How to Determine Overall Tire Diameter for Picking Out Storage Cover Based on Tire Size

Published 11/05/2019

Question:

Thanks Jameson. But my travel trailer tires do not have the same formula of numbers on the side of them. On the sides they say Vantra LT 185 R14C, and I'm not sure what that means since it isn't like my truck tires that say P 265/75R16 or some other tire with a similar number sequence like that...there isn't a 75R + some other number.

asked by: Melba M

Expert Reply:

As long as you are okay with a little math you can easily determine the diameter of a tire with the size like you mentioned.

The number 205 of the tire size represents the section width of the tire, in millimeters. 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

That means a 205/75R15 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.

So 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 in the size, 15 in our example, represents the diameter, in inches, of the wheel the tire is mounted on.

Now that you know the section width, section height and rim size of the 205/75R15 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.

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

I attached a page that has all of the tire covers we offer as well. You can use the filters on the page to see the fits once you know the diameter.

expert reply by: Jameson C

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Melba M.

11/5/2019

Jameson C.

11/5/2019

185R14 tires have a diameter of 25.7", a section width of 7.3", and a wheel diameter of 14". That type of size does not have an easy way to calculate diameter. Easiest option would be to search the size followed by "diameter" on Google.