Quote:
Originally Posted by MikeInNH
55psi...Sorry...No way....
I have Cooper Discover LT tires on my truck....And the recommend tire pressure is 32psi.
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The high psi numbers come from the idea of maintaining the load reserve of the stock passenger (P) tires at door sticker pressure. LT tires require much more air pressure to carry the same load as Ps of the same dimensions.
Comparing against the load capacity of the stock tires when de-rated because of their application in an SUV produces a psi of 44 for the new switched out LT. Using the load capacity, not de-rated, produces 49psi. Some instructions say to round up to the nearest 5psi increment which produces 45 and 50, respectively. Load tables can differ slightly from each other, so allowing for that and then factoring in the 5psi rounding is presumably where 55psi comes from.
SInce the stock load reserve is very generous, LT load reserve can be maintained on paper with pressures less than the above, but since speed ratings also take a hit on the tire switch, it doesn't seem like a great idea to stray too far from the above adjustments. 32 psi is pushing it, imo. That's the equivalent of about 20psi in the stock tire.