Reviewed: Zencranks PAS crankset
An extended review of Zencranks' unique PAS crankset surprises Lennard Zinn and upsets some basic assumptions in pedal/crank design
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Not to be confused with Sugino’s Zen track chainrings, this crankset’s full name is Zencranks PAS (Power Augmentation Systems), and you’ve never ridden anything like it.
I performed a long-term review on the system, comparing it to two conventional cranks, one of standard length and one of comparable length to the Zencranks. I was beyond skeptical when I first saw the system, but came away surprised at how well they worked in terms of climbing speed.
Zencranks have the pedal bearings built into each crank arm and an extension arm pivoting at that point, which is connected to the pedal, whose spindle will not rotate. The system makes the trajectory of the metatarsals of the rider’s foot far more egg-shaped than with most pedal systems.
Zencranks are the brainchild of Dr. Zeno Zani, who achieved fame for positioning Italian cycling stars like Marco Pantani and Mario Cipollini on their bikes. He has written two books about bike positioning, Pedal Well and Disorders and Remedies of Poor Bike Positioning.
When I first received these cranks directly from Zani and his business partner, Stefano Doldi, two years ago at the Italian Expobici show, it took me a long time to get them on my bike, and that was not entirely because their FRM bottom bracket system is more of a pain to install than most. I disbelieved Zani’s assertion of the value of this egg-shaped foot trajectory, especially his claim of a 50-watt increase in power output, since I had been trained to believe in the benefits of a round pedal stroke. I had long drunk the Kool-Aid from Time, Shimano, and others of the efficiency to be gained by getting the foot as close as possible to the center of rotation of the pedal, whereas Zencranks greatly increase that distance. Until I looked at them closely, they reminded me of the articulated cranks on which Paula Newby-Fraser won the Ironman in Kona a few times, but they are actually diametrically opposed to Newby-Fraser’s cranks in function.
Zencranks come from the opposite philosophy of Shimano Dyna-Drive cranks and pedals on Dura-Ace EX and AX and 600 AX groups (on which Alexi Grewal won the Olympic road race in 1984). Modern equivalents for those whose memories don’t go back that far are the Side-Mount Pedals or the Vista Magic pedals. Rapid bearing wear and the appearance in the mid-1980s of clip-in pedals killed Shimano Dyna-Drive pedals.
After Look clip-in pedals had the market cornered for a few years, the pedals’ inventor, Jean Beyl (also the inventor of the spring-release ski safety binding), left the company and came up with the Time pedal. From the beginning, Time’s claim to greater efficiency was not only that its pedal offered free-float but also that it also brought the foot closer to the pedal spindle than did the Look pedal. Time explained this reduced “rocking torque” as an efficiency-robbing demand on the leg muscles forced to constantly work to keep the foot over the pedal spindle.
With clip-in pedals, we had lost the perfect circle traced by the head of the first metatarsal that Dyna-Drive had offered. Instead, all we could do was try to get the foot closer to the spindle, and the popularity of pedals like Time, Speedplay, and Keywin can partially be attributed to this. But now Zani wishes to change our minds and get our feet much further from the pedal platform.
Putting the Zencranks through the paces
I rode three different sets of cranks for extended periods on the same bike: 200mm Zencranks, 177.5mm SRAM Red 22 cranks, and 205mm Zinn ZIS2 cranks. Besides riding them hundreds of miles on flat roads and hilly roads, I performed a number of full-out climbing tests on a 7.3km section of Flagstaff Mountain that gains 1,940 feet in elevation. I rode the Zencranks off and on for over a year, and consistently for a month, before doing this timed test on Flagstaff.
Over what for me these days is about a 33-minute climb, I found the Zencranks to be around two minutes faster, or took six percent less time, than the 177.5mm cranks, and they were around a minute slower, or took three percent more time, than the 205mm cranks.
My times on the Flagstaff climb were 34:37 and 34:48 on the Zencranks on June 19 and June 26, respectively.
My times were 37:13, 36:24, and 36:06 on the SRAM cranks on July 3, July 10, and July 13, respectively.
My times were 33:30, 33:00, and 33:57 on the Zinn cranks on June 16, August 20, and August 27.
In all cases, I rode as hard as I could go. Of course, some days are always going to be better than others, and multiple runs are required to see any kind of a trend. [For those wondering why I didn’t use a power meter, holding a given power output (which would have had to have been measured in the hub rather than in the crank or pedal for obvious reasons) would result in the same time on the climb. Or, measuring average power output or total work done when going full out should have resulted in the same relative results on a steep climb without significant wind.]
The one-month gap in the middle of the testing with the 205mm cranks was due to a little scare with my heart, which resulted in a hospital stay, an echo cardiogram, an angiogram, and a month of 24/7 ambulatory cardiac telemetry monitoring of my EKG. Sometimes (maybe particularly over age 55), it’s hard to do a long-term test without life sometimes getting in the way. …
In addition to the time differences, I also noticed that the Zencranks felt comfortable to spin at high cadence, not significantly different than the 177.5mm standard cranks, despite the foot coming up so much higher at the top. The 205mm standard cranks do not feel as comfortable when spinning rapidly.
Clipping into the Zencranks is a significant downside to the system. Since the pedal sits so high above its center of rotation, it flips down and does not flip up simply with the toe like a normal Look Keo or similar pedal would.
Results from the extended Zencranks review
At first blush, it may look to you like a 200mm Zencranks arm is equivalent to putting a block between your shoe and your cleat equal to the length of the little link attached to the pedal shaft (in this case, 20mm, although future versions for 200mm and 195mm will be 15mm) and using a 200mm crank. This is true, except for the fact that you get 20mm higher cornering clearance with the Zencranks. At the bottom of the stroke, the foot only goes down as far as it would with a 180mm crank, but at the top it goes up as high as it would with a 220mm crank.
At the point of highest power, namely 3 o’clock on the crank circle, it is equivalent to a 200mm crank with its consequent 11-percent increase in leverage over the 180mm. The effective crank length effectively decreases from 3 o’clock to that of a 180mm crank by bottom dead center.
On the upstroke, due to the foot pointing down, it is close to following the same trajectory as with the 180mm crank. The illustration here compares a 190mm Zencranks crankset with a 15mm link arm to a 175mm standard crank, a scaled-down version of what the 200mm with a 20mm link compared to a 180mm standard crank would look like. Because the foot comes up so high, there is an increase in the gravitational kinetic drop of the mass of the foot, leg, and pedal. Zani claims that the cost of lifting the foot that high does not counteract the gain from dropping it.
I know from well over a decade of doing crank-length tests on Flagstaff Mountain with myself and with other riders, that a 10-percent reduction in time is to be expected with a 25mm increase in crank length, as long as the longest length does not exceed 21.6 percent of the rider’s inseam length. The results of this review tend to bear this out.
I recorded a six-percent decrease in elapsed time with an increase of 22.5mm in crank length between the 200mm Zencranks and the 177.5mm standard cranks, but it’s only the full 22.5mm increase in crank length for a portion of the power section of the stroke. For the 27.5mm increase in crank length between the 177.5mm and 205mm standard cranks, I saw the 10-percent drop in time I’ve seen repeatedly over the years. And the three-percent increase in time with the 5mm decrease in crank length from the standard 205mm to the 200mm Zencranks is more than I’ve seen in the past for that amount of length difference, but that could perhaps be explained by the fact that the Zencranks are only 200mm for a portion of the power stroke.
I’m a tall guy, and the 200mm Zencranks I reviewed are the longest the company offers, but they are still 5mm shorter than the cranks I normally use on all of my road and cyclocross bikes. The 200mm Zencranks size is meant to be a replacement for a 175mm standard crank and requires relatively little saddle repositioning to accommodate it. That is because the little connector link arm from the bearing shaft to the fixed axis of the pedal is 20mm long, so at the bottom of the stroke, the pedal platform is the same distance from the saddle as would be a Look Keo pedal attached to a 180mm crank.
My leg inseam is 38 inches (96.5cm), and 205mm is a relatively standard 21.2-percent proportion of my inseam length, identical to that of a rider with a 32-inch inseam on a 172.5mm crank. I would need 225mm Zencranks with the 20mm pedal arms to get the same saddle height and pedaling clearance as with my 205mm cranks, if they had Look Keo pedals on them. But given that the 200mm Zencranks gave me an effective 25mm decrease in crank length at the bottom of the stroke, I had to raise my saddle by an inch, and another 6mm for the switch from my Speeplay pedals to Looks, or a total of over 3cm. As I’ve built the bottom brackets of my personal bikes higher to accommodate the longer cranks I use, this effectively put me way up high.
However, most people using stock frames with standard crank lengths could switch to the Zencranks with very little adjustment of seat height. A more forward saddle position (and consequent increase in stem length) would be required to maintain the same relationship of the knee over the pedal as before.
The saddle would need to only go down 5mm for a rider switching from 175mm cranks and Look Keos to 200mm Zencranks, and not at all if the rider had Speedplay pedals on 175mm or Looks on 180mm. Pedal cornering clearance would also be the same as with a 180mm crank and Look Keos, save for a reduction in cornering angle clearance due to the Zencrank’s wider pedal stance.
The stance width of the Zencranks is considerably wider than most, as the arms splay out farther than most cranks, and the link arm takes up space between the arm and the pedal. Doldi tells me that future iterations will have a reduced Q-factor.
For the rider on a stock bike with standard crank length, the Zencranks have the advantage of offering the leverage of an 8mm-25mm longer crank through much of the power phase of the stroke without the large decrease in pedaling clearance and reduction in cadence that such a crank length increase would ordinarily bring.
Zencranks are UCI-compliant and are available in 180mm, 184mm, 190mm, 195mm, and 200mm lengths, with varying lengths of the link arm between the pedal and the bearing in the end of the crank. To achieve UCI compliance, the link arm is integrated into the pedal in the next generation. Also in the next generation, the stance width has been reduced by 6mm on the drive side and 7mm on the non-drive side. Bottom brackets will be available for BB30, press fit shells, and BSA and Italian-threaded shells. A new cleat shim called ZenSlip CAS (Cadence Accelerating System) will be available to change the inclination of the pedal; it is intended to accelerate the motion of the foot through the dead spots.
Minimum suggested rider height for Zencranks is 5-foot-4 (163cm), with a minimum inseam of 31 inches. Zencranks are as yet not easily available in the U.S., but they can be ordered online, and the price appears to be negotiable. The Zencranks in this test weighed 1,369 grams for the crank arms, pedals, and bottom bracket without chainrings and chainring bolts (130mm BCD spider arms).