Choosing Trailer Tire Load Range and Size for Safety Margin on 5th Wheel Trailer

Updated 04/16/2019 | Published 04/14/2019

Products Featured in This Question

Provider HD ST235/85R16 Radial Trailer Tire - Load Range G

(249)

$286.83

Question:

Currently have 235/85R16 tires on 38 ft Big Horn 5th wheel. Toyo 215/75R17.5 are rated for 4800 lbs H rated Toyo 235/85/R 17.5 are rated at 6000 J rated My local tire guy says go with Toyo 245/70R17.5 which are j rated Also 6000 lb. he says they are close to same diameter. I wonder if that’s too much tire? Thanks

asked by: Steve W

Helpful Expert Reply:

Changing to higher load range trailer tires means they will tend to run cooler and this is always a good thing. The highest weight rating we offer for your current tire size ST235/85-16 is 4400-lbs, with the G-rated Taskmaster Provider radial # TTWPRG235R16. This tire has a speed rating M, meaning it is good to 81-mph.

You can decide how much tire you really need by dividing the Big Horn's GVWR by the number of tires on it. For example, the Bighorn 3370EL has a GVWR of 16K. This means that at this maximum loaded weight each tire has to support 4000-lbs. If you typically run lighter, say 15K, then the Taskmaster # TTWPRG235R16 would give you a solid safety margin of 650-lbs per tire. You would not have to buy new wheels is you stick with the current size. Having 2000-lbs per tire safety margin would be nice but may well be overkill.

Moving to a larger tire size is often possible but with that you need to be sure you still have enough sidewall-to-frame clearance, at least 3/4-inch, and enough space above the tire for normal suspension travel, generally no less than 3-inches.

The diameter of your current tire size 235/85R16 tire is about 31-1/2-inches. Width is about 9-1/4-inches. The diameter of a 245/70R17.5 tire is about 31-inches and the width is about 9-1/2-inches. So, in the majority of situations these two tires sizes will be interchangeable.

expert reply by: Adam R