Recumbent power training

Observations on sweaty self-abuse in the garage, as I have one last mid-life crisis fling with bike fitness!

Observations on sweaty self-abuse in the garage

This spring I’ve had a turbo set up in the garage with the High Baron on it, and I’ve been doing 2×20 minute intervals.

I haven’t ridden a recumbent seriously since August, and I wasn’t in the best shape then either. However, I’ve kept up my hundred miles a week commuting on a DF through the winter, and a fair bit of running.

I’ve never done structured training before for any sport. I’m aiming to do better at a couple of sportives (Etape Caledonia in May, Tour o’ the Borders in August) than I have previously from just commuting mileage. Call it an early midlife crisis…

Potential FTP / diamond frame performance

I’ve assumed my recumbent FTP could get as high as ~300W since I climbed Alp D’Huez last summer, on a normal bike, at an average of 291W – which took me just over 58 mins.

I was halfway through a week of big climbs and riding solo, so maybe that’s even an underestimate (I’m sure I could have gone harder with someone to chase!)

Either way, it’s some kind of line in the sand – if the physiology of recumbent riding was the same as diamond frame, I should be able to hit an hour at 290W in short order.

Rude intervention of reality

My opening session on the High Baron was three five-minute intervals, just to avoid destroying myself after six months of upright riding.

Optimistically I started at 304W, which dropped to 285W for set 2, then just 263W for set 3. I couldn’t push it any higher. Depressing stuff!

One Month

After a month, I could scrape out 2×20 minutes at 265W in exchange for much sweat and pain.

month1

The interesting thing is that I’m challenging my cardio more than I expected. 20 minute intervals at 265W on the High Baron got my max HR up to 165bpm on the first interval, 170bpm on the second. In contrast, climbing Alp D’Huez for an hour at 291W on the DF only got my heart up to 159bpm (one factor that makes me think my FTP was actually quite a bit higher).

From “real life” riding I always feel “leg limited” on the HB versus “lung limited” on diamond frames (and I can hit 185bpm running, so I have the ability to deliver a fair bit more O2 than I’m using on either bike). In contrast, the turbo is definitely exposing a central cardiovascular limitation.

This leaves me with a bit of a puzzle over what sort of training I should actually be doing, not to mention a worry that riding the High Baron on a turbo might be structurally different from riding it on the road somehow.

The plan was to keep churning out my hundred miles a week of diamond-frame commuting at a low wattage, then add in two high intensity workouts each week on the recumbent. However, I figure that since my wattage can be so much higher on a different platform, maybe 20 minute intervals on the recumbent are not ideal, as they won’t really be working on the intended energy pathway?

At the same time I think this is an unrealistic way of reasoning. If the hardest I can go on the recumbent for an hour is 265W, then that’s my threshold power and I should be using that for threshold intervals on the recumbent (and go up to 290W for threshold intervals on my DF, if that was relevant).

Let’s not even consider whether 2×20 is the appropriate type of workout! 😐

Two Months

Towards the end of the second month I started to get pretty tired (I think adding these workouts, simultaneously increasing my commutes as the weather improves, plus running, was having a cumulative impact).

month2

I took a “rest” week (actually a hiking holiday) then did an FTP test loosely following the Coggan protocol – a short hard interval to drain your legs a bit (8 minutes at 301W) then a 20 minute all-out effort.

I did want to die, but I managed 288.5W (first ten minutes at 285W, second ten minutes at 292W) which gives an FTP of ~275W based on 95% of the longer interval.

This is still at least 15W shy of my diamond frame FTP, although I should probably validate that by riding the same test protocol on the turbo on my racer – but it’s definitely progress.

I’m not sure how much of this is improvement to my general fitness, to recumbent-specific muscles (hip flexors etc) that were lagging behind, or maybe just to my pain tolerance… but I’ll take it.

I now have five weeks until the Etape Caledonia, so armed with this FTP estimate, it’s time to think about what sort of training to do – probably don’t want to turn up at an 80 mile ride having only done 20 minute turbo intervals, for starters!

Etape Caledonia -4 weeks

Four weeks to go before the Etape Caledonia, which is my “B” event (I mainly entered it so I would get my recumbent out of the garage before June!)

As I haven’t ridden the High Baron for more than an hour since last summer, I decided it would be a good idea to [URL=”https://www.strava.com/activities/540340314/”]ride the route[/URL]. Partly to check for any corners that I can’t take at full speed, partly for the long ride training aspect.

It’s 80 miles / 130km but only 1,200m / 4,000ft of ascent. It took me 4:10 moving time (19.5mph average) with just under 25 minutes of stops (half of that was getting breakfast, the other half was watering the verge… FFS!)

I felt my power was pretty poor on this ride, but I think my expectations were unrealistic considering I had no taper and didn’t eat any carbs before heading out / only had a light energy drink on the bike.

Interestingly it felt like my efforts at short rises were noticeably stronger (even though this is above-threshold wattage) whereas I wasn’t able to ride anywhere near my threshold otherwise – the sustained central portion of the ride I was just putting out 200W, and the long flat finish I was right down at a 160W average.

There are a few niggles with the High Baron to sort out, then I think I’ll repeat the dry run in two weeks’ time. That will give an ample taper into the event, and we’ll see what happens!

Tour o’ the Borders is the goal, but the Etape Caledonia route is also quite a bonny one. It will be fun to ride this event in its own right 🙂

Fast 700c recumbents – power test

A side-by-side comparison of the speed of the Schlitter Encore, Optima High Baron and M5 Carbon Highracer

Side by side M5 CHR, Schlitter Encore, Optima High Baron

I’ve been riding a review copy of the Schlitter Encore recently, along with the Optima High Baron which carried me to a 7th place finish at this year’s Tour o’ the Borders.

To complete a nice side-by-side performance test I borrowed the demo M5 Carbon Highracer from Laid Back Bikes in Edinburgh – brief side by side comparison here.

The test protocol was simple – go to the promenade and ride up and down beside the sea (nice and flat) holding a given power for the whole of a lap without touching the brakes, then see how fast I went on each bike.

I varied as little as possible between the bikes, including using the same wheels (where possible) and power meter etc. I also tried for the calmest conditions in terms of wind, although naturally in Edinburgh it was impossible to find a calm day.

Just a note – it would be much better to perform virtual elevation calculations for each bike. I think there is a good bit of error in the testing described below, but I just can’t find a convenient route that doesn’t require use of the brakes (compounded by living in the world’s windiest place… it’s a hassle!).

Until someone produces a proper calculation, we make do with cruising beside the sea in the sunshine… I suggest that these results are taken as indicative only, though for what it’s worth I do feel that the ordering matches my gut feel of how each bike rides.

Headline results

It turned out to be a little tricky to get exactly the target wattage for each run, so first of all here is a graph of speed per watt for each bike (all laps of both directions averaged) to give a comparable ranking of “bang for your buck”.

overall-speed

To add extra context, I’ve plotted previous data from a head-to-head comparison between my DF racer and the Raptobike Midracer which was not captured at the prom (and obviously on a different day, three years ago!)

As you would expect, while you go faster at 250W than 200W, higher power gives diminishing returns due to the exponential increase in wind resistance, so the high power runs (plotted in red) show less speed per watt than the lower power runs (plotted in blue).

The ordering hopefully won’t come as much of a surprise, with my DF racer languishing at the bottom of the pile. The M5 Carbon Highracer was fastest, followed closely by the Optima High Baron, with the Schlitter Encore coming in just behind. Probably the most interesting thing about this for me was how little separated each bike:

rawdata

The next chart breaks down the laps by direction. You can see variation between the bikes that is only really attributable to varying wind speed as the test went on (the Encore does better downwind and worse upwind than you might expect, presumably because the wind speed / direction wasn’t steady). That said, if the Encore was less aerodynamic you would expect to see it hurting more on the upwind laps than the downwind ones (the big open cockpit riding in the airstream etc?):

wind direction

Assorted caveats

TL;DR – the CHR is a shop demo and not optimised for naked speed, the Encore is a new-to-me review bike and I haven’t spent a lot of time tweaking it, while the High Baron has been mine for three years and I’m very comfortable on it!

Here are a few confounding factors to consider in detail:

– I’m not tall enough to ride the CHR with my power chainset (170mm) so I was using a PowerTap wheel and plain 155mm cranks instead. The PowerTap reads 1-2W higher based on testing conducted with both meters fitted on a turbo trainer (so this slightly disadvantages the CHR, by about half of one percent – down in the noise of wind gusts unfortunately).
– I used the same 32 spoke 3-cross Archetype wheelset with 28mm Schwalbe Ultremo tyres on the Encore and High Baron, but the M5 CHR doesn’t have enough clearance, so I had to use the provided Shimano R500 front with Schwalbe Durano Plus tyres (faster wheels but slower tyres on the CHR).
– The Archetype wheelset has a Shutter Precision hub dynamo on the front, the R500 does not. (The lights were off, but there is still a small amount of extra friction, amounting to the equivalent of a couple of feet per mile extra gradient).
– I used a Radical Aero seatbag on all three bikes, but on the CHR I used the stock bag from Laid-Back-Bikes which still has the fabric bottle holder on the side – I cut this off on my own Aero seatbag.
– I didn’t have a mirror fitted on the Baron or Encore but had a small mirror fitted on the CHR, although I turned it parallel to the wind for the test.
– Both the M5 CHR and High Baron are running dropped chains, but the CHR has a bit of chain tube to make it more useful as a shop demo, which will add some (an unknown amount of) friction to further disadvantage the CHR.

Seat Angle

Refer to the posts linked in the first two paragraphs for photos of all three bikes (I’m afraid I’m still working on formal reviews of the M5 CHR and Encore, so don’t have comparable shots of them to stick in a rollover).

My High Baron is as reclined as the frame will allow, but the M5 CHR can go flatter with a bit of modification to fit a lower seat pillar, as can the Encore (to a lesser extent – the seat back was closer to the max recline without doing something drastic).

If you’re willing to ride with a really low angle seat you can certainly get more speed out of these two bikes than I’ve demonstrated, whereas the High Baron is probably about as good as anyone is going to get it. (M5 have the world hour record on a similar design where the rider lies flat on his back!). Of course, you may not want to ride around flat on your back with special measures to avoid looking under your bars to see the road ahead. There’s a reason that almost all bikes are sold with a seat at these angles or above…

You could also put a tiller on an Encore very easily, and get your arms tucked up out of the way (while the J-bars are one of the big selling points of this design, you are sticking a couple of feet of pipe into the airstream above your knees, and also your arms are spread wider). But maybe you’ll decide that a nice handling bike which is pretty fast is fast enough! There’s more to life than speed at any cost…

Weight

Finally, I didn’t attempt to equalise the weight of the bikes, since I’m not interested in purely their aerodynamics, rather the “complete package”, and on the flat the difference should be minimal anyway. However, note that the M5 CHR and Schlitter Encore both weighed in at a little over 10kg (22lbs ish) whereas my High Baron weighs more like 11.5 – 12kg in current form.

All could be lightened but the High Baron will always be heavier. This, plus frame and cockpit stiffness, would show up in a bigger way on an actual cycle ride with hills, dropping the High Baron down the ranking.

I believe (subject to a full dismantling and the weighing of individual parts) that the Encore can be made lighter than the M5 CHR.

Anyway… hopefully this is of interest, and as ever, feel free to drop a comment below…

Randonneuring: recumbent efficiency

Measuring the difference in wattage between equivalent performances on a 400km brevet, recumbent vs upright

It’s easier lying down… but not by as much as you might think.

I’ve written before about the power advantage my High Baron recumbent enjoys over my normal road bike, but only in the context of a ~20 mile commute to work. I found that on average each recumbent mile cost 36.2kCal, versus 47.3kCal for each upright mile.

If that held out for a long brevet, it would be a significant advantage to the recumbent platform (a 3800kCal saving on a 600km brevet, for instance). But how comparable is my commute, an hour pretty much as fast as I can go, with an all-day or even a multi-day effort?

Now that power meters are getting a bit more commonplace, it’s easier to answer this question without going to heroic solo efforts in the name of science.

recumbent_vs_road_bike

I rode the National 400 out of Dingwall this year, 256 miles (or ~400km! 😉 ) with around 14,000 feet (4270m) of ascent. Rather than ride the National 400 route twice on different bikes, instead I’m going to compare my power with another rider who did the course on the same day. The advantage of this is that weather etc. is exactly matched, but the danger is that energy use is proportional to weight (especially going uphill) and also the speed you travel at, and if these aren’t controlled, you might not get such useful data. In particular, if riders are drafting you may as well call the whole thing off!

Fortunately in this case our speeds were fairly closely matched and neither was drafting at all. I chose four segments between controls in the middle of the ride for comparison, as our average moving speeds were 16.496mph (recumbent) vs 16.507mph (upright), probably close enough! The total distance was 137.6 miles, the ascent 7,500 feet and the route profile between each control is as follows:

seg1

seg2

seg3

seg4

As you can see, it wasn’t the hilliest of routes, but there was a respectable amount of climbing. The first segment had a bit of a headwind, the others a tailwind. See the overall map view:

map

Before looking at energy used, it will be useful to calculate the respective weights. I looked at a fairly steep hill (7-8%) to broadly isolate the weight component. In this case the recumbent sustained 7.7mph for 247W, while the upright got 8mph for 239W. Knowing fairly accurately the all-up weight of one rider, we can crudely solve for the all-up weight of the other. In this case my own weight (inclusive of bike, spare clothes, tools, 2L of water) works out at roughly 6.5kg heavier than the rider on the upright.

Ideally we would have had a set of scales at the arrivée, but what can you do! This will be useful in a moment as a caveat on the overall comparison…

Knowing duration and average power we can calculate total energy consumption across each platform. See the table below for some of the detail:

Notwithstanding the weight penalty, the recumbent rider travelled at the same speed using 8.5% less energy.

Overall the recumbent used 5240kJ (36.9kJ per mile) whereas the upright used 5715kJ (40.27kJ per mile). The calculated efficiency for the recumbent is interestingly close to the 36.2kJ from my previous comparison, but the DF efficiency is much better than my commute’s 47.3kJ per mile. Quite a different result overall to the 24.5% saving on my commute – I suppose this highlights the difference between riding at 15mph and 20mph, which is my average speed for a commute, in terms of the recumbent’s aero advantage.

(I’ll just take this opportunity to point out that my recumbent, pictured below, didn’t weigh 6.5kg more than the upright, although it contributes a couple of kilos for sure. If I’m honest, it’s probably mostly the rider who was a bit more portly!)

highbaronchainline

When you break it down a bit, as expected the relatively flat stage over the watershed from Lairg to Achfary (roughly 30 miles, 800 feet of climbing, into the wind) shows a dramatically better result for the recumbent than the other stages (hillier, no headwind). I was travelling at 18.4mph while the upright rider made 16.7mph – yet I used just 885kJ to get between controls, compared to 1091kJ for the upright – an increase of 23% in energy spent AND a reduction in 1.7mph average speed…

Anyway, that’s quite enough geeking out on power data for one day. Hopefully this is thought-provoking – please drop a comment below if you have any feedback!

How accurate is Strava power / calories?

What happens if you compare PowerTap power / energy to the figures calculated by a service like Strava?

No surprises here…

I’ve been putting in a lot of miles over the last few weeks on different bikes. I don’t have power on all of them, so it’s been quite interesting to see how many watts / calories a service like Strava will calculate compared with the real amount as measured at the wheel.

This downhill segment provides a particularly stark contrast:

power

Crikey, Strava is out by around 3500 – 4000% (average of 6.67W measured, 252W calculated)… not a very good result!

The picture is better when you look at the overall energy use, which makes sense as you’d hope optimising a fake power figure for cycling mainly on the flat is a much easier job. Across these six runs, Strava calculated an average of 660kJ versus 558kJ measured, which is only an error of 15.5%

Finally, what about going uphill (a short segment at 4% gradient)?

power2

In this case the calculated power is significantly lower than reality: 11.8mph for 263W (calculated) versus 11.5mph for 292W (measured), an error of 13.7% (allowing a couple of small assumptions to normalise speeds).

Beware calculated figures! Depending on the ratio of ups and downs on your ride, you don’t even know if they’re an over or an underestimate…

Recumbent efficiency

Even if you aren’t able to go as *fast*, are you more efficient on a recumbent bike (even while climbing)? Yes indeed!

Go further per calorie – by going laid back

I’ve been putting in the miles on one of my upright bikes recently, ahead of a race where riding recumbent isn’t an option.

I thought I’d spice things up by swapping a session onto the High Baron, using the same PowerTap wheel to see whether I could make anything interesting of the data.

As I suspected, I was faster on my upright than on the High Baron. I wasn’t going flat out on either bike, since I’ve been doing ten or more rides a week – I was only subjectively investing the same effort on each. The outcome mainly reflects training on one bike (many hours) over the other (very little)… the specific effects of training shouldn’t surprise anyone.

What is more interesting is to compare the power I had to use to achieve each performance.

recumbent_vs_road_bike

The route is a little under 25 miles with just over 1300ft of ascent (40km / 400m). Overall, I managed 17.5mph average for 230W on my upright, compared with 16.7mph for 168W on the High Baron.

I think there was more of a headwind on the High Baron ride, but since that only advantages the recumbent, let’s assume that wind conditions were the same:

Each recumbent mile cost 36.2kCal, versus 47.3kCal for each upright mile.

If I’d been racing myself, I’d obviously have won on the upright, but that’s just one way of looking at a performance. What if I was riding an ultra-distance event where I’m mainly limited by how much I can force myself to eat and how little sleep I can survive on?

For every 36 miles ridden on my upright I’d be an extra 11 miles further down the road on my recumbent (for the same effort) and once performance becomes limited by something other than absolute power (i.e. limited by fuel, fatigue, comfort, or any similar factor) that’s really going to tell.

Even on a 200km brevet my average power in the closing hour or so can be as low as 150-175W. I can achieve that on either type of bike, and then you’ve got to think of the next 200, 400, 1000km…

Screen shot 2013-09-20 at 01.00.43

Convergence on hills, as expected

I’ve previously compared the performance of recumbent and road bike in ‘ideal’ conditions (flat without wind) and found a large advantage in favour of the recumbent (250W vs 150W for the same speed).

On the other hand, I’ve also previously bemoaned terrible performance on all-out hill climbs (the MetaBike took 36% longer), where absolute muscle recruitment and platform efficiency is paramount.

It would be expected then for a mixed route / mixed conditions performance to show much less advantage than the ideal case, depending on the proportion of time spent climbing and the proportion at high speed (where aerodynamics offers significant benefit). A flat TT would be very close to the 100W advantage shown in my earlier test, while a hilly ride would be closer to break-even, or perhaps to disadvantage the recumbent altogether, as in the second test.

Pleasingly this is the case for the rides in question: I was 0.8mph faster on upright for 62W extra, which is a much prettier picture than getting the same speed for 150W extra!

If I isolate the hillier section of the route I see 14.1mph for 350W (upright) against 10.6mph for 245W (recumbent). The lack of absolute power is dramatic, but again, only important if each second counts for its own sake (as in a road race or head-to-head hill climb).

Much more interestingly, the efficiency gap has closed right down, to 89.4kCal per mile (upright) against 83.2kCal per mile (recumbent). But…

The recumbent is still more *efficient* on a 10mph climb, albiet *slower*

Since so many people seem prone to equate slow climbing with poor performance it’s hard to emphasise this too much.

If you’re touring you’re hardly going to ride for four hours dead then stop wherever you are at the roadside. You probably have a destination and getting there a few minutes either side is not important compared with getting there in comfort or for less sweat and toil.

If you’re riding an ultra distance event, it’s not likely that you’re so strong that you can maintain high wattages for days at a time; it’s more likely that you want to get the maximum ‘bang for your buck’ when it comes to spending your body’s limited capacity for exertion.

Only if you’re racing over fairly short distances does absolute power outweigh efficiency.

If we buy into the hypothesis that recumbents reduce the muscle mass you can recruit by isolating your legs (which is one possibility) you can see that they really will start to shine as the miles rack up.

recumbent_efficiency1 (1)

Caveats

Other than the obvious (small sample size, indicative only…) the big caveat here is that I’m still measuring power at the wheel and not at the crank. This means it’s possible that one or other of the bikes is systematically under-reading the effort required. What if the much feared phenomena of drivetrain or frame losses mean that the recumbent really requires an extra 50W at the pedals to hit 250W at the cranks?

It’s impossible to answer this question without access to a crank-based meter at the same time as the PowerTap… if anyone has both and would like to run a few tests, get in touch!

For my part, I don’t really see how such a large difference can be accounted for through drivetrain losses: for starters, an idler that sucked out 50W would get as hot as an old-fashioned incandescent bulb, which is patently not the case.

Certainly there are many questions about recumbent performance that remain unanswered, but hopefully this chips away at another aspect of the problem (even if it raises as many questions as it answers!)

Any comments, as ever, gratefully received…

CycleOps PowerTap Pro review

The ability to optimise your riding position, equipment choices and even your nutrition make any power meter into a tremendously powerful tool…

You can do so much more with a power meter than train, but it’s a good start. The ability to optimise your riding position, equipment choices and even your nutrition make any power meter into a tremendously powerful tool, one that’s increasingly prevalent amongst today’s keen amateurs.

When it comes to choosing a power meter, in 2013 your choice still boils down to an expensive crank-based one (SRM, Quarq, etc) or the more reasonably-priced CycleOps PowerTap hub-based system.

There are two basic choices in the current range, the Pro (reviewed here) and the far more expensive G3 series (which are lighter and easier to service).

Wiggle have a 24% discount at the time of writing (check with Chain Reaction too, as offers come and go).

Since their introduction in the early 1990s, power monitors have supplanted heart rate monitors as the ultimate measurement of choice for cyclists interested in the most efficient path to smart training and improvement. … If you’re reading this, you already know it’s the way to go for smart and efficient training. (pez.com)

Compared to other Power meters

For the purposes of 99.99% of people reading this review (that means you) the accuracy differences between power meters are insignificant. That doesn’t mean that they don’t exist (or that they might not be important in some specific circumstances) but unless I made my living riding, I can’t say I’d worry about it when there are so many more important things that impact your training.

powertap (1)

Consistency is important, but accuracy? Not so much. If you look around online it doesn’t take long to realise that almost everyone doing measurements isn’t able to / bothering to control confounding factors to within the stated accuracy of the meter anyway. Given the huge cost difference, getting a PowerTap hub-based meter rather than a very expensive crank is a complete no-brainer. Really, what are you thinking? 😛

German company Power2Max are offering a comparably-priced crank but it’s still early days for them, with reports of consistency issues (which is much more important than absolute accuracy – it doesn’t matter much if your reading is always 10W too low, so long as it reads the same thing for each ride!).

That said, the big advantage of a crank-based meter is that you can swap wheels (training vs race) and measure the difference between, say, deep and shallow rims with ease. So I’d love to get some time on a Power2Max and post a detailed head-to-head. (Hey Power2Max people!)

Compared to other PowerTap hubs

If you already have an Ant+ compatible PowerTap hub, there’s little advantage to be gained from a switch to the PowerTap Pro. The weight saving is simply insignificant (40g versus the old Pro+). On the other hand, if you have an old wired PowerTap model then this is definitely going to offer a great improvement, as you can tie it with a wide variety of head units, particularly Garmin’s excellent Edge GPS series.

For my money, I’m not too sure the expensive G3 series is as sensible a choice – it saves a little bit of weight, but at hefty cost. Why not spend the same money upgrading other parts of your bike for much greater weight savings?

See the section below for details of the weight implications anyway…

powertap4

Weight

A nice lightweight rear hub for a road bike comes in at about 275g, if you want something reasonably practical and not overly exotic. By comparison the PowerTap Pro weighs a relatively hefty ~450g, a premium of around 175g. What will that cost you in terms of speed?

It’s easy to calculate but I’ll give you an example working here… say you weigh 75kg and your bike weighs 8kg, the difference between wheels being 175g for the PowerTap hub. Calculate a ratio between the two weights:

(75+8+0.175) : (75+8) = 1.002:1

Pick a climbing speed for the PowerTap hub (15mph) and multiply by 1.002 to get the climbing speed for the normal wheel for equal effort (15.03mph). At the end of a 15 minute steady climb the PowerTap wheel would be 0.03*0.25 = 0.0075 miles behind (around 12 meters).

15mph is 6.7 meters per second, so the PowerTap Pro loses two seconds every 15 minutes of solid climbing. That’s the physics – the effect is obviously negligible on anything less than a steep hill.

The ability to pace yourself according to your established power threshold easily offers the ability to pull in two seconds every 15 minutes. I realised an improvement of seconds per minute due to superior pacing when I started hitting Strava with my PowerTap.

Flexibility

You’ll hear this one of two ways:

  • The PowerTap is built into a wheel. This is bad, because you can either have a training wheel or a race wheel but not both.
  • The PowerTap is built into a wheel. This is great, because you can measure power on any of your bikes in moments (try that with a crank!)

At the end of the day it depends what your priority is. You want to maximise the amount of time you spend on the bike with a meter, so plan to build a wheelset that suits your own purpose. Hopefully my weight section above has helped convince you that “even” a PowerTap Pro is quite suitable for racing on, and training too…

If you only have one bike, that would make the case for a crank-based meter stronger, but if you have multiple (or think you might upgrade to a bike with a different bottom bracket format, for instance) then the PowerTap’s a clear winner.

powertap1
With sufficient pain, you can improve the area under the graph…

Calibration / Pairing

This couldn’t be easier: tell your head unit (Garmin, iPhone, Android or other) to search, then spin the wheel. It will acquire immediately.

Calibration instructions are provided. It’s not something that will give you any issues – the important thing about a power meter is not absolute accuracy in any case, only consistency (an improvement of power by 5%, whether your hub reads 10W lower or higher than the guy next to you, is still an improvement of 5% and you will still be climbing at least 5% faster!)

Expense

There’s no denying that the PowerTap is an expensive tool for the vast majority of us who aren’t racing professionally. That said, compared with the money you’ve probably spent on bike gear over the years, is it really so much to allow you to record with accuracy and precision how much force is going through your back wheel, with all the analytical power that places at your disposal?

You’re saving a lot of money compared with paying for a coach (and if you do have a coach, you’ll both get a huge amount more out of your training). It might either free up some training time for other life pursuits (or household chores!) if you just want to intelligently match the riders in your regular weekend group, or allow you to make a step change in performance if you keep putting in the same hours.

I’ve found the pacing provided by a PowerTap to be a tremendous help on long distance events (even though, by and large, I use a non-PowerTap wheel on those events – it’s improved my ability to ‘feel’ effort no end).

In short, if you’re even vaguely keen on measuring and improving your performance the PowerTap is the only game in town. Whether it’s worth the money or not to you personally? Only you can say!

As I mentioned above, these hubs are often on offer, which could reduce the sting. Wiggle have a 24% discount at the time of writing (check with Chain Reaction too, as offers come and go).

I worried that I might regret my first PowerTap due to the cost, but I’ve never looked back. 🙂

Service / repair

One advantage of the PowerTap G3 series is that the electronics are located in the hub cap only, so it’s easy to detach this and return for servicing if you are unlucky enough to find a fault. The PowerTap Pro, on the other hand, would require you to return the whole wheel for an electronics fault. Fortunately, there’s a UK service centre!

I haven’t been in this situation, but there are plenty of customer reports praising their rapid turnaround, so I’m not sure it’s really a reason to buy a hub that costs a massive amount more. How inconvenienced would you be to have to ride without power for a week?

Battery changes (standard coin battery) are straightforward while the bearings can also be serviced by your local shop provided they use a press and don’t slam the electronics around with a mallet. Which should be obvious really.

powertap

Conclusion

The CycleOps PowerTap hub is not a cheap bit of kit by any means. Nevertheless, despite being (only) a keen amateur, I haven’t suffered a moment’s remorse.

I’ve been able to accurately calculate the minimum calorific cost of my commute (800kcal / day), benchmark the performance of different riding positions and equipment choices, and more (sometimes I even use it to train! 😉 )

If you’re serious about understanding what’s going on when you ride, and becoming a stronger rider, I totally recommend it.

Wiggle have a 24% discount at the time of writing (check with Chain Reaction too, as offers come and go).

Like me, you’ll soon forget the cost.

Vital stats: PowerTab hub weights

Hub Weight
2012 Pro 446
G3 325
G3C 315
Pre-2012 range
Elite+ 624
Pro+ 485
SL+ 412
SLC+ 402

Recumbent position power loss

A short article comparing preliminary power tests of recumbent and upright platform, and discussing recumbent power loss.

This is another article in the vein of the 1 minute hill climb, looking at (but not necessarily answering!) issues around recumbent and upright power production.

Background

I haven’t ridden many recumbent miles since the 200km Erit Lass last September, but I have kept up my five mile commute on my upright hack bike that whole period. I consider myself to be quite badly out of recumbent-specific conditioning (despite coming in 21st in my category on the Tour o’ the Borders).

tour of the borders recumbent
The new Optima High Baron cleans up the field on the Tour o’ the Borders…

As I recently started getting serious with the Optima High Baron, I thought it might be interesting to benchmark my power on the two platforms now, and look at whether it converges over time. In my opinion it’s also an interesting window onto the experience of novice recumbent riders who try to transition from their upright bikes expecting a gain in performance.

I’m going to display the data from two PowerTap stationary trainer intervals. The sessions were uncontrolled except that I tried to shoot for my highest average power in each case over a 12.5 minute interval (interestingly, in both cases I ended up picking things up at the end – bad pacing?).

The intervals were on different days, first thing in the morning before work. For what it’s worth the recumbent went first…

Interval Upright Recumbent Power loss
1 minute 355W 296W 19.93%
5 minutes 290W 239W 21.33%
10 minutes 275W 220W 25.00%

A 25% drop in power means that on a climb the upright would pull away one mile for every four miles the recumbent rider travels – it’s a pretty big gulf!

Context

[edited to add this section, as I felt the article originally was lacking in context]

Consider this: received wisdom often tells us that recumbents do not climb as well as conventional bikes because they are heavier, and/or because they are less efficient due to some combination of frame flex, or drivetrain friction due to the idler systems involved. However, I believe this is demonstrably false.

In the first case, we can categorically evaluate the impact of extra weight using simple science, with or without a power meter (see my article on bike weight and performance).

However, with a power meter it’s possible to precisely define both limiting factors of weight and power output and, as in this case, I believe climbing performance will always turn out to be limited by reduced power output and not by increased weight.

However, by measuring power at the wheel and not at the cranks we do leave open the possibility that the drivetrain is consuming 50W or more in increased friction, however unlikely that may sound. My answer to this (and ultimately to all questions of inefficiency in the recumbent bike proper) is that if the same work is being done by the human body, but it’s just being lost somewhere en-route to the road, we should see a very similar physiological impact to the activity.

This is manifestly not the case, as in the two intervals discussed below: the recumbent one is not only far fewer watts, it had manifestly lower cardiovascular demands (even though it was as hard as I could push the pedals), relative to the upright session.

I’ll follow this up as promised with something that includes HR, although that’s of only limited use in evaluating demands on the body, as we’ll see…

[back to the original article:]

Torque vs cadence

torquepower

Comment

Don’t read too much into a sample size of one, however, counter-intuitively the power gap increases with duration. You would expect proportionally greater failure to generate power over short periods if the upright position simply allowed a greater mass of muscle to be recruited (albiet inefficiently), as many hypothesise.

As I’m sure the difference between recumbent and upright riding position tends towards equality in the very longest events, this initially suggests a reverse-U shape. Clearly more investigation is required… I personally think this is showing both a fundamental difficulty in producing recumbent power but more importantly a significant and specific lack of conditioning in a couple of key muscles that is inhibiting overall performance.

While it’s tempting to blame inefficiencies in the physical recumbent drivetrain, I don’t think this is a significant issue because my cardiovascular reaction to these two intervals was very different – the upright session left me feeling nauseous and faint where the recumbent one left me a bit sore but after a short break, I felt able to match it again.

Exactly not what you’d expect if the power output was actually the same in both positions, but the recumbent frame was losing it to friction ‘upstream’ of the PowerTap.

I’ll make an effort to do proper 20 minute max efforts on both platforms and keep an article update with how the figures change and (hopefully) converge as I start to assume better form.

Upright stationary trainer interval – 12.5 minute best effort

Edit: I’ve added a screen grab from Golden Cheetah to the one from Ascent (I had to crop the latter quite aggressively to get it to fit):

recumbent-power-comparison-new2

gc_df

Recumbent stationary trainer interval – 12.5 minute best effort

Edit: I’ve added a screen grab from Golden Cheetah to the one from Ascent (I had to crop the latter quite aggressively to get it to fit):

recumbent-power-comparison-new1
gc_bent

Food for thought! I’d love to hear any thoughts in the comment section below:

See also discussion on this post in BROL.

Cycling drafting advantage

I recently took the opportunity to record some power numbers on the drafting advantage while cycling in a small group…

Pulling vs sitting in, measured in watts

I recently took the opportunity to record some power numbers on the drafting advantage while cycling in a small group on a brevet in southern Scotland.

Because I already have good power figures for my racer (via PowerTap hub) on the flat in calm conditions, it was a neat contrast to do the same on a real road, with a headwind, as part of a group.

draft-power1

Although the conditions were not controlled (the road was rolling and the wind wasn’t constant – neither was the speed or effort of the group), it was a steady enough effort that I feel confident presenting it here. Average speed for the leg was ~18mph.

The headline figure is that riding at the head of the line cost about 100W more than sitting in (i.e. 250W versus 150W). Drafting is a huge advantage when cycling!

For contrast, riding solo in lab conditions on the flat, I get 16.5mph at 150W and 19.5mph at 250W.

From simple physics, if a climb can be done at 10mph at 150W, 250W means climbing at 16.5mph. A huge difference.

Endurance riders

From these power figures we can calculate the overall saving in energy from a prolonged period of riding co-operatively. An hour at 250W requires more than 900kcal; even riding in a pair (for a total of 30 minutes on, 30 minutes off) reduces this to 720kcal:

draft-power2

Riding in a group of four drops it right down to 630kcal – or expressed another way, compared with a solo rider you will get one hour of progress down the road “free” with every two hours you put in.

The graph above shows the endurance duration of a rider in different scenarios; I chose 2000kcal somewhat arbitrarily because it approximates how much glycogen your body stores in muscles and liver.

“Buy two, get one free” is a huge advantage over long distances. While no cyclist needs to be told that drafting works, it is interesting to see by just how much!

No wonder even a loose group can make real headway…

An aside on recumbents

I haven’t yet had the chance to collect decent data on pulling versus sitting in a group on a recumbent.

However, I do find it interesting that when I tested the RaptoBike midracer against my road bike I found approximately a 100W aero advantage at these speeds (150W giving 19.4mph recumbent, where 250W gave 19.6mph upright).

This ties in nicely with my rule of thumb that riding a recumbent is like having a group to draft behind all the time…

Powertap: kilojoules and calories burned

Your PowerTap gives kilojoules – this is the most accurate measurement of your energy investment outside of a lab. But how should you convert into calories?

why kJ = kCal is a good estimate

Your PowerTap hubproduces a figure for total work performed in a ride – measured in kilojoules. This is the most accurate possible measurement of your energy investment outside of a lab. But how should you convert this figure into calories?

I’ve already written about the calculations required to convert wattage into calories, as this is more natural when planning part of a ride or workout (you wouldn’t express your threshold power in joule-hours, you’d express it in watts).

However, once you’ve actually done a ride or workout, your Powertap will give you a figure for total work performed, measured in kilojoules (kJ). This is by far the easiest way to work out calories consumed and by a stroke of good fortune you probably just want to use the kJ number for kCal.

powertap-cal1

Assumptions and working

The efficiency of cycling humans is between 20-25% (so your body’s many systems and inefficiencies burn 4-5J of energy for every 1J you deliver to the pedals).

This means we should divide any “measured joules” figure by 0.2 to 0.25 to get it expressed as “real joules”.

By a happy coincidence, a calorie is ~4.18 joules, so to turn the “real joules” into calories we’re about to do broadly the opposite (a joule is 0.24 of a calorie).

For a human with 24% efficiency, you can cancel the last two steps exactly, so that measured joules = real calories. Since the range is 20-25% efficiency this is an underestimate (lots of people will burn more calories than the calculation suggests, but few will burn less).

Obviously your bike is not perfectly efficient either- you will be losing a couple of percent of your power between the balls of your feet and the rear wheel, so the number of calories burned is going to be even higher than that figure.

However, for almost every purpose imaginable, you really want your kCal estimate to err on the low side.

powertap-cal2

Why a low calorie estimate is a good thing

Take an hour workout averaging 200W (consuming 200W * 3600s = 720kJ)

Let’s imagine you are actually at the bottom end of human efficiency (you burn a whole 5J to create 1J of power). For you, the ride requires 865kCal.

The assumption of someone nearer the top end of the scale (burning 4.17J to create 1J of power) requiring 720kCal to complete the same ride leaves a gap of 145kCal.

If you ate aiming to replace calories burned in this workout, the worst case scenario is that you will come up 145kCal short. A pound of fat is around 3600kCal, so after twenty-five of these one hour workouts you’ll have lost a pound of bodyweight you didn’t intend.

If you are one of the very, very few people who needs to avoid a pound of fat loss after twenty five workouts then you’d be better using a more conservative estimate (such as multiplying kJ by 1.1 or 1.2) but for almost everyone the unexpected loss of this extra pound of weight will be a happy mystery.

P.S. Depending on where you live, you may have kcal on food packaging (like the UK) or just “calories”, which is always really kcal (there’s some mumbo-jumbo about Calorie = 1000 calorie, not that people capitalise like that in real life, but see Wikipedia).

Optimising long distance cycling speed

It’s tempting to zero in on a lighter ride (carbon frame, lighter wheels, etc) but is that really because it’s an effective way to increase speeds, or is it just easy to quantify?

Done a brevet or twenty but not as quickly as you’d like?

Go faster on your bike…

The issues are the same whether you’re struggling to make the cut on a 200km, trying to improve your safety margin or build up a sleep buffer on a longer randonée, or even if you’re finishing comfortably within time but want to go round quicker.

Hey – maybe you’re just sensible and want to ride at the same speed as the group, but for less effort!

randokit

It’s tempting to zero in on a lighter ride (moving to a carbon frame, lighter wheels, and so on) but is that really because it’s an effective way to increase ultra distance speeds, or is it just because it’s so easy to quantify?

So before you splash the cash on an amazing pair of wheels… stop!

I just caught up with a fairly old topic on the forum: New “Comfortable” carbon frame or steel folding bike for LEL2013? I spent a little time writing a response to that discussion but thought it might be worth developing here:

Identifying an upper bound for weight-related performance gains

It’s rather difficult to exactly quantify the advantage of a reduction in weight because of the complex interplay of static and rolling losses, accelerations, etc. However, it’s actually quite easy to put an upper bound on the benefit, as follows:
Continue reading “Optimising long distance cycling speed”