Originally Posted by
rm -rf
10 speed adds one more step in the middle.
9 speed 12-25 cassette:
12-13-14-15-17-19-21-23-25
10 speed 12-25 adds the 16 tooth cog.
12-13-14-15-16-17-19-21-23-25
From
Sheldon Brown's gear calculator--A list of the percentage difference between gears. A 9 speed would have a 13% jump from the 15 to the 17 cog. That's a pretty noticeable difference for me. I tend to shift often, to find the gear that's "just right". But is it worth a lot more expense?
12 tooth
8.3 % difference
13
7.7 %
14
7.1 %
15
6.7 %
16
6.3 %
17
11.8 %
19
10.5 %
21
9.5 %
23
8.7 %
25
This is very good response - cog 16 is indeed very good to have, but the alternative is compact crank 50/34 with 12-23 9 speed cassette, cog 16 included, combination which provides you with very decent transfer ratio range, if you don't race.
Other than that, for a lot of folks it's worth having 10 sp just because of this and problems with 9 sp spares - 10 speed is here to stay for a very long time, 9 sp is fading out.
Also, standard 53/39 crankset with 13-25 9 speed cassette is still very good combo, cheap, only 8% narrower transfer ratio range comparing the above compact combo.
Trust me, you can go far and fast with this one.
cheers