Originally Posted by
Pompiere
Is there any way to tell what size wheel a cyclometer is supposed to work on? I have a couple, but I don't know if they are for 27" or 26" wheels. I'm not too crazy about them, I find the constant "tick, tick, tick..." annoying.
The one I have (pictured above) could be taken apart if one was careful. Inside there was a planetary gear of some sort with a different ratio on each side. You could turn it over to get the other wheel size. You'll have to to some countin' and calculatin' to figure out which side goes for which wheel, but the idea is that the smaller wheel needs to make the digits move less for each wheel revolution. I recall seeing this in the literature that came with it, but my memory stops there. I can only suppose that the size options were for 26" and 27"/700c wheels.
Mine didn't go tink tink tink when it was new. It got stiff with age and thus noisy, which is why I finally pulled it off the bike.