Why do you make cranks over such a wide range of sizes?
Because people range so much in size!
When I first got into riding seriously, I got the longest cranks I could (180mm), because it made sense to me that with my 6’6” height I should have the biggest frame, widest handlebar, longest stem and longest crank available. That logic after all held true with clothing, beds, cars, etc., so why not with bikes?
Later, when I got my first really nice racing bike, a Masi equipped with 177.5mm cranks, I noticed that when I switched those cranks to 180mm, I immediately started dropping the guys I’d been climbing evenly with. The next year (1980), when I was first on US National Cycling Team and was having my bike fit checked, Edward Borysewicz (“Eddie B.”), the US head coach at the time, told me I needed considerably longer cranks yet. My quest for cranks longer than 180mm began then and never stopped until I could offer proportional-length cranks for tall (and short) people.
Little kids’ bikes have small wheels and short cranks as well as small frames, stems and handlebars because it works best that way. A small child is so inefficient as a rider that he or she cannot get the bike going if it is not close to optimally efficient for them in terms of sizing. Remember that, besides being new to balancing on a bike, a kid’s bike is much heavier relative to their weight than your is to your weight.
As the child grows, kids’ bikes available to them have increasingly longer cranks and larger wheels, as well as bigger frames, stems and handlebars.
Given that, doesn’t it seem a bit strange that when we become adults our bikes all have the same wheel size and essentially the same crank length? Are we all suddenly optimally suited to the same crank length and wheel size? Nobody questions that there needs to be a wide range of frame sizes, stem lengths, and handlebar widths to fit everybody. However, you can count on your riding buddies and bike shop salespeople questioning it if you want to ride a crank outside of the given 5mm range from 170-175mm.
Many of the standards in the bike industry are based on traditions that started pre-WWII (even pre-WWI) when people, at least in first-world countries, were smaller on average than they are now. And it also stands to reason that the last thing crank manufacturers, distributors, and bike shops want is the expense in tooling and inventory of as many crank sizes as there are bike frame sizes (or shoe sizes!).
How do you determine crank length?
For most road riding, we recommend a length between 21% and 21.6% of a rider’s inseam. (Inseam is measured in bare feet from the ground up to the top of a level broomstick pulled up firmly into the crotch.) This is based on seven years of experience of selling custom cranks. A shorter length is often called for on a mountain bike and a cyclocross bike (see below). For most track events, a shorter crank is also advisable.
How will the proportional length cranks affect my cadence?
Riders who already ride lower cadences often find no cadence change when going from, say, 180mm to 205mm; they instead just report a straight increase in speed, and, usually, comfort as well. However, riders who tend to keep a cadence of 90RPM or higher will find that to be unsustainable with a longer crank.
What cranks do you offer?
Currently we make road cranksets with external bearings and an integrated spindle in 185-220mm lengths in standard double, compact double, and triple configurations. They fit SRAM/TruVativ external-bearing bottom brackets.
In our traditional crank design that we’ve been offering since 2001 and that fits on a square-taper bottom bracket spindle, we make all lengths from 130mm to 250mm in road and mountain-bike styles. We offer almost any road spider configuration under the sun, including 110mm, 130mm, 135mm, 130/74mm, 135/74mm, and 110/74mm bolt circle diameter (BCD). Our mountain bike cranks come with a 5-arm 94/58mm BCD spider.
All Zinn cranks come with a bottom bracket included in the price. We of course also sell cranks in standard lengths from Shimano, SRAM, Campagnolo, FSA, and many others.
Do long cranks hurt cause knee pain?
Our customers without a history of pedaling-related knee pain using cranks in the 21-21.6% of inseam length range almost universally report no new knee pain with the longer cranks. We are choosing a length that is in keeping with the length that champion cyclists use relative to their leg length, so your knee and hip angles will be no tighter than theirs, and your percentage of extension and flexion of your muscles will also be no greater. So mechanically, there is no reason you’d have more knee pain.
Lower cadence is often associated with knee pain, but that is without changing crank length. If you pedal at a lower cadence but have more leverage, the peak load can be the same. If you pull a stuck nail out of a board with short claw hammer, you feel more strain in your arm than if you pull it out using the claw on the end of a long crowbar.
What about pedal clearance in corners?
Clearance depends on the crank, the frame, the pedals, the rider’s technique, and the type of event/ride. In the ideal situation, the frame is built to fit both the rider and the crank for the type of riding they do; then the bottom bracket height can be adjusted to provide the desired pedal clearance. At Zinn Cycles, we generally build the bottom bracket on a frame getting a 200mm crank 25mm (one inch) higher than the BB of a frame made for 175s.
However, the majority of our crank customers are not putting their Zinn cranks on frames we or another custom builder has made to fit them. The longest crank we recommend for somebody using a stock frame is 200mm, and only if they are not even thinking of racing criteriums. In a criterium, more power is worthless if you open a gap to the next rider in every corner that you have to close at great expenditure of energy because you had to restart pedaling later to avoid hitting your pedals on the road. I think it inadvisable to race criteriums on a stock bike with a standard (265mm) bottom-bracket height using any longer than a 175mm or 180mm crank.
We do have successful tall masters racers competing on our cranks up to 195mm who must use a stock frame due to sponsor constraints. But they adjust their riding style and choice of events accordingly.
For anybody who has a question about whether they’ll have enough pedaling clearance if they buy a crank from us, we recommend taping a styrofoam block the thickness of the length difference they are considering to the bottom of their pedals and notice if or when they touch it to the road.
What other changes do you make to a custom frame for the crank?
The reason stock big frames have super-shallow seat angles is not because the bike handles better with the rider’s weight cantilevered out over the rear wheel, causing them to pull wheelies on steep climbs, but because the cranks are not proportional in length the length of the rider’s legs. In order to get the knee over the pedal spindle with a crank that is disproportionately short for the rider, you have to have a shallow seat angle to move the saddle further back. If the cranks were proportional to the leg length, the seat angle could be standard. On a custom bike, it would only be based on the ratio of thigh length to lower leg length (longer thigh, shallower angle, shorter thigh, steeper seat angle).
The same holds true for tiny frames with super-steep seat angles, of course. Steep seat angles are used to get the knee over the pedal with a stock crank that is overly long for the rider, and to avoid the toe hitting the front tire. With a proportional-length crank, a small rider could also ride a normal seat angle without having the knee way behind the pedal, and pedal-overlap issues would be reduced as well, hence no need for a steeper seat angle to pull the crank away from front wheel as well. And then their bars would not need to be as high, because their knees would not be coming up so high hitting their chest and tugging on their hamstrings.
Should you use the same length for a road bike and a mountain bike or cyclocross bike?
1. Unlike most road riding, which is more steady state with consistent cadence for long periods, thus making full use of the long crank, mountain biking in technical terrain and cyclocross racing involve frequent drastic changes in cadence. Spinning the cranks back up to speed is better accomplished with a shorter crank, while powering up long climbs is best accomplished with a longer one. So I try to strike a balance between those requirements and look for crank length more like 20-21 percent of inseam length for the mountain bike or ‘cross bike (as opposed to 21-21.6 percent of inseam for a road bike).
Of course, a the same crank length as the road bike works well on a mountain bike or ‘cross bike that is used for riding on dirt roads and relatively smooth trails.
2. I designed the bottom bracket height on the Megabike and Gigabike for a 200mm crank. On a custom hardtail or a custom full suspension bike, I can adjust this, but I highly recommend against using any longer than a 205mm on our stock-sized full-suspension 29ers for anyone who rides them in technical terrain, to avoid banging the pedals on rocks frequently.
3. A stock mass-produced mountain bike will probably not have a high enough bottom bracket to ride on technical trails with a crank any longer than 175mm or perhaps 180mm.
Are there any tests showing what length crank is best for a certain rider?
I’ve done a ton of testing of crank lengths, and the fact is that it may not be possible to properly do such a test that gives a blanket result of X length is best for Y rider. Others have tried as well. You can find many papers written on the subject. I have yet to see one that met the criteria of repeatability.
In the mid 1990s, I did many months of crank length testing at VeloNews that I published in the April 10, 1995 issue, with a followup test in the April 29, 1996 issue. I went so far as to build an ergometer that held the flywheel and apparatus for a Monark ergometer; it was essentially a Monark ergometer (which I was familiar with because that’s what we used at the Olympic Training Center when I was there as part of the National Cycling Team) that took standard parts. (Most ergometers have square seatposts, a seat tube that is not coming off at a standard angle from the center of the BB, a non-standard BB shell, a non-standard stem and bar and no way to mount these things.) Boone (a now defunct crank maker) made us cranks from 100mm to 220mm, and I made a super-long adjustable stem. We tested a range of riders from 4’11” to 6’6″. All were highly trained cyclists.
Problem is, if you allow the rider to get used to a certain crank, it throws off the test, because you cannot guarantee the same level of conditioning health, etc. on each crank they test. You also can’t do them all at the same time, because the subjects become tired out when you do a step power test as we were doing. And the cadence must be matched to the crank length – you have to pick a cadence for a step test. So if you use 90RPM with a 170mm, then you scale the RPM proportionately up for shorter lengths and proportionately down for longer ones. But changes in cadence and amount of muscle extension/contraction and joint flexion/extension require adaptation for efficiency. But you can’t do that if you have a group of cyclists who are racing and training for events of interest to them. And no test that I’ve ever seen took good cyclists and paid them to maintain a consistent training level over an extended period. We certainly couldn’t do that at VeloNews. Without that, it will never give good results, and even with it, the time frame would become so long that environmental changes also might lead to distorted results.
Our results from those 1995 VeloNews tests without being able to control those things showed that:
All riders, regardless of size, produced more power longer as the crank length increased
All riders regardless of height could ride at low power outputs with a lower heart rate on shorter cranks.
I believe that you would see separation based on rider size if the riders were allowed to get accustomed to each crank length, but it was not possible. The length differences were so vast that their personal bikes could not be adapted to them and give them the same setup. And they all had certain racing goals, so they weren’t willing to ride for weeks on end and do events on some setup they’d been given in the lab. So they just came in and jumped on the ergometer and did tests every couple of days.
And then of course a proper test requires a double-blind procedure, so the test subject does not know what they are testing. That’s not possible with vastly differing crank lengths requiring huge changes in the set and handlebar position on their personal bike.
I did another test for VeloNews around 2002 using a PowerTap and timing riders on a one-mile climb varying from 10 percent to 17 percent. Three well-trained 6’5” riders used 180mm, 185mm, 190mm, and 200mm cranks and went up the climb as fast as they could, using the different cranks in random. Two of the riders had 180mm on their own bikes, and the third had 200mm, but none had the chance to get used to any of the other crank lengths besides the one they’d been using. Every rider was faster on each progressively longer crank, but the time differences were so small over this 8-minute climb, and combined with the inability to control environmental factors as you can in a lab, that I felt it was statistically insignificant, so I never published the results.
I’ve continued to do lots of straight climbing tests with tall riders with lots of crank lengths. This consistently shows an increase in speed with increasing crank length, but again, performed outside, there are too many other variables you can’t control — wind, temperature, barometric pressure, humidity, traffic, etc. to make it ever stand up to scrutiny. So I never was satisfied that I had a test that you could publish in a journal, so I never did.
So, it comes down to the individual to do the testing on themselves and to gather enough data that it smoothes out differences in environment, training, etc. that you can look at long-term trends. Some of our customers have done that and are convinced they are much faster with the longer cranks. There’s one testimonial on our site from a guy (Steve McGrath) who is careful about doing these tests as accurately as possible. With myself, I’ve done that for years on a certain 30-minute climb here to the point that I can say with certainty that on average I’m 2 minutes faster on a 205mm than on a 180mm on that climb. But I’ve done it for so many years that I can’t compare the early tests with the late tests, because I’m 50 now and I started doing them when I was 21. And that 21-year-old speed is not coming back no matter what crank length I use or how much lighter my bike is now or how many more gears it has now or how much easier to shift it is now than in 1979.
Longer cranks = more power; even the arguments against longer cranks say that, but how do you address the issues of reduced ability to spin?
One benefit of spinning is spreading the load over the work cycle so that the peak power on each downstroke is reduced while maintaining a given power output. This is the entire reason behind the Lance Armstrong/Chris Carmichael high-cadence adaptation. You will notice, though, that Jan Ullrich, try as he might in the offseasons to develop the same kind of spin rate for the same reasons (a) could not do it (b) could not be efficient at it, (c) found it uncomfortable, and (d) for the above 3 reasons did not see the benefit of reduced heart rate and lower lactate concentrations at the same power output that Armstrong did. The reason cited was that it was inefficient to move his legs, which were so much, longer, bigger, and heavier than Armstrong’s, around and around at such a high cadence. He was more efficient at a lower cadence, and I have generally found that taller riders, especially heavily muscled ones, tend to be gear mashers (low-cadence riders).
Now, with longer cranks, you get the same benefit as you do with spinning, but at a lower cadence. For the same reason that it is harder to pull a stuck nail out with a claw hammer than it is with a crowbar, you can reduce the peak load on each downstroke at a given power output by increasing the leverage, which is what a longer crank does. And if cadence decreases proportionally with crank length, linear foot speed along the circle remains constant; there are some who cite this as critical, since it determines the speed of muscle contraction.
Furthermore, one would have to assume that the crank length that, say, a Lance Armstrong wins 7 Tours on is a pretty efficient length for him. And that the range of knee and hip angles (flexion and extension) he uses is optimal. Same with the range of extension and contraction of his individual leg muscle fibers and entire muscles themselves. So what makes us think that a long-legged rider working like a sewing machine with a short little crank (for them) or a short-legged rider working through a huge crank circle (for them) is going to be efficient? Should we tell them that’s the way it’s supposed to be simply because the range of available cranks is essentially not a range at all?
But if the crank length is in the same proportion to the taller or shorter rider’s leg length as Armstrong’s is to his legs, then all three of them will move through the same joint angles and muscle extension and contraction rates.
What about reduced ability to accelerate?
In events where acceleration is at a premium, probably a shorter crank is a benefit. That is my guess and seemingly my experience, but I’ve also not seen compelling data on it, for the same reasons cited above. Magnus Bäckstedt, a recently-retired (from the Garmin-Slipstream team) ProTour sprinter and former Paris-Roubaix winner, was happy on a 190mm crank I made for him. He and Garmin-Slipstream biomechanist Allen Lim determined that he was more efficient, he knew he was more comfortable, and, in combination with his Rotor rings, he felt that his jump (initial acceleration) was faster and felt more able to continue ramping up the speed. The problem was gearing. At the 75kph speeds of ProTour sprints, he could simply not turn the 190mm fast enough. He has to turn a 53 X 11 at 124RPM to go 75kph. To go 75kph at 110RPM, he would need a 59 X 11 gear, which is not only hard to find, it shifts terribly. And while a proportionately larger wheel and tire size would eliminate the problem and allow him to use the same gears as everyone else, we all know that no tire or rim manufacturer is clamoring to change standards for racing bikes. So he abandoned the idea. But it does help explain why taller riders lover 29er mountain bike wheels, or even 650B ones.
Won’t you produce the most power with the cranks you train on?
You will perform relatively better on a crank you’re accustomed to than on one you are not. All riders still produce more power on longer cranks. It’s just that, were they as accustomed to them as they were to the ones they usually use, one would expect to see yet more of an increase due to adaptation.
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