How to Increase Trailer Tire Weight Capacity Without Increasing Wheel Width

Question:

I want to replace the 13inch wheels and tires on my Com-Fab PWC trailer with 14inch wheels and tires. The thinnest 14inch tires I can find are 205/75 profile, which are 8 inches wide. The manufacturer tells me that they doubt 8 inch tires will fit without sidewall rubbing and maybe even hitting the outside edge of the fender, which is only 7 inches wide. What I really need is a thinner 14inch tire, that has a 5 or 6 inch tread. Does anyone make one? Thanks!

asked by: Patrick H

Expert Reply:

If your interest in increasing the size of your trailer tires is to reduce blowouts then there is another way to do this without having to go through the clearance/fit issues that can come up when using a larger tire than the trailer maker originally specified.

Most special trailer (ST type) tires are offered in more than one weight load range. In fact, the 13-inch trailer tires we offer, sizes ST175/80-13 and ST185/80-13, both are available in multiple Load Ranges.

ST175/80-13 tires are available as follows:
Load Range B: 1,100 lbs at 35 psi
Load Range C: 1,360 lbs at 50 psi
Load Range D: 1,610 lbs at 65 psi

ST185/80-13 tires are available as follows:
Load Range C: 1,480 lbs at 50 psi
Load Range D: 1,725 lbs at 65 psi

I mention this option because the main reason trailer tires fail is excess heat. Excess heat in a tire can arise from incorrect inflation, driving faster than the tire speed rating or by overloading it with more weight than it is rated to handle. Trailer tires should always be inflated to their maximum psi as noted on the tire sidewall; driven within their speed rating (65-mph unless otherwise indicated); and operated within their weight Load Range rating.

Sine both of the above 13-inch tire sizes fit on the same wheel widths (4-1/2, 5, 5-1/2-inches wide) you could potentially replace your ST175/80-13 tires with size ST185/80-13. The larger size is only 10mm wider (0.39-inches) and its diameter is only 7.6mm larger (0.3-inches). This change would allow use of a higher-weight-rated Load Range D tire like # AM1ST79, good for 1710-lbs at its rated pressure of 65-psi.