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Open Roads Forum  >  Towing

 > Tire Pressure-Sidewall number, or number on trailer?

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gijoecam

Midwest

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Joined: 07/22/2011

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Posted: 04/09/12 07:43am Link  |  Print  |  Notify Moderator

The sticker on the camper applies only to the tires they shipped it with, and that means make, model, size, and load rating. Deviate from those tires with the replacements, and the sticker is then, at best, a decent starting point for determining the appropriate inflation pressure.

The camper manufacturer does not design, engineer, build, or test the tires they install on their campers. They contact a manufacturer who consults their load/inflation pressure tables for the particular make, model, size, and load range of that tire, and that's what the tire manufacturer will recommend that tire be inflated to for those load carrying conditions. That may or may not coincide with the max inflation pressure indicated on the sidewall.

The only time the max inflation pressure on the sidewall should be used is if the tire is carrying its max rated load. Note the wording molded right into the sidewall states, "Max inflation pressure XX lbs @ YYYY lbs of load." It does NOT say, "Inflate to XX psi". There is a reason for that.

Now, in some cases, max pressure is appropriate. Our popup's tires were rated for 1740 lbs each, and the trailer had 3450lbs on the axle, or roughly 1725 per tire (assuming a 50/50 side to side weight distribution). In that case, the tires should certainly be inflated to their max pressure.

The 1/2-ton truck we used to tow that, on the other hand, has E-rated LT tires on it, good for something like 3000lbs/tire at 60psi (IIRC). However, if one consults the load/inflation pressure charts for those tires, at the truck's gross axle weight on the rear (i.e. the MAX the truck is rated to handle) the load on each tire is something like 1700lbs, and an inflation pressure of 38psi is recommended. Why on earth would I run them at 60psi just because that's what's molded into the sidewall as the MAX pressure they should ever be run at? Doing so results in a rock-hard ride, increased suspension component wear, and reduced traction and tire life. That makes no sense to me?!

BenK

SF BayArea

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Posted: 04/09/12 10:46am Link  |  Print  |  Notify Moderator

Ditto gijoecam's EXCELLENT post, right on target

Add that the tires listed max carry weight PSI is not solely for weight
carry, but to keep it's shape during E-maneuvers at max weight


-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...

mowermech

Billings, MT

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Posted: 04/09/12 03:18pm Link  |  Print  |  Notify Moderator

Of course, one could always do the "Chalk Test".
Take the rig to a large, hard surfaced area. Make a cahlk mark across the tread of the tire that you wish to inflate.
Drive around on the hard surface for a while.
Look at the chalk mark.
If it is worn off in the center only, the tire is over inflated for the load. Deflate it.
If the chalk mark is worn off on the edges, but not much in the middle, the tire is under inflated.
Add air.
If the chalk mark is worn off evenly across the tread, the pressure is just right for the load.
Go camping.
Yes, it really IS that simple! No scales, no weight to plug into formulas, no computations, just a chalk mark across the tread!
Or, just inflate to the sidewall pressure regardless of load, and quit worrying about it!
The choice is yours.
Good luck.


CM1, USN (RET)
2002 Fleetwood Southwind 32V, Ford V10
Toad 1: '06 PT Cruiser, Kar Kaddy dolly
Toy (and Toad 2): 2001 Dodge QC SWB, 360 Magnum, Auto, 4X4
"When seconds count, help is only minutes away!"

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