On Bicycles, and.... what else is there?

Despite an early afternoon meeting for which I risked tardiness if anything went wrong, I felt a strong need to test my fitness on the Noon Ride, Wednesday edition, which climbs my favorite climb anywhere: Old La Honda Road. After the cheap LR44 batteries I'd last installed in my Powertap gave up the ghost a few weeks into my Basel Switzerland experience, I found some superior 357's (silver oxide) in a local combo department store / food store. This should have had me up and running but I didn't have the tool to remove the cover on the hub. I eventually brought it to a local shop, to see if the guy there could remove it with an open-end adjustable wrench, but it was too tight and the metal wrench risked damaging the flats on the hub cover. So I decided I didn't need power all that much in Europe and to wait until I got home. Indeed, the cover was on quite tight for some reason, and after applying some Tri-Flow to the interface between the cover and the hub, applyin...

After the last comparison, which was a ride with some steep hills in San Francisco, I did a few more rides comparing Vector to Powertap. On that previous ride, my maximal power curve had been somewhat depressed on the Vector. Further investigation showed it appeared to be due to two points where cadence anomalously dropped on the Vector (but not the Powertap). Since Vector multiplied force by cadence by crank length to get power, if any of the three is off, the power is off. The first of these two rides was a spin around Mountain View at lunch, stopping along the way to drop a package at the post office, then pick up some cherries at the local market (Ava's), then after a bit of a loop, a stop at Trader Joe's for figs and apricots. I made good use of my handlebar bag, combing some solid power efforts with fresh summer fruit for the afternoon. Here's the maximal power curve from that ride: The next day I rode into work with SF2G, the Dawn of the Dead variant of Bayway....

Last time I compared Powertap to Vector on my Winter Allaban, I had failed to properly set the crank length on the Garmin 800. I'd set it on the Vector, but the menu item on the Garmin is a bit tricky to find, as it only appears when it is in communication with a Vector, so if you scan the menus without activating the Vector and pairing the Edge to the Vector you'll never see it, as I did not. I actually first confirmed my Edge was asserting the wrong cranklength by running the settings.fit file through fitdump. But this is a digression. I basically repeated my first calibration ride, heading steep 14th Street to Buena Vista in San Francisco and doing one-legged climbing on a more gradual grade, then riding home and doing a sprint. I previously did three comparisons where the maximal power curves of the Powertap and Vector were remarkably coincident after I scaled one of the powers by an empirically determined factor close to the 85% value which I later discovered was the r...

I typically use my Powertap on training rides, but when racing, I've not done so since I placed third Ross's Epic Hillclimb up Pine Flat Road in Sonoma back around 2008 or so, At the climb, I'd decided the added weight of my Powertap wheel was worth it for the pacing advantage of power. Unfortunately, my battery died on the start line, so I carried the substantial extra mass of the Powertap up the hill for no advantage. Despite the lack of power, though, I had arguably the best climb of my life, staying with a critical surge I might well have not gone with had I been pacing off the meter. That surge led into a flat/slightly descending part where being with the group was a critical advantage. When the climbing began again, steeply, I felt as if I was going to crack, but then most of the others cracked more. Without the weight of that wheel I may well have been one place better. But power is also useful for post-ride analysis. But for that, I rely on the standard power...

The plot thickens... Another day, another ride. This time I made sure to do a static zero test before the ride. I further checked that I had the latest firmware in my Edge units (Mac WebUpdater says I did). I was full of hope that the crank length fix had corrected things. So I set off on a ride to fetch new contact lenses, but where I took "scenic detours" up five significantly steep, significantly painful climbs in San Francisco. For the record: 17th from Market to Twin Peaks (and on to Twin Peaks summit), Sanchez from 17th to 18th, Church from 18th to 21st, 21st from Church to Sanchez (these two are contiguous, but I took a break in between, not initially planning to ride 21st, which is daunting), and finally, just because I felt like I could, the ever-painful 22nd from Vermont to Carolina. No luck. My suspicion now is that the head unit is overriding the crank length setting. Issue is I don't know how to change the crank length in the head units. In the 510 ...

Last time I did a comparison of my Powertap versus Vector. I'd had strong reason to believe the Vector was reporting low, and the test confirmed it. The maximal power curves lined up fairly nicely when I multiplied the Vector power by 0.84 (emphasis on fit to high powers). Since the Vector should measure more power than the Powertap, this indicated an error somewhat greater than this. You'd expect the Vector to measure more power, because the Vector power includes power which doesn't make it to the rear hub and is instead lost in the drivetrain. This power loss includes losses which are proportional to load (like bending the chain under a high-tension state at the top of the run) and losses which are independent of load (like spinning the pulleys). The result is that drive train losses, as a fraction of total power, are higher at lower powers than higher powers. What I saw was consistent with this, which was a good sign. The obvious candidate was that I'd not inse...

On my relatively new randonneuring bike, which got its first serious long-distance test in the Memorial Day Ride (MDR) this past week, I've been using Garmin Vector Pedals I was lucky enough to get. The Garmin Vector, of course, offers the advantage of "true" left-right power, since it is effectively two independent power meters, one for the left, one for the right. But even though I've had the pedals on there for awhile, I've been ignoring the power data. I didn't trust it. It's not that I didn't think the Vector is a good product, but rather I didn't trust the installation decision I made to not install any washers. Of course, I could have just added the washers, but that would lose interesting data. I wanted to do a direct comparison with Powertap to quantify what the reduction in power, if any, was. Being generally lazy about this sort of thing, I procrastinated... until today. In this post I compared power data versus climbing rate on ...

In Dec 2011 I compared Strava power estimates to Powertap measurements for the Cortland Hurl , a previously popular climb for SF2G . Unfortunately the Hurl has gone out of favor with the Google riders, but recently I did a ride with a leisurely spin up the climb, which has been an occasional fitness test for me. New to the ride was my use of Garmin Vector, mounted on my heavy (10.5 kg) Winter Allaban. You'd expect a relatively high watts at a given VAM with the big bike with fat tires at relatively low pressure. So I was curious to see how the watts I reported on the climb compared to my previous trend. Here's the result: The data are sparse, and it would have been a lot better had my Vector ride been at a higher VAM. But it is strongly compelling that the Vector is reading low. The Strava estimates are certainly low in particular due to an underestimation of mass. The Strava method of asking for "bike weight" and "rider weight" omits the weight of eq...

The cleverest way I've seen to check cadence data is due to Robert Chung. He uses cadence and speed in conjunction with an assumed wheel rolling circumference to calculate the for a bike for each data point. If cadence and speed were measured perfectly, I'd be able to see exactly what gear the rider was in at every point where he was pedaling (no coasting). On the other hand, if the cadence or speed are measured sloppily, then the gear calculation would also be sloppy. The key insight is that gears are discrete: there's a countable number of choices. So if I can extract the gear, I should see only a discrete set of results: plotting gear over time should show steps, with transitions between the steps corresponding to shifting, with deviations from the steps only when the rider is coasting with the cranks stationary, or, hopefully not often, spinning the cranks while coasting. The issue with this approach is it depends on both speed and cadence being of equal quality. ...

In the previous post I compared power from the Stages power meter to power from the Vector power meter (or meters, since L and R are separate) measured by DC Rainmaker on a ride he did in DC after the Vector release in Boulder, Colorado. Since Stages is measuring power only on one side of the bike, it is natural to compare the results with Vector, which measures power on each side of the bike separately. Before that, I showed that the Vector total power agreed well with Powertap and Quarq. If I assume that validates total power for the Vector, then it validates L and R power separately, since total power is derived from L and R power (the validation would be invalid if there were errors which naturally canceled between the L and R side, but I can't identify any). But Stages does one thing I really like: it measures cadence multiple times per second, instead of relying on an average cadence associated with the time for a full pedal rotation. The constant cadence approximation l...

DC Rainmaker has posted another dataset to his blog ( Zip file here ). His early installation issues behind him, these data serve as a valuable comparison between the power meters he's using: the spanking new Garmin Vector, the Quarq Elsa, Powertap, and Stages. The point of this post is to quantitatively compare the powers. But first some discussion... Each of these power meters is measuring power at a different point in the transmission path. Vector gets first shot at it, picking up power transmitted through the pedal axle. Stages is next, measuring power in the left crank arm. Next, Quarq measures it in the crank spider. Finally Powertap picks up the power which manages to make it to the rear hub. The largest losses are expected between the Quarq and hub, as mechanical losses in the chain and in the rear derailleur pulleys converts mechanical power into heat before the Powertap sees it. Between the Vector and the Quarq, it takes more imagination. Brim Brothers, not yet...

"Back in the day" it was common to have a "racing bike", or at least "racing wheels", and a set-up more generally used for training. The idea was the training bike would take more wear & tear, while the racing bike was kept in more refined condition for racing where small efficiency gains were truly important. Examples of tradeoffs include: cost: given a fixed amount of wear & tear or damage risk, it's better to use a cheap part than an expensive one, since the cheap one is easier to replace. Examples of this include wheels, cassettes, and chains: these parts wear out (wheels from rim brakes, drivetrain from normal use) and if the performance gains of expensive stuff aren't important in a particular ride, it makes sense to go with the cheaper parts for these. reliability: lighter parts tend to be less reliable, with less wear life, so even at the same cost (which they're not) it makes sense to stick with more durable stuff if the t...

The Cortland Hurl is the only significant climb on the SF2G Bayway route. According to Strava, it gains 25 meters in 400 meters, an average grade of 6.3%, although the grade is non-uniform. It starts out fairly gradual, then steepens, then gets gradual again towards the top. I like to make a good effort here when I'm feeling good during morning commutes. Typically I'm behind at the top of the steep bit, but I tend to do fairly well on the final gradual portion. If I'm having a good day, depending on who's there and how they're riding, I have a chance to be first to the top. I've not ridden with a power meter for a year now. I sort of lost interest: I just like riding my bike and I don't care what the power meter data are, so why carry around a heavy, expensive Powertap wheel? Strava gives me a fairly good idea how I'm doing with its segment timings. However, in addition to speed numbers Strava also produces power estimates. In fact, it will u...

Garmin released its Edge 500 head unit at around the same time as CycleOps released its Joule. Each of these was an ANT+ Sport compliant head unit which could read power data from compliant power meters like the Quarq and PowerTap. However, otherwise they almost couldn't be more different. The Joule's focus was on functionality. Power users like to analyze their data, CycleOps reasoned, so we're going to give the user as many options as we can fit to crunch power numbers and even do history analysis. This sounded good, but the head unit is the wrong tool for this job. Riders would upload their data at the end of the ride anyway, for example with Golden Cheetah or WKO, then may be from there to a web site like Training Peaks. So the result was a heavy, bulky, and expensive head unit which sold like coldcakes. And despite all the cost and complexity the unit lacked GPS. Why burden a head unit designed for a power meter with GPS? The Wattage List old-guarde esche...

I don't use my PowerTap on hillclimbs because it's too heavy, and I don't use my PowerTap in mass-start races because sometimes you've just got to dig deeper than you think you can. But for Terrible Two, I decided within the last few days I wanted it. Sure, hauling that 1020 gram wheel up 16 thousand feet of climbing was going to add work, and work equals time. But a double century for me isn't about minimizing work, but rather in minimizing work done over threshold. And to keep my enthusiasm in check on the early climbs the power numbers would be useful. Additionally, as a diagnostic tool it would be really valuable. I wanted to compare the power I could sustain on later climbs to those I was able to hold on the earlier climbs. Now, I've already documented here my torque measurements suggest my Powertap reads low. The steeper the climb, the more low it reads. This error is on the order of 10 watts or so, so view numbers reported here with that sort o...

Saris sent me back my powertap wheel after I'd sent it to them for torque-tube test. Hats off to Saris: they did it w/o charge and returned it to me quickly. But had they actually done anything? Unfortunately I didn't follow up their quick return with a quick re-test. Honestly, I found it liberating to not have power numbers telling me how lame I was every single ride. It was fun to just ride. I didn't need the power meter to tell me if I was going hard or not. But eventually I couldn't ignore it any longer. So time for the torque test, again. My procedure was slightly modified, after what I'd seen a friend do with his. To optimize the crank orientation (the weight needs to hang perpendicular to the crank or the torque estimate will be off), I grabbed the rear wheel and rotated in, forward and backward, until I saw the Powertap torque reach a maximum value. But here I deviated from my friend's approach: instead of using this number, I grabbed the brak...

My off-season (well, not so off-season at this point) focus on trail running this year has really killed my legs. As a result, I've been generally suffering on Old La Honda during the Wednesday Noon Ride. Guys I am accustomed to staying with have been simply riding away from me, chatting in a relaxed voice, while I suffer, gasping, in their wake. But now that's going to change. It occurred to me during my recent Pirates Cove Trail Run that my Powertap, which as I've documented hasn't been reporting accurate power anyway, can be put to a far better use. The key is the piezoelectric effect. The Piezoelectric effect, as applied to measuring power, results in the following relationship: voltage = (torque ‒ τ 0 ) × K, for some τ 0 and K. However, trivial algebraic manipulation yields: torque ‒ τ 0 = voltage / K, where torque ‒ τ 0 is "useful torque" sufficient to overcome the built-in tension in the powertap hub. What this says is if instead of forcing a c...

Prior to sending my Powertap back to Saris for calibration, I decided to do one more torque test (previous posts: my wheel , comparison with other wheels ), this time bypassing the Powertap internal zeroing, and go directly to the raw torque numbers, which are available in torque mode on the Cervo head unit. My procedure: weigh test load (a bucket of fresh kitty litter) with my Ultimate hanging scale = 14.63 kg go into test mode for each gear tested: shift into gear of interest: 36/12-13-14-15-17-19-21-23-26 on my wheel, 36/13-14-15-17-19-21-23-25-28 on C's wheel. record torque load pedal with mass find orientation which maximizes torque reading record torque remove mass record torque subtract avg of unloaded torque readings from loaded torque reading I plot theoretical torque delivered to the hub on the x-axis, with the y-axis showing the measured value, for each hub. It looks good for C's wheel, but as before, my wheel is off. Curiously, each hub reported a slightly larger n...

My torque test I described in my previous post indicated something was wrong: obviously the powertap was reporting substantially less torque than I was applying. So something was up. Of course, it could be one of three things: with my hub, with the rest of the drivetrain, or with my test protocol. An example of a test protocol problem would be error in determining the weight I'd loaded on the pedal, or a problem orienting the frame, or things flexing in a way which modified the actual torque applied by hanging the weight from the spindle. Lots of possibilities. So when doing experiments, you always want a "control case". It's better to compare the results of two similar experiments than to compare the result of one experiment with theory. So I borrowed a wheel, one I suspect works well, and tested that. Here's the result: It's nice having access to a second PowerTap: these things aren't cheap. You can see from the results that this one tests better i...