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How to Select Correct Special Trailer Tires to Fit Rims and for Correct Weight and Speed Capacities

Question:

I have the 5 on 4 and a half tire rim. My current tires are 195-70-R14. I dont see tires offered in that size . Can your tire size you offer work ? Also what load rating do I need? I see C and B offered. No place on the site explains whats best

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Expert Reply:

I can help you select new tires for your 14-inch rims that have the popular 5-on-4-1/2-inch wheel bolt pattern. I can also help explain some of the particulars about choosing new special trailer (ST-type) tires. The two help articles about trailer tires that I linked for you will be handy reference tools.

You are correct that we do not offer trailer tires in size 195/70R14 but we do offer 14-inch trailer tires in a 205-millimeter width and in a 215-millimeter width. These tires are slightly wider than your 195-mm size. A 195mm tire is approximately 7-1/2-inches wide; a 205mm tire is approximately 8-inches wide and a 215mm tire is approximately 8-1/2-inches wide. Wider tires can be used if they fit your rims and if their increased width does not pose clearance issues with the trailer frame, fenders or other components.

A 14-inch trailer tire can only fit a wheel/rim of that 14-inch diameter but any given 14-inch tire size may fit more than one wheel/rim WIDTH. As examples, a trailer tire of size ST205/75-14 will fit a 14-inch rim with a width of either 5-inches, 5-1/2-inches, 6-inches or 6-1/2-inches. A tire in size ST215/75-14 will fit 14-inch rims of several widths too: 5-1/2-inches, 6-inches, 6-1/2-inches or 7-inches. This wheel and tire width compatibility is shown in the chart in the linked article on tire sizing.

A particular tire size, say the ST205/75-14 for example, is made in different weight load ranges, each of which can handle a specific maximum amount of weight. A Load Range B tire in this size handles 1430-lbs @ 35-psi pressure; a Load Range C tire can handle 1760-lbs at 50-psi; and a Load Range D tire can handle up to 2100-lbs at 65-psi.

The way to choose tires is to determine the trailer's GVWR, its gross vehicle weight rating, which is the most it can weigh when it is fully loaded. Take this maximum safe trailer weight and divide by the number of tires on the trailer to determine the minimum weight capacity needed for each tire. Let's say your trailer's GVWR is 6000-lbs. If it has two axles, with 4 tires, each one needs to be rated for no less than 1500-lbs. In this example a Load Range C tire would provide a safety margin of 260-lbs per tire, and a Load Range D tire would provide a safety margin of 600-lbs per tire.

Trailer tires also vary in their rated maximum speed. Speeds also use a letter code like weight ranges. For instance, Speed Rating L means the tire is good to 75-mph; speed rating M means the tire is rated for up to 81-mph.

The right trailer tire for any given application will have a weight capacity higher than what you will ask it to handle; a speed rating of at least your fastest intended driving speed; and will always be maintained at the maximum COLD psi pressure that is molded into the tire's sidewall. For instance, the Kenda ST205/75R14 tire # AM10235 has a D weight load range rating, an M speed rating and it requires a COLD tire pressure of 75-psi in order to deliver these rated capacities.

It is never appropriate to under- or over-inflate a trailer tire for any reason.

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