Join Date: Jan 2006
Location: Columbus, IN
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If you're loading the truck up, inflate the tires to their stated limit as their load ratings on the tire are for that pressure.
too low pressure WILL cause handling problems, wear problems, heat problems, damage, and blowouts.
too high pressure (within the rating of the tire) may cause slight, almost unmeasurable loss of traction (till you get crazy overinflated), and a harder ride.
After working in a shop and 2 dealerships for several years I've seen 2 examples of tires with stereotypical center (overinflation) wear pattern. Both were on ford rangers (which are even lighter in the back than our trucks despite being heavier overall) that never rotated the tires. I've seen over a dozen examples of cars with underinflation wear that the owners religiously kept the tires at the door-sticker pressure.
over/underinflation is a function of how much it's carrying. if going to a wider tire, yes you do lower pressure *slightly* to be textbook perfect. in the real world, the difference is less than the difference between brands. speaking of which, I've seen cheap tires more than 2" narrower tread for the same size than a high quality tire. on the same vehicle, the cheap tire is bulging out and almost riding the sidewall at HIGHER pressure than the good tire at "proper" inflation (When I worked in the shop: 235/75r15 (stock for dakotas, 4wd S10s/blazers, rangers, etc) mastercraft AS/4 vs any Cooper Discoverer
Also remember that the number on the door jamb is COLD inflation and accounts for heating during driving. including driving down the highway for hours when it's 100f out. My Cressida's owner's manual even say "for extended highway driving, increase cold inflation pressure to 35 psi"(from 31 or 32)
All said and done, tires are overengineered by a huge factor. When you see people putting 6k lb SUVs on 2 wheels and driving down the road, they're usually inflated to 90+psi (or so I've read in a few places that talk about it). If they weren't, they'd blow out every time you ran over a pebble
Oh, and make sure your spare is inflated too. I lost track after a week in the shop of how many people's spare tire had zero pressure in it. Take a wild guess how useful that is.
"You don't get to judge me for how I fix what you break"
'94 Pontiac Firebird LT1, T56
'90 Cressida, 7M-GE, M5
'91 Toyota Pickup, 22R-E, M5, 2wd