Which Trailer Tire Size Replaces B78-13B Tires

Updated 09/06/2016 | Published 09/02/2016

Products Featured in This Question

Karrier ST175/80R13 Radial Trailer Tire with 13" Galvanized Wheel - 5 on 4-1/2 - Load Range D

(2390)

$153.16

Loadstar ST175/80D13 Bias Trailer Tire - Load Range B

(3775)

$69.07

Question:

The brochure for my camper says the tire size should be B78-13-B. Whats currently on the camper is 3 of a 175/70R13 and 1 of a 185/70R13. 1- Are the tires that are on it, equivalent to what the brochure size says. 2- Is the odd tire size a problem? Isnt the 175 or 185 the width of the tire? 3- If whats on there isnt appropriate, what Should Be on there? I really dont want to spend the money to buy 4 new tires.

asked by: David W

Expert Reply:

B78-13 is an old tire size designation that isn't used much anymore. The modern trailer tire equivalent size is ST175/80-13. All of the tires on the trailer should be the same size, load range, and construction type (radial or bias ply). Having one that is a different size can cause uneven tire wear, tracking problems (how the trailer follows the tow vehicle), potential suspension issues, and unspecified weight carrying capacity.

The 175/70-13 isn't a trailer tire size. If the tires on there show a P in front of the number or otherwise do not have ST in front of the size then they are not trailer tires. The ST stands for special trailer.

For an ST175/80-13 load range B you can use # AM1ST74. I strongly advise switching the tires to 4 of these. You can use the same wheels you have now so you don't have to spend the extra money for wheels.

expert reply by: Michael H