Should the Same Two 4.80-12 Tires Have the Same Outer Diameter.

Updated 11/16/2021 | Published 11/15/2021

Products Featured in This Question

Westlake ST225/75R15 Radial Trailer Tire - Load Range E

(541)

$201.62

Kenda K353 Bias Trailer Tire - 4.80-12 - Load Range C

(3777)

$51.22

Taskmaster 4.80R12 Radial Trailer Tire - Load Range C

(285)

$100.04

Question:

I just bought new wheels and tires for my boat trailer. They are 4.80-12. They were delivered mounted and inflated. The difference in overall outside diameter was visually apparent to me. I measured them to be 3/8” to 1/2” different on nominal 20” diameter. What is an acceptable tolerance for OD or side to side tires? The boat, motor and trailer combined is about 1,400lbs. They were delivered with different pressure in each and sat outside in the cold for a few hours. I have set them to same pressure and brought them inside to equalize these possible reasons for the difference. Please advise. Thanks

asked by: Gary

Expert Reply:

Assuming you have the same two 4.80-12 tires, they should have the same outer diameter. It sounds like the reason for the difference was the different psi in each tire. Once you have filled both to the max psi, the diameter should be identical.

The only other reason they might vary is if it is two different tires. For example, the Kenda # AM10062 has an outer diameter of 20.5" when inflated and the Taskmaster # TT48012C has an outer diameter of 20.63" even though both are 4.80-12 tires.

expert reply by: Robin H