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Stupid tire width question(4 posts)

Stupid tire width questionfiltersweep
Aug 31, 2002 8:09 PM
OK- if I am using tires that are 23mm wide and switch to 20s, does it also change the total radius (meaning the tire "height" also changes) ? My understanding is that it does, as evidenced by setting up computer callibration, but some guy I was speaking with (on a rather tangential philosophical issue) swears there is no difference... and I cannot find any info about this other than info regarding tire WIDTH.
re: Stupid tire width questionwolfereeno
Aug 31, 2002 8:30 PM
If the distance between the rim and the tread is different then, then yes, the circumference of the wheel would be different too. And since you multiply that diff by 2*pi it might make a significant difference. But if the depth of the tire's the same, then no difference. I'm a sticker for accuracy so I'd measure it after inflating anyway.
Rollout is the only accurate measurewilsonc
Aug 31, 2002 9:12 PM
It definately does make a difference switching between 23 and 20mm. I have found that even between different brands/makes of tires in the same width (ie 23mm) that the rollout distance can be different. Not necessarily dramatically different, but different. Plus if you want to get even more accurate with your rollout measurement, the bike should be weighted down with you body weight to simulate the tire deformation at the contact patch.

Tire diameter questionKerry
Sep 1, 2002 3:10 PM
As others have stated, the (mounted) tire diameter changes with a change in "width". I put width in quotes because the last time I checked, an infated tire has a circular cross section. You can't change with width and height independently except by adding or subtracting material from the tread or side walls. Your "guy" can swear all he wants, it won't change the simple facts. Whether this difference means anything to you is another story.