Sunday, November 11, 2018

Sheet metal cogs and tinfoil chains

An article on Ars Technica extolling the "improvements" in bike technology since the 1980s has been popping up on social media today to give my ulcer a workout. Observations by technophiles who aren't mechanics help fuel the headlong rush of the bike industry into fragile technology that is a pain in the ass to maintain, and often impossible to fix.

People love gizmos. Bikes started out on the forefront of mechanical innovation in the 19th Century. As they were superseded by the automobile, they languished in neglect, evolving only a little until influxes of cash and public interest in the 1970s and '80s inspired a rising curve of development that really foamed up in the 1990s with the mountain bike boom and the expansion of the aero/tri segment.

The 1990s brought engineers off the sidelines as hobbyist users and shoved them deep into the design process. Much of this was fueled by the demand for mountain bike suspension systems that would work with the heavy and inefficient human engine, but once you get a serious case of engineering it spreads far and fast. A public conditioned to crave expensive new technological things and accept that they are junk within a year or two at most was ripe for such changes in the bike industry.

For the first 100 years or so, bicycles were evolved machines, not designed machines. Even now, the designers have to study what has been working and figure out why it did before they can screw with it. A hundred years of trial and error honed the vehicle in its various forms to meet a variety of needs. A couple of decades of technological promiscuity have led to some genuine improvements and a lot of expensive and unhelpful complications, not to say downright handicaps. People who think in absolute terms will laud the vertical dropout and its offspring, the through-axle. People who, on the other hand, understand the value of a variable rear wheel position will be stockpiling old steel frames with long horizontal dropouts. They're not just for fixies. 

I would go through the article and dismantle it point by point, but if I read it for more than a few seconds my head explodes, so I'm not going to do that. I have to accept that the battle for public perception was lost a long time ago. The best I can do is put better advice out there for the few people  who will still appreciate the versatility and freedom that a simpler bike offers to the average underpaid toiler. As it was in the 1880s, is now and ever shall be, a bike is a good investment for a working stiff, as long as it is well chosen.

A Trek Fuel full suspension mountain bike last week provided a nifty example of how a designed weak link, intended to fail under stress to preserve more important and expensive parts of a system, can be bypassed when those more expensive parts become more fragile in the greedy quest for more "features." The rear derailleur hanger of old steel and aluminum frames used to be part of the dropout on that side. It would occasionally get bent on a road bike, in a crash, or if an improperly adjusted derailleur shifted into the spokes. With the coming of mountain biking, bent hangers became common because riders would pick up sticks or other debris in the chain and drag it into the derailleur as they continued to pedal. Steel frames could be straightened from some pretty alarming looking deviations, but an aluminum dropout was usually ruined. Aluminum frame builders started providing replaceable hangers. The concept spread to become the norm. Derailleur hangers are now one of several jigsaw puzzles that repair facilities have to solve on a regular basis.

Some early replaceable hangers were made of such soft alloy that they actually bent just from the ordinary stress of shifting. The first run of hangers on Specialized Stumpjumpers in the mid 1990s were notorious for this. If they weren't, they should be. The Big S eventually started making hangers out of steel, and has now evolved functional alloy versions, but it actually took them a couple of years to face their blunder. Denial was as big a force as "innovation" in the bike industry in the 1990s.

Having finally hit the right level of fragility in the hanger for the drive trains of the time, the industry looked at it no more. They moved on to adding as many cogs as possible to the rear cassette and making chains as thin as necessary to fit the stack of saw blades that now makes up a modern gear cluster.

One dozen sheet metal cogs, so thin that they have to be pinned together with little rivets to keep the damn things from folding under load

Compare the 8-speed chain (top) with the 12-speed chain (bottom) While either can be bent with sufficient stress, the force required to tweak the tinfoil specimen is far less.

The cassette in the top picture is a 12-speed 10-50 SRAM Eagle. Ten to fifty. The biggest cog is the size of a chainring. It's the thickness of a chainring, too. They can't get away from that. Anything that big has to have the strength to support itself, connecting rivets or not. 

By killing off front derailleurs, the industry avoids the biggest bender of chains, but I have ridden double and triple front chainsets for 43 years and never bent a chain. Meanwhile, to provide some vestige of the former range of available gears, the industry has to cram more cogs in the back, over a range that requires a rear derailleur like a crane to cover the span and manage the chain wrap. That's a long cage, my friends. And a skinny, skinny chain. The chain line sprawls so widely that the chain is vulnerable to bending just from the normal deviation. Add a traumatic factor like a stick in that dangly derailleur cage and you'll be lucky to get away without trashing the chain along with whatever else gets mangled.

In the case of the Trek Fuel, the tech who checked it in saw the twist of the rear derailleur and stated that the bike needed a new derailleur hanger. But when I looked at the hanger it appeared pretty straight. The alignment gauge confirmed this. This is after we had to buy a new alignment gauge, because the old Park DAG-1 doesn't have a long enough nozzle to get into a derailleur hanger buried beneath rear suspension pivots. Our old, old Campy gauge worked, but the DAG series has a more sophisticated system for checking alignment around the circumference of the rim. It's tweakier to use, but gives a more fine-tuned look at any problems. Or, in this case, lack thereof.

The robust replaceable hanger had stood firm. The evolution of the drive train has moved the weakness in the system out to the $125 derailleur instead of the $32 hanger.

Once I replaced the derailleur, the drive train made a very slight clink noise while running the chain on one of the cogs down on the high end of the cluster. Thinking that this may have been the gear in use when the stick jammed, I wondered whether the sheet metal cog had picked up a slight kink. Because cog teeth normally exhibit a cyclic pattern of offset teeth, a slight but larger deviation is hard to assess. Because the clusters are all riveted together, if any single cog had been rendered unusable, the rider would have had to purchase an entire cassette at $215 retail. If it was only the chain, that's a mere $42. But you can see how the cash cost of a minor mishap can add up very quickly. The fail-safe part of the system was the least affected by the accident in which it was intended to take the most damage. That stress was distributed to the rest of the parts. 

The damaged derailleur was bent in the middle, so that the upper and lower pivots were no longer parallel. The rider said he stopped pedaling the instant he realized that the stick was in there, but the derailleur still went into the spokes. With a tubeless tire, spoke repairs can extend to dismounting the tire and possibly having to replace the sealed rim strip. Fortunately, the bends in the spokes did not appear too sharp, which would create a stress riser. I was able the true out the minor deviation in the rim without racking up uneven tension.

An autopsy on the bent derailleur revealed that the four pivot pins of the parallelogram were bent, making the derailleur twist increasingly as the rider shifted toward the larger cogs. You can get some replacement parts for the SRAM Eagle 1x12 derailleur, but not those parts. Removing them is a destructive process, because they are riveted. Just like SRAM Double Tap road shifters, the part you can get is not in the area that actually breaks.

I'll keep taking the money to work on this crap, but I will never stop pointing out that it's expensive, ephemeral bullshit: the exact antithesis of everything that made bikes a great piece of technology for decades. The mythical free market demonstrates time and again that the consumer's taste for excruciatingly engineered junk sucks all the money away from simple, durable items of lasting quality.

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