Custom carbon cranks

Mårten sent photos of the short carbon crankset that CARBONTRIKES has customized for my future racing trike. It’s probably one of the lightest triple cranksets on the planet, if not THE lightest: less than 700 grams with 53-39-30 chainwheels.

"We have tested your 130 mm crankset. It felt little strange to us, but we aren’t used to short crankarms. We have also tested the crankset with high overload and it looks good." Mårten Danielsson, CARBONTRIKES

Crankset photo 1 Crankset photo 2 Crankset photo 3

Short cranks are not so rare on recumbents, many recumbent riders use them and like them. I’m one of those. The problem with short cranks is that high quality short cranks are almost impossible to find, as conventional bicycle industry is using only three standard lengths, 170 mm, 172.5 or 175 mm. Anything shorter or longer is a rare breed. Considering the wide spectrum of human body lengths, that 5 mm difference in cranks is utterly ridiculous.

However, I have not seen a single scientific study, which explains why short cranks would have a positive effect in cycling performance. It might even be so that the optimum crank length is different for upright and recumbent bicycles. Nevertheless, with short cranks your knee angle evidently remains smaller, so…

  • Claim: Less stress for knee joints. This is actually not totally sure, as some studies have shown that the pressure inside the knees reduces the more the knee is bent. However, my very own knees seem to think this claim is true.
  • Claim: You are able to produce more force. You can squat with heavier weights when doing only partial squats, BUT at the same time, deep squats would recruit more (several) muscles, which could be beneficial on heavy sprints, maybe endurance wise too. Also, it’s not the force, which is important, but the power (which is torque * rpm, and torque reduces with short cranks using same force).
  • Claim: you can spin quicker (comfortably use higher cadence), so you can partially move the load from the leg muscles to your vascular system. This might be beneficial endurance wise, as your vascular system is designed for endurance. Also, faster your cadence, more you produce power with same torque. Unfortunately, you’ll also use more energy for nothing, just fighting your legs weight against gravity and moving the air around.
  • Claim: Your aerodynamic drag will be smaller, because the reference area created by your legs will be smaller. This is mostly true for recumbents only, and even for them it’s partially depending on where the cranks (bottom bracket) are located at.

Whether it’s scientifically reasonable or not, I like short cranks and I even have some unscientific numbers to throw in: using my road bike with 170 mm cranks I could reach maximum of 120 rpm cadence on rollers. With 130 mm cranks (and my current HPV Scorpion recumbent trike) I constantly reach 170+ rpm while doing short power sprints. 120 vs. 170 rpm is a huge difference.

About my “gear inches” with 170+ rpm cadence: 53 front, 11 rear and 1.3 multiplier on SRAM DualDrive, 406 rear wheel means the speedometer goes up to 110 kph. If only I could repeat THAT on the track, too, d’oh!

At the moment I feel my natural cadence on rollers is somewhere around 105, while 115 starts to feel a bit uncomfortable. I do the power sprints with ultra high cadence using a recumbent version of dancing-out-of-the-saddle: you lift your bottom up from the seat so that your body is tensioned between cranks and upper part of the seat, legs spinning violently. It probably looks ugly and crazy, but generates serious wattage and requires using your body’s core muscles, which is a bonus for your general fitness.

Thanks for reading.