Originally Posted by
FBinNY
I hate to be a pain, but you and the post you corrected are both wrong.
Bicycle tires, like any flexible tube will form a near perfect circle when inflated. The basic physics is that shapes under internal fluid pressure will deflect to maximize volume for the perimeter (circumference).
Of course this depends in the structural factors that would resist that tendency, so won't apply near the rim.
In the case of bike tires, with supple bias ply sidewalls, the resisrance is near zero compared to the high inflation pressure.
Note that the circle is at the wall, so different tread and wall thickness will cause the outpear more oval.
Thanks for the correction, and I agree that it is not a linear response when narrowing the rim dimension. I would love to see the actual numbers. In my own experience, when using a very supple tire and wide rim, the outside diameter went down noticeably. The image provided proves nothing and is based on the theoretical response of a tire when placed on various rim diameters. If an open non-moulded tire like a Challenge or Rene Herse was modelled, the results would be substantially different.