Monday, May 08, 2006

SRAM tech note

Between good and bad, this is slightly to the good side:

A young customer, barely driving age and without a car, crashed his mountain bike and kneecapped his SRAM X-7 trigger shifter for the rear derailleur. The impact snapped off the return lever that releases the derailleur down to higher gears. While repairing the bike I discovered that the shifter would still operate using the nub of the broken lever as a push button.

If the rider had not snapped off his derailleur hanger and disemboweled the derailleur in the same incident, he would have been able to limp around. The ergonomics couldn't be any worse than they were when the shifter was new. Those return levers are tucked inconveniently up under the outer lever.

In other SRAM-related news, we were setting up this year's crop of F600 Cannondales when Ralph discovered that the Shimano LX derailleurs did not seem to want to work with the SRAM shifters.

A charming man named Ed, at SRAM, dismissively told Ralph that there could not possibly be a compatibility issue between a front shifter and derailleur.

"You could shift it with a two-by-four," he snapped.

Look for the SRAM 2X4 Gruppo some time in 2008.

This is the same SRAM that likes to make a big time about their 1:1 actuation ratio and all the precise engineering that goes into their products.

A SRAM derailleur eliminated the problem, which was that the shifter did not seem to be able to pull enough cable to keep the derailleur cage from rubbing the chain in a number of gears.

Subsequently, when I assembled an F600 and confirmed Ralph's findings, we tried to take the matter up with Cannondale. They, too, discounted my couple of decades of wrenching and Ralph's ten years of it, referring to us in an internal email as "that ski shop" that's having trouble adjusting the front derailleurs.

We did indeed get the Shimano derailleur to work with the SRAM shifter once we hung our full body weight on the cable to get as much tension as we could. The results we consider barely adequate, but the corporations involved don't seem inclined to issue any different parts. Once those cables settle in, and any time they loosen up the slightest bit thereafter, the front derailleur cages will rub. Be prepared to use a lot of barrel adjuster to maintain the needed tension.

When riders have to use a lot of barrel adjuster, that means the adjusters are run out far enough to be vulnerable to bending. Inattentive riders may even run them out to the end of the threads. At that point the adjusters wiggle back and forth, damaging the threads of the shifter body itself. This damage can make it impossible to thread the adjuster back in.

Measuring the arms on either side of the pivot of both the SRAM and Shimano derailleur, we found that the arms of the Shimano derailleur were every so slightly asymmetrical. The more speeds you add to a drive train, the more tiny differences make a difference.

But what do we know? We're just idiots in "a ski shop."

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