I visited a HD Store looking to purchase a set of HD Black Typhoone Wheels (17 rear and 21 front) but I was told that the 21" wheel could not be mounted on the original forks due to some "spacing issues" that the Spacer Kit could not resolve; and hence I would have to undergo major changes (including changing the fork) in order to place the 21" HD Black Typhoone wheel. HD "specialist" reccomended me not doing that since it would be very costly; but still I immediately replied back stating that my Street Bob already had a 21" spoke wheel, and that I did not understand exactly what they where trying to explain to me; it just did not make sense! Isn't a 21" spoke wheel the same as a 21" solid wheel? (in terms of height) Cause I know that the width of tire has to be a certain size for the wheel and space in the front fender, but it still does not make any sense that I have to undergo major changes. Any one has any answers?

 

Harley have in recent years fitted 1 inch diameter bearings and wheel spindles to some models. I don't know the answer to your question, but it is possible you have 3/4 inch bearings and spindle. If so, the ends of your forks are machined to take a 3/4 spindle not 1 inch.

That's the best I can do! May be nothing to do with diameter, but how the wheel is fitted to the bike.