# Spare Tire Carrier Recommendation for a ST205/75R15 with 5 on 4-1/2 inch Bolt Pattern

Question:

How do you measure tire diameter? Are we talking about the wheel diameter or the outside tire diameter? I have a tire size of ST205 75R 15, which is a 15 inch wheel. It has a bolt pattern of 5 lugs on 4.5 inch. This looks like the ideal tire carrier and I would like to know if will work before I purchase. Thank you,

1

In order to determine your overall tire diameter we will need to do a little math (yay).

I attached an FAQ on how to do this also, but I will walk you through the process.

The number 205 represents the section width of the tire, in millimeters. To convert to cm you move the decimal point once to the left. This is the measurement of the tire at its thickest point. If you want to convert centimeters to inches, divide the number of centimeters by 2.54. 1 Inch is about equal to 2.54 centimeters.

Example: 20.5 cm / 2.54 = 8.070 in

A 205/75-R15 tire would have a section width of 8.070 inches.

The number 75 refers to the sidewall aspect ratio. This will help you find out the height of the sidewall, from rim to tread. This is also called section height. The second number in a tire size indicates the ratio between tire width and height.

Example: 8.070 in x 0.75 = 6.053 in

A 205/75-R15 tire would have a section height that is 75 percent of 8.070 inches.

The last number, 15 in our example, represents the diameter, in inches, of the wheel on which the tire is mounted.

Now that you know the section width, section height and rim size of the 205/75-R15 tire and wheel, you are able to determine the total diameter. The section height, or sidewall on the tire, is 6.053 inches. Multiply this by 2 to determine the amount of tire extending out on both sides of the wheel. Imagine drawing a straight line across the tire and wheel, directly across the center.

Example: 6.053 in x 2 = 12.106 in

Add the combined section heights of the tire (12.106 in) to the wheel size to get the combined diameter of the tire and wheel.

15 in + 12.106 in = 27.106 in

So I would recommend you go with the Fulton Hi-Mount Spare Tire Carrier # FSTC1000301. This is our most popular spare tire carrier with a ton of positive reviews that would work well with your spare