Tire pressures

[milner351]

If the car is new enough to have steel belted radials when it was produced, and you're still running the factory size tires, then the door frame placard pressure makes sense.
In Europe and other places, they quite often publish a couple different pressures depending on load, even for passenger cars.

For trucks there can be a huge difference between the front and rear pressure, on the One Tons I've had in the past it was 55 front 80 rear with Load Range E 10 ply radials, quite often I'd lower the rears to 55 unless I was hauling or towing to keep my kidneys and fillings in place while driving unloaded.

Most newer cars run in the 35psi range, a while back pretty much everything ran 32.

For our older cars that were made before radials were, and you're now running radials, I think something in the 30-35 range makes sense.

[John Brewer]

I agree with you john brewer.

Justin, works for me. 60 in the front and 65 in the duals in the back with tires rated at 80lbs.!

[dieselhead]

It looks like most disregarded my suggestion to contact the tire manufacturer. The tire manufacturer wants your tires to last a long time. I have 10 ply rated/80 psi Toyo LT296/65R20 tires on my 2005 Dodge 4WD 2500 diesel. Discount Tire inflated them 60psi front and 70 psi rear when they mounted them, they also torqued the lug nuts 145lbs when they should be torqued 135psi. Discount had no recommendations for loaded versus unloaded tire pressures. My truck rode very rough with this much air so I contacted Toyo and they recommended LIGHT/NO LOAD: front 40psi, rear 35psi and HEAVY/MAX LOAD: front 46psi, rear 51psi. I had always been told that when you have a heavy load to inflate your tires to the max psi cold but I know now that was bad advice. I have 22k on these tires (65k tires) and have had them rotated tires 3 times so far. Each time they measured the tread depth and so far they are wearing perfectly even. Remember back when the Ford Explorers were having all those blow outs with Firestone tires? I think Firestone almost went bankrupt because of it. It turned out that instead of just buying tires from Firestone that were the correct size for a Ford Explorer like most car manufactures do Ford had Firestone build a bunch of tires to their specifications. Firestone had no idea which cars Ford was going to put them on. It turns out that these Firestone tires were way undersized for the Ford Explorer and started blowing out.

[AndyB]

For factory sizes (or fairly close), I start with the door tag and go from there. With significant changes (e.g., I'm 0.5" wider on the wheel and 30mm wider on the tire right now), you see a need to move further away from the tag's spec (I'm like 15% higher than the tag says, tires wear flat and the steering feels better).

The door tag is a good starting point, but it's just a starting point.