Wednesday, July 9, 2008

What's in the stand today...

...or yesterday. This bike will be traversing the California Alps during this weekend's Death Ride. Its owner did a final, long 95 mile ride through Sonoma County's back roads last week. After that ride, he felt like the 50/34 coupled with a 12-27 might not be sufficient to get him over all the five passes of the long, 129 mile option - especially the initial Ebbett's Pass 10 mile, 7.5% to 10% grade with a finishing mile in the 12% grade range. And he's a very strong rider too.

He's running a 10-speed Dura Ace STI shifter. There just aren't many options (I've got an idea on how to make a larger range 10-speed cassette based on some Giro d' Italia tech reports - more later) for lower gearing with this set-up. A triple crankset was out of the question so here's what I came up with:

J-Tek Shiftmate #2. This handy gizmo is a pulley system that effective changes the cable pull of a Shimano 10-speed shifter so that each click moves the derailleur across each cog of a 9-speed cogset.

9-speed? But this is a 10-speed bike? Yep, 9-speeds. I converted his bike to a 9-speed drivetrain allowing the use of an 11-34 XT cassette. 50/11 for bombing down the passes and a 34/34 as a bailout for spinning up the pass. Even a standard road triple with a 30/27 doesn't have this low of a gear.

Because he also had a short cage Dura Ace derailleur that would have the capacity to wrap that much chain, I threw on a sweet M-952 XTR derailleur I had laying around (doesn't everyone?).

At first, the shifing was a little vague. Would shift up fine, but down shift a little rough. When down shifts were working fine, upshifts weren't clean. About 80% of this I attributed to the cable taking a better seat around the pulley. It wraps around the pulley twice and with a brand new cable there was some initial seating the cable had to do to wrap tightly around the pulley. The other 20% is due to the Mrazek's cable stops which are threaded into the frame and are allowed to turn freely to find their own cable line. Actually, I think it causes the shifting to be less than precise - which was confirmed by the owner saying that shifting was always a little slow. In my attempt to get the system to work perfectly to my expectations, I could only succeed in getting it to work as well as it had previously - which means it worked just fine.

There was one trick up my sleeve that did help shifting. This generation of XTR derailleur has a neat feature that increases the spring tension in the derailleur. By turning the silver screw in the photo 180 degrees, you can increase the spring tension. The derailleur now returned with a more positive feel.

Ready to tackle the Death Ride. It's an odd looking frame, but is super comfortable, according to the owner, and that's what counts.

(What's playing: Nick Lowe Endless Sleep)


Anonymous said...

IRD makes a 10 speed 11-34 cassette. Not that it matters now. :)

Guitar Ted said...

Hey, nice solution with the parts on hand. Good show!

(I'm just a little jealous of your XTR derailluer there though. Wish they would have stuck with that)