Posted by robmoz on April 09, 1998 at 18:13:30:
In Reply to: Just my imagionation or what? posted by OC on April 07, 1998 at 20:47:56:
yes, it is your imagination. First, lets define terms. the first number given in a tire size is tire width in millimeters, the second is aspect ratio (ratio of sidewall height to tire width, the first number), and the third is wheel diameter in inches. You say they should both have the same "tread diameter". I assume you mean tire diameter. No they won't have the same diameter. The 205/55-60s wil be slightly bigger (diameter) than your 205/50-16s. They will have the same width though. They are both 205 mm wide. I believe you may be using the word diameter incorrectly as meaning width.
Your rims both have the same diameter (16"), but yours are .5" wider. You both have mounted 205 mm wide tires on different width wheels, which just means that his will have a little more sidewall bulge than yours (I have 205s on a 6" wheel, with no prob.). If you do mean rim width instead of diameter, you are correct that tire width MAY increase with rim width. This does not automatically mean that your tires are wider though, it just maybe means you could mount 215s or 225s on and he can't. His (forgive the gender assumption) may actually appear narrower (optical illusion) since they are the same width but a larger diameter.
The manufacturer has nothing to do with the size as sizes are standardized across all makers.
hope this answers your question.