Originally Posted by
Jacque Lucque
Not quite so. The vast majority of modern freehubs have spacing for 9 speed cassette's and if you wish to run 8, you use a spacer in it's place.
Close, but no cigar.
A 9-speed cassette puts 9 cogs in the same amount of space that an 8-speed cassette puts 8 cogs. Obviously they have to be spaced more closely. Both the cogs and the spacers between the cogs are different.
To turn an 8-speed wheel into a 9-speed, just install a new 9-speed cassette. It'll even come with it's own new lockring.