Wednesday, May 02, 2007

Equipment - PowerTap SL

(above two pictures) My primary bike as it is now. It recently acquired Look Keo Carbons, a PowerTap SL, and I put some matching tires on a black front wheel (Campy Eurus) to match the DT rimmed SL hub. I happened to have ridden to a local deli to buy lunch and my Coke was still in the cage. I learned to carry it that way when I saw Marc Wauters (of Rabobank, now retired) carry a Coke bottle like that. So I emulate the pros. Sue me :)

(above) A close up of the PT SL head. Wires and all that, I know. My Specialized cyclometer for races - my Reynolds DVs still have a magnet and I still have the fork mounted pickup for the Specialized. Usually I care about average speed and max speed. If things work out, I'll have a racing PowerTap wheel at some point.

(above) The rear pickup. I have a heavy skewer as that's the Cycle-Ops trainer skewer.
(above pic) Note that the fin is angled inward. At first I couldn't get transmission data (or it was intermittent). There is poor documentation on how to mount the fin so I waited till I went to my next race and looked for PT setups. I saw one guy with the fin tilted inward so I copied him. It has worked fine. I rode my bike over extremely roughed up pavement (they're repaving about a mile or two of a road) and although I literally almost lost my bike from under me a few times, the PowerTap worked fine.

(above) The cadence pickup. I just included this as a reference for people having problems picking up cadence. Note the duct tape residue under the ziptie just behind the bottom bracket - signs of my initial test fitting.

So all those pictures mean only one thing. Well to me it does since I only changed one thing on my bike recently.

I got a PowerTap SL.

I really liked knowing my power output and being able to upload my training ride data seemed really cool to me. I don't train enough to use it too much for any specific purpose - although it'll be cool to try and max out the wattage. I have a GTech Pro - a G-force measurer for cars - and I am by no means any sort of a car racer. But I enjoy checking out my fast exit and entrance ramps and like to try to (safely) hit new max G numbers. It's quite illuminating comparing different cars. For the record I've broken 1.0 G's and my 0-60 best was 5.19 seconds.

Now for those that don't know me personally, I am not a person to buy something on a lark. I research, list things, do a pro-con balance sheet, budget, and when I'm about to make a decision, I do it again. Repeat this three or four times, add a new variable or two, repeat, and you understand how it can be frustrating to go shopping with me. I've adapted and now can buy thngs like a shirt after thinking about it for less than 30 minutes. But bike (and car) equipment - I agonize over every decision.

For example, I recently bought pedals. And I knew I wanted to get new pedals.

In 1997.

As a stop gap measure I bought some total blowout SPD-R's (Shimano was introducing the Lance pedal). I got another set of SPD-R's when a friend/teammate decided to get with the program and get "real" pedals. After pulling out of the pedal while set at low tension, I cranked the tension to prevent a repeat. This worked except I had to hit my heel with my hand to unclip. I searched high and low for another pedal. After years of this I was about to give up and try really hard to get my beloved Aerolites back up to speed when Look came out with the Keo line.

I have to admit, I used my fiancee as an rolling test lab. I got the Sprints for her last year and she loved them. I learned Bicycling Magazine liked them too. And after a total of about 10 years, I took the plunge and bought the pedals for myself. As I pointed out previously, I didn't just buy the pedal. I bought three sets for me. And shoes to boot.

Back on the PowerTap.

After I burnt up my temporary Cycle-Ops E-Trainer (a wattage trainer, basically a stationary PowerTap, and owned by the same folks), I started looking at the crop of wattage "things" out there. Basically there are two types of units - stationary and mobile.

I was looking for something that would allow me to gauge watts, heart rate, and cadence. A big plus would be upload capabilities like the Gtech so I could dissect my training ride efforts in detail afterwards. And finally, a raceable wattage meter would be good so I could see what I actually do in races.

Stationary units typically cost much less than mobile ones - I guess it's cheaper to build a big wattage thing than a little one. $800 gets you a pretty sophisticated looking trainer which will do all the required stuff - wattage and heart rate and all that. But it's pretty hard dragging a trainer around in a criterium.

Although the cost of a mobile unit is more, I felt I'd have to bite the bullet.

My hesitation to spend a bit more money reminded me of a round of purchases I regret to this day - one of night lights for bikes. Unwilling to ante up the (at that time) $300 or so for a minimum Nite Rider, I ended up buying three other systems, all of which failed, leading me to buy, you guessed it, a Nite Rider.

So I decided that if it cost a bit more it'd be okay, within reason. A few years ago the only thing out there was the SRM. These are durable and accurate cranks with some kind of pressure sensors - sensitive to minute pressure changes - which allow one to measure how much power the rider is applying to the cranks. Since only the crank is affected, any wheelset can be used (and without any weight penalty).

My friend Gene rides with an SRM and it's been trouble free - but at well over three grand for the setup, well, let me tell you, I could buy a lot of things for my bike for that much money. These were the exclusive territory of the pros and the most dedicated racers.

Since SRM came out and all the pros instantly got them, competitors have introduced a slew of less expensive wattage units. My search would involve SRM substitutes. Among them are the PowerTap, Polar, Ergomo, and the iBike.

The Power Tap measures torque at the rear hub. The Polar measures chain tension and speed or something. The Ergomo measures torque at the bottom bracket. The iBike measures altitude, grade, windspeed, speed, and extrapolates how much work you have to do to go as fast as you're going.

The iBike is the equivalent of trying to measure actual work required to move the bike, not just the energy put into a particular bike part. As it's unproven, even though it's cheaper, I skipped the iBike. The iBike scenario reminded me of all my failed head light purchases - each light promising excellent life with lower cost. And each one failed miserably. Without a lot of time out on the road, the iBike was simply a risk I was unwilling to take. Unless someone pays me (or gives me a free or severely discounted product) I am not willing to be a beta tester. The fact that every pro hasn't gotten one also dissuades me a bit.

The Polar relies on some inputs and relies on careful positioning of a pickup. Because of the setup factors, I simply don't believe it's accurate. It also has very poor granularity (the time between measurements) and will miss the cool peaks I'm looking for in a power meter. Independent tests seem to support this idea. A silent verification is seeing how many pros actually use them and how many pay for them on their own - none.

The Ergomo folks had the bad fortune to introduce their system just as everyone got rid of the mostly-solid axles and went to outboard bearings. To be fair their system is as close to the SRM as possible - no wheel limitations, measures actual torque. Get a quick wheel change and you can still see how many watts you're generating.

The Ergomo's use of an obsolete bottom bracket design (which happens to work with my current cranks, but that's beside the point) forces the user to use what amounts to be obsolete cranks. A lower cost might save them, but to be priced something like twice as much as a PowerTap SL doesn't make sense, not at this time, not with their non-adaptable design. My perceived value on the Ergomo does not match their own perceived value so it was marked off the list.

And the death knell for the Ergomo - my hidden agenda of a stiffer, 200-300 gram lighter crank and bottom bracket. Although that probably won't happen for half a decade, I didn't want to shut that door just yet.


The only survivor is the PowerTap - but they have three different models. The original was a clunky black-capped hub that virtually melted in water. Okay they didn't melt but they definitely stopped working. The same hub with a more sophisticated computer (and the hub had a yellow cap on it) costs more but melts all the same. This simply meant you lost more data when it rained. They recently introduced the SL, a better sealed unit which also cut a significant amount of weight out of the hub. And finally they introduced the SL Wireless with twice the memory of the SL and no wires from the hub to the head.

Since it rains in Connecticut, the original PT's were out. And since there are tons of EMF type things around here (there are two 50,000 watt broadcasting antennas near my riding routes, one within 500 meters, the other less than 100 meters, and my family's house is next to the second one so I go there somewhat regularly), I didn't trust the wireless. So the SL it was. For some reason, I chose the 32H. I think my choices were 32H and 28H.

By the way, it took me only two years to make this decision - definitely a fast track item.

I was checking out some eBay listings afterwards and almost bought a really nice set of Reynolds DV clinchers (one front wheel, two rears with one a PT). But with an original PT "melt in water" hub, I knew I'd have to buy another hub, probably an SL, and that would push the cost to, well, an SRM. And if I had an SRM I could ride my Reynolds that I already had. So the sweet trio of Reynolds were out.

Since it cost so little to have a wheel built around the hub, I decided to take the easy way out and get the wheel, not just the hub. And later I figured I'd relace it with my Zipp 440, a rim that's been waiting patiently for about 10 years to race again (sound familiar?). I've been saving it for something I'm sure. I insist on it. Ask my finacee.

One problem. PT hubs must be laced with crosses on both sides. Unfortunately, I learned of the cross requirement only after I had the shop order the hub. I was thinking "32H hub, 24H rim, just do a 16 right and 8 left lace up. Done it before, can do it again." Since you can't do even a 1x with 8 spokes, that was out. Actually, it might be possible. I'll have to check it out. But it seems improbable.

Ultimately I think I'll have a race wheel and a training wheel. Probably not an unusual setup for most of you out there but it just means finding a 24 (or less) hole SL hub and an appropriate deep dish carbon rim.

So how is the PowerTap?

The Cliff Notes version - works great, terrible presentation.

First I had to replace the batteries in the head unit and the heart rate strap. The strap is encoded, contrary to the poorly printed manual included with the unit. I say "poorly printed" because there's one part that refers to the chart on the opposite page. That chart is actually in a totally different section and not labeled. Some brilliant deductive research allowed to find the chart and decipher its meaning.

Incidentally, because the heart rate band is encoded, there's no more walking away from the bike and then coming back - at that point the head thinks you're someone else and refuses to pick up your heartrate. The head does a duckling kind of thing - it bonds to the first heart rate band it hears. It doesn't like any new band (including the same band later). If the head falls asleep then it'll wake up and repeat the bonding process.

The manual, incidentally, doesn't mention this at all. It simply says "The chest strap is not coded".

After my deductive logic puzzle work, I mounted everything on the bike. I used tape because it was going to rain for the upcoming race (boy did it ever) and since I didn't want to test the waterproofness just yet, I wanted to remove the rig once I confirmed it worked. After testing it and finding all the batteries on the dying side, I took everything off. I did see a PT SL wheel in the race though and the guy didn't seem to be totally ticked off at his wheel afterwards.

When I finally dried out (and got some other pressing stuff done that had nothing to do with bikes) I remounted the PowerTap stuff and did a shakedown ride on the trainer (again). And since I didn't have a battery for the heartrate strap, I used my Timex HR watch for heart rate. Incidentally I love this watch and its reasonable price - so much so that my fiancee, my sister, and two friends got them as well (I bought them for my sister and fiancee - so beat that). My PT trainer ride went well so I went for a ride outside. That went well so now the SL is on my bike permanently.

Normally at this time, if I were a regular rider, I'd be posting a nice graph showing how I averaged 320 watts for my ride, did a TT effort at 530 watts, and sprinted at 1600 watts.

But I haven't. Please let me explain.

I downloaded my first few rides to the computer. To display the graph you have to put in some personal info like your name. And you put in some personal power measurements - like a 4 (or 5) minute wattage max as well as a 30 minute max. Meaning the maximum average you can hold for that amount of time. The default is pretty optimistic - I think it's 500 watts for the short effort, perhaps 300 for the longer one. I figured mine would be under 400 and under 250.

I have to be very frank here. I didn't expect too much. And I was right, but by a bigger margin than I expected. It seems my 30 minute average (I was working pretty hard) is under 200 watts. And my 4 or 5 minute is well under 300 watts.

So as not to give everyone definitive proof that I'm about to get dropped the whole time I race, I decided against sharing such vital information. It's like a national security thing. Except it has to do with finding out exactly how I ride. And I figure I don't want to share that just yet.

As terrible as it might seem, that aerobic stuff wasn't a surprise. What did surprise me was that a moderately hard try at a jump only netted me 1385 watts.

That was shocking.

Shocking bad. Not shocking good. Although I didn't go very fast - I jumped from a virtual standstill and only hit about 35 mph - it was a slight uphill, a bit of a headwind, and I figured that the power should have gotten well into the 1500's. I've hit over 1200 on the trainer with the tire slipping like mad, so it just seemed like a given I could do a 1500 watt sprint.

But I didn't.

So now, after my break in Vegas, I'll chase that number with a vengeance.

I told someone it takes me about 30-40 sprints to find my sprinting legs. I hadn't thought of it till I was saying it but it's true. It's usually a very hard 2-2.5 hour session which gets me close. I can feel the speed coming on, I get my sprinting second wind, and I start using the right gears more often. The gearing is key as I always over gear when I'm not sprinting well - take a look at some of those helmet cam vids.

The first session would probably cover 15-20 sprints - on a seven minute, two mile loop, my standard sprint workout loop, 20 sprints would take 2:20.

After a second very hard 2-2.5 hour session, I feel a lot better - and in fact in one of the second session sprints, I might have even had a "good" sprint. I define a good sprint as both a fast and smooth one. I can feel the power at a reasonably high cadence. When I say high, I mean road high, not track high, so probably 120 rpms or so - I'll learn when I download some PT data.

The second session would see another 15-20 sprints. Hence my "30-40 sprint" number.

The key is having that "good" sprint. That's when I know I've done my work. A good sprint is really good when I find myself running out of gears. When you run out of gear in a 53x11, you're not going slow. 120 rpms would be about 46 mph. And, although I really didn't want to admit this, that is my target speed based on a leadout and no unfavorable conditions (i.e. no headwind). I don't think I've broken 41 or 42 mph in a few years so 46 is really a pipe dream.

On the same road, with a 54x11 and a lot more fitness, I used to consistently hit 44-46 mph, topping out at 48 mph. That was a long time ago and I was a lot fitter. It's a dream worth chasing though.

Sprints anyone?


Anonymous said...

great post. and congrats. i recently got the sl as well, and poured the spec sheets and reviews over the ergomo, ibike, sram,etc.

cycling peaks wko+ software is supposed to be the bomb for pt users. i'm still learning, but the wko+ is everything people rave about. if you want to spend another hundred dollars.

Anonymous said...

I'm wondering how comfortable your position is - or do you have a long torso?

Anonymous said...

Aki's got a very long torso attached to his sprinting guns.

So, Aki, for comparison's sake, what is the peak output of a Cipollini or Zabel in a sprint? What should we compare you 1500w to?

Aki said...

Definitely a long torso as I comment here. To quote: "I ... have a long torso for my height. I know I have short legs and a long torso because when I commuted on a train, I'd usually be the second or third tallest seated person in a car of about 100 people. But when they stood up, I was definitely in the bottom 40th percentile in height."

I actually want to get a longer TT and a steeper ST - but I waver on that as I'd have to get a custom.

re: power - in Florida I was riding with my friend Gene (he with the SRM). In one all-out sprint for a town line (there were four of us on the ride - the others a Cat 1 male and either a Cat 1 or 2 female) I did a pretty good sprint. Ends up Gene got pretty outdistanced in the initial jump - and he jumped at 1200+ watts. He told me I had to be doing over 1500 watts (he actually said it might be something like 1800, but that might be a tad optimistic). So, whether or not it's accurate, I'm waiting for a 1500-1600+ reading to pop up on my screen.

Anonymous said...


I think my sprint number got garbled in the communication. The highest power outputs I see in a sprint are about 1150 watts. I know you can really pop a sprint as compared to me so your number will be higher. I am not sure, but the interval your power tap is storing information might also make a difference. Finally, the absolute power number can differ between devices (especially if not calibrated correctly). Tom C., who you know, is a excellent sprinter told me his max power numbers from his power tap and they numbers seemed low. To me the absolute numbers are not as important as repeatability and from all I hear the powertap is excellent in this area.

I agree with lee b in that Cycling Peaks software is really good. They developers there did a good job in taking all of the output from a power meter and presenting it in a logical, easy to understand format. For example, one feature that I always look at after a race (I race with the SRM) is the peaks. Cycling Peaks software shows you the wattage information for the 5, 10, 20 & 30 second peaks as well as the 1, 2, 5, 10, 30 and 60 minute peaks. In those peaks it gives you min/max/avg information for power, heart rate, cadence, speed, pace and crank torque. Comparing this info during the course of a season or from year to year is a good way to access progress (or lack thereof).


Aki said...

So maybe my 1385 wasn't so bad as Tom C has kicked my butt almost every time we're in a sprint.

My planned sprint workout for tonight was nixed so I'm hoping for a nice workout perhaps Monday.

I got some CD with the PT, have to see what it is. I didn't pay much attention to anything in the little foam container except the actual device and the CD for the desktop program.