Models, Books, and Shirts
Gifts For The Car Guy!
Car Movies
Trans Am Parts
Car Television
Search Trans Am on Ebay
About my '78 T/A
Books That I have Read
Rare Pontiacs
Tips & How To
Old Car Ads
Web Surfers Cars
Car Posters
Where to Buy/Sell your T/A
Old Trader Ads
Other websites that I have created
Site map
My Photographs


The Tire Rack...Your online performance source for wheels.

How to choose the right tire

Here are some simple formulas to help you decide which tire size to use.

Here are the formulas with some examples:

1.Section width: To convert from millimeters to inches, multiply the given mm by .03937, For example the stock section width of a WS6 tire is 225 mm's So 225x.03937=8.86 inches. The section width is the widest point of the tire, not patch.

2. Section height: First you need to find sidewall height. This is done by dividing the section width by 25.4: 225/25.4=8.858 inches.

Then multiply the overall sidewall height by the aspect ratio: 8.858x.70=6.2 inches.

Then to get overall size multiply the sidewall height by 2 (top and bottom) and add rim diameter: 6.2x2+15"= 27.4 inches.

So let's plug in some others.


255/25.4=10.04 inches.

10.04x.60=6.02 inches

6.02x2+15=27.04 inches overall tire height.




5.79x2+15=26.58 inches




5.6x2+15=26.2 inches

Here is the 235/60 15 on my T/A

Here is the 255/60 15 on my T/A


Feel free to drop me a note. * I am looking for some good articles for the third and fourth gen birds. If you have any that you would like to see on this site send them to me and I will post them on my site.     

  • The information in here is just an outline.
  • The author claims no responsibility for the info contained in these pages. 
  • If unsure of any tip or modification seek a professional for the job.
  • In some states this may violate pollution laws
  • Check with your state on the laws.
  • Not affiliated with Pontiac or General Motors