11sp replacement cassette wont fit!

I have a rear wheel with a DT Swiss 240 hub with a HG freehub. Its mounted to a WTB i19 650b rim that i use on my gravel bike.

I have just removed a Shimano 11sp cassette. The lockring is marked CS-HG800-11.

I am trying to fit a Shimano 105 cassette with lockring marked Shimano CS-5800, but it wont fit. There are no spacers on the freehub but the smallest sprocket on the cassette just turns and doesnt engage with the freehub splines. I cant get a lockring to fit. Its as if the new cassette is wider than the old one, yet they are both 11sp.

What am i doing wrong? Can anyone shed any light on the issue.

Thanks

Ian

Isn’t HG800 an 11-34 variant, which fits on a 10-speed hub, but has spacer to fit on 11-speed hub?

Did you change cassette size?

Road 11 speed cassettes are wider than MTB ones. I think the changerover is the 11/34 cassette.

You might have an 10 speed road/MTB freehub body.

Ha, it appears this is an mtb hub and i need the narrow hg800 cassette.

Thanks all….argh!

You have a 10 spd (with 11 cogs) cassette in the HG800 and an 11 speed road cassette in the 5800. You will need the 11 speed road freehub to go with it.

I never remember which way round this is, and invariable put a spacer on when one isn’t needed or (like the op) wonder why my lock ring isn’t locking anything…

Change the free hub or do as I have done many times. Take a grinder to the splines until the cassette goes on properly. I believe it is 1.86 mm you take off. Got about a dozen hubs that use 11 speeds cassettes. 4 started life that way. The rest are modified as above.