More gears - new cassette - job done - right???

WRONG!!!

It would be easy to think that you might change (say) an 8 speed cassette for a 10 speed and with a bit of twiddling to re index the gears all will be fine - but its not the case!

Your shifters have been set up very carefully in the factory to shift a number of times and that cant be changed. They have also been set up to shift the correct distance between the cogs. Why??? Well if you look at the admittedly poor photo below what I was trying to show is that the 10,9 and 8 speed cassettes are all about the same width (or height in this picture)

What you will also hopefully see is that the gaps between the gears are different (compare the 10 with the 8)

So an 8 speed shifter wouldn't be able to cope with the first(or last) 8 cogs on a 10 speed cassette - the gaps are all wrong.

What you CAN do though - is swap 8,9 and 10 speed cassettes on the same freehub - so if you want to go from an 8 speed to a 10 speed you will need a new cassette and a new shifter....and a chain (the 10 speed chain will be narrower) - but not a new freehub / wheel.

8/9/10 to 11 speed? well......the 11 speed cassette is actually taller than the others - so if your freehub is already 11 speed compatible you should be OK - if not - hey - new wheels!!!! Result!!!

#Science