Categories: Technique

Sur la Plaque: Mechanics of the Big Ring

I’ve been riding for long enough to know that what “feels” good and and what “is” good in terms of technique are two independent sets with a small intersection; it’s very important to put a lot of thought and research into what you’re doing to make sure it offers a benefit.  Research takes “work” and “time”, so I’m not very fond of that approach.  Instead, I like to do a lot of “thinking”, leveraging both my inadequate expertise in mechanics and my unusually high degree of confidence in my ability to reason in order to jump to conclusions that benefit my initial assumptions.

For example, I believe there is an advantage to riding sur la plaque, or in the big ring, as opposed to riding in the same size gear on the small ring.  I generally find that when I’m strong enough to stay on top of my gear, climbing in the big ring feels less cumbersome than when I climb in the small ring at the same speed.  The downside is that it is like playing a game of chicken with your legs; it works very well if you are able to keep the gear turning over smoothly, but should you fall behind the gear, and your speed evaporates as you fall into a spiral of downshifting and decreasing speeds (not to mention morale).

All this can be explained away by having good legs or not (un jour sans), but I think there is a mechanical advantage as well.

First, there is the duration of the effort.  As they say, it never gets easier, you just go faster, but I firmly believe faster is easier, provided you are strong and fit enough to support the effort.  The faster you climb, the less changes in gradient and road surface impact your speed.  Not to mention that while all athletes perform the same amount of work when they cross over the same climb regardless of the duration of their effort, athletes doing so in less time suffer for a shorter period of time than do those who go slower.  Marco Pantani claimed that despite knowing the suffering that was just around the corner before his attacks, he was motivated to go as fast as possible in order to make the suffering end sooner.

Second, there seems to be a mechanical advantage of riding in the big ring.  I’m a little bit hazy on the physics here, but it seems to me that the crank arm is in effect a second-class lever and, while maintaining the same length crank arm (lever) and fulcrum (bottom bracket), by moving into the big ring, you are moving load farther out on the lever, providing a mechanical advantage over the small ring.

WikiPedia defines leverage as:

load arm x load force = effort arm x effort force

In our case, since the speed is constant, that means that the load force (to turn the pedals) is also constant.  And, since the load arm (crank) is a fixed length and the effort arm length is increased when moving the chain to the large chainring, the effort force is reduced in order to maintain a balanced equation, meaning that it doesn’t just feel good to ride sur la plaque, it actually is good.

All that said, this theory completely ignores the energy loss of bending the chain as you start to move the chain from straight at the center of the cassette towards the edge of your cassette, in particular when riding in the big ring and crossing to bigger cogs.  Q-Factor has an impact on how much your chain is bending as you ride in bigger and bigger cogs, but I think there’s a measurable loss if you are crossing your chain completely (big ring to biggest cog); and I suspect is is entirely possible that the big ring’s mechanical advantages are outweighed by losses in chain friction.

frank

The founder of Velominati and curator of The Rules, Frank was born in the Dutch colonies of Minnesota. His boundless physical talents are carefully canceled out by his equally boundless enthusiasm for drinking. Coffee, beer, wine, if it’s in a container, he will enjoy it, a lot of it. He currently lives in Seattle. He loves riding in the rain and scheduling visits with the Man with the Hammer just to be reminded of the privilege it is to feel completely depleted. He holds down a technology job the description of which no-one really understands and his interests outside of Cycling and drinking are Cycling and drinking. As devoted aesthete, the only thing more important to him than riding a bike well is looking good doing it. Frank is co-author along with the other Keepers of the Cog of the popular book, The Rules, The Way of the Cycling Disciple and also writes a monthly column for the magazine, Cyclist. He is also currently working on the first follow-up to The Rules, tentatively entitled The Hardmen. Email him directly at rouleur@velominati.com.

View Comments

  • @Marko
    :)

    I'm not the kind of rider to shirk Rule 5 duties... (Which one is it, Holists or Cogniscenti who think Rule 5 is all that matters?)... basically, I'll ride a bike that makes me go fast, the amount of pain won't change.

  • btw, the dude in the picture for this article sort of looks like Joe Strummer. Not sure if he was a cyclist but he certainly lived his life in the big ring.

  • right on. i always find it entertaining checking out bikes that aren't widely available in the U.S. At least I've never come across a Boardman here. I'll buy a copy of CycloSport America on occasion and dig the adds for Euro bikes I'll never see in my LBS. Looks like a nice bike. I've got the same crankset on my ALAN albeit with c-x sized chainrings (48-36) that oughta get some barbs thrown at me around here.

  • @Marko
    Boardman is a British manufacturer and the company takes it name from and is "run" by Chris Boardman, so I'm not surprised there aren't (m)any in the US.

    Still trying to get used to this double tap stuff. And the thing with buying a bike from Halfords is that basically nothing was setup, I pity the fellow who doesn't know how to index gears and buys a bike from them.

  • @Nathan Edwards
    Word. I'm familiar just don't see them here. Hopefully he won't get bought out by Trek and then have his brand pulled out from under him like Lemond did here ;-)
    That's the evil of bikemarts and online shopping no? Non existant service almost and peeps who think bike maintenance is limited to adjusting saddles, inflating tires, and installing pedals. I guess the upshot is it forces those of us who have no choice but to shop there to become more self-reliant and buy more tools. I'm a perpetual breaker of Rule 58 but then again don't really have a choice. In fact, I just ordered a set of these online this morning, picked them up at cost.

  • @marko
    what the fuck: 23mm tyres?

    @Nathan Edwards @marko
    Boardman has quite a bit of involvement in the brand, designing, soucing eqipment etc. Judging on what he has done so far and his justification and general astuteness, I'd be hugely surprised if the brand was sold on to another bike company. Their biggest task is overcoming bike snobs.

    @brett @Nathan Edwards
    Bollocks to that. I'll get my fitness first before riding up the really big hills. Even my flat ride has around 200m of climbing in a 18km loop. My point, is that you don't go and ride up 15-20% gradients on an easy ride - such as the day before a race. Likewise if you're just coming back from injury and haven't ridden for six months, every railway bridge will seem like a mountain. But you will not find me on a compact.

  • Jarvis :I've also realised that the No Compact Rule should be extended to be No Compacts or Triples. It's all the same, all it does it make you slower. How does that fit into Rule #5. Human nature about not wanting to suffer more than is necessary: if you have a lower gear, you will use it.

    Jarvis is on the mark. If you are initially struggling on a hill in your lowest gear, say a 39x23, but HTFU and keep at it, you'll eventually master the gear on the hill. If you start whining, "I need climbing gears!", and put on a 25 or 27, you'll use them, and use them. In the end, you'll ride slower with the smaller gears.

    Having a Rule prohibiting triples would be embarrassing. Like having a rule prohibiting Levis.

    But I'm all for a Rule on compacts. It is a matter of style. A matter of protecting the history, traditions, and culture of the sport against the wicked forces of capitalism. Outside of making some compacts for legitimate ends, ferocious race-paced 20% grade climbing, they are good only as a tool for separating you from your money. It's the same old game. New innovation leads people to buy new stuff rather than to stick with their time-tested old stuff.

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