Technical question

Discussion in 'Cycling Training' started by novetan, Oct 22, 2012.

  1. novetan

    novetan New Member

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    A comparison of a front chainring/rear cog with 44T/11T (gear ratio=4.18) against a 54T/13T (gear ratio of 4.15), all conditions being equal, ridden by the same cyclist including similar cadence, will gives almost same distance.

    My question is will the thigh feel the same tension? (can’t put it better words but hope you know what I mean).
     
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  2. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Yes.

    IOW, at the same power, which produces the same speed and implies a given cadence in a particular gear the crank torque and pedal force will be the same if the gear ratio is the same whether you get that via a 44/11 (4:1) or 48:12 (4:1) or 52:13 (4:1) assuming the same crank length and wheel/tire diameter in all cases. None of those gear combinations will feel 'bigger' or change the force/torque requirements for the same power at the same cadence.

    There are some secondary effects related to things like chain wrap and perhaps chainline which is one reason a bigger chainring coupled with a few more teeth on the cog (larger cog diameter) that yields the same gear ratio may be a bit more efficient but that's splitting hairs for most folks though time trialists sometimes pay attention to those things.

    -Dave
     
  3. novetan

    novetan New Member

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    Tks giuys. Got it.
     
  4. alienator

    alienator Well-Known Member

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    Note that 44/11 has a gear ratio of 4. There will be a 3.8% between a 44/11 and a 54/13 with respect to the 44/11. If you were producing P power at a cadence of 80 in the 54/13, you'd have a cadence of 83 at a power, P, in the 44/11. If you had a gear ratio of 4.18, I seriously doubt you'd notice the difference if you went to a gear ratio of 4.15. The difference between those two with respect to teh 4.15 gear ratio is a whopping 0.7%.
     
  5. vspa

    vspa Active Member

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    i was told there is a difference but my friend didn't explain why, i don't know, maybe the big chainring will give you a little more leverage ? im using the big chainring more often with bigger gears to move my training into L3, as a leisure minded adult cyclist i was doing too much of L2 lately,
     
  6. jpr95

    jpr95 Active Member

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    There are 4 things that determine your final drive ratio: crank length, chainring size, cog size and wheel diameter. Crank length and wheel diameter don't change while you ride. However, when you change gears in the front, the crank-to-chainring ratio changes, as does the chainring-to-cog ratio. When you change gears in the rear, then your chainring-to-cog ratio changes, along with the cog-to-wheel ratio.

    In terms of turning the cranks, using a larger chainring actually gives you LESS leverage--the resistance (the chain) is farther from the fulcrum (the center of the chainring) and closer to the applied force (which is at the pedal axles). The net effect is that, with a larger chainring, it takes fewer turns of the crank to cover a certain distance, but requires more input force from your legs. On a steep enough incline, you may not have the necessary leg strength to even move the bike, much less do so efficiently and without injury.
     
  7. danfoz

    danfoz Well-Known Member

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    I was contemplating this when choosing my last crank. I had a friend that said the same as vspa's but I take that with a grain of salt. 53's pretty much the norm these days, but 50T seems to cover more real world application for me, including racing speeds. I once spent a week going back and forth between the two. My non-scientific observations were over a smaller delta of chainring teeth than yours but my legs certainly couldn't feel any difference when running approx the same gear inches.
     
  8. jpr95

    jpr95 Active Member

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    I think a 50T chainring will cover more real world application for the vast majority of non-racers. I can go up to a 52/11 on my current ride, and I've topped it out at about 110 RPM pedaling downhill. But the limiting factor was that my legs were already somewhat fatigued from riding a few hundred miles in the previous 5 days, so I couldn't apply my maximum force, nor my maximum cadence (that I would have with fresher legs). I know of only one hill locally where I might be able to go for a higher cadence in that gear ratio, but that is a 4-lane, divided highway that is currently under construction and has been since before I got my current bike over 18 months ago (may try when construction is done--it has a very wide shoulder).

    That said, I spend most of my time spinning my 39 ring. At 90 RPM, I can do 20 MPH in about the 13 or 14 cog in the rear, and still have a decent chainline.
     
  9. daveryanwyoming

    daveryanwyoming Well-Known Member

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    If the total gear ratio (including crankarm length and loaded wheel diameter as pointed out above) are the same then to a first order everything else is the same in terms of torque, cadence, speed, power and how it feels.

    The second order effects are things like extreme chain angles to achieve the same gear ratio (e.g. 51x17 vs 39x13 with a 13 tooth small cog, the mid cluster 17 will generally give a straighter chainline which reduces lateral loading on the chain and can reduce frictional losses, especially if the crosschaining results in front derailleur cage rub) or chain wrap where tighter wrap radius (e.g. 11 tooth cog vs larger mid cluster cog) results in slightly higher frictional losses in the chain. But these losses are typically small for most normal riding situations (don't cross chain to the point where your chain is sawing through the front derailleur cage).

    There's no big magic in riding your big ring vs your small ring if the gear ratio is actually the same. But in general we don't chose and in most cases aren't set up for exactly the same gear ratios in both the big and small ring. So if you're comparing a slightly different gear when rolling the big ring then yes, it's possible that gear feels better for the terrain you're on or the speed you're riding. In that sense you might very well prefer to roll the big ring on flatter terrain and similar but slightly different combinations in the small ring might not feel quite right.

    I generally like to roll the big ring, it just feels like it flows better but I'm also riding bigger gear combinations than what I'd get through most of my cluster in the small ring so it's not an apples to apples comparison.

    -Dave
     
  10. jpr95

    jpr95 Active Member

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    The only downside I've seen to riding my 39 ring is that I have a "hole" in gear ratios due to having an 11-28 cassette. That is, I don't have a 16-tooth cog, and at times, I find that using the 15-tooth is too high of a gear and the 17-tooth cog is too low of a gear. As I get stronger, this is less of a concern, though. Riding in the 52 ring would only exacerbate the problem because I would be spending more time in the larger, more widely-spaced cogs in the rear. In other words, staying within a ratio of about 2.2 to 3.5 gives me only 5 choices in the 52 ring (15,17, 19, 21 and 24 cogs), but 6 choices in the 39 ring--and most of those choices in the 52 ring are pretty hard cross-chaining with my triple crankset. It has caused me to consider a different cassette, dumping the 11-tooth cog in favor of one with a 16...even if that means taking two apart so that I can keep the 28-tooth cog (I like having the 30-28 combo on a couple hills that I hit on an annual weeklong tour when my legs are tired).
     
  11. danfoz

    danfoz Well-Known Member

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    I had the same problem when fitting anything bigger than a 23t on the rear, missing out on the 18. Not a problem except for one particular TT with a brutal headwind where I was either bogging in the 17, or not able to rev the 19 efficiently.

    I finally got my answer to "why the heck do we need 11 speeds?" (I now get to have a 25t and keep my 18t)
     
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