Okay, some racing tires have a weird designation, and I don't know what all the numbers mean, and I couldn't find anything by Googling.

Here's and example:

16/65-15

I know the -15 is rim diameter, but I don't know what the other two are. I think maybe 65 is aspect ratio.

Here's examples of what I'm talking about:

http://www.subesports.com/products/?...Michelin+Rally

 

The first number is the width which if I remember right is in milimeters. The second number is the sidewall size. Its 65% of the total width of the tire. So to make it easy, if you had a 100/65/15, it would be 100 mm wide, 65 mm tall sidwall and 15" rim size.

 

Sorry, I read your post too quickly, I didnt see that you were talking about racing tires. I thought when you typed the 16/65/15 I thought you lest off the 5 for 165/65/15. Not really sure what they mean by the first 16 unless you are looking at some really skinny front tires for a rear wheel drive car. lol

 

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Edit: Ahh.. ignore this post, didn't see above response while I was typing.

 

16=16cm=tread width (not section width)
65=65cm=height overall
15=rim size

Kinda like how american tires are sometimes rated non P-Metric like a 31-10.50-15 for instance (course thats height then width but you get the idea).

What rally tire ar you looking at in that size? Any other than the Michelin, or is it only the Michelin?

 

For instance, here is how silverstone determines their rally sizes:

http://www.taborrallyteam.com/silverstone/s525.html

As you can see the 16 and 65 are only approximations.