Changer de Braquet

Some people are supremely good at it, reducing complex situations into matters of simple black and white. This isn’t my particular area of expertise; I enjoy wading through the pools of ambiguity a bit too much to go about bludgeoning this beautiful world into absolutes. In fact, I would venture that delighting in nuance is part of what distinguishes La Vie Velominatus from the simple act of riding a bicycle.

I’ve spent the summer wrapping myself in the Rules handed down by the Apostle Museeuw during Keepers Tour 2012, with particular emphasis on Rule #90. Climbing Sur la Plaque is a cruel business, rising upwards under the crushing weight of physics as you fight to maintain your rhythm and momentum. At first, it’s a struggle to maintain speed on the smaller climbs as you learn how to change your pedaling action to compensate for changes in gradient. You focus on loading the pedals and forcing them around; the moment you lose the rhythm, gravity sinks her claws into your tires and tries to drag you back down the hill. On the other hand, if you maintain your cadence and power through the ramps, what is usually an intimidating slope will disappear under your wheels, making molehills of mountains.

If the Big Ring is a hammer, then not every climb is a nail. (I realize too late that referring to the road as a nail is sure to bring the Puncture Apocalypse on today’s ride.) The guns get more massive from the practice of Rule #90, but it comes at a hefty price: souplesse withers like a delicate flower as one seeks to conquer the art of mashing a huge gear. Indeed, one of the great pleasures in Cycling is to sense a certain fluidity of your stroke which belies the feeling of strength in your muscles as you continue to heap coals on the fire.

This requires an art altogether different from moving Sur la Plaque; it relies on turning the pedals at a higher cadence and shifting gear whenever the gradient changes. Rhythm holds court over everything else and is maintained at all costs. As the gradient steepens, the chain is slipped into the next smaller gear; as the gradient eases, it is droped back down. Not every climb suits this style of riding; the rear cluster must be matched perfectly to accomodate the changes in pitch such that maximum speed is maintained and the legs allowed to continue their relentless churn. When synchronized perfectly, it is the gateway to La Volupté; when not: disaster.

Such is the nuance of shifting gear, such is the nature of Cycling.

153 Replies to “Changer de Braquet”

MartinD says:

Oct 11 2012 at 3:14 am

@mouse

@frank

@MartinD

@frank

On the other hand, I’m 100% sure you have a better mechanical advantage in the 53Ã—26 than in the 39Ã—19 or whatever the equivalent-sized gear ratio is in the 39.

Without wanting to seem more of a grumpy old bastard than absolutely necessary …

10 and 11 speed cassettes and compact cranks certainly mean that the idea of putting it in the big ring isn’t what it used to be. My 1977 Peugeot PX-10 came with a 45-52 and 5 speed 13-21. This cluster was of course just used for training. Everyone raced on a 13-17 (a beautiful Regina Oro version for me – probably the classiest thing on the bike). Some friends had 42 tooth inner rings, but I don’t think anyone had a 39.

It was relatively flat where I grew up, but windy enough that a large part of many races was in the small ring.

I think it was some time in the 80″²s when the 39 was introduced after the modern spider was developed. Another good thing. Before that, 42 was as low as you could go.

Wow, a 13Ã—17. Was it hard to see with all that hair on your chest?

Yeah, 13Ã—17 was what you wanted ’cause it looked so fucking cool. You of course would be spat out the back on the first hill, but you’d look cool doing it.

You were right about the timing of modern cranks with the smaller BCD that enabled chainrings t ogo down to 39, but I know for a fact that Campagnolo made either a 40 of 41 that fit on Super Record cranks around about 88 or 89.

I recall being looking on very jealously as my teammate showed his off before the start of the Provincials that year on a very hilly parcours.

There wasn’t anything very steep in South West Victoria. I think the biggest climb I ever did in a race was only 100 m vertical rise or so. Besides we all had 13-17s so it didn’t really matter.

The feeling I remember before getting dropped was switching backwards and forwards between adjacent gears like the 15 and 16 with one feeling too hard to push and the other like I was spinning too fast. The desperate search for that perfect gear was always a sign of impending disaster.
Nate says:

Oct 11 2012 at 4:54 pm

@Cyclops
Beers says:

Oct 11 2012 at 5:45 pm

@frank

@snoov

Interesting, I wonder if the large rings (less friction) balances out with the straighter chain, which I’m assuming also has less friction.

That’s always got my noodle going. With how close the chain rings are on modern cranksets, I’m not sure its a significant difference between being in the 39Ã—25 vs 53Ã—23. But being in a bigger cog in the back is for sure more efficient by a considerable margin; consider turning the wheel by the axle vs turning it by the tire; the farther out the chain is, the better. Similarly, in the big ring, you’re creating better leverage by sitting in the 53.

But the matter is muddied considerably by friction of the chain entering the chainring, less friction by distributing the load over a larger surface and bending the links less, and the bend in the chain as it moves from chain ring to cog.

All delightfully nuanced and messy, per the subject of the article.

Interesting Frank. Considering the chain distance from the axle, you are correct, it should be more efficient to run a chain around a larger curve. Quite some research has worked on exactly how efficient a chain is at transfering power.

I thought of this, and considering the effort applied by the rider to the drivetrain through the fixed length of the crank, the leverage applied to the chainline must be reduced because the force of the resistance you are pedalling against (the hill and your gravitational mass through the chain to the crank) intersects at a point on the crank arm further out and closer to the pedal axle when you are in big ring. Thus reducing the mechanical leverage The Guns have on the drivetrain?

Presuming you are in the same mathematical ratio, with the big ring or the small ring, and The Guns are providing the same effort (your max watts), with the small ring the crank arm has more leverage on the chainline, than in the big ring?

Just a meandering thought, and welcoming your retort.