What is the Diameter of Loadstar ST175/80D13 Bias Trailer Tire with 13 Inch White Wheel # AM3S140

Question:

I own a 1993 Coleman popup camper with a GAWR of 2000 lbs and GVWR of 2300 pounds. I had 10-inch wheels before, but I recently lowered the axle beneath the leaf spring and have greater clearance. QUESTION: If the specs say the outer diameter of a mounted tire is 24, than is that the same as 12inch from the center of the axle to the outer edge of the tire? Meaning, if I have 13inch from the center of my trailer axle to the wheel well, then a 24inch diameter tire should be 12inch from center axle to edge, leaving 1inch clearance. Is this correct?

asked by: Jamie B

Expert Reply:

When inflated to the maximum psi as indicated on the tire, which is how trailer tires should be inflated, the diameter of the tire, or height from the ground to the top of the tire, will be 24 inches for # AM3S140. This would mean that if you measure from the center of the pilot hole on the wheel, it should be 12 inches to the top and 12 inches to the bottom.

However, when under load, the weight of the trailer is going to push down towards the top of the tire and the bottom of the tire may smoosh out some under the weight. Ultimately, you would not have exactly 1 inch of clearance but less if at all. The spindle, not the axle, may also be slightly higher or lower than the axle centerline which will also throw things off a little.

The suspension also has a certain amount of travel that could have an affect on that clearance as well.

Using the correct tire and wheel for the trailer is the best bet. having larger tires does not allow the trailer to carry more weight because that is limited by the axle capacity. If you are having problems with blow-outs, make sure that the tires are always inflated to the max psi indicated on the tire and always use trailer tires (ST in front of the size) because passenger car tires are not rated for vertical load associated with trailers. I have linked an FAQ article on trailer tires for you.

Raising the trailer will also change the center of gravity and can lead to trailer sway and a different ride.

expert reply by: Michael H