What Is The Metric Size Conversion For The A78-13 ST Trailer Tire Size

Updated 03/28/2013 | Published 06/25/2010

Question:

I have a 1994 Spartan Elite boat trailer. It has Loadstar A78x13ST original? tires on it, and I want to replace them. Since A78x13 is no longer made, what would be an equivalent size I could use? There isnt a lot of room between the fender and the tire, so I wouldnt want to go any larger in circumference or width. Thank You.

asked by: michael r

Expert Reply:

The replacement size for the A78x13ST original tire is the ST175/80-13. The overall diameter is 24.1 inches and the overall width is 7 inches. You might want to measure on your trailer to make sure you have the clearance for the ST175/80-13 size.

The Loadstar ST175/80D13 Bias Trailer Tire with 13 inch White Wheel, # AM3S030, you have referenced is a bias tire on a 13 X 4-1/2 white wheel. The tire is a Load Range B, which means it is a 4-ply rated and has a maximum load of 1,100 lbs. at 35 psi.

You will want to check the maximum load on the A78x13ST tire you have to make sure you get the correct load rating for your trailer.

The ST175/80x13 size is available in a bias tire with a load range of B (1,100 lbs. at 35 psi), load range C (1,360 lbs. at 50 psi) and load range D (1,610 lbs. at 65 psi).

It also comes in a radial tire with a load range of C and a load range of D.

The difference in the bias tire and the radial tire is that the radial tire will give you a smoother ride than the bias tire and better stability with the newer, continuous rib tread design.

I am including links to the page of radial tires available in the ST175/80x13 size and a page of bias tires in that size. Also, I am including links to a couple of FAQ pages that will describe tire sizing and frequently asked tire questions.

expert reply by: Jeff D

Sean R.

3/3/2013

I just replaced my old trailer tires, date code 2002.The old ones were Nanco A78-13ST but right on the tire next to the size numbers it says Replace ST16580-13. I have verified that these were the correct original tire size for my trailer 1991 ShoreLandr B1715.I replaced with Nanco ST165/80D13 as stated on the old tire and can see that a 175 would not have probably fit as I already have tight clearances.My question is why does the old tire actually say replace with a 165 when every site I go to says the replacement is a 175?

Patrick B.

3/28/2013

I could not say for sure. Could be because 165/80D13 can be hard to find. Could also be because Nanco tires run a little big anyway. I do know that we do not carry that size, so my gut says it is because it is a hard to find size. I do not know for sure. The 175 size would be 10mm wider and 16mm taller.