Thursday, April 8, 2010

The Prince And The Pea

At the risk of beating a long-dead horse, how about one more spring tuneup post?

My old cassette: eight speeds, 11-28. My new cassette: eight speeds, 11-30. 

No big deal, right? Just a slightly lower stump-puller. Nothing wrong with that.

But look closer. Old cassette: 11-12-14-16-18-21-24-28. New cassette: 11-13-15-17-20-23-26-30. 

But again, no big deal, right? Just a one-tooth difference per cog across the meat of the order. Odds instead of evens. Who cares?

Um, me. Over the last couple days, it's seemed like every gear was just in the wrong place. I was either spinning like a maniac or grinding my kneecaps -- and with my mom recovering from double knee replacement this week (hi, Mom! get well soon!) I do not want to put any undue strain on my hinges.

So, being compulsive, I went to the gear chart (my favorite was created by the late, great Sheldon Brown) and found that a 44-tooth ring would shift those odds back to almost-perfection... but that ring would be uncomfortably close to my chainstay (even the 42 is pushing it).

Grinding the gears in my head, it dawned on me... the tandem has an 11-32 eight on it. That's 11-12-14-16-18-21-26-32. Evens instead of odds. The lower six an exact match for my old 11-28. And lookee there, an even lower 32-tooth stump-puller. Cool! The test fitting in the stand was a success: my mid-cage rear derailleur handles the 32, and my chain is just barely long enough (I don't mind pushing that, since a short chain helps prevent dropsies on a one-ring setup). I'm taking it on a test ride as soon as I hit "publish" to see how it performs in reality.

(Before anyone accuses me of robbing the tandem to pay the single, the 11-30 immediately went on the two-seater. I always feel like I'm in the wrong gear on that bike anyway, so maybe this will help. And losing a 32-tooth low to a 30 isn't such a big deal when you can bail to a tiny little granny ring.)

Test ride time. Wish me luck!

1 comment:

Anonymous said...

Yep, always run the numbers! And try to learn where the gears all are, assuming that the gear chart isn't filled with duplicates.

the 13-15-17-20-23-26-30 sequence is remarkably evenly spaced, and can be used to build a good half step (or 1 1/2 step) gear arrangement. Not sure how it compares to the 12-28 you mention.

that reminds me that I need to tweak my go-fast 'bent.... need to go to a smaller granny, and install a freewheel with a smaller range. The gears with that 11-30 9 speed cassette are just too widely spaced. A nice 12-27 9 speed works much better! I might end up spinning out the 52 x 12 sometime (especially on a 650C 'bent), but it's worth it.

have fun,

Steve K.
in central IL