VariCrank Adjustable Length Crank

RacerMate announces the introduction of the VariCrank TM Adjustable Length Crank. With the availability of accurate electronic bicycle ergometers like the CompuTrainerTM and Velotron™ ergometer/trainers which measure wattage and heartrate and analyze pedal stroke (SpinScan TM), it is now possible to isolate and measure the effect of crank length on an individual’s cycling performance.

In the past determining the correct crank length for an individual cyclist has been primarily a trial and error process with limited basis in science. Few bike shops offer sizes outside the standard crank lengths of 170mm, 172.5mm and 175mm. And testing the effectiveness of different crank lengths on the road is time consuming and often yields inconclusive results because separating the effect of crank length from other variables on the road is very difficult if not impossible. The combination of VariCrank with CompuTrainer/Velotron has changed this situation because it is now possible to change the single variable, crank length, while leaving all the others constant.

One protocol to establish a more efficient crank length for level road cycling follows:
(1) First week. Set the VariCrank to match the cyclist’s current crank length to establish a baseline measurement. Ride the CompuTrainer in the Coaching Software Ergo mode at a set wattage that can be maintained for at least 30 minutes without excessive effort for each crank length and RPM session. For each testing session first warm up on the CompuTrainer for at least 10 minutes at 75 to 100 Watts, and do the coast-down calibration step. Adjust the press-on force to 2.00 or as close to that as possible. On the first day ride at 60RPM for the 30 minute session and at the end of the session record the average heartrate and Pulse Power number. Repeat this process at the same time of day for 2 more days at the same wattage level. On day two, ride at 90RPM and day three at 110RPM.

(2) Second week. Adjust the VariCrank length either up or down by 2.5mm and repeat the process. If the average heart rate decreases (and Pulse Power number increases) the new crank length is more efficient. Continue increasing or decreasing the crank length until the average heart starts to increase. The crank length which results in the lowest average heartrate is the correct crank length for level road cycling. In addition, by looking at the RPM and average heart rate you can determine the most efficient cadence for the athlete for each crank length.

Other protocols can be set up using the CompuTrainer’s ability to create hills to determine the best crank length to use in hilly country. VariCrank adjusts quickly (less than a minute) to any length from 165mm to 185mm in 2.5mm increments. Since adjusting the crank length has no effect on chain ring alignment no other time consuming adjustments are required. Hence, it is entirely feasible to use VariCrank on the road and to adjust the crank length to match the terrain. VariCrank is precision machined from 6061T6 Aluminum Alloy and has a hard anodized black finish. It is built to last indefinitely, carries a 5 year limited warranty, and is prodigiously strong. A set of VariCrank weighs 2.2 lbs.

Patents have been applied for.

Order online here, or call our sales department at 800-522-3610.