Originally Posted by
Iride01
Are you certain about the rear hub model. I'm not certain a 11 speed cassette will work with just any 9 speed Shimano rear or what ever yours is.
A FH-TX505-8 is a 8 speed free hub that is compatible with 9 speed cassettes, but I'm not sure if that moves on up the road in compatibility with 11 speed cassettes.
I think the Deore 11-51 cassette he's using is a Shimano mountain cassette. This article indicates that the Shimano 11-speed mountain cassettes are the same width as 10-speed road cassettes (I believe I've read elsewhere that that is accomplished by substantially dishing the largest sprocket; I'll see if I can find that reference too. I'll also see if I can find a better reference.)
https://www.lightbicycle.com/newslet...ty-Manual.html
If that's indeed the case, he may need the 1mm spacer normally required to use a 10-speed cassette on a 8/9/10-speed hub to take up the extra space.