cassette mix & match question

[blkhotrod]

i have 2 dura ace 7800 cassettes.
#1 corn cob 21-11 in excellent shape
#2 25-11 older cassette with lower gears pretty bad.

i have a race which has 6000' climbing and need a good cassette.....so can i

take the 25-23-21-19 single piece from the older cassette and put it behind the bottom 6 gears from the good 21-11 cassette= 25-23-21-19-16-15-14-13-12-11

thanks

 

[alfeng]

Sure. If the larger cogs are in reasonably good condition, then "Why not?"

BUT, try it before the race to ensure that there aren't any conflicts with the chain.

 

[maander`]

i have 2 dura ace 7800 cassettes.
#1 corn cob 21-11 in excellent shape
#2 25-11 older cassette with lower gears pretty bad.

i have a race which has 6000' climbing and need a good cassette.....so can i

take the 25-23-21-19 single piece from the older cassette and put it behind the bottom 6 gears from the good 21-11 cassette= 25-23-21-19-16-15-14-13-12-11

thanks

The 16 - 19 is a bit of a jump isn't it?

 

[alienator]

The 16 - 19 is a bit of a jump isn't it?

16-19 is a real big jump, and it's in what is a sweet spot on a cassette for a lot of people. It's likely because of the 11 tooth cog on the one cassette. 11 teeth is hard to justify sometimes. On a descente in 50/11 at 100 rpm, that'll give you 35 mph. Of course with a 53 it's faster, at 37 mph. A lot of people would argue that an 11t doesn't even make much sense on a descent, that a 12t wouldn't cost you that much. Plus, with a 12t, you can another cog in that 16-19t range. FWIW, a 53/12 at 100 rpm gives you a speed of almost 35 mph. You're talking about gaining 2 mph with an 11t high gear instead of a 12t (This was assuming a tire circumference of 2100 mm......I thought I'd be generous.).

 

[swampy1970]

Did Shimano ever officially produce a 11-25 Dura Ace 7800 cassette? I know they now make one for the 7900 group.

On the 12-25 the 17-19 and 21-23-25 were combined on the alloy carrier.
On the 11-21 the 17-18 and 19-21 were combined.
So unless you get creative with a dremel or a drill you're stuck with the 5 largest sprockets...

If you're mixing a 11-21 and a 12-25 then you could get:

11,12,13,14,15,17,19,21,23,25