Swapping cogs in a cassette?
 

Does anyone still do this? On a 9 speed?

I've long thought about changing from the 12-25 on my bike to maybe even 12-21. I have a triple, so technically I can always use the granny 30T while going up hills--no problem there. However, I honestly ride in the 42T chainring 90% of the time; 42x21 is for hills, 42x17 is generally the flats. I'd like to add maybe 18&16, instead of having the 25/23/21/19/17/15/14/13/12. From what I can see on my current cassette, the 17 is taking the brunt of the load (surprising, since I'd think the 21T hill gear would be getting that abuse).

My only fear is that I'm going to have worse driveline issues, since that would mean I am more likely to use the whole cassette instead of just the middle gears. [I do not to use the 25T while in the middle chainring, and generally avoid the 21T.] I'm already hard on chains (improper oiling). So I'm wondering if I could/should make something like 25/23/21/19/18/17/16/14/13/12--I can live with bigger jumps at either end.

Presuming I could even find gears like that, that is.

You can swap but there are two drawbacks.

First of all it's very expensive compared to buying stock cassettes.

Second, your cassette has the shift gates positioned so the chain can smoothly move to the next sprocket with the teeth phased to accept it, or lined up with the gaps, rather the rollers. That's the glide in Hyper glide. If you switch sizes the phasing is lost (each sprocket is phased based on it's neighbors) so some shifting smoothness can be lost.

Since your changes are subtle the difference may not be to great, but you'll still be spending more than you need to.

9 speed or 10-speed? The "ideal" 12x25 cassette you list is a 10-speed but that configuration (no 15T cog) is not available. A 12x25 10-speed is available with the same range except it has a 15T cog and no 18T. A 9-speed 12x23 cassette is available with the same cogs except it deletes the 25. As noted, buying an entire cassette is cheaper than buying a few individual cogs and works better too.

I have the remnants of some cassettes, spare cogs just laying around waiting for a project. I don't know if they're HG or not - and they are used - but you're welcome to whatever ones I have that you need to fill in missing slots. Just PM me.

I've done swapping, but starting to get away from doing that since I'm not quite as hard up financially.

I've done the 12-21, but found the 18T was nearly redundant between the 17 & 19.
I've settled on a 12-23 for most uses.

http://www.loosescrews.com/index.cgi...d=746935221132

I've found that the 18 fills a nice gap between the 17 and 19 and wouldn't buy a cassette lacking an 18 cog if there were any other options like a triple crank and/or 13 starting cog.

In the 8 speed era I ran 50-40-30 x 13-14-15-16-17-18-19-21 which worked like a 7 speed straight block on the Colorado plains east of Boulder but had a low like 42 x 28 (or 39x26, or 34x23) for the Rockies west.

With 9 cogs I added a 23 on the end and traded the triple for 50-34 which although the over-all range and spacing matched was a bad idea.

With 10 cogs I'll return to the triple with 12-13-14-15-16-17-18-19-21-23 or 13-14-15-16-17-18-19-21-23-26 (I'm 40 pounds fatter and can use the low gear in real mountains).

You can get a restricted school racing cassette which ends with a smallest gear from 13T to as big as I think 17T. That would let you use your big ring a lot more, which will reduce the force on your chain.

If school racers are not restricted in the US you can get them from Germany or the UK.
Rosebikes in the UK have a very good range of cassettes, down to single Shimano sprockets. Miche do a good range of school clusters.

I haven't tried it but another option is to remove the penultimate small cog and insert an extra biggest sprocket. That will break the Hyperglide function but it may not matter if you only use the big cog for long high speed descents. And if you are offered an extra gear to get up the hill are you going to think "no thanks, I insist on Hyperglide"? You can file off the HG index spline to allow the cog to rotate to a better position but it will likely not end up perfectly placed.

When making a custom cassette, to some extent you should be able to preserve HG by trying to obtain sprockets that belong between the cogs they're going between... but if you want to have an 18 between a 17 and a 19, I think you're out of luck on that score. It should mostly be possible to have a matching cog on at least one side, though.

There's a thought... might help in some situations.

You're right, I listed 10 gears on my 9 speed cassette.

I gave into temptation, and just ordered a 12-23 last night (on sale etc). Will see if I like it. If not, it was a cheap experiment. The 25T only got used off-road, which is probably not someplace I oughta ride all that often. The 12-25 actually has a pretty good range, but I just want finer steps in the middle.

I did peer down this morning, and 42x17 chainline wasn't bad--it was biased slightly away from the bike. The new cassette should have the 17T in a similar spot. Climbing in the 21T might be a worse chainline, but again it'll be worth trying.

Thanks.

I've never missed the 18T either but the one cog I really like is also fairly rare and that's the 16T. I had to go to a 12x25 or 12x27 10-speed to get it if I wanted the low gear they provide.