Determining Tire Pressure

fla-gypsy wrote:
The vehicle maker gives you the psi to use based on the OEM tires. They cannot possibly fathom what each owner will replace those OEM tires with and makes that information invalid once the OEM tires are replaced unless replaced with the identical tire in every respect. Come on and lets think a little please. No vehicle maker is sticking their neck out on replacement parts obtained by the end user. Once the OEM tires are replaced use the tire makers inflation chart. Holy moly sometimes I just SMH.

Not exactly.

ALL tires are standardized - especially those that fit on a Class C motorhome. It does NOT matter who manufactures the tire, the tire is designed to the same load table.

Both the vehicle manufacturers and the tire manufacturers reference the same tire standards, so what the vehicle manufacturers put on the vehicle tire placard will be applicable for ALL tire manufacturers, not just the original tires - unless, of course, the vehicle manufacturer screws up, then all bets are off. (It has been known to happen, and the vehicle should be recalled to fix it!)

Hiker_01 wrote:

fla-gypsy wrote:
The vehicle maker gives you the psi to use based on the OEM tires. They cannot possibly fathom what each owner will replace those OEM tires with and makes that information invalid once the OEM tires are replaced unless replaced with the identical tire in every respect. Come on and lets think a little please. No vehicle maker is sticking their neck out on replacement parts obtained by the end user. Once the OEM tires are replaced use the tire makers inflation chart. Holy moly sometimes I just SMH.

Concur. Info on our trailer says to inflate tires to 80 psi, but tires that are currently on trailer says 50 psi max. My guess is somewhere along the line someone changed out tires, so definitely going to go with tire rating, not what is on trailer.

While I agree with you in this case to go with the Max PSI ON THE TIRE, I wonder if these replacement tires are "heavy-duty" enough for your trailer. Not making a statement - just asking.

If you tow a vehicle, pull onto the scale with it in tow. I imagine you could drive it up separately if you want to know its weight and haven't got the tow setup in place. Scale will give you

Steer (front axle)

Drive (rear axle)

Trailer (towed vehicle)

When we pulled up with our 31-ft towing a midsize pickup, the three fell in place on the scale (really three scales) when we pulled the front axle up to the marked spot. The scale attendant (usually inside with/as cashier) should be able to help you position to get the vehicle(s) correctly placed.

Sounds like the best idea is to "dial it in" over a period of time. Wednesday I'm taking the old gal into the RV doctor to have the LP system checked out and filled. After that I'm going to visit a Flying J that's nearby, fill up with fuel and then weigh on their CAT scale. I believe I can put it all together from that point. Thanks everyone for all your input, and fla-gypsy, I'm sorry my newbie ignorance annoyed you so much. I'm just trying not to kill my family and/or someone else's including yours.

Many times when people complain of poor handling it's because they used max inflation instead of weighing their fully loaded rig.

fla-gypsy wrote:
The vehicle maker gives you the psi to use based on the OEM tires. They cannot possibly fathom what each owner will replace those OEM tires with and makes that information invalid once the OEM tires are replaced unless replaced with the identical tire in every respect. Come on and lets think a little please. No vehicle maker is sticking their neck out on replacement parts obtained by the end user. Once the OEM tires are replaced use the tire makers inflation chart. Holy moly sometimes I just SMH.

Concur. Info on our trailer says to inflate tires to 80 psi, but tires that are currently on trailer says 50 psi max. My guess is somewhere along the line someone changed out tires, so definitely going to go with tire rating, not what is on trailer.

fla-gypsy wrote:
Oh my goodness when will this stop?

When vehicle manufacturers stop putting the LOWEST pressure rating because it will give their vehicle the cushiest most comfortable ride.
It's their vested interest. ;)

Have you ever noticed that tires purchased from a tire shop and installed on a vehicle are never inflated to max pressure. The shop wants the buyer to have a comfy ride.

Oh my goodness when will this stop?

If you call your tire manufacturer with the weight of your vehicle
their customer service will give you the correct PSI.

The door PSI is for MAX.

So if ypu are under MAX your tires are over inflated.
A good indicator of over inflation is poor handling and braking.
Does your RV feel like if is on ice?
If so ypu most likely have over inflated tires.

FYI on E450 chassis vehicles:
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.

Duel = axle lbs
70 PSI for Duels = 4440 lbs
75 PSI for Duels = 4660 lbs
80 PSI for Duels = 4940 lbs

If your E450 Sticker says:
GVWR 14050 then
Front GAWR 4600 lbs.
Rear GAWR 9450 lbs.
65 / 80 PSI

That would be MAX.
If your weight is under that then you are over inflated.

Tyler0215 wrote:
The tire company puts a recommended pressure on the tire for a reason!

Tire companies put the max pressure on a tire, not the recommended pressure. The max pressure is the pressure required if the tire is operated at maximum loading.

Weight the axles and set tire pressure according to the tire manufacturer's load chart. I add an extra 5 psi for margin.