Changing Tire Size on 2008 Forest River Flagstaff Pop-Up Camper 176ST  

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Expert Reply:

Changing the tire size on an RV like your Forest River Flagstaff pop-up model 176ST is possible as long as you have the clearance needed for the wider/taller tire size.

The general rule for minimum sidewall clearance at the frame is 3/4-inch; and the rule for vertical clearance is no less than 3-inches so that normal up-and-down travel of the suspension does not cause tire tread contact with the interior of the wheel well.

The article I linked for you lists many trailer tire sizes, with weight load ranges and overall diameters which will help you see which larger sizes might be compatible with your pop-up. For instance, a 185/80-13 tire like # AM1ST79 has an overall diameter when mounted and inflated of about 24-1/2-inches. A tire of size 205/75-14 like # AM10235 has an overall diameter of about 26-1/4-inches.

Your trailer's GVWR is shown as 2100-lbs so you'll want to be sure that any tire you consider as a replacement has a weight capacity for at least half of that weight, but obviously more capacity to provide safety margin is a good idea. Usually we will have several weight Load Range options in any given tire size.

Another thing to consider is the tire's speed rating. Special trailer tires can be rated for 65-mph, 75-mph (speed rating L) and 81-mph (speed rating M) or other speeds. The speed rating matters just as much as the weight rating because both overloading a tire and driving faster than it is rated to go will cause excessive heat build-up. Heat is the root cause for most tire failures.

The ST205/75R14 wheel/tire # AM32161 has a Load Range D tire and a 5-lug wheel which combined have a weight rating of 2200-Lbs and a speed rating M, meaning good to 81-mph. Take half the tire's diameter (half of 26-1/4-inches, or 13-1/8-inches) and measure this distance from the center of your hub to see whether there is enough clearance for this size to operate safely on your camper.

expert reply by: Adam R

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