Question about climbing, RPMs, and pedal force

Discussion in 'Cycling Training' started by jpwkeeper, May 1, 2013.

  1. jpwkeeper

    jpwkeeper Member

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    Need some help from the math guys on this one, because what my head tells me must be true, my legs tell me is false.

    So I'm trying to improve my climbing technique in a place that doesn't have many hills, just endless rollers.

    I'm going up what passes for a hill around here and pretending that I'm already bottomed out in my gearing (in order to make the hill seem twice as steep as it really is as a training exercise), but trying to maintain cadence. Obviously I can't keep this up since I'm going over the wattage output I can maintain (I'm not monitoring power, just using that as a general term).

    So I slow my cadence from 90 to 75. I don't change gears. This should, I would think, feel easier. Same gear, lower cadence, lower wattage, lower speed, so the force of each pedal stroke should be less.

    But it feels harder to turn the pedals at this lower cadence.

    Am I missing something? Shouldn't it feel easier, everything else (incline, wind, and gear) staying the same?

    Now, given how most conversations here go, keep in mind I'm not saying that riding at the same speed with a lower cadence should feel easier. I'm saying lowering your cadence without changing your gear, thus losing speed, should feel easier.
     
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  2. alienator

    alienator Well-Known Member

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    At a lower cadence, the force to turn the pedals doesn't change, just the power output (which goes down with lower cadence for a given gear ratio). The only way to change the force required to turn the pedals while riding is to get in the drops or select a lower gear ratio.
     
  3. RapDaddyo

    RapDaddyo Active Member

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    You don't need to simulate climbing by riding at a different cadence. Some people change their cadence when they climb, but I don't. What differentiates climbing is that your power output needs to be more constant. On the flat, you can get away with easing up or coasting for a few seconds because you don't lose much bike speed. On a climb, depending on the grade, if you ease up or coast, you quickly lose bike speed, so you have to stay on the power constantly. Anything that will allow you to ride for a long duration at constant power is, by definition, a simulation of climbing. I don't know how much wind you get where you live, but a good headwind is good for simulating climbing. As to rollers, we often go hard on the upgrade and then go easy or coast on the downgrade. Instead, ride a steady power on the upgrades and downgrades. You'll have to gear up to avoid spinning out on the downgrades, but if you practice it you can maintain a relatively constant power on all but the steepest of downgrades.
     
  4. dhk2

    dhk2 Active Member

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    Assume you intended your statements to apply only for steep climbs at low speeds, where aero drag can be neglected. As I'm sure you know, starting from regular road speeds, both the power output and force will drop as you slow in a given gear due to the fact that aero drag force decreases as the square of the speed.
    .
     
  5. alienator

    alienator Well-Known Member

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    My statement assumed steady state conditions, i.e. constant wind, Crr, rider/bike weight, road grade, and power output.
     
  6. alienator

    alienator Well-Known Member

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    I'll add that riding in a higher gear can simulate climbing, too, especially as cadence while climbing is typically lower and force on pedals is higher.
     
  7. An old Guy

    An old Guy Member

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    It should feel easier because power output is nonlinear in RPM.

    For convenience lets assume that 90rpm corresponds to 18mph. 75rpm corresponds to 15mph (75/90*18).

    Since drag increases faster than speed:

    [email protected] = 18/15*[email protected]+extra

    [email protected] = 90/75*[email protected]+extra

    [email protected]/90 = [email protected]/75+extra/90

    [email protected] = [email protected] + extra torque

    So going slower should require less torque.

    ---

    If you want to get better climbing hills, get a trainer and set and grind out constant power for whatever length of time you want. It is just like hills - coasting does not work.
     
  8. daveryanwyoming

    daveryanwyoming Well-Known Member

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    +1 Good post RDO...
     
  9. jpwkeeper

    jpwkeeper Member

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    I hear what you're saying, but I'm a 230 pound novice riding a big honkin' hybrid, so when I run out of gears my only option (other than paper-boying or getting off and pushing) is to lower the cadence. The reason I'm practicing at lowering my cadence is that I'm really bad at it; in fact I catch myself increasing my cadence on climbs. I have back issues and I worked really, really hard at bringing my cadence up t compensate, so it feels weird to try to bring it back down a bit.

    There aren't many, but on the few steep climbs (which are never more than .5 miles long) I get to the top and I'm near max HR in my lowest gear, so I've got to lower the cadence to get through those without blowing up. I was trying to train for a Gran Fondo in the mountains of Western Maryland, but had to drop out due to a scheduling conflict, so now it's just a point of pride.

    Our wind is gusty and very, very swirly, so no help there. I've intentionally gone out in 18Mph wind to see if I could get a line going straight into it, and on those few occasions I find one I do use it as you describe, but they're few and far between.

    So what do you do when you meet a climb (like let's say 1.8 miles at 18%) where you can't maintain your cadence?
     
  10. jpwkeeper

    jpwkeeper Member

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    Yeah, I've got a guy willing to sell me his fluid trainer for 75 bucks, but my garage is seriously full so I have no place really to set it up right now and had to pass. I was going to purchase it for exactly that reason.
     
  11. alienator

    alienator Well-Known Member

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    Have you considered getting a cassette with lower gear ratios?
     
  12. dsb137

    dsb137 New Member

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    FWIW, I live in the mountains, and I have climbed at your weight (even a little more, but we don't want to talk about that...), and there just isn't any way to get around the physics of it. At any given slope it takes a certain amount of watts to propel a given mass at a particular speed. It doesn't have anything to do with your cadence.

    So, the only answer is gearing, the lower the gearing you have, the slower you can ride, and the steeper the grade you can climb. Whether or not you can make 1.8 miles of 18% depends on whether you can ride at a speed that allows you to climb at an intensity that you can sustain for the length of time it takes you to get to the top.

    Having said that, I have found that 'playing' with lowering and raising cadence on a climb can shift things around enough to help a bit... just a bit.

    This might help:
    http://mybloodybikeblog.com/theoretical-climbing/

    Dave
     
  13. RapDaddyo

    RapDaddyo Active Member

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    An 18% grade for 1.8 miles is a challenge, regardless of one's weight. Toss in a total weight of 250lbs (rider + bike) and you have an even larger challenge. Add the lack of low gears for such climbs and you have an impossible challenge. The first challenge is power, not cadence. At 250lbs total weight, it takes a lot of power to generate enough bike speed to stay upright. It gets very difficult to keep a bike upright at less than about 5mph. A quick calculation shows that to ride a 1.8 mi hill w/ 18% grade and 250lbs of total weight, you need to maintain about 460 watts for about 22mins. That's an impossible challenge for most riders, regardless of gearing and cadence. The gearing problem just further complicates an impossible challenge. Here's why. Regardless of what we may think we're doing, we all generate all of our power in a small arc of the downstrokes from about 45 degrees from top center to about 135 degrees from top center. When our cadence is high, the momentum from one downstroke brings the other pedal over the top to the power position effortlessly. When cadence is too low, we have to apply pedal force all the way around and that's difficult. So, yes, gearing matters in order to be able to have a functional cadence on steep sections, but even if you were geared for a comfortable cadence, your bike speed will be too slow to maintain balance. So, my advice: avoid such hills until you can ride at 460W for 22 minutes.
     
  14. alienator

    alienator Well-Known Member

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    Physical reality can be a bitch. When Cobo won on the Angliru (average 13.1% grade over 7.8 miles, with the steepest grade being 24%) in 2011, he did so with bottom gearing of 34/32. Pretty much every other rider rode across the finish line looking like a shattered, empty shell.
     
  15. jpwkeeper

    jpwkeeper Member

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    OK, I should double-check these things before I click Submit.

    14% at 1.1 miles, not 18% at 1.8 miles.
     
  16. edd

    edd New Member

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    Are the rub is - if you want to be good at a particular terrain, you need to train in that terrain.

    Optimum cadence can vary with bike speed. Climbing a steep hill the bike speed slows and you search for other gears and as stated by other here, the power needs to be constant. You will naturally look for the cadence you are best at producing constant power (unless you run out of cogs). For example one might climb at 75 - 80 cadence. When the road flattens out and bike speed increases you drop into the big chain ring and things change dramatically - low cadence is the enemy - because of the exponential roll-out factor.

    On the flat road the wind holds you back. On a steep hill it is gravity. They feel very different.

    Best advice - Find a bloody big hill to train on.
     
  17. jpwkeeper

    jpwkeeper Member

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    I'm already running 28x34 (and no, I didn't do that backwards; my biggest fear in buying a road bike over my hybrid is having gears that are all > 1:1). So basically mountain bike gearing. I can spin at 90 RPMs and go like 6Mph, but on an 8% incline I blow up really fast, and it's not all about my fitness (I tend to spin faster on climbs, probably since I've done nothing but rollers since I started) so I'm breaking up the monotony by trying to learn better climbing technique. I'm also trying to go too hard too early in the climb, and recovery just doesn't happen even when you slow down.

    I'm just big and not very fit, and I'm working on that, but trying to improve technique keeps those rides from being just a workout.

    It also doesn't help that my lower back really, really hates it when I get out of the saddle, so I'm trying to learn to climb sitting down.

    2012 was my first full year riding and I only managed 1016 miles. I realize I need to ride more, but that's hard with two young kids so I'm trying to get the most out of what time I can put into it. I remember reading about strategies for "pretending" to climb in order to train for hills (overgearing, headwind, static wattage which is really hard to do) when you have none, and the sensory feedback I was getting was contrary to what I thought it would be.

    And I am getting fitter. This year the same effort and speed on the same route produces around 5BPM less heart rate then last year. My triglycerides are 16 points lower than two years ago without changing my diet or taking medication.

    I played with the climb computer linked in the article someone posted. It was fascinating, but while wattage dropped significantly with the lower cadence and lower speed, effective pedal torque dropped of much, much more slowly, which is probably what I've been experiencing. In my granny gear on my theoretical 14% incline, pedal torque only dropped from (estimated here) 249 to 240 while wattage dropped much, much faster.

    I think I need to focus how my legs feel more than how hard I'm pushing on the pedals.

    @All on this thread, thanks a bunch for the feedback. Really useful stuff and it makes me think that I'm not crazy, just fat and slow which I already knew.
     
  18. maydog

    maydog Well-Known Member

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    Don't get discouraged, an 8.0% climb is steep. You gearing should be more than sufficient to get over it. Your kids can be a good training tool - put them in a burley trailer and the hills, even the small ones, become much steeper.

    Keep focused on a smooth pedaling form and leg quickness when climbing. Concentrating only on force production will slow cadence and prematurely exhaust the legs.

    Simulating a climb on flats is doable but becomes more or less a sprint or time trial. If you have a nearby hill that takes more than 30 seconds to climb, you are probably better of training on it doing repeats.
     
  19. edd

    edd New Member

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    May need to improve flexibility though the hips and build some strength/endurance in your glute-meads, they stabilise your hips in and out of the saddle.

    Worked wonders for me
     
  20. dhk2

    dhk2 Active Member

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    Yep, pedal torque (aka force) required for steep, slow climbs is essentially a constant in any given gear. So, slowing your cadence in the granny gear from 90 to 45 rpm cuts speed in half (and power in half), but the force required stays the same.

    One way to improve your ability to conquer the steep ones is just to learn to climb as slow as possible, giving your legs as much O2 as possible for each pedal stroke. Sadly, I've gotten good at balancing down below 3 mph on the steep climbs...maybe because I get a lot of practice due to the terrain......and my current challenging power-to-weight ratio.
     
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