats was 3820 lbs. the rear with full water tank and 1/2 fuel....7560 lbs.
The tires are 225/75 X 16...E rating.

I went to Michelins pressure/load chart and found that 65 psi should be sufficient for both axles. The numbers on the chart are set per axle not per tire. I was hoping to get opinions and observations from others as to how they look at this decision and any advice or experiences. I am going to attempt to attach the chart and a couple of pictures of the rear duals showing the amount of sidewall flex at rest.

[Travelin2]

Thanks for all the input. We have just purchased this rig and are going over some things before our first adventure in it. I figure we have two or three hundred more pounds of additional stuff to add so I am looking at approaching the 8000 pound mark in the rear on the inflation chart. I'm a believer in letting the tires be the first part of the suspension system and having them being harder than necessary makes for a more jarring ride, so I am agreeing with the 55 front and 60 rear crowd. I do keep a heat gun onboard so I will be watching that consideration closely at first.

This rig is a 24 foot rig with a rear kitchen, so it doesn't have near the axle weights as the longer rigs. The model is noted in my signature for those asking about the size.

[cgmartine]

Travelin2, I don't know what size motorhome you have, but if it is a 32 footer like mine, those pressures seem too low to me. I have a Tioga 32M, and I always run 72 in front and 80 in the rear, and it gives me the best ride and handling.

[Little_Outpost]

I read the chart to say Front-single @45 which will easily support 3580lbs and Rear-dual @56 (interpolated because each 5lbs of pressure difference between 7500 and 7980 is equal to 96lbs of weight. So on the rear at 7596 would cover your 7560.
Rick

[crasster]

If you want better MPG (Very slight) use sidewall. If you want smoother ride, go with MFG pressure OR 5psi lower than MFG pressure (slightly less MPG).

[j-d]

We Cant Wait wrote:
The 65 in the front axle might give you a bit of a hard ride. As I read the chart I'd run 55 in the front and 65 in the rear.

Agreed. I got 55 Front and 60 Rear, BUT:

More Front PSI than the load calls for is worse for Stability than it is for Ride. More pressure than called for, reduces the size of the "contact patch" between the tire and the road.

Radial tires want to track straight and E-Series Fords can use help to go straight. The tires need a good contact patch to do it.

[sharker6]

The written sidewall pressure is an internal air pressure. How you load the external tire pressure is up to you. Your safest with what's on the sidewall.

[WILDEBILL308]

GordonThree wrote:
Glad to see this, versus the common nonsense statement "always run max sidewall."

It would be intelligent to run the maximum sidewall preshure until you have actual weights to work with.
Bill

[PSW]

We have a similar size coach except on a E350 vs 450 but our weights are not going to be that much different. We tend to run on full water and fuel as well as more junk than we need. I concur with the comments above. Personally, I run 60 front, 70 rear and check the pressure every day in the morning before traveling. I also carry an infrared thermometer and check tire temperature during the day when we make a rest stop. That lets me know if one of the tires is building up excessive internal heat. We Cant Wait in the post above is on target in my experience. You can sometimes greatly improve the ride with a little less air. More is not necessarily good in this case.

Also, you might think about changing your tire pressure if making a long trip on a very hot day. In the Southwest we often run several hundred miles down an interstate when it is 100F ambient and that pavement will cook an egg....and add more than you might think to your tire pressure.

Seems every rig is a little different and everyone's concept of an acceptable ride is also different. I think you will find a lot of discussion on this topic if you use the search function on this forum.

Paul

[GordonThree]

Glad to see this, versus the common nonsense statement "always run max sidewall."

[We_Cant_Wait]

The 65 in the front axle might give you a bit of a hard ride. As I read the chart I'd run 55 in the front and 65 in the rear.