A couple of weeks ago, we had a lively and interesting conversation here on the blog about the pros and cons of simplified 1×9 derailleur drivetrains. In the post that launched the discussion, I brought up the fact that I rarely, if ever, use anything other than the center chainring on my city bikes:
I’d say that I’m going to give a 1×9 drivetrain a try, but the fact is, I’ve effectively been using a 1×9 drivetrain for a number of years. You only have to look at my crank to see what I mean; the outer ring was replaced with a chainguard long ago, and the inner ring has zero wear on it. I do plan on replacing the triple with a single crank, if for no other reason than to make it official.
Well, yesterday afternoon I “made it official” by swapping the Sugino XD2 “Quickbeam” crank and 110mm Shimano UN54 bottom bracket on my LHT for a Sugino RD2 track crank (for 3/32″ chain) and 103mm Sugino BB-103 bottom bracket. Because I’d already removed the front derailleur and shifter/cable, there was nothing to do other than swap the BB and crank. It certainly wasn’t necessary to replace the crank, but I no longer had a need for a double or triple on this bike, and track cranks provide a few advantages:
- Track cranks are lighter than doubles or triples. This is the most often cited, but least important reason for swapping cranks as far as I’m concerned.
- Track rings are less likely to cause chain derailment. Because most chainrings designed for doubles and triples have a small number of shortened teeth to improve upshifting, at least in theory, they’re more likely to cause chain derailment. Honestly, in practice I haven’t found this to be the case (I’ve yet to drop a chain on a road bike set up sans front derailleur), but it’s something to be aware of if you’re running a double or triple sans derailleur and regular derailments become an issue.
- Track cranks have lower Q-factors than doubles or triples. This is the big one, and it’s certainly the most compelling reason to run a dedicated 1×9. Q-factor (aka “tread”) is defined as the horizontal width of the cranks measured from the outside to the outside (where the pedals attach). The lower the Q-factor, the narrower the distance between the rider’s feet, and the less strain there is on hips, knees, and ankles. A low Q-factor places the legs in a more natural position, and because we walk with our hips, knees, and feet in vertical alignment, it’s not really possible to have a Q-factor that’s too low. Besides providing this significant ergonomic advantage over double and triple cranks, low Q-factor cranks also provide more pedal clearance while cornering.
I’m happy to report the swap went without a hitch and the new crank looks fabulous. On the 103mm BB, the chainline is 45mm, which perfectly aligns the chainring with the center of the rear cluster (see above). The major plus is that the Q-factor dropped by a full 20mm, from 165mm with the XD2, down to 145mm with the RD2. This is not an insignificant difference, and I’m sure my worn out knee will be thanking me for it in the coming months.
The only remaining question is what, if anything, to do about a chainguard. Because I don’t like the feel of my pant cuff rubbing a chainguard on every pedal stroke, I often ride with a cuff strap anyway, so I’m going to go without a guard for the time being and see how it works out.