Cranck Length

Bike-Improvement c.v. Gsm: 0492/ 31 00 71 Herentalsebaan 22 b 2520 Ranst ING: BE37 3630 9072 2928 Btw: BE0838.572.819 BIC code: BBRUBEBB
This point can lead to heated discussions in all conversations. We have done a lot of research on this and performed many tests ourselves. We have come to a surprising conclusion and this is .... the smaller the crank length the better. Below is a detailed explanation. Previously, a calculation formula was used to determine the correct crank length including, for example, the formula that starts from the inside leg length. The inside leg length is x 2.16 = crank length in mm. In other words, someone has an inseam of 80 cm x 2.16 = 172.8 mm. According to the formula, this person would therefore have a crank length of 172.5 mm. To go even more extreme, someone with an inseam of 90 cm would have 90 cm X 2.16 = 194.4 mm. So, in other words, this statement does not apply at all.


Long Lever
Short Lever
We take as example a rider who uses a crank length of 175 mm. We are now going to adjust his posture to a crank length of 170 mm. At the lowest point the crank is half a cm shorter. In order to keep exactly the same knee angle, the saddle must be placed half a cm higher to compensate for the shorter crank. The shorter crank length ensures that the hip angle in the body is much less sharp and less pressure is exerted on the stomach / lungs. There is also a better blood flow to the legs which in turn evokes less acidification in the legs. Because we now have to bend our knee in the above-mentioned case 1 cm less when our pedal is at the top, you can immediately exert more power. (Now bend your knees all the way down, and then come straight up. Note that this is difficult at first and as you get straighter, it gets much easier.) We often get the comment: "But you have longer cranks, so you can put more power!" This is only partially true. A crank is a lever and you can only exert more force as the lever becomes longer. Now, on one rotation with a crank length of 175 mm, a path of pi x D = 3.14 x 17.5 = 54.95 cm is laid down. Now, on one rotation with a crank length of 175 mm, a path of pi x D = 3.14 x 17.5 = 54.95 cm is laid down. For a complete rotation, the advantage of the crank length of 175 mm is only 6.4 cm compared to a crank length of 170 mm and only 4 cm compared to a crank length of 172.5 mm. This means that you will only benefit 11.7% during one rotation with a longer crank in the first case and only 7% in the second case. See figure above; distance A B. On the other hand, at the dead point, when the bottom bracket is at the top, a shorter crank can overcome the dead point more quickly. This is a greater advantage than the profit that can be obtained from longer cranks. By driving with shorter cranks, you will drive much smoother, less strain in the knees (because the knee is less bent and also stronger) and less load in the lower back. A research done by the American Jim Martin, PhD in exercise science at the University of Utah, even indicates there is improvement of power occurs with a shorter crank up to 145 mm. Only afterwards there is a loss of power. Furthermore, the test shows that the body consumes more energy with a longer crank than with a shorter crank, because the body has to put more effort into the longer crank to overcome the 'dead' moment at the top of the pedal circle. The problem with this study, however, is that there are actually no brands that produce cranks shorter than 160 mm and even those are very hard to find. As far as I can see at this moment, only the PowerCranks are available in a shorter length. But even with a crank length of 170 mm to 165 mm, the increase in power is great. The other advantages mentioned previously are also present. Remarkable is that just very recently, Campagnolo has produced a shorter crank of 165mm in their entire range of groupsets. Shimano and Sram already had this before. Another significant detail. Cancellara has been switching from 177.5mm cranks to 172.5mm cranks in his last years as a competition rider. Also on the track the riders use short cranks (160mm). This was due to the fact that they were less likely to hit the track with their pedal during the turns. This did not affect their speed in any way. Unaware they used the advantages of shorter cranks. The cadence also has a certain influence on the crank length. The slower the cadence, the more you will benefit from driving with longer cranks. Mind you, this theory does not apply until you have a cadence of less than 75 rev / min. Another study by Guido Kaandorp of the Faculty of Science of the Free University of Amsterdam even shows that even a crank length of 140mm does not result in a loss of power compared to longer cranks (170 to 180mm). On the contrary, the short crank allows a much smoother increase in acceleration. Especially the hip angle increases with shorter cranks and that has the biggest impact. (Hip angle is the angle between trunk and upper leg when the lever is at the top)
Some explanation for the two tables. MCF value must be as small as possible. The power involved here is the power provided by one leg. Here we clearly see that the lower the pedaling frequency, the greater the crank length may be. We therefore speak of a pedaling frequency of less than 70 rev / min. Our Conclusion: For U17 riders it is highly recommended to drive with a crank length of 165 mm, especially since they are very limited due to their smaller gear. (52 x 16) From junior category, a crank length of 170mm would be the best. If you are smaller than 170 cm we would keep the 165mm. Full grown riders larger than 190cm could ride with 172.5mm cranks See website: