Can Going to Larger Trailer Tire Size Give Additional Ground Clearance

Question:

Hi—I have ST 175 80R 13 trailer tires with five hole wheels on my boat trailer. My problem is that the two fixed boat rudders scrape the ground at the new marina boat ramp. Raising the rear trailer height by several inches would solve this problem. I’ve tried lowering the trailer coupler as much as possible to no avail. So, to obtain the needed extra rear trailer clearance by several inches, I’m thinking of replacing the tires with one size up and also adding another layer of rear trailer bunks 2x4s. What’s the next size up for ST 175 80R 13? And what do you think of my plan?

asked by: Bill

Expert Reply:

The overall diameter of your tire size of ST175/80R13 is 24.1 inches. The next size up that would give you a noticeable diameter increase would be the size ST205/75-14 which has a diameter of 26.3 inches. Since the diameter of a wheel is split on either side of the axle that would mean that you would gain 1.1 inches of ground clearance. For a wheel and tire in this size that has a 5 lug pattern we have the Karrier part # AM32156 which would work well. This is a pretty common change that trailer owners will do to gain additional ground clearance so overall it's a solid plan as long as you have room for the additional diameter and width of the larger size. Another option is to lift the trailer suspension.

You can do this by moving the axles from being above the leaf springs to below the leaf springs.

The diameter of your trailer axle will determine the size of the parts that you will need to order. If your axle is 3 inches diameter, the Dexter Trailer Springs Over-Under Conversion Kit, # K71-385-00, would be a great choice and if your axle is 2-3/8 inch diameter you could use the Over-Under Kit, # K71-384-00. These kits can be installed without welding but the manufacturer strongly recommends having the new spring seat tacked in place on the other side of the trailer axle.

expert reply by: Jameson C