Tire Sizing

Thursday, October 1, 2009 by Ethan Burns
Let's look at tire sizing for a moment.

POP QUIZ
195/70R14    205/60R15    245/45R16
Which of these tires is the widest, and which is the tallest in overall diameter?

Dissecting the code you find the the first number 195 is the actual width of the tire in millimeters.  

Divide this by the 25.4 to get the section width in inches. In this case 7.6" or about 7-5/8" wide as measured at the bulge of the sidewall. Treadwidth is usually a bit less then section width.

The second number 70 suggests that the sidewall is 70% as tall as the tire is wide.

This is NOT an acutal measurement and means NOTHING without the first number. I get a number of calls from guys telling me that they want some 60 series or 50 series tires. I can't help these guys if they don't know how tall a tire they need for their application.

195 x .70 = 136.5mm  (meaning the sidewall is 136.5mm tall)
136.5mm divided by 25.4 = 5.37" sidewall
Remember there are two sidewalls (top and bottom) and one 14" wheel separating them.
5.37 + 5.37 + 14 = 24.7" overall diameter
70% of a wider tire will be also taller.

So when calling to order tires for a custom hot rod please know your height and width requrements. 

So get your calculator. Which of these tires is the tallest?

The answer is:

They are all the same height.

Comments on Tire Sizing

Tuesday, July 9, 2013 by joe martin:
I have a 2012 challenger redline V6 with 20" rims. Me , I want the old look of larger tire sidewall. I'm thinking of going to a 18" rim and going for the largest sidewall without rubbing the rear fender wells. I understand it will slow down speed odomitter sum. The fronts 18" = rubber size on the current 20"rims. Would 18" rims fit the redline option.
Monday, July 15, 2013 by Ethan:
While a 2012 vehicle dosent exactly fit into this blog about classic cars and hot rods, it is possible to down size your car from the 20" wheels to 18 wheels. We do it all the time for winter snow tire packages. A 235/60R18 is a likely choice. Just give us a call and we can help.

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