I thought the 1st # indicated the width of the tire and the 2nd indicated the width of the sidewall. I have a set of t2 rims/tires and they are 205/55R16 and a set of n/a rims/tires and they are 205/60R15s, but the t2 rims are a 1/2" wider... So does it vary from tire manufactor to manufactor??? What exactly do the 1st and 2nd #s stand for...

 

First number is tread width in mm



Second number is aspect ratio - sidewall height divided by tread width x 100%



Third number is wheel diameter

 

be careful though.... first number is not always accurate, some tires have wider contact patch than others with the same 1st number...... maybe the first number indicates the distance between the 2 sidewalls

 

Those numbers are just "ballpark", there are large variations between manufacturers and even between product lines. If you want more accurate info go to the manufacturers web site and look at the tire specs. It'll tell you rolling diameter too so you know exactly which tire will work when you get plus size rims, so your speedo will be the same.

Good luck

 

yeah...what he said

 

It's just like shoe size...different actual sizes for different brands.

 

Tiretech This is what I use whenever I want to change tire size. It never failed yet. True not all tires are exact, but close enough.

 

Wait a second, so there's a way to upsize the rim/tire combo without having to recaliberate the speedo?

 

When the Rim gets bigger, you downsize the aspect ratio.

 

Width of the rim also plays a factor. Putting a wide tire on a narrow wheel can take away contact patch...



With low profile sidewalls you generally need a wheel closer to the treadwidth of the tire.