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.
So moving to a compact drive on my new bike I found that it’s more challenging for me to stay on top of the large chainring. On my old bike I was on the large chainring probably 90% of the time, now I’m on it much much less than that. I like the new look of the velominati btw.
@Marko
Hm, interesting…does that conflict with the theory here? I think it might. I would think your big ring, whether or not it’s compact, should have an advantage over the small ring, and that a bigger ring is better – provided you can get on top of the gear, so I don’t know if what you’re feeling is mechanical or some other factor. We really need our resident physicist, Jim, to chime in here.
Are there maybe other factors going on? Are you in the same position relative to the BB? Maybe you’re spinning more these days than you did before?
And thanks, re: the site. We’re working to get it easier to get to archived content, since readers seem to focus on the most recent post, we’ve simplified the main layout, showcasing comments and recent, popular, and random posts. I’m glad you like it.
Since I’ve swapped to a 34/50 compact crank (I’m old) – It’s changed my riding style. I now live in the big chainring and only use the 34 for actual climbing.
Old school me cringed at using the big ring/big cassette combo for awhile – but now I don’t care. It works without a problem (I’m running 10 speed Ultegra).
With the 50, I find myself going a bit faster and hitting hills a little more aggressively then usual. It’s almost turned my bike into an actual “10 speed” with the 34 ring only used as a bail out gear for steep climbs.
At first, I wasn’t sure I liked the compact set up, but now after a year or so – I dig it.
@Dan O
I haven’t gone compact mostly because I can’t get the Record crank in a 177.5 in anything other than the standard fitting. It would be great, though, because it is so easy to pull the cranks, you could swap out if you wanted to.
I have, however, made the plunge to a 25T pie plate in the back (up from my 11-21 block back in the flatland!) and I’m seriously considering a 26T; since the larger cog in the back should offer the same mechanical advantage with regard not to the crank, but to the wheel. I spend lots of time in the ol’ 39×25 here in Seattle on these grades!
It could just be that I’m fatter and out of shaper. Thing is though, I’m about 2-3 kph faster on my regular routes than I was on my old bike. But i’m mostly on the small ring. So on the one hand I feel like a huge Nancy and on the other I feel like Thor. As far as fit goes, my new bike is certainly more comfy. Which reminds me, I gotta send in those riding position pics for public scrutiny
@Marko
Well, of course you could be fatter or out of shaper, but that doesn’t match up to the 2-3 extra kph’s of love you’re feeling on the training rides.
I’m wondering if this is less a mechanical advantage thing and more just a change in position and new pedaling style? Is it possible you were pushing gears that were too big on the old bike and now you’re just settling into a higher cadence that may work better with your physiology?
I don’t think the size ring you’re pushing is a reflection of your Nanciness. I think the amount you piss and moan about inclement weather is a reflection on your Nanciness and I don’t hear any of that, so we’re good. And, your extra kph’s are definitely a reflection on your Thorness.
The Dutch seem at once scathing and complimentary. How duplicitous.
@Marko
Ha! And the funny thing is, I thought I was being really supportive. The Dutch are so awesome, we don’t even know when we’re scathing!
@Marko
Hmmmmm…….you don’t know Nancy like I know Nancy. I just got passed by a woman today and she was on a compact crank, she spun by as I was crushing the old 39×26 in a sweaty lather. MF’er.
I rented a carbon Trek with a compact crank in Utah and I dug it, maybe the 39 is holding me back? Or I’m an old weak pussy……I’ll let some Dutch guy do the math. I’m afraid to.
Yeah John, I surely would have been passed by her as well or inumerable other Nancy-haters. I’m lucky though, there are only perhaps 15 dedicated cyclists where I live and I’m one of the more fit ones so that doesn’t happen to me often. All my Nanciness comes from within.
and from the Dutch
@Marko
@john
The worst is being out on my swett rig, my kit just so, rockin’ around town like a tough-ass before getting handily passed on a climb by some commuter with a messenger bag, wearing skinny jeans, and riding a fixie. That sound you’re hearing? Deflating ego.
Yup, that would sting a little, Frank.
Trek have done well from Greg in the past when he was the sole American champion so its a shame that things have come to this level now
@Dan O
I destroyed a rear deraillier by crossing the chain… Basically, it caused the chain to come off and get wedged between the chainrings and the chain stay with catastrophic effects… so now I don’t cross the chain.
Can’t you delete this post?
I have just noticed the need for a new rule. Thou shalt never run a compact chainset.
@Jarvis
@david
Noooo! Please only make that a Rule in the Cognoscenti Rulebook. I don’t race, I’m an old bastard, there are steep unavoidable climbs everywhere I turn out here. The compact crankset is my fall back position. I haven’t gone there yet but it’s that or the emergency room or death on the side of the road in the dirt fumbling for my cell phone to call 911 or awaiting the Grim Reaper.
OK, fair enough, maybe that’s what we are talking about? HTFU you big pussy.
@john @all
My suggestion is not only based on style, but on practice as well. When I returned to road cycling (short, boring story), I was on a budget and bought a cheap Pinarello. It came with a compact chainset, it was the worst piece of cycling equipment I’ve used since Bio-pace chainrings. I had to convert each gear into the 52/39 equivalent. It is moronic. I have since replaced it with a proper chainset.
My velomihottie tried the compact for a week before demanding that I remove it and out a proper chainset back on.
It is far more acceptable to put a 28tooth sprocket on the cassette than it is to run a compact.
I must protest. Until I started looking at new bikes I would have agreed. But then, being a math(s) student I did the math(s). If I never/rarely spin out my 53/12 and often don’t even sprint in it, then a 50/12 will probably do… if it doesn’t, I’ll go out and buy a 11-25 Cassette. Besides, try climbing some of the steep stuff round here on a 39/25 when you’re training below 80% HR
I bought said new bike today…
@Jarvis
Yes, it’s Jarvis’ idea. I like it, though. I second the nomination.
@john
NAILED IT. (Said with hand gesture and a soothing timbre to my voice)
@Jarvis
Mine demo’d a Cervelo R3 SL with one installed and nearly refused to buy the bike, she hated it so much. Even going up a 15% grade on the test run, she said, “Fuck this thing. Going into the low gear is like dropping the anchor.”
What’s a compact chainset?
@Nathan Edwards
That’s actually an excellent point. If you’re a giant pussy on the descents, a compact might make sense.
@Steampunk
Same thing as Viagra.
@Nathan Edwards
As much as we love hearing that, that comment is useless without a photo.
@all
Drinking beer and posting is awesome.
@frank
You damn kids with your young bodies and your hard-as-nails wives. The compact(50 and 34 chainrings…Steampunk) only makes sense in the mountains and if you use it to train, like Nathan. You do lose the 53×12 or 53×11 downhill/tailwind ass hauling but it might offset the can’t sit down or bike flips backward, completely redlined, I’m considering walking up this fucker, 20% wall, 39×26 grind I face around here, occasionally, because I’m a big pussy.
@frank
like Jon Stewart?
Drinking beer and posting is awesome. hehehee
@john
I hear tell your velomihottie will drop every one of us on June 19.
@Nathan Edwards It sounds like you are going to race, or are racing, if you want to train strictly below 80% of your max HR. Well, if you are, consider. It’s very easy to spin out a 53×12 in a pack with a 5-10 mph tailwind, if that. It happens all the time. You are likely to get dropped with a 50 x 12, unless you can turn the pedals far faster than everyone else. And if you’re going uphill, aren’t you going downhill? You may get dropped racing downhill with a 50×12. And you’ll never win a downhill sprint.
You may know more than I about compacts. I don’t know anyone with one, but, from what I understand the pros use them only on very steep uphill finishes.
@david Let me rephrase that, following Rule #5. You will get dropped racing down hill.
@frank
shhhhhhhhh! She thinks she will but only because she can drop my sorry ass. She beat me up Mt Washington. She has lost touch with that lonely feeling of going anaerobic and watching people disappear up the road.
@david
For solo training, I think a compact makes sense. It gives you a nice, smooth block with relatively lower gears.
The same way vaseline gives you a nice smooth…Lets just say the standard is better.
I ride a compact. Made the switch through attrition. Came on my cross bike, got moved to the new road frame due to compatability issues and dwells there. Call me a pussy but I like it. It hasn’t made a difference in my riding, only my following of Rule #5 has. I don’t race though (if I did I’d have to drive 5 hours every weekend) so I can see those points. It comes down to the cassette. One of my wheelsets has a 12-27 and the other an 11-25. Big difference there.
@frank That looked like it was about to be a first class piece of sarcasm. Why hold back? Run out of beer?
I still ride a 53-42 and yes there are times when it would be nice to have a bit more spin but right now when I am trying to peak in three weeks a 39 would just seem girlie?
The disadvantage is that you’ll look like Cadel Evans, manhandling his bike, rocking back and forth like drunk sailor trying to find the next bar in the attempt to use his entire body weight to move the pedals one more revolution. The switch to 39s definitely boosted the elegance of the sport.
You know, you can get 52t rings for compact cranksets. So you can have a 52/11, with a 36 or 34 and a 21, 23 or 25 out back for your low gear, depending on how many hills you ride.
In Wellington, compacts make sense. I’ve never run out of a top gear with a 50/11. And even this guy ran compact when he lived here, and he could tear all of you a new one just by looking at you.
@frank
If you insist http://www.facebook.com/album.php?aid=433745&id=661440205&l=8cddb188be
I’ll ride for a while and then might buy an 11-25 then I’ll have a bigger ratio than the 53-12 I have on my other bikes, and I’ve never been dropped for anything other than being worse than the others.
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.
I have requirements for a certain level of fitness, any hill/mountain (not sure we have mountains in the UK) that i can’t get up in 39×25, I don’t go up until I’m fit enough. This does mean that on my return to cycling I will be riding up and down the only flat road in the area for months.
I raced on a compact once – I was on a borrowed bike – horribly unfit and still ran out gears
@Rob
agree a 39 is girlie if you’re only three weeks from peaking. When I’m fit*, I’ll ditch the 39 in favour of a 42, I get a better climbing rhythm on a 42.
@john
my wife isn’t hard-as-nails, but she is a Velomihottie.
@Nathan Edwards
Why are you riding up steep hills when on training rides of 80%HR? Or do you not have a choice? If the latter surely the logic works that if you stick with the 39, you will get fit enough to get up the hill at 80%HR, whereas getting a compact just stalls your fitness at it’s current level
*can’t see this happening any year soon
@Jarvis
Got no choice really… probably just my style. Don’t worry I still know how to suffer and when it’s not a sub 80% ride some of these climbs are done at 50rpm or less in a 39-25. I can Rule #5 but I’d rather not destroy my knees doing it.
And yes, we have no mountains in the UK, but we do have some steep stuff… just doesn’t go on as long as the Zoncolan.
@Nathan Edwards
So where are you? I was recently trying to class some of the climbs around these parts. The longest climb I can come up with is about 10km and it’s on my doorstep.
@Jarvis
Durham (University)
Longest round here is a bit shorter than that I think, at least one that has any gradient. I think theres one that goes for many km at about 5%, only ridden that one in thick fog/mist, so I have no idea what it looks like.
Jarvis
Avoiding hills because you are too macho to ride a compact is the epitome of soft. While you’re riding around on the flats, real men are climbing hills…
It’s a bit like this…
New Rule: No compacts, triples and knees are not an excuse. HTFU