Monday, September 14, 2009

Derailleurs and Horst Links

I'm stuck in Atlantic City, NJ on business. What a rat race. I think every-other building has Trump in the name. The boardwalk is kind of cool, right on the ocean and all. I have a meeting at the C4ISR Symposium on Tuesday (if you really want to know what that is, you'll have to Google it).

I don't evaluate bike gadgets very often here, but a recent tweak on my Titus Racer-X stands out. I originally had the bike built up with full XTR kit a year ago. I believe only one version of XTR derailleur was available at the time. I've actually been riding the current crop XTR for a couple years now, since I rebuilt my Dean Ti hardtail with the stuff. One thing I noted on the Dean was ghost shifting on gnarly terrain. I think the return spring (high gear normal) was weak, so the derailleur would actually bounce around a bit and cause missed teeth under power. Unnerving.

I put the same rear derailleur model on my Racer-X. It does the same thing. It is not a matter of adjustment or frame geometry. It just doesn't like to be jostled around. The Racer-X had an even more nagging problem. The derailleur would basically sit right against the Horst Link pivot and clatter away, metal to metal, on even the slightest bumpy terrain. This drove me nuts, almost to the point of abandoning gears.

Side view of Shadow derailleur. Note very short cable routing.

Then I caught a review of a Titus FSR suspension bike in a magazine. On that bike, they actually moved the derailleur hanger back, such that it was out of Shimano's spec, but avoided slapping into the bike frame. The review blasted Titus for this, as the chain now did not have enough wrap around the cogs and occasionally slipped. This is unforgivable. Fortunately I did not get one of those Titus models. The magazine article also pointed out that this was totally unnecessary, as the Shimano Shadow derailleur has a hard stop and completely avoids frame slap on Horst Link suspension frames. I promptly put an XT model on order.

Well, my Shadow derailleur came in last week. It is very different from a standard Shimano derailleur. Maybe you've seen the adds for it in the mags. It sits within your frame boundary, thus far less likely to get snagged by roots, rocks or sticks. This is a big deal in New England. They call it the Shadow because it sits within the shadow of your frame. Parts of the derailleur are inverted from a regular derailleur, so pieces come very close to your spokes. Since it has a hard stop about the mounting bolt, it does not need a long loop of cable housing. In fact, I cut out about 75% of the derailleur housing loop. The shift cable now pretty much comes straight down the seatstay into the derailleur. Sticks won't catch that either now.

The Shadow sits inside your frame, protected. End of cable had to be cut off very short, else it made a nice "card in spokes" sound.

I put 85 trail miles on it this weekend. I was pleasantly surprised to find that it not only eliminated derailleur slap against frame, it also completely eliminated ghost shifting on rugged terrain. The XT model feels very beefy, and the springs are very stiff in it. Yet it weighs only about 30g more than the too-light duty XTR model I replaced.

I believe Shimano went too far with the current XTR derailleur. Sure, shifting is feather light and fast, but ghost shifting every time you hammer over root or rock gardens suck. I'm tempted to replace the XTR derailleur on my hardtail too. I believe there is an XTR version of the Shadow available, but for big bucks. All derailleurs should be built like the Shadow.


Anonymous said...

where are you going to bike? Or is a repeat of the stair running on order?


Hill Junkie said...

I don't need shin splints for a week again! Will be back home Tuesday night, so no bike. Body could probably use back to back rest days after this past weekend.

Paul said...

Funny - for a while all XTR was low-normal (aka "rapid rise"), and (in my experience) worked just great. But people complained so they started making high-normal too - but your experience is that it doesn't work well.

I've gotten so used to low-normal shifting (both triggers go to an easier gear, both thumbs go to a harder gear) that I'd get confused with the Shadow.