Can 145R12 Load Range E Tires be Swapped For 13 Inch Tires

Updated 04/11/2023 | Published 04/10/2023

Question:

I have a 22foot pontoon boat and my trailer uses 145R12 load range E tires. Im nervous of driving on the interstate at 70-75 MPH for two reasons. First, the tires have a 65 MPH speed rating. Second, Im worried that the small diameter will require excess revolutions at high speed and will shorten the life of the bearings. Is my bearing concern legitimate? Could I just swap out the tires and wheels for an R13 size tire/wheel with a higher speed rating? I realize this may create a clearance problem for the plastic fender. Im just trying to make the best out of my current trailer situation w/o buying another trailer. Many thanks!

asked by: Mike P

Helpful Expert Reply:

Nope, a 13 inch tire won't fit a 12 inch wheel so you'd have to switch both the wheel and tire. That said, your 145R12 tires are 21.3" in diameter and 5.7" wide while the smallest 13" tire (175/80R13) are 24.1" in diameter and 7" wide. So switching would mean you'd add just under 1-1/2" of height and just over 1/2" of width on your tires; you would need to ensure you still have clearance inside the trailer frame and likely have to get rid of your fenders. If you want to do that you can, and switch to higher-speed rated tires:

- Karrier ST175/80R13 Radial Trailer Tire with 13" Galvanized Wheel - 5 on 4-1/2 - Load Range D # AM31994

The # AM31994 have an 81 mph speed rating, are load range D with a 1,610 lb capacity per tire, and the wheel has a 5 on 4-1/2" bolt pattern (that's likely what you have but if you aren't sure I've linked a help article below which shows how to measure).

You're right to worry about going 75 mph on the highway with 65 mph rated tires, as that builds up heat and the tire is eventually going to blow out. The revolutions isn't an issue whatsoever, but you'll definitely blow through tires at that speed.

expert reply by: Kyle S