Originally Posted by Airdale
The cold inflation pressures found on the tire placard are always the correct pressures for the original equipment tires and any replacements of the same size. Deviations from the tire placard pressures for such things as towing will be found in the owner’s manual - if needed.
When Passenger tires are used on a pick-up truck, SUV or passenger van, the maximum load capacity depicted on the sidewall must be decreased by dividing it by 1.1. The vehicle manufacturer will insure that factor is taken into consideration during tire selection and setting the cold recommended inflation pressures found on the tire placard.
Yes and no. The placard tire pressure assumes an average (normal), not maximum load. Depending on the SUV or van (can't say for US-made trucks), the placard tire pressure also may be optimized for ride qualities rather than what is best for the tire.
In most cases I deal with (V6 SUVs and smaller, minivans), the tires will perform and wear better if the pressure is increased above the placard pressure when towing or carrying near maximum loads. Most tire shops that know what they are doing will recommend the same if they know the circumstances. And no, this information is not in any owner's manual I have seen.
In an ideal world, we would be constantly be resetting tire pressures based on actual loading. And we would have charts showing recommended pressure for a given load. And we would have an easy way to determine actual loads on the tires.
Since my world is far from ideal, I use the placard as a minimum tire pressure starting point. If my TV is heavily loaded, I'll add 6lbs+ to placard while staying under the max tire sidewall pressure. If I'm descending down to lower altitudes (I start out at 7000ft), I'll add another lb or two. Outside air temps at both home and destination influence my thinking, too. If my vehicle has a full load of people but not much else, I'll add 3lbs+ to placard. I allow the extra pressure to dissapate over time (tires typically lose a little pressure every month). Since following these guidelines, I have gotten very even wear across the tread. Pressures are adjusted monthly and before each major trip.
For the ST tires, I simply go with sidewall max pressure at beginning of each trip, and call it good.
Now: 2014 Rockwood A122 A-frame
2008 Hyundai Entourage (minivan) with Equalizer 600/6000
Then: 2000 Coleman Westlake PUP
1993 Ford Explorer (no WDH/anti-sway - never again)