On 2010-09-15 09:29:30 -0400, Arye > said:

> It's true that that 185 and 195 indicate the tread width. However, the
> 60 indicates the ratio of diameter to width, so it goes up
> proportionally.

Strictly speaking you are correct of course.
However, 60% of 185 versus 60% of 195?

Without going into heavy (for me) math, I will speculate that the
difference in diameter will come to about 2%. If I'm going 51 and my
speedometer is showing 50, I can certainly live with that margin of
error.

cheers