wmtire

Bob, we have done an unscientific, real world test on tires (usually not trailer tires though) that come into our shop with the tread separated, that will probably fly in the face of conventional wisdom. If they haven't lost air pressure, we measure it. The majority of separated tires aren't underinflated, but the opposite...they are overinflated, sometimes WAY overinflated. I see a lot of times that people will air a radial tire up visually and not use an air gauge. All radial tires have a "squat" to them, that most people think is underinflation. They air them up till the squat is gone, which is dangerously overinflated. When you overinflate a tire drastically, you basically pull the belts away from the rubber. The tire is made to flex, but usually in a certain direction, which isn't the direction you are pushing it with air pressure., which pulls the rubber away from the belts.

When a tire is way overinflated, there isn't an immediate noticeable result of separation, but the underlying damage is done nonetheless. Even if you correct the inflation, most likely the tire will come apart within 30-60 days in my experience. There will be other factors that contribute to this including use and temperature. When we catch a customers vehicle that is way overinflated, we give them our prediction on what is going to happen with their tires.....and we're usually correct.

There are 2 more considerations in inflating a tire to think about. Air, as with most gases, expands as it gets hot. When you drive greater distances and in hotter climates, the air pressure inside the tire will increase due to this expansion. If you know you are going to be in conditions that the tire will get hotter for extended lengths, it is a good idea to let a few pounds out before driving, to allow for the expansion. Tires technically have a built in reserve capacity for overinflation, but I see this exceeded due to air expansion and incorrect inflations. Always check your tire pressure before trips, when it is technically cold pressure, to get an accurate reading. Make adjustments from cold pressure, not hot expanded pressures (unless absolutely necessary).

Another thing is maximum air pressure on tires. Maximum air pressure listed on a tire doesn't necessary mean operating pressure. A tire is manufactured for a wide array of different applications and weights. A tire may run the maximum for one application but less for another. Most charts just show the maximum air pressure and corresponding load. Maximum air pressure means just that----the maximum that it is tested to safely operate under a certain weight condition. Recommended inflation for your application (in this case the trailmanor), is what the manufacturer recommends to safely and comfortably carry the load. Most of the time, it won't be the maximum.

Sometimes the manufacturer recommendation is incorrect, as time will tell. Remember the Firestone/Ford deal? A lot of it could have been avoided had everyone not used 26 psi as Ford recommended and Firestone agreed to at the time. They both learned and bought a lesson with other people's lives on that one.

It was also discovered that Ford spec'd the tire without a nylon cap at the edge of the tread belt. It saved them a whole $2 bucks a tire. Firestone is just as culpable, because they sold the tires without it. Hindsight being 20-20, they should have said no to Ford, but they didn't....and probably are more guilty in a way. Ford doesn't build tires, Firestone does.