Special hub requirements for an 11-speed group In a question earlier today (Changing cassette from 8 to 10 or 11 to meet the Shimano 105 5800 groupset) the Op asserts that they would need to change their hub, if they wanted to go from a 10- to 11- speed cassette.

I'm not very clued up on 11-speed systems, was wondering why this is the case? And, presumably, when they say "hub", they mean just the freehub body?



Or do they mean something else/more?
Shimano/SRAM 11 speed cassettes are wider than 8/9/10 speed ones.  So yes, you need a new, wider freehub body, unless your old one was not very old and used a spacer to fit a 10-speed cassette.

People with non-Shimano brand hubs are less likely to find replacement freehub bodies, it seems, leading to replacement of the whole hub, or even the whole wheel if the old rim isn't worth relacing.

For more on this, read the last question and answer here: http://velonews.competitor.com/2013/09/bikes-and-tech/technical-faq/technical-faq-drivetrain-compatibility-for-10-and-11-speed_301392

There's also a compatibility chart here: http://www.slowtwitch.com/Tech/Cassette_Spacers_2013_3978.html

Campagnolo cassettes are the same width for 9, 10, and 11 speeds, so you don't need to do anything in most cases.