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.
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Hoho.
@david
We have a few 20% gradients round here (not that I've measured them), defo alot of 12% stuff, that's what the compact will be useful for. And yes I will be riding up the 5% in the 50 or in 34/15, and still at 90-100rpm.
There are a lot of implicit references to Rule #10 in the recent conversation. If there's a contradiction in the Cognoscenti way, it's striking a tidy balance between performance and pushing body and mind as close to the redline for as long as possible.
There's a fair amount of hills around here that are nasty bastards at 10% and a few of 18-20%. All I know is that right now I need a compact to get up them without dying.
Mind you, I've never found it easy to push a 53x12 on a flat solo, so maybe I am a huge girl.
700C Wheel At 90rpm (taken from slowtwitch)
53-39 Rings, 11-21 Cogs 50-34 Rings, 11-21 Cogset
High speed 33.2 MPH 31.3 MPH
Low speed 12.8 MPH 11.5 MPH
Changes between each gear are the same (cssettes re the same). The tradeoff is easier climbing as the expense of a small loss of top speed. This s the lightest configuration for either set up.
53-39 Rings, 11-23 Cogs 50-34 Rings, 11-21 Cogset
High speed 33.2 MPH 31.3 MPH
Low speed 11.7 MPH 11.5 MPH
Low speed now almost the same. 11-23 cassette is heaver with gear ratios wider apart.
53-39 Rings, 12-25 Cogs 50-34 Rings, 11-21 Cogset
High speed 30.42 MPH 31.3 MPH
Low speed 10.74 MPH 11.5 MPH
The 12-25 cassette lowers the top speed on the conventional Crankset and makes climbing easier but at the cost of even wider gear ratios and weight.
53-39 Rings, 12-25 Cogs 50-34 Rings, 11-23 Cogset
High speed 30.42 MPH 31.3 MPH
Low speed 10.74 MPH 10.18 MPH
With slightly wider gear ratios the 11-23 cogs further ease climbing with the Compact Crankset while maintaining top speed.
53-39 Rings, 12-27 Cogs 50-34 Rings, 11-23 Cogset
High speed 30.42 MPH 31.3 MPH
Low speed 9.98 MPH 10.18 MPH
12-27 is about the biggest (heaviest) cassette seen on Tri Bikes. Almost the same climbing can be achieved with the 11-23 cogs with a compact Crankset with a higher top speed, closer gearing and reduced weight.
Again, it's the cassette. Those of you arguing against compacts, what's your cassette?
Maybe the weight issue is all about the cassette, but that isn't what this debate is all about. Not many bikes are sold with compacts and an 11-21. Most are 11/12-25. This is my point.
Maybe it makes more sense if you do run a 21, I would have to check out the ratios where the cross-over is between the big and little rings.
My issue with the compacts are that it's as much about the action of using the available gears and the the fact that the ratio of the chainrings look wank on compacts.
Besides, on most climbs up to 10% you only need a big ring. Rule #5
I don't want to belabor the point. (Well, maybe I do.) I don't really know how the Rules are established. So, I don't know whether continued discussion has a point or not. But, . . .
Lost in the hunt for phantom contradictions and the mathematics of gearing are the two initial points made against compacts, which have not been addressed by the compactophiles. 1. Jarvis: choose lower gears, and you are choosing to go slow. Jarvis is right. Where you have an option between (A)choosing gears that initially allow you to smoothly and efficiently pedal up hill, and (B), suffering in higher gears until you're strong enough to master them on a climb, Rule 5 clearly endorses (B). And here we see how magnificent Rule 5 is. If we follow it, we'll end up a faster, stronger climber in the end--a better cyclist. As Steampunk has pointed out as well, selecting a compact in this situation clearly violates Rule 10 a well. That's a huge double-hit against the compact. (A young cyclist starting out with a compact!? Who honestly believes that is good?)
2. The difference between a 53x12 and a 50x12 will be huge in many situations, where a 53x12 will be spun out. I like how Marko says the difference between a 53x11 and a 50x11 is a "small loss of top end speed" for the 50x11. Heh. It's a huge loss of top end speed if you'll do any riding with good cyclists, whether in races or group rides. Of course, you can monkey around with the rear cog in order to get bigger gears, but then what's the point? At the bottom end, now, you've only got a slightly lower gear than you would if you put a climbing cassette on your standard drive train.
The more I ride with good cyclists, in races or in group rides or just out casually, and the stronger and better I get, the more I'm looking for bigger gears, not smaller gears. When I next change my drive train over, I'm going to a 54x11, with a Rule 5 loving, ass kicking straight block.
Yet Juniors are limited in terms of gearing, so if the gearing is the same what difference does it make if they're running a compact?
Unless we think it's a good idea to twat their knees early doors?
Whilst I understand the rule I'm not entirely convinced that its that big a deal. It's not what you ride, it's that you ride. No?
@guycollier
new cyclists are not necessarily juniors. and it's not what you ride, but neither is it "that you ride", it's how you ride
I think the thing this discussion is missing is the loss in leverage on the compact set; you're reducing your lever arm pretty significantly and thus you have a loss of leverage, making the compact relatively more difficult to turn. Further, you're bending your chain around a smaller circle, which increases friction. Lastly, you are distributing the load on the chain over a smaller surface area, also increasing the resistance.
Physics is on the side of whoever can turn the biggest chain ring.