Tire inflation pressure

[rfsod48]

I have seen it posted many times to inflate tires 5-10# over rv listed tire pressure. Why would you do this?

[rgatijnet1]

rfsod48 wrote:
I have seen it posted many times to inflate tires 5-10# over rv listed tire pressure. Why would you do this?

Because even if you weighed the coach today, and you set your tire pressure at the exact pressure according to the tire charts, your weight would start shifting as soon as you start your trip. My coach holds 75 gallons of fuel, or approximately 480 pounds. As I use fuel, weight shifts. I usually travel with some water in my fresh water tank. Lets say 20 gallons in my 60 gallon tank. That equals another 160 pounds or so that shifts as it goes from the fresh water tank to either the gray tank or black tank.
Of course we may stop for groceries along the way which can add weight but it will also shift weight as we store or use those groceries. The same thing happens as your clean clothes move from the closet to the dirty clothes hamper.
Basically the weight of your coach is an ever changing number on each wheel. If you inflated it to the exact minimum amount of weight needed to carry the weight, you could easily go overweight by the second day of your trip, only because weight has shifted from one wheel to another. The extra 5-10 pounds allows for weight shift and also allows you a little protection if you have a very small leak and lose some air during your days travel.

[tropical36]

rfsod48 wrote:
I have seen it posted many times to inflate tires 5-10# over rv listed tire pressure. Why would you do this?

First, it should be done by weighing, as the RV's sticker has no idea what the load is and is just assuming GVWR.
When weighing just the axle, one side could weigh more than the other, as well as adding or shifting weights with people or other.
Changes in ambient temps. as you travel.
A developing slow leak that might take a day or so to catch.
Conflicting tire gauges and a little over is always better than being under.
Tires will run cooler and save a sip of fuel as well.

[dan-nickie]

:B

[Tom_Barb]

Ivylog wrote:
I go 5 over my weighed pressures because I'll still travel in a good cross wind. It will shift enough weight to the downwind side to overload those tires if at the minimum pressure.

When using a TPMS you can find the proper pressure you should be running, when you get out in the wind, you can watch the tires that are flexing more raise the pressure and temp. The windward side will actually decrease in temp. and the pressure will drop.

[Tom_Barb]

dan-nickie wrote:

Tom/Barb wrote:

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 know that a lot of tire shops inflate the tires to the max listed on the sidewall of the tire.
If what you say is true, then almost all tires on the road are probably over-inflated.

How many coaches are running at gross weight? Would you want the tires to be pressurized to max all the time?

How many coaches are running truck tires? Do they require max pressure running on a coach?

You can find the sweet spot for tire pressures with a TPMS that gives TEMP / PSI.

My Front axel runs cold at 97 PSI and will heat to 105 degrees and stay there all day in hot weather. the rim and tire say 120 pounds max. at 120 you may as well have iron tires.

the rear varies about 5 pounds side to side

when you allow the pressure to be too low cold, the tire will heat beyond the manufacturers recommended temps and actually become un vulcanized and blow apart.

150 degrees is what most tire manufacturers recommend as the maximum safe temperature.

[wolfe10]

rfsod48 wrote:
I have seen it posted many times to inflate tires 5-10# over rv listed tire pressure. Why would you do this?

It is confusing, because this original post did not specify what "rv listed tire pressure" he was referring to.

Most assumed he was talking about the tire manufacturer's inflation tables which specifies PSI based on actual weight.

Very different than the GVWR sticker pressures which are for each axle loaded to its Gross Axle Weight Rating.

Factoring that in clarifies a lot of the "variance".

[rk911]

rfsod48 wrote:
I have seen it posted many times to inflate tires 5-10# over rv listed tire pressure. Why would you do this?

there are as many reasons as there are people doing it. maybe they've actually weighed their RV and then consulted the inflation guide for their make/size of tire and found the 'RV listed' pressure to be wrong. IMO it's not "wrong" to over-inflate your tires (up to the max weight rating for the tire) but it's certainly unnecessary and could result in handling and braking issues.

load your RV as you would for travel, at a minimum get individual axle weights, consult the inflation tables for your tires and inflate accordingly.

[Ivylog]

I go 5 over my weighed pressures because I'll still travel in a good cross wind. It will shift enough weight to the downwind side to overload those tires if at the minimum pressure.

[fla-gypsy]

wolfe10 wrote:

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!

Any new person reading this thread is totally confused by now but this is the correct "safe" pressure to run. It is possible to use individual weights for each tire position but is totally not necessary if you fill to maximum specified by the vehicle makers cold PSI rating and you can be assured you have acheived the maximum weight carrying capacity for those tires.

[dan-nickie]

Tom/Barb wrote:

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 know that a lot of tire shops inflate the tires to the max listed on the sidewall of the tire.
If what you say is true, then almost all tires on the road are probably over-inflated.

[jorbill2or]

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 ?

[dan-nickie]

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?

[wolfe10]

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!

[Tom_Barb]

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.