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Should I air down or not and to what PSI?
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Ford says to pump up the tires to max load because of the Explorer tire problems of a few years ago. Nothing wrong with the Explorer or the tires on the Explorer, but too many folks drove at high speed with a heavy load without putting enough air in the tires. The result was blowouts, wrecks, deaths, and Ford getting sued. So naturally, Ford is a bit gunshy about lawsuits by stupid customers.
So ignore that blurb in the Owner's Guide and go by the tire load/inflation table for your size tire. That table is published by the Tire and Rim Assn (TRA) and adapted by every tire maker and the Rubber Manufacturer's Assn (RMA).
Here is the load/inflation table for your tires:
LT275/70R18 LR E mounted on pickup with single rear wheels:
<font class="small">Code:</font><hr /><pre>
Minimum .. Max load
PSI for .. per tire
this .. for this
load .. PSI
You need to weigh the truck on a CAT scale to get front and rear axle loads. Be sure to fill up with diesel before hou hit the scales. Then divide that axle load by two to get tire load. Then apply the above table. Get weighed at least twice; once when "unloaded" and again when loaded to the gills.
1. Your normal "Unloaded" truck with full fuel tank and with driver, toolbox full of tools and extra fluids such as oil, cooler full of cool, junk in the back seat, maybe Sweetheart riding shotgun, maybe a week's worth of groceries in the back seat:
Front axle = 4,700 pounds or 2350 pounds per tire
Rear axle = 3,600 pounds or 1,800 pounds per tire.
GVW = 8,300 pounds
2,350 pounds load on each front tire requires minimum 45 PSI. So maybe make it 50 PSI. If you do lots of cruising in excess of 70 MPH, then go up another notch to 55 PSI.
1,800 pounds load on each rear tire requires 35 PSI. So maybe make it 40 PSI. If you do lots of cruising in excess of 70 MPH, then go up another notch to 45 PSI.
2. Loaded to the gills with a trailer or camper:
Front axle = 5,000 pounds = 2,500 pounds on each front tire.
Rear axle = 6,500 pounds = 3,250 pounds on each rear tire.
GVW = 11,500 pounds
2,500 pounds load on each front tire requires minimum 50 PSI. So maybe make it 55 PSI. If you do lots of cruising in excess of 70 MPH, then go up another notch to 60 PSI.
3,250 pounds load on each rear tire requires 70 PSI. So maybe make it 75 PSI. And only if you do lots of cruising in excess of 70 MPH when loaded to the gills would you go up another notch to 80 PSI.
I hope you aren't careless enough to be cruising at over 70 MPH when grossing 11,500 pounds. So for that example weight on your axles, about 55 to 60 front and 70 to 75 rear is the right tire pressure for you.
But when not loaded to the gills, drop the tire pressure to about 50 front and 40 rear. You'll be a lot happier with the ride of your pickup, and your tires should last a lot longer.