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Assuming one is biking on flat roads and assuming equal power in both scenarios, how much faster would one go using clipless pedals versus flat pedals?

[Note that this question relates to: https://bicycles.stackexchange.com/questions/5647/how-much-of-a-difference-do-toe-pedal-clips-make-in-comparison-to-platform-pedal. I apologize if someone else has asked my exact question.]

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Depends on your personal pedalling style.

  • None - if your pedal stroke is just to apply power down on the front.
  • Minimal - if you can modify your stroke such that the rear/rising foot does not weight the pedal at all, then that power is not wasted in lifting your rearmost foot.
  • Little - There are riders who can drag their feet back across the "floor" of the pedal stroke which helps add power, and also recruits different muscles.
  • Some - for a power sprint max-effort, there are riders who can both pull back around the bottom and then pull up on the rear part of the stroke. In theory this provides the most power possible.

Exactly how much faster this makes you depends on how much power you can personally deliver through your pedals. A power meter is the tool to measure this, on your bike. Strava's power estimator is useless at this.

You might be able to use a power-meter equipped spin bike at a Gym, but that's not real on-road riding where things may be different.

Do consider also:

  • Power sprints are short - I'd be hard pressed to power-sprint for more than 10-15 seconds.
  • Professional riders who have had pedal-stroke analysed still don't pull up or slide back unless they're in a sprint. Pro's have some of the worst choppy pedal strokes around.
  • Personally I find foot retention to be a confidence thing - I know my foot will not slip even in the wet, so I can put more power in without fear of slipping. That's useful.
  • Cleated shoes are relatively aerodynamic, with rounded corners and soles. This alone helps improve airflow, as does the smaller/lighter cleat.

You can play around with http://www.bikecalculator.com/ and get some interesting results. EG if you can produce 5 watts more power then that could be 0.3 km/h faster for everything else being the same.

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With flat pedals, the only thing holding your foot to the pedal is friction. Friction only exists if your foot is in contact with the pedal -- what physicists call "normal force" or "contact force". No force, no friction, and your foot is off the pedal, by definition.

Because of this fact, you have to exert some amount of pressure to the pedals all the time, particularly on the back-stroke...unless you have super Jedi warrior reflexes and can move your foot in exactly the same arc as the crank, your foot is either going to come off the pedal, or it's going to have to be pressed against the pedal at least a little bit to maintain traction. This "little bit of retarding force" directly counter-acts the main driving force of the other crank...you are literally working against yourself; your legs are working against each other...and this extra effort that must be expended to maintain traction also won't show up in a power meter, depending on the design of the power meter.

It's a physical fact that flat pedals require you to keep your foot pressed against the pedal, and this backward force generally is non-productive and actually detracts from forward force. The main argument is how significant of an effect this is. There have been studies to measure the difference, but not all of them directly measure the right things. The current consensus is that the effect is small, and efficiency for most practical purposes is not greatly different between flat pedals and clipless/clipped pedals. To directly answer your question, I believe attempts to find a difference through practical testing (the straight road, direct comparison test) have failed to find a reproducable difference.

It may be a difference too small to matter, but other things considered, clipless should be more efficient because the need to apply this retarding force to the cranks is removed.

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    What's the difference between "There have been studies to measure the difference, but not all of them directly measure the right things" and "I don't understand the studies on the subject so I'll just claim they're wrong"?
    – ojs
    May 20 at 7:30
  • Actually, the required contact force is irrelevant to the overall efficiency of your pedaling: As much as it is a fact that you need a force to stay in contact with a flat pedal, it is a fact that you need to lift your foot/leg back to its upper position on the upstroke. Whether you use the muscles in the upstroke leg, or the muscles in the downstroke leg to lift the upstroke leg makes no difference to the energy that your muscles consume. So, as long as you are not sprinting (= your strength is not the limiting factor), the required contact force makes no difference to your performance. May 21 at 0:12
  • @cmaster-reinstatemonica I guess you're assuming the upstroke leg is passively resting on the pedals rather than pressing down using its own muscles, but even so there are muscle-efficiency questions: Does the downstroke leg work as efficiently lifting the added mass of the upstroke leg as it would without? A simple physics explanation isn't enough (I wish it was as physics is what I do for a living). Classical mechanics says you do no work if you're not moving (W = ∫Fdx = 0 for constant x) but try holding your bike over your head and claiming you're doing no work
    – Chris H
    May 24 at 14:22
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    @ChrisH Of course, the efficiency of muscles is not constant with respect to applied force and/or speed of contraction. But I've got no reason to believe that changes rapidly at the working point of biking. That working point should be as close to the global maximum as possible, after all. That said, you absolutely have a point when it comes to the calves: If you let the pedal lift your leg, you are stretching your calves under tension, so whatever energy they consume (mechanically and chemically) is lost energy. I confess that I failed to consider that detail. May 24 at 16:03
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As cycling power is normally measured at the cranks, i.e. at the input to the drivetrain and not in your muscles, you'll go exactly the same speed as with flats given your "same power" constraint.

Where clipless pedals can help is in improving efficiency by keeping your foot in an optimal position, or improving peak power if you pull up on the pedals (this is rarely sustainable for long). You may also be able to push round more of the stroke, which can help get more power out of your muscles. At their very best, compared to your feet sliding around on the pedals, you should get more power for the same perceived effort, but to actually measure this would be very tricky.

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  • Thank you. Yes, I meant "same level of exertion." It is good to know that this is different than "same level of power."
    – bill999
    May 24 at 15:41
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    @bill999 I'm a physicist who does some teaching, so I'm inclined to use a strict definition of "power" as something you can measure in watts. Understanding the limits of my subject, I accept that the ability of a human to produce that power in a useful form is affected by many factors that I can only address approximately
    – Chris H
    May 24 at 15:45
  • Makes sense. I am glad that I was able to learn something new.
    – bill999
    May 24 at 15:49
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"assuming equal power in both scenarios"

As Chris H said, pedaling power is usually understood as the power provided to the cranks, averaged over a full rotation, regardless of physiological efficiency. Same power = same speed if all else is equal (aero, incline...).

You probably meant "given the same level of exertion, how much faster will I go with clipless pedals?".

From what I read and based on my own mountain bike experience riding both types of pedals, going clipless gives you a power advantage during explosive bursts. This comes in handy on very steep technical climbs, when you need to pass large roots and rocks. Road riders will benefit from it when sprinting, or accelerating in trafic.

This study clearly demonstrates the power advantage over a 30s sprint: The average across test riders is 617W with clipless, Vs 566 W using flats. That is a 9% advantage in power, which translates to a 3% advantage in speed. Using the default parameters with this model, I get a speed of 50,7km/h with clipless Vs 49,1km/h with flats.

However, this extra power is not free, you will tire faster if you're using weak muscles to help stronger ones.

I could not find any study clearly demonstrating a speed advantage on a long flat course. Actually, "semi-scientific" videos like this one by GCN show that there is no power gain except in a sprint.

You might be wondering why everyone rides clipped-in at Tour De France or similar events. Riders spend most of the race in a peloton, shielding each other from the wind, with lesser team members taking turns at the front to help their leader. Whoever manages to save the most energy for the final sprint wins.

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  • Thank you. Yes, I meant "same level of exertion." It is good to know that this is different than "same level of power."
    – bill999
    May 24 at 15:41
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    Technical stuff clipped in assumes a certain base level of skill, but it gives you an extra degree of control over the bike which is well worth having - and coming to a halt isn't efficient. I'm a novice on the MTB but have started riding clipped in, at least solo. The pros are often ready for a sprint, but also clipping in means the feet don't slip and drop power, while still keeping the pedal and shoe light. A bad slip could cause a crash, but more likely is having to reposition the foot, which means reducing the power to do so; cleats avoid that.
    – Chris H
    May 24 at 15:49

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