I am trying to figure out how old speedometers are matched to their drives, to provide correct speed readings.
For instance, with Dorcy, the face of the speedo indicates the wheel size it is intended for, i.e. 20'', 26''. In all the sets I found online, regardless of what the face indicates, the drives are the same - the 26 hole, 2.5'' diameter ones, with no stamping on them. So Dorcy made the adjustment to wheel size in the mechanism of the speedo head rather than the drive?
I found a speedo by Cycle that has 20 stamped on both the speedo face and the drive. Note how this (slightly smaller) drive has 20 holes (not 26):
So now I'm thinking wait, do the number of holes in the drive indicate the size of the wheel?
And to make things more complicated, I found a drive that is in fact stamped 24''-27'':
Can anyone make sense of all of this? The Dorcy sets I mentioned are loose (no box) for sale online, so there's no real way to verify they're actually original sets and not just put together by a clueless seller. In fact some sellers even aren't ashamed to falsely state that these will "fit all wheel sizes"(which while they physically might, they won't provide correct readings).
For instance, with Dorcy, the face of the speedo indicates the wheel size it is intended for, i.e. 20'', 26''. In all the sets I found online, regardless of what the face indicates, the drives are the same - the 26 hole, 2.5'' diameter ones, with no stamping on them. So Dorcy made the adjustment to wheel size in the mechanism of the speedo head rather than the drive?
I found a speedo by Cycle that has 20 stamped on both the speedo face and the drive. Note how this (slightly smaller) drive has 20 holes (not 26):
So now I'm thinking wait, do the number of holes in the drive indicate the size of the wheel?
And to make things more complicated, I found a drive that is in fact stamped 24''-27'':
Can anyone make sense of all of this? The Dorcy sets I mentioned are loose (no box) for sale online, so there's no real way to verify they're actually original sets and not just put together by a clueless seller. In fact some sellers even aren't ashamed to falsely state that these will "fit all wheel sizes"(which while they physically might, they won't provide correct readings).