Recommended Tire Size for Boat Trailer with B78-13 Trailer Tires

Question:

I have a boat trailer that has B 78 13 ST tires very old and cracking on the sides. What tire and tire size would replace this out dated size?

asked by: C .

Expert Reply:

Good news, I can help.

A trailer tire size 175/80-13 will replace a B78-13 trailer tire.

A 175/80-13 is going to have 3 load ratings and two styles: # AM1ST74 is Load Range B Bias trailer tire with a 1,100lbs capacity at 35 psi, # TTWTRTM1758013C Load Range C at 1,360 pounds at 50 psi, and # AM10210 Load Range D at 1,610 pounds at 65 psi. This size will have a diameter of 24.1 inches. The # AM1ST74 and # AM10210 tire size will fit on a 13 inch wheel that is 4-1/2, 5, or 5-1/2 inch wide, while the # TTWTRTM1758013C will fit on all 13 inch wheels. The Taskmaster and # AM10210 tires are also rated for 81 mph while the other Kenda is rated at 65mph. The two styles are bias and radial. Bias are going to be better for rough terrain like agricultural terrain, but if you plan on doing any highway driving to tow your boat from lake to lake, then I recommend the radial tires because they perform better and last longer.

You will want to make sure that the tires you select can support the weight of your boat and trailer. The tires are rated per tire so you would double the pounds for a single axle with 2 tires. (example: 2 TTWTRTM1758013C tires rated at 1,360lbs= 2,720lbs for a single axle trailer). If you choose tires rated higher than your axle, you still have to go by the axle weight capacity. If you choose tires rated lower than the axle capacity, then you need to go by the tire capacity.

I have linked the above mentioned products, all the ST175/80-13 tires, as well as a few Help Articles to this page for your convenience.