Crank Length: Consider Going Short?
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  1. #1
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    Question Crank Length: Consider Going Short?

    One thing that's always been a mystery to me in cycling is crank length. I typically run 172.5mm simply because that's usually what comes on my 58cm bikes. However, is that an optimal crank length for me or anyone else for that matter?

    I've recently considered going with a 165mm crank, which is the shortest length the Shimano Ultegra R8000 crank set is available in.

    My reasoning of possible benefits for going with a shorter crank include:


    • Less shoe/tire rub. I have huge feet (size 48!). A shorter crank arm would potentially mean less shoe / tire overlap.
    • Ability to maintain higher cadence. By having to move my feet in smaller circles, this would theoretically mean I would be able to maintain higher cadences. I try to strive for a cadence between 80 - 100 RPM but often find I drop below that when I don't focus on it.
    • Less knee strain. Shorter cranks would mean less bending of the knees, especially at the top of the pedal stroke. Some argue this would also mean less lower back pain.
    • Lower weight. Marginal gains! Although the weight difference would be negligible, it would be something.
    • More ground clearance. A shorter crank would mean fewer chances of smacking the pedal on the ground in a corner. I did that once and it scared the crap out of me... I'm glad I didn't crash.
    • More aero(?) Keeping my feet closer to my body on the down-stroke might potentially be more aero?


    Thoughts? Are any of you riding short cranks? If so, I'd like to hear if you think it was worth the change...
    Last edited by PoorInRichfield; 04-05-2020 at 08:06 AM.

  2. #2
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    Quote Originally Posted by PoorInRichfield View Post
    One thing that's always been a mystery to me in cycling is crank length. I typically run 172.5mm simply because that's usually what comes on my 58cm bikes. However, is that an optimal crank length for me or anyone else for that matter?

    I've recently considered going with a 165mm crank, which is the shortest length the Shimano Ultegra R8000 crank set is available in.

    My reasoning of possible benefits for going with a shorter crank include:


    • Less shoe/tire rub. I have huge feet (size 48!). A shorter crank arm would potentially mean less shoe / tire overlap.
    • Ability to maintain higher cadence. By having to move my feet in smaller circles, this would theoretically mean I would be able to maintain higher cadences. I try to strive for a cadence between 80 - 100 RPM but often find I drop below that when I don't focus on it.
    • Less knee strain. Shorter cranks would mean less bending of the knees, especially at the top of the pedal stroke. Some argue this would also mean less lower back pain.
    • Lower weight. Marginal gains! Although the weight difference would be negligible, it would be something.
    • More ground clearance. A shorter crank would mean fewer chances of smacking the pedal on the ground in a corner. I did that once and it scared the crap out of me... I'm glad I didn't crash.
    • More aero(?) Keeping my feet closer to my body on the down-stroke might potentially be more aero?


    Thoughts? Are any of you riding short cranks? If so, I'd like to hear if you think it was worth the change...
    There's really no compelling study of crank lengths that defines "optimal" length for riders, despite over a century of trying. There are "what seems to work" charts, and there are "I know the real answer" charts, but nothing with strong data to back it up.

    And we're talking a difference of a couple of coins' thickness, maybe (so little effect on shoe overlap).

    Ground clearance is a clear benefit, if you're doing a lot of hard turns/riding fixie.
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  3. #3
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    Quote Originally Posted by xxl View Post
    Ground clearance is a clear benefit, if you're doing a lot of hard turns/riding fixie.
    I ride a Trek Domane which has a low bottom bracket and so I'm speculating I might benefit from a shorter crank more than the average rider.

    As you stated, there doesn't seem to be a definitive answer on what the "right" crank length is. What I am noticing when I read comments below YouTube videos on the topic is that multiple people have expressed less lower back and knee pain when going to shorter cranks. At 45 years of age, reducing pain is becoming more and more of an issue.

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    JSR
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    I normally run 172.5 on my road bikes. My grocery getter has 170. I find knees and lower back seem to be stressed more with the shorter crank arms. Maybe more oomph (less leverage) required when going through the top of the stroke? I dunno, but that’s the sensation I get.

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    Lennard Zinn offers custom cranks of all sizes, from very short to very long.

    Even better, you can rent an length-adjustable crankset to see which length you prefer.

    Before you switch to such a short crank, I think it would be a wise investment to rent the crankset and experiment.

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    My knees have always preferred to make smaller circles.

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    A number of years ago a friend of mine discovered he had two different length crankarms mounted on his bike. This was after riding the bike for a season while tuning it up for the coming season.
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    .je
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    Would moving your cleat 2.5mm accomplish the same thing? If it didn't feel funny to do so?

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    Quote Originally Posted by .je View Post
    Would moving your cleat 2.5mm accomplish the same thing? If it didn't feel funny to do so?
    I'm not clear on what you're suggesting? Moving the cleat doesn't change the diameter of the circle your foot travels, it makes the circle further forward or further back, technically speaking, and impacts how much leverage your feet have on the pedals (which impacts all sorts of stuff). I prefer my pedal cleats as far back as possible (i.e., the pedal axle as close to the center of my foot as possible.)
    Quote Originally Posted by Peter P. View Post
    Before you switch to such a short crank, I think it would be a wise investment to rent the crankset and experiment.
    Thanks for the link and I agree, I would certainly like to try something before making a huge investment. I'm considering ordering these cranks on eBay. While not free, that's not a lot to spend for an "experiment".

    While thinking about this topic, I looked at the cranks on my new bike that I haven't ridden yet and discovered they're 175mm which is super disappointing as they're longer than anything I've ever ridden before and I want to go shorter! Anyone want to swap a brand new 175mm Ultegra R8000 crankset for a 165mm set?
    Last edited by PoorInRichfield; 04-05-2020 at 02:19 PM.

  10. #10
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    Quote Originally Posted by PoorInRichfield View Post
    Moving the cleat doesn't change the diameter of the circle your foot travels, it makes the circle further forward or further back, technically speaking, and impacts how much leverage your feet have on the pedals (which impacts all sorts of stuff).
    Yes you're right! I should have thought about that a little longer. Thanks for clearing that up.
    Since it doesn't raise pedal height aren't you making a little FIY bio-pace? For free? Just theorizing.

    OP, if you want to feel a short crank, maybe try a dept store bike from long ago, they often had 165mm cranks. IMO feels like you don't put as much power to the pedals (sucks in so many ways).
    Last edited by .je; 04-05-2020 at 03:13 PM.

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    Quote Originally Posted by .je View Post
    OP, if you want to feel a short crank, maybe try a dept store bike from long ago, they often had 165mm cranks. IMO feels like you don't put as much power to the pedals (sucks in so many ways).
    LOL! El-cheapo exercise bikes with super short crank arms is the one reason I'm afraid to go with a shorter crank... don't want to duplicate that scariness on my road bike!

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    Quote Originally Posted by PoorInRichfield View Post
    [*]More ground clearance. A shorter crank would mean fewer chances of smacking the pedal on the ground in a corner. I did that once and it scared the crap out of me... I'm glad I didn't crash.[*]More aero(?) Keeping my feet closer to my body on the down-stroke might potentially be more aero?[/LIST]

    ..
    Seriously?

    -Have your pedals been hitting the ground? Is .75 cm enough to stop that if so?

    -No.

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    Quote Originally Posted by Jay Strongbow View Post
    Have your pedals been hitting the ground? Is .75 cm enough to stop that if so?

    -No.
    Yes, "seriously". Read my post again. My Domane has a low bottom bracket and yes, I have hit the pedal on the ground. And yes, a few millimeters of extra clearance has a considerable impact on pedal strike.
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    Last edited by PoorInRichfield; 04-06-2020 at 06:13 AM.

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    Note: When going around a right hand corner, raise the right crank and stop pedalling.

    Seriously, if your pedalling around a corner, when you start leaning, stop pedaling. Yes, I don't always follow this advice and have hit my pedal. At that point you had better be 'in it', no big deal.

    And you can tell the difference between leaning 15deg to 17deg? I don't thinks so.
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    Quote Originally Posted by duriel View Post
    Note: When going around a right hand corner, raise the right crank and stop pedalling.
    Yeah, pedaling through a corner isn't something I do often, but sometimes yah gotta keep the power flowin' to keep-up!

    Anywho, I listed multiple benefits of shorter cranks of which pedal strike is only one...

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    As someone already stated, there doesn't seem to be a definitive answer on what the "right" crank length is.... however;

    I made the change about two years ago when a bike fit calculator recommend I should be using 170mm vs a 172.5mm which came with the bike as original equipment. What I also noticed is that I push a standard chain ring (53/39) much easier and I am also noticing less lower back and knee pain.

    Could just be a placebo effect, who knows... but its working for me and I'm going with it.
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    Cyclist: Bike fit variables: No. 2 crank length
    ‘Shorter cranks will almost certainly help most riders be more comfortable on a bike,’ he adds.
    ‘They help soften the impact of cycling on the body. Think about it: the equation is 2πr, so crank length changes that circle significantly, and going shorter appreciably reduces the range of joint movement.


    ‘We didn’t evolve around producing power with a flexed knee and a flexed hip. If you can do anything to open out the hip angle it’s most often a good thing.’

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    There have been all sorts of formulas recommended over the years. Some say it's the shoe size, others say it's the femur length, some others say it's the overall leg length. I've tried from 170mm to 175mm. I felt 170mm and 172.5mm to be about the same. It's one of those things in cycling that you just have to try on your own. I bought used cranks to determine which one works for me. When you sell the one/s you don't want, it's much smaller loss (profit in one case) than testing with new ones.

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    Another vid from GCN on crank length.


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    Quote Originally Posted by bvber View Post
    Another vid from GCN on crank length.
    I watched that yesterday

    This is a really good article on the topic:

    CyclingTips: Crank length: Forget leverage and power, it’s all about the fit

    The article discusses the history of the topic, whether or not crank length correlates to power loss (it doesn't), and the bio-mechanics of crank length... Not to mention a photo of a crazy-weird bike that has no down-tube.

    ...noting that longer cranks increased flexion and the range of movement required at both the hip and knee. This wasn’t the case for shorter cranks, leading the authors to recommend that where there is indecision, cyclists should opt for a shorter crank to reduce the risk of injury.
    I think I'm pretty sold on trying a set of 165mm cranks, since that's the shortest length commonly available and considerably shorter than my current 175mm cranks.

    From all I've read on the topic, the only advantage I've found for longer cranks is that you have more leverage when starting from a dead stop. Since that means nothing to me, I'd much prefer to save my body some stress.

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    Another really good "must read" article if this topic interests you. This blog post is from a gentleman who actually did some testing to see if crank length changes (within reason) made much different when climbing...

    Blather 'bout Bikes: Crank Length? Whatever...(within reason)

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    If you want to try shorter cranks, just go for it. You don't have to convince everyone that they're better to justify your decision.

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    Quote Originally Posted by tomato coupe View Post
    If you want to try shorter cranks, just go for it. You don't have to convince everyone that they're better to justify your decision.
    False. If I don't get unanimous approval from all the grouchy RBR forum members, they will make fun of me until the end of time. Are you new to RBR? :-D J/K

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    Back when I started riding 30 years ago, conventional wisdom was that I should use 175 length cranks based on my height and inseam. I blindly accepted that and never gave it another thought. As others have mentioned there doesn't appear to be a whole lot of science behind this. I have rented bikes with 170 cranks and I don't recall noticing any difference.

  25. #25
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    Ya just got to experiment. I ended up with 172.5's. 170's hurt the insides of my knees and 175's hurt the outsides, the kneecaps. And yes, I was occasionally scraping a pedal around corners when I ran 175s. My wife's 165's, meantime, feel silly. Like I should be wearing clown makeup.
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