 How much does crank length affect your cycling performance and what is the optimal crank length for you? Today, we'll be taking a look at what the science has to say in regards to this question. We'll be looking at studies that test performance differences between different crank lengths, how your height and leg length affect your optimal crank length, and whether or not changing your crank length will affect your cadence. Welcome back to another video. My name's Dylan, and for weekly science-based coaching videos, just like this one, be sure to subscribe. There are different competing theories out there about what the optimal crank length is. Some go longer to try to get more leverage, and some go shorter to try to spin faster, and then others never really thought that much about it and just run whatever cranks came on their bike. Yeah, I can already tell this is gonna be a video for nerds. I'm out. Is there an optimal crank length, though? The bike industry seems to have settled on a norm of 170 to 175 millimeters, but could going longer or shorter than this offer an advantage? There are some people that seem to think so. For example, pro cyclist Adam Hansen runs 180 millimeter cranks as well as going to other extremes like super narrow 38 millimeter wide bars, a setback seatpost run backwards with the saddle slammed as far forward as it can go, and a slammed negative 15 degrees stem. Sounds comfortable. Track cyclists go in the other direction, often opting for 165 millimeter cranks. The reason has to do with spinning such a high cadence on the track. Everyone has their opinions, but let's get into the research and see if we can get to the bottom of this crank length question. This study on the effect of crank arm length on power production in cycling tested subjects 30 second sprint performance using 110, 145, 180, 230, and 265 millimeter cranks. Not too surprisingly, given these extreme jumps in crank arm length, the 180 millimeter cranks came out the winners in terms of power production. These are the results we probably would have expected. However, similar studies might leave you scratching your head. This study using the same 30 second test with 125, 150, 175, 200, and 225 millimeter cranks actually found that the 150 millimeter cranks produced the best results. I don't know about you, but I've never heard of somebody running 150 millimeter cranks unless it was a child on a kid's bike. When applying the best fit parabolic curve, it appears that the optimal crank length is slightly shorter than the conventional 175 millimeters. Now we aren't talking about a big difference here. A 50 millimeter difference in crank length only resulted in about a 1% drop-off in power. If you compare this to a similar change in saddle height, for example, we're talking about a five to 8% drop-off. The study also separated subjects into those who had long legs and those who had short legs, finding that the optimal crank length did appear to be shorter for those who had shorter legs. This is of course why bike companies stock smaller sized bikes with shorter cranks. However, it seems from the study that perhaps they may even be stocking larger sized bikes with cranks that are too long. And this isn't the only study to find this. This study on determinants of maximal cycling power tested maximum power production with crank lengths ranging from 120 to 220 millimeters. Interestingly, the riders actually produced the most power with the 145 millimeter cranks, although it wasn't a statistically significant difference over the standard 170 millimeter. Although again, we're talking about a small difference here. Cranks that varied 83% in length only elicited a mere 4% difference in power. The optimal crank length was 20% of leg length, although the use of 170 millimeter cranks would only reduce the power of the shortest and longest legged subjects by less than half a percent. For those of you who don't know how short 20% is, for your average person with a 32 inch inseam, that's 162.5 millimeter cranks. Now remember that we're talking about fractions of a percent here, but it is starting to make sense why track riders typically go with shorter cranks. Now, of course, these studies are only looking at sprint performance. And while that is important, most cyclists are probably more concerned about their performance during longer efforts when choosing their crank length. Also, we aren't picking between 120 and 220 millimeter cranks when we go crank shopping. The range of available options is much tighter than that. And it seems that the industry is at least close to the right range. So what about a closer difference in crank length, like 170 versus 175 millimeters? This study looked at just that, testing the effect of small differences in crank length on efficiency. They ran three tests. One where subjects ran their preferred crank length and one on cranks that were five millimeters shorter or longer than that. The results showed no difference in heart rate or gross efficiency between the three crank lengths. Considering that studies that test huge differences in crank length only find small differences in performance, it makes sense that a study that tested smaller differences in crank length, like five to 10 millimeters, wouldn't find any statistically significant difference. As we've seen though, leg length seems to play a large role in determining optimal crank length, or does it? This study investigated the effect of crank arm length on oxygen consumption. Subjects wrote at 68% of VO2 max using 165, 170 and 175 millimeter cranks. Interestingly, no significant correlations were found between each subject's most efficient crank arm length and leg length. The results of the study suggest that each subject has a most efficient crank arm length, but it does not appear that the optimal crank arm length can be predicted by leg length. Well, that certainly throws a wrench in our spokes. It seems like the deeper we dig here, the more conflicting information we get and the further we get from finding an actual answer. Let's do some more digging and see if we can get a clearer picture. This study on the influence of crank length on the performance of well trained female mountain bike athletes tested female cross country riders with an average height of 168.5 centimeters or five foot five inches. They used 170, 172.5 and 175 millimeter cranks. And what they found was that the athletes took longer to reach peak power with longer cranks. However, there was no other significant differences in performance across power, strength or endurance outcomes between the three conditions. Many women do run shorter cranks and many women's specific bikes get stocked with shorter cranks. From a performance standpoint, there's probably a marginal difference at best, if any at all. But again, it seems that perhaps for sprint performance, shorter may be slightly better. Changing your crank length can also affect your cadence. Going back to the study on determinants of maximal cycling power, they also found that the optimal pedaling rate decreased with an increase in crank length. Basically the longer your cranks, the lower your preferred cadence will be. Could this have an effect on your performance? This study on the effect of crank length on joint specific power tested subjects maximal power with 150, 165, 170, 175 and 190 millimeter cranks. The study revealed that crank length had no significant effect on relative joint specific power at the hip, knee or ankle joints when pedaling rate was optimized. The key there is when pedaling rate was optimized. When subjects had to keep a consistent cadence, it was a different story. When pedaling rate was constant, crank length had a small but significant effect on hip, knee and joint power in the 150 versus 190 millimeter cranks only. They concluded that for competitive cyclists changes between cranks of standard length, 165 to 175 millimeters, do not compromise maximum cycling power or modify the relative joint power contributions to pedal power. So we're getting another study here that's essentially saying that crank length doesn't matter but it will affect your cadence. Is that a bad thing? Maybe choosing a longer crank will cause you to ride at a lower cadence fatiguing you quicker. In this study on the effect of cycling cadence on knee extensors, they took eight well-trained triathlates and had them perform three tests at their freely chosen cadence, then their freely chosen cadence plus 20% or minus 20%, which ended up averaging to a cadence of 69, 86 and 103 for the three tests. What they found was that muscular activation levels did decrease after the tests. However, it didn't matter what cadence the test was performed at, the decrease wasn't statistically different. And this study on the effect of cadence on efficiency in cycling concluded that pedaling cadence did not have a dramatic effect on efficiency. The available research on cadence may be surprising to people who think you have to spin to win or look to whichever pro is on top of the current moment and try to emulate their cadence. The evidence that actively changing your cadence will improve your cycling performance simply isn't there. This review article on optimal cadence, some things up nicely stating that it would appear that a single optimal cadence for all cyclists does not exist or indeed a single optimal cadence for an individual cyclist. The cadence at which perceived exertion is minimized would seem to reflect the optimal trade-off between the most metabolically efficient cadence and the most mechanically efficient cadence. Basically, the cadence that is most comfortable for you is the one that you should ride at and there's no reason to believe that this is any different when adjusting crank length. Adopting a slightly faster or slower cadence due to longer or shorter cranks is neither a good or a bad thing. So where does this leave us? Well, keep in mind that when we're talking about the performance differences of changing your crank length, we're talking about minute differences. It takes making a huge jump like up to 200 millimeters or down to 120 millimeters to see a noticeable drop-off and even then the drop-off isn't as much as you might think. Standard bike cranks of 170 to 175 millimeters are in the right range and you'd be hard-pressed to find a difference between them. This is a good thing because it means you aren't beholden to one crank length to try to maximize your performance and you can instead choose your crank length based on other factors. Going back to the study on the effect of crank length on joint specific power, they state that cyclists can select crank lengths on the basis of other factors, such as reduced aerodynamic drag or reduced injury without the concern of compromising their maximum power capability. I would go with the crank length that makes the most sense from a bike fit perspective and it's probably a good idea to have the same crank length on all your bikes so that you can get used to that length. It might feel a bit weird to do a ride one day on your road bike with 165s and then hop on your mountain bike the next day with 175s. That being said, bigger travel trail bikes are now often being specced with shorter cranks to minimize pedal strikes. If that's important to you, then go for it. It'll likely make little to no difference in terms of power production. The one exception I see here is with sprinters. If having a good sprint is important to you, then the evidence seems to suggest that you may be able to eke out a few more watts with shorter cranks. However, remember that the difference we're talking about here is marginal. So basically what you're saying here is that the people who don't care about crank length and run whatever size cranks came on their bike were right all along. Great, thanks for wasting 10 minutes in my life. Thanks for watching. I hope you guys found this information helpful. If you did, be sure to give it a like, subscribe, and share it with your cycling friends. I'll see you in the next one.