Tire inflation pressure

Tom/Barb wrote:

hbillsmith wrote:
What do you mean by magic number? I assume you mean a different cold pressure for each tire that then heats to the mfg max pressure such that when rolling down the road they all appear equal on the TPMS. Right?

You'd never want to be at the maximum tire pressure even when hot.

The magic number is the cold tire pressure, (for that tire) that when running will be high enough to prevent over flexing of the tire side walls, yet low enough to not exceed the tire wheel maximum pressure.

I'm not sure this is true . Tires are rated at cold .- unused for some hours - not hot running psi for a reason . When hot they can exceed that number and do if inflated by weight to the max psi. Otherwise you could be under inflated for some time ?

Tom/Barb wrote:


You'd never want to be at the maximum tire pressure even when hot.

Tom, this goes against everything I have ever read or heard.
Can you tell me where you got this information please?

dan-nickie wrote:

rfsod48 wrote:
By rv recommended pressure I mean what is posted by manufacture of mh on weight sticker listing GAWR.

No, I don't think you should add air over the 'sticker' as that is typically stated as the pressure at 'maximum' loaded coach.
That will get you a rough and squirrelly ride.

Totally agree. The PSI on the GVWR sticker is for each axle LOADED TO ITS Gross Axle Carrying Capacity!

hbillsmith wrote:
What do you mean by magic number? I assume you mean a different cold pressure for each tire that then heats to the mfg max pressure such that when rolling down the road they all appear equal on the TPMS. Right?

You'd never want to be at the maximum tire pressure even when hot.

The magic number is the cold tire pressure, (for that tire) that when running will be high enough to prevent over flexing of the tire side walls, yet low enough to not exceed the tire wheel maximum pressure.

rfsod48 wrote:
We are new owners of a 2005 fleetwood bounder 38 n which has a recommended tire pressure of 90 psi. I just had my mh weighed , could only do each axle. Loaded for travel steer axle was 9520 and rear axle was 16760. My tire size is 275/70R22.5 for steer and dual. According to Goodyear chart 10800 inflation is 90psi and for dual 4980 per wheel is 90 psi. Would it be suggested to go to 100 psi for each wheel?

That would be a reasonable thing to do.

rfsod48 wrote:
By rv recommended pressure I mean what is posted by manufacture of mh on weight sticker listing GAWR.

No, I don't think you should add air over the 'sticker' as that is typically stated as the pressure at 'maximum' loaded coach.
That will get you a rough and squirrelly ride.

What do you mean by magic number? I assume you mean a different cold pressure for each tire that then heats to the mfg max pressure such that when rolling down the road they all appear equal on the TPMS. Right?

Your best tire pressure is one that will be high enough to run without heating beyond the tire's maximum temperature. But not so high that it will exceed the tire/wheel maximum pressure when it does heat to running temperature.

Considering that the side wall flexing causes heating, and weight causes side wall flexing, it is a best guess as to what the tire pressure will be advised by the tire or coach manufacturer.

The only method I know of that will find the best pressure is the TPMS that will give pressure and temperature, and a experiment in pressure trials.

I started at the recommended pressure, and found that the tire heated to 125 pounds at 100 degrees, 5 over max. So I increased the pressure, the next morning I found the pressure was 90 PSI, cold but none were the same. I then treated each tire as a separate experiment. until I found the magic number. Now we inflate to that number when we find them low.

rfsod48 wrote:
By rv recommended pressure I mean what is posted by manufacture of mh on weight sticker listing GAWR.

That's a good place to start but until you actually weigh the coach axles and then look up on the tire manufacturer chart ( they have them for ea tire size brand) then set the pressure to what the chart says for that tire, with That specific weight . Some add 5 lbs to that number as a safety margin as long as it doesn't exceed the max tire pressure .... Cold .. For the specific tire.
Manufactures pressure is a good guess biased on the average coach not what you actually have loaded in the thing . ( normally more than they allowed! ) by using gawr gross axle Max you may be over inflating ( rough ride ) or you may be over gross axle weight ... A no no

By rv recommended pressure I mean what is posted by manufacture of mh on weight sticker listing GAWR.