Replacement Modern Tire Size for B78-13ST Tires on Tandem Axle Boat Trailer

Question:

I am replacing four tires on a tandem boat trailer with hydraulic surge brakes. The current tires are B78-13ST load range B 1,300 lbs or so I recall. I would like to use the same galvanized rims that are on the trailer as they appear to be in good shape without any visible rust. This is a boat trailer and all-up weight is less than 4,000 lbs boat = 2,000 lbs empty plus 120hp 2 stroke. Trailer is about 1,300 lbs. Can you advise which replacement tire to use? Thanks.

asked by: Phil

Expert Reply:

The old B78-13ST tire size translates into a modern ST175/80-13 tire size which is compatible with a 13 inch diameter rim that's 4-1/2, 5 or 5-1/2 inches wide.

We offer a load range C radial tire (1360lbs at 50psi) part # TTWTRTM1758013C or a bias ply, same load range as part # AM1ST76. Either tire would offer plenty of capacity. I'd recommend the radials, as radial tires tend to run cooler. Since excessive heat is the number one enemy of tires, the cooler you can keep the tire, the longer they'll last.

I'll link you to our Trailer Tire FAQ article, which I hope you'll find helpful.

expert reply by: Mike L