While that logic totally checks out in my head too, I only know what it’s like to be me, and I don’t want to make assumptions. Let’s reverse the scenario: what if the study cohort was average height south-east-asian females (5’1ish)? It’s pretty messed up to say, but I don’t think anyone would cite the paper.
I am not really taking a side in this debate, I just want to add more color and context to this crank-length discussion. I am trying to avoid what media does with research: condensing an entire study into a click bait headline: " Why Shorter Cranks Are Better (According To Science)". This gets consumed by the public and becomes the assumed truth for the next 20 years.
The complete headline should be: Shorter cranks can produce 4% more power for fit 5’10 males spinning at >120RPM for 6.5 to 9 pedal strokes.
How individuals interpret that result applies and apply it to their designs and riding styles is up to them.
When I read this paper, I draw these conclusions:
The optimal RPM of shorter cranks is faster
The optimal RPM of longer cranks is slower
Peak power was achieved with ~168mm cranks and 125RPM
The test had a very narrow scope and a very narrow group of subjects
I think that’s a pretty reasonable take and not stubborn just for the sake of being a contrarian.
I had not actually read this study, very interesting read. The authors found that the ‘cyclic velocity’ (product of cadence and pedal speed) produced similar power curves for each crank length. Peak power occurs at an approximate cyclic velocity of 4 for each curve.
So, making the massive assumption that this narrow study is generalizable to anybody, I threw it into excel and calculated the cyclic velocity for a range of crank length-cadence combinations. The trend is that you’re going to need to spin faster on shorter cranks to get closer to the best cyclic velocity for power production. If something prevents you from spinning fast, like running out of gear on a steep climb, trying to clear rocks, or you just have a natural preference for a lower cadence, then the longer cranks get you closer to that peak power cyclic velocity.
I found this info on the effects of pedal speed and cycle speed on the muscles to be very interesting. With short cranks (proportionally to me) I feel that the muscle shortening velocity is too slow, and muscle excitation state is cycling too frequently. That could be the inefficiency I was trying to explain.
Foot speed is just foot speed. Rpm doesn’t matter.
There are lots of other studies, too. They all came to about the same result. How much more do you want? If you’re just not interested in stuff that could improve people’s riding experience that’s fine, I guess.
I can understand the larger industry not being interested (retooling costs money). But I’m surprised custom builders haven’t latched onto this. Maybe we collectively aren’t weird enough anymore!
Just reading this thread as I put 165s on my fatbike to improve ground clearance (low bb is fantastic but where I ride in the winter is quite technical) and really excited to see what other differences I notice.
I’ve used 175’s for 30 years until about 5 years ago when I tried 170’s then 165’s. I now use 165’s on all my bikes and have lowered the BB heights as much as I can without being dangerous. It’s awesome. I’m almost 6’ 2” tall but have a 32” inseam so I’m built like a gorilla. It does take getting used to, but mostly because we’re not used to it, and there’s this institutional “pressure” for 175’s as being the best and normal.
I encourage everyone to try 165’s exclusively for a month and see what they think. Road and MTB, singlespeed and geared. Then go back to your old crank length and see how that feels.
The only place I notice the shorter crank being different and possibly worse is on steep technical climbs where I expect to cover more ground on each pedal stroke and the shorter cranks need more rotation to clear those technical spots. I’ve gotten used to it and don’t notice it anymore but that was an initial impression that would be more noticeable climbing out of the saddle with low RPM’s and on singlespeeds.
I’ve often tried to get customers, people of the same height or shorter than I am, to use 165’s or 170’s but most resist and are afraid to change thinking it’ll cause knee issues or lessen their power output. That is why studies like these are so great to have in our back pockets, to show it isn’t necessary to worry about power output and shorter cranks can actually benefit riders in more than one way, especially when the bike is designed around them. I’ve convinced some to go with 170’s from 175. But getting anyone to try 165’s has been almost impossible unless they’re 5’ tall women.
I’m all for proportionate crank lengths but i like having the option for short and long cranks and the industry is making very few of either end. Only small shops like White Industries and Ignite even offer 180’s (am I right?). Race Face has had 165’s for awhile for Enduro and DH cranks but only White and Ignite offer that length as far as I know.
Yeah I think that might be it for who makes 180s. I’ve got some old Shimano XT 180s that I’m hanging onto until I decide to go custom. Ignite doesn’t even offer mountain 180s as standard (but they offer down to 155), but I know @anon68659156 got some custom 190s made from them I’m pretty sure. How much extra did that cost?
With a 32" inseam the 20% metric puts you on a 162.5mm crank so yeah, awesome.
I’ve got a 160 on my fatbike from Ignite, feels fine but is noticeably shorter than the 165. Great for the fatbike though where need to sit and spin for traction. I got that one when I was recovering from knee surgery and helped me get back on the bike sooner when I didn’t have full range of motion.
I believe Ian at Ignite charges $300 more for a custom crank length.
poopieprancer,
Thanks for checking out the article! You’re a great example of having long legs and likely being able to tolerate longer cranks, but you’re riding relatively short cranks for your size.
Why limit the slider to 175?
It’s rarely a detriment to go shorter with crank length (in your case 10-20mm shorter as you are on 180’s), but going too long has much worse implications on fit and ergonomics.
It all comes down to shorter riders should have shorter cranks, while longer riders should have longer cranks.
Transitioning to shorter cranks will often feel shorter. Keyword feel. But were you actually slower? That’s the big question. Leverage really feels great and is easily more easily perceived than speed.
That’s the right move to shrink gearing the same proportion as the crank length change.
I wouldn’t suggest changing to short cranks for the thrill of it. Rather, swapping crank length should come from an ergonomic/anatomical/range of motion point of view. Many riders that are on too long of cranks will benefit from the reduced joint angles and stress. It sounds like you’re on appropriately sized cranks for your proportions, not everyone has that luxury.
Hi Appleman! Thanks for contributing here, that’s awesome.
Totally makes sense that too long is worse than too short due to excessive joint angles. I still think too short is a problem, but more of the muscular variety. Ultimately it’s a bit frustrating being forced onto short cranks and will continue to be one of those unknown unknowns for many tall people unless they’re made aware.
I realize this isn’t your problem and don’t expect you to start offering long cranks, but I do wish you would consider changing the sliders for tibia length and inseam to show the actual calculated crank length numbers, and then add an asterisk stating that cranks longer than 180 are not widely available and that most bicycle’s bottom brackets are too low to safely run longer cranks, but that this is your ideal crank according to the metric. And at least make it go to 180 even if you don’t sell 180s. I’m not that tall in the grand scheme of things and my tibia and inseam are off your chart.
Thinking about dropping the BB and trying short cranks on my next MTB frame.
Do people think a 70mm BB drop resulting in 301mm height seems low (unsagged, 120mm fork)? This would put my pedal at 136mm with 165 cranks. My current pedal height is 142mm (unsagged, 130mm fork) which is pretty good for my typical very rocky terrain.
Should I push it even lower to 75mm drop for the sake of experimentation? I’m designing this frame to be more of a smooth trail ripper, not focused on performance in rocky technical stuff.
I’m not as concerned with what size cranks I “should” be riding, looking to play with geometry.
300mm seems ok to me. I wouldn’t say it’s too low considering the 165mm cranks and desired ride characteristics but I probably wouldn’t go any lower. Granted I have a preference for a higher BB’s in general. Currently my 29er is sitting at 320mm, sagged 130 fork, 175mm cranks. I’m also riding SS and find my feet often end up in less than ideal positions when climbing steep terrain.
