Tire pressure for new class C

[Jack_Spratt]

First timer with new class C. Leprechaun 260 dsf. Ford E450.
GVWR 14500
Rear 9600
Front. 5000
Door pillar recommends front 75....rear80psi
Checking when I got home all tires were at 60#
There are no scales within 50 miles of here so I was hoping to hear
from someone else with a similar rig what they run for pressure.

[Mich_F]

Off Pavement wrote:
I'd recommend checking the tire manufacturer's recommended load and inflation tables. To do so requires getting actual front and rear weights and for my vehicles actual loaded weight, I run 55 front and 65 rear.

I would suggest bumping up your front tires to 60 psi (assuming you're running E and not D tires). I believe that you shouldn't run your tires at less than 75% of the max psi for the tire. Might not be true, but why take a chance, since it will give you more of a cushion and probably won't affect the ride quality. 😉

[Harvard]

Jack Spratt wrote:
Thanks for the help
I will air them up tomorrow

Beware....you may end up with too little effective runtime +caster.

Ford ships these E350/E450 Cutaways off the assembly line
with +3 to +4 degrees of Caster. Those settings are
OK for city driving BUT you want to have +5 to +6 degrees
of Caster for highway driving, OTHERWISE:

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:

There are at least two ways to increase the effective
runtime caster (see Self Aligning Torque):

1. Decrease the tire inflation pressure to the required
minimum for load (to increase Pneumatic Trail), and or

2. Increase the caster angle during an alignment
(to increase caster trail).

If you find an improvement in reducing the tire pressure
you will be amazed what it is to add +2 degrees of caster. IMO.

[Off_Pavement]

I'd recommend checking the tire manufacturer's recommended load and inflation tables. To do so requires getting actual front and rear weights and for my vehicles actual loaded weight, I run 55 front and 65 rear.

As an example, here is Michlin's light truck tire chart...

https://www.michelintruck.com/reference-materials/manuals-bulletins-and-warranties/load-and-inflatio...

[bukhrn]

S1njin wrote:
*most* folks are compliant rolling 70 psi Front and 80 psi Rear.

That's what I use.

[BFL13]

wildtoad wrote:
Keep it simple... Use what’s on the pillar for your first couple of trips. If you find the ride too harsh, get it weighed and use the real weights to adjust the tire pressures based on the tire chart.

After a few trips you will know what you bring, and then you can get it weighed if for no other reason to verify that you have not overloaded it.

The sig 1991 Class C is overloaded at the back with nothing else in it. I have to go over the door PSI for the back tires to meet the actual weight as seen on the scales. I can do that higher PSI with Es instead of the OEM Ds the door specs call for.

I don't think Ford, who made the "incomplete truck", expected the RV maker would build a house on it that sticks so far out the back, that the leveraged effective weight on the real axle is so large.

It might not show up so much on a 22 foot Class C, but it sure does on a 28 footer.

[Dennis12]

Its possible the tire manufacturer may know. Look on the tire, run what it says !

[IAMICHABOD]

All very good answers so far,to make checking those air pressures a lot easier I would suggest getting new extended valve stems installed.

The best on the market,that are the original,are Tire Man.

Chuck is the original designer of these an he has been around for years. If you have any questions just give him a call, he is always happy to help. Any others are just cheap reproductions of the original.

The kit looks like This it is for all 6 wheels,they also come with flow-thru valve caps so you don't even need to take then off to check the pressure.

Here is a list of all the products he sells.

Congratulations on your new Rig.

[wildtoad]

Keep it simple... Use what’s on the pillar for your first couple of trips. If you find the ride too harsh, get it weighed and use the real weights to adjust the tire pressures based on the tire chart.

After a few trips you will know what you bring, and then you can get it weighed if for no other reason to verify that you have not overloaded it.

[Beverley_Ken]

As Drew said, go with the door sticker recommendations to start, until you get your loaded, ready to go weights.
With 80psi in the front, the handling on ours was terrible, The
Michelin chart pressure for our weight was 60psi in the front. The handling was back to normal when i reduced the pressure to 70psi.
I checked the tires last fall and after 12000 miles, the front tires are wearing more in the centre of the tread, than the outside, Maybe I should start running at 65 psi. The Michelin chart says 60.

Ken

[Sam_Spade]

Jack Spratt wrote:
First timer with new class C. .

Brand new.....or just new to you ?

If it is used, the AGE of the tires is important too.

Follow the sticker recommendation unless you have some solid reason not to. Never go lower; not worth the risk.

[Jack_Spratt]

Thanks for the help
I will air them up tomorrow

[Mich_F]

Assuming you 225/75 tires, according to the Michelin Tire load rating chart, 60# in the front tires is good for up to 4,380#, while 60# in the rear tires are will support up to 7,980#. Those numbers may or may not be OK for you. I suggest you just go by the door pillar until you have a chance to weigh it fully loaded. 😉

Michelin Chart

[S1njin]

*most* folks are compliant rolling 70 psi Front and 80 psi Rear.

[DrewE]

The door pillar recommendations would be a decent starting point; they're set assuming full gross weight load on the axles, and that's often not too far off for a class C. I would guess that it's more likely for the front axle to be well under gross, and proper inflation there (avoiding overinflation) is rather more important to good handling than on the rears, so when you get a reasonable chance to weigh the motorhome it may be worthwhile to adjust the pressures if the axle is well under gross. It's preferable in my opinion to have a little more pressure than necessary than to have not enough (assuming one isn't going above the maximum pressure ratings of the tires or wheels, of course).