Hi Iain!
Just sat down at the computer and saw your questions about the kinesiology doctoral study I participated in so many years ago, where particular note was made of crank length and RPM and volumetric efficiency. Let's take your questions in turn...
When you were doing your cadence tests were the test done against a load or free spinning?
Kinda both. You see, Iain, the researcher was a friend at the time and he was interested in bicycles but not bike-mad as I was (am?), so I kind of got sucked into the whole thing (I was a willing lab rat who was burning with curiosity to quantify my physical abilities. Seemed like a fair trade).
The study had a number of methodological flaws and in the end, my participation and data were not included. They were excluded not because the data was bad, but because the methodological focus became more standardized and fortunately gained more internal validity along the way.
At the time I was tested, Jim (the friend) was trying to modify what amounted to an exercise bike, and the bottom bracket was threaded oddly (Swiss, as I recall) so it could not take the cups needed for the BB spindle we needed that would be T/A compatible (the brand of crank available at the time with the greatest possible variations in length). The upshot of it was, I volunteered
my bike sized for
me and
my rollers and
my front wheel stand for the rollers, so the whole test rig was biased to uh, "me". The data couldn't be extrapolated to the rest of the test population, but it helped Jim hone in on the research design he needed for the full study.
At the time I came on-board, the study was woefully designed in light of today's research tools. He had no light markers or wire-frame analysis for positioning and position analysis. There was no measurement of power production except by interpolated fractional horsepower (such a gross measure as to be worthless). No watt-meter or joule or erg measurement.
My rollers had ("have" as I still own them) sealed bearings and 4.75in/12cm turned alu drums with adjustable sealed bearings and an add-on resistance device that consisted of a rubber-tired wheel with sealed bearings that can be cranked against the last drum to increase resistance. We couldn't figure out how to instrument the amount of drag produced, so we left the resistance wheel out of the equation and I only pedaled against the friction of the drums -- which we also had a terrible time standardizing and measuring. Unlike a flat ground plane, the drums presented a convex surface to the bike tire, and increased friction from tire belt and casing distortion (I've always found my rollers put a lot of wear on my tires in a short amount of time). Add in the friction of the adjustable sealed bearings and the rubber drive belt between the first and second of the three rollers, and that was pretty much the resistance I had to pedal against. Not a lot, but not nothing, either, and who knows how much? And, the front wheel was missing from my bike 'cos the fork was on the stand. There's no way
I could have stayed centered on the rollers at those cadences, though there have been accomplished "roller-racers" in the past who managed to spin incredibly high cadences on rollers. I've read some of the accounts and seen old news footage and view them with a mix of awe and incredulity. My peak rpm was a short-lived thing, and at the time, I thought I'd be short-lived as well. It took a lot out of me. I was pretty astonished at the measured rpms.
I no longer have the VO2 Max results, but I know I was pulling a *lot* of air. At the time, I had exercise-induced asthma, and if the testing had not taken place in a warm room, I couldn't have done it. Cycling in cold air set me to wheezing and my oxygen uptake fell sharply in the outdoors winter months.
Anyway, Jim eventually settled on a different exercise bike as a test rig and he did eventually earn his PhD, but by that time I was no longer involved and I don't know the particulars of how the final testing was all set up. I'm glad it worked out, as the preliminary phase I was involved in had a number of methodological problems but was fun for me.
I ask as I have been planning on getting some Zinn Proportional Length Cranks with the ideal crank length in the range of 21% – 21.6% of your leg length...Do your favoured 170mm cranks fit in this range?
I don't see how they could, Iain, but so much depends on how leg length is measured for such recommendations. There's so many variables that have to be standardized. I stand 5ft11in/180.3cm tall, and I know my standover measurement for ordering Sherpa was 88cm/34.65in standing in my heelless Detto Pietro Art. 74 cycling shoes. That measurement effectively changes on the bike due to the cleat stack and orthotics and pelvic angle of approach depending on whether I am forward on my ischial tuberosities (sit bones) when on the drops or rocked back on the hoods or tops. Jim's study did find (my) pelvic rotation affected effective leg length by altering the location of the hip socket in relation to the pedal/crank at the bottom of its travel (BDC or Bottom Dead Center). There is also the problem of how much the rider prefers to have his/her knee bent at BDC, which is a function of saddle height and distance behind the BB. There's a dizzying array of variables to account for and standardize.
If we take my 88cm standover measurement (floor in cycling shoes to "hard points" at underside of pelvis at or near the pelvic sympysis), then according to Zinn's formula my cranks aren't long enough. If we take my measurements from the center of the hip joint, then the cranks are even more too-short according to his formula. At 21% of my 88cm, I "should" be running 18.5cm/185mm cranks. At 21.6%, I "should" be running 19cm/190mm cranks. And...I can't. The circles I would pedal are too large for me to comfortably manage. Cranks longer than 170mm make me "feel" as if I am pedaling too fast as well as "too large" and I just can't manage it. When I was young(er!) in those uni days, I could just manage it once, but had enough sense not to push it. Now, I wouldn't try. Maybe age (experience!) has left its mark, but I have found my personal "sweet spot" and won't leave it. I have often thought it might be nice to go with 175mm cranks to get a little more torque on the frequent climbs that are part and parcel of leaving my Willamette Valley on three sides, but...no. I got a nice set of Deore 175mm cranks in trade from a friend a few years ago, mounted them on the bike and...no. Uh-uh. Just can't manage it.
I'll be the first to say there's probably something going on besides the physical geometry of it all. Muscle-memory is a powerful thing, as are personal preferences and going with what "feels right". In fact, those might be the major factors for me. Especially so where I came to cycling as rehab for knees injured in a car accident in my high school years. I just don'wannah mess up my knees again, and I've found spinning fast and light on 170mm cranks actually helped my rehab, kept my knees healthy, and are the recipe for keeping them happy. If my knees are happy, so am I. It is entirely possible that with practice I could adapt and do pretty well, but if I have a ready solution, why try? I'm a happy camper and don't wanna harsh my mellow over it.
On a related topic, I thought my tread width (as it was called in the late 1890s-early 1900s) or Q-factor (as it was called by Grant Petersen in the early 1990s) or "distance my feet are apart" as I call it would be a huge factor in my cycling comfort, but -- amazingly to me -- it hasn't been a big deal. I've always set-up my bikes with the lowest possible Q-factor I could manage, but Sherpa has the widest effective Q measurement I've used and...non-issue. Sherpa's Q at the outer crank pedal face is 178.6mm. My Miyata 1000LT was 163.1mm. My other bikes (all with triple cranks) are at or near 158mm. I was sweating bullets over it and even thought I might "have" to swap-in my old drivetrain to the new bike but nah, it's fine. Quite a revelation to me. My handlebars are getting wider and wider over the years, as well. From 37cm at the tops of my old randonneurs at the brake hoods to around 44cm on the tandem and Sherpa. Of course, I "seem" to be getting wider as well. The guys in my family tend to do a "chest-expansion" thing as they get older and (weight gain aside), we get thicker through the chest and wider across the shoulders. Dunno why. Not supposed to still be growing at age 52 (FIFTY-TWO?!?
How'd *that* happen?!? I'm 19 inside...), but shirt sizes and chest measurements don't lie.
When riding the tandem with a small stoker, I often look back in horror at the lateral ankle-knee-hip articulation I see going on behind me. The smaller stoker is sitting atop a triple crank with 170mm arms *and* a crossover drive on the left side, making for an incredibly wide Q-factor. It is all aggravated by the angle of approach; the lower saddle increases the effective angles, making it all that much worse. Hmm. Perhaps this is a reason why I can't get tandem stokers (see:
http://www.thorncycles.co.uk/forums/index.php?topic=4021.0 ).
In your comment to Jawine, you said...
As for fixies, not for me, they scare the daylights out of me. Some bad experiences with pedal strike when I tried one in my younger years. Not nice at all.
Oddly enough, I like 'em, but only so long as the BB is high enough to prevent pedal strike. Like you, Iain, I've managed to catch a pedal on occasion in the past, and it was a distinctly unpleasant and sphincter-squinching experience. I often ride "faux-fixed" in the early season to build some "souplesse" or suppleness in my legs. I just put the bike in a suitably low gear (58-62 gear-inches) and stay with it, not coasting and "pedaling-down" in rpms as my brakes go on to keep the simulation. Works wonders for getting the legs loosened and the revs back up where they belong for me (110-120rpm in such low gears is pretty standard for me at cruising speed. Remember: Gotta keep my knees happy).
Iain, as you may have figured by now, I'm mightily interested in things such as crank length and how they affect performance, so I'd be delighted if you drop a note at some time in future to let me know if you get the longer Zinn cranks and how they feel. Or better yet, a post on the list, so others could benefit. Great stuff! Thanks for the reposts/quotes and links.
Poor Jane's thread has grown well beyond her original question. Hope she comes out alright in the end. About getting the cranks put right, she said about the shop...
It is difficult as they come out with all sorts of rubbish to cover the botch up.
Shame on them; for shame! Best to own up and make it right as soon as the problem comes to light.
All the best,
Dan.
