For the last few years there have been a handful of hot debates in the road world, among them being whether to run tubeless or not? Disc brakes or not? Narrower handlebars or not? And, shorter cranks or not? Traditionally, what length cranks your bike runs has been based on the size of the frame (smaller frames use shorter cranks) and today the majority of bikes are built with one of three sizes; 170mm, 172.5mm and 175mm.
Of late, mountain bikes have begun running shorter cranks to minimize pedal strikes, but the idea of running shorter cranks on road bikes has been around for a few years now and it has more to do with finding a proper bike fit and improved performance.
The most notable move to provide riders with added crank length options has come from Minnesota frame builder Matt Appleman who has introduced his own machined aluminum cranks. The 2XR Appleman cranks embrace the growing popularity of shorter cranks by offering an expanded range of sizes (135-175mm in 10mm increments). In addition to the added sizes, the $485 cranks are also available in ten different colors!
While the short versus long crank debate carries on, we decided to ask our own Dr. Johnathan Edwards to chime in with a more scientific look at what the benefits are.
ARE SHORTER CRANKS A BENEFIT?
Is there a benefit to shorter crank length? It’s a debate that has lingered on for over 25 years – longer or shorter, more power, greater efficiency, less metabolic cost, better aerodynamics, etc. It is true that bike manufacturers are trending towards smaller crank sizes. For example, cranks as long as 180mm were available, but we do not see the long arms much anymore.
There are a handful of studies about crank length and cycling, all trying to find differences in power output, metabolic cost, or excessive joint strain due to varying crank lengths.
This 2001 study by J.C. Martin & W.W. Spirduso is one of the most comprehensive on crank length. They measured the maximum sprint power output (over 1,000 watts) on sixteen trained cyclists, each using a wide range of crank lengths (120, 145, 170, 195, and 220 mm). The optimal crank length was 20% leg length or 41% tibia length. The authors put it here: “Even though maximum cycling power was significantly affected by crank length, use of the standard 170 mm length cranks should not substantially compromise maximum power in most adults.”
In 2002, Martin and Spirduso found no significant difference in power output.
This 2002 study by J. McDaniel et al., “even with our wide range of pedaling rates, pedal speeds, and crank lengths, muscles’ ability to convert chemical energy to mechanical work was remarkably stable.”
In 2011, Paul R. Barratt et al. Our results substantiated previous findings that crank length per se is not an essential determinant of maximum cycling power.”
In 2016, Ventura Ferrer-Roca et al. . Therefore, in case of doubt between two lengths, the shorter one might be recommended.”
These studies on crank length, power output, joint anatomy, and energy cost showed minimal real-world cycling difference that would pertain to real-world cyclists. Yes, there are differences when you are Mark Cavendish trying to produce 2000 plus watts, just as we would expect for Usain Bolt wearing different running shoes. Furthermore, studies may not be the best place to look for verification of the benefits of varying crank length. Most of these studies were done with little funding and the pure passion of the researchers. The number of subjects tested is tiny, making it difficult to conclude anything, leaving regular cyclists scratching their heads when the bike shop tries to sell them the latest innovation in cranks. They are testing extreme power, lengths, and situations.
Aerodynamics may be a reason to shorten cranks; a 2.5mm reduction in crank length (which needs a 2.5mm seat height increase) improves aerodynamics (not necessarily comfort) by optimizing the hip angle and dropping your front end closer to the front of the bike. In a bike fit adjustment with Bradley Wiggins, they went from 177.5mm crank arm to a 170mm crank arm, which dropped his front end by 30 millimeters. He improved his aerodynamics by 3.5%. So, if you are a tall, elite time trialist, this may be an advantage.
At the end of the day, if the crank length is in the ballpark and the fit geometry is reasonable, most cyclists will adapt to the crank length and be happy pedaling their bike. The main takeaway is that crank length doesn’t make a huge difference.
For more: Appleman Bicycles