bradcycles

Any thoughts as to which would be the power meter solution for a calfee tandem with lightning crankset?

Any other power meter solutions that would be good?

CliffordK

I was looking at pedal power meters earlier... One difference I noticed was the computer interface:

Look Keo Power - Bluetooth
Garmin Vector - Ant+
Powertap P1 - Ant+ & Bluetooth

I think Garmin Vector also has a single pedal option.

Is Powertap without pods?

I didn't actually get the pedals to evaluate, so I was just looking at specs. I hadn't seen the Powertap pedals yet... they look nice. There are also crank based power meters which you might explore.

Alcanbrad

I have often wondered if pedal or crank based power meters would give meaningful results on a tandem. I would believe differences in captain and stoker power could potentially result in false additions or subtractions to what the power meter is reading. I certainly can tell when my stoker is slacking and when we are being chased by a dog. If there were power meter pedals on both cranks, there would need to be 2 monitors and I am not aware of any SW that would correlate the two streams.

Take a look at the ibike Newton https://www.ibikesports.com/ (no relation to Apple or the iphone) This solution uses sensitive accelerometers as well as a wind sensor. They even show a tandem as one of the possible applications. Reviews I have read in the past have been favorable as to the accuracy, ease of initial set up, and use, as well as the SW application that comes with it.

Full disclosure: I do not own one but probably will at some this season. I know a couple of people who have them and like them.

agriskman

It seems that pedal power meters measure power at the pedal stroke so why would they give a errant reading on a tandem? Anybody know? I am thinking of buying garmin vector to try them out.

CliffordK

A hub based power meter will give you the combined effort for both individuals.

I don't see any reason why the Captain and the Stoker couldn't have their own power meters... And they may not need to integrate the information at all. And, the stoker could simply keep his or her own meter, or give it to the Captain.

Since Garmin already does a single pedal... and interpolates dual pedal cycling.

You could do some thing similar, take a two pedal setup, and give the right pedal to the Captain and the left pedal to the Stoker. Then simply double the combined power. Hopefully your software could deal with the right/left differences.

One problem, however, with splitting the pair is range.
When I was reading about the Look pedals, I think one was setup as a master, and one as a slave, so the two pedals would communicate between each other, then send the combined info to the recording device. That may or may not work with 3 or 4 feet of separation.

Are you buying this through your LBS? Will they let you "demo" the system?

Team Fab

DC Rainmaker

very thorough testing of all power meters

Alcanbrad

Think about it this way. The captain has a pedal or crank based power meter and during a power stroke his or her foot is attempting to apply 10 ft-lbs of torque (numbers just made up). At the same time the stoker applies a burst of 15 ft-lbs. THe drive train is going to accelerate away from the captain giving the captain a lower reading than 10ft-lbs. When you view the power curve, does the curve represent what you are doing, or what you are doing plus or minus what the partner is doing?

Power meters are best to analyze and develop a consistent power stroke throughout the entire rotation of the crank. Knowing peak power is nice, but not the most important measurement. At best on a tandem it would show the differences in consistency between captain and stoker. Are the differences in your measured power stroke totally you, or you modulated by your partners output?

On a tandem, knowing the power applied to the rear wheel is the only meaningful measure. Measurement at the hub is the most exact method. I don't know if power tap makes a tandem hub, but you are talking a custom wheel (though not unusual in tandem land).

Team Fab

Both crank based and pedal based meters should filter out any input from the other rider as all they measure is the force applied by the foot to the pedal or crank. If stoker were to put so much power that they actually get ahead of the captain then the captains meters would read zero. But in the real world that doesnt happen unless you are going down hill and then both meters would read zero.

If one person is stronger than the other it will have no effect the meters will still read the actual force being applied. I think at this time however unless you are riding a timing chain on same side as drive drive side the only meters that will work are one sided crank or pedal based.

Rear wheel will give you a reading of both captain and stoker but has little value as one person can have a good day and the other a bad day giving the same result as both riders having a medium day. All it will tell you is that the team is having a day that is better than another.

Dean V

We use a power tap wheel and find it to be quite good. Sure there are limitations in not having individual power numbers but it is also good having a total output as it is a team effort after all. If one of the team has ridden solo with a power meter they will have a feel for what they are contributing and have a fair idea of what the other is doing. Combined with heart rate you can get a pretty good overall picture. Also if one rider is much weaker than the other they may be somewhat discouraged looking at individual power numbers.

Alcanbrad

And there in lies the problem. You are correct, the pedal or crank meter will measure the actual power applied to the pedal. When your partner pedals harder, it is easier for you and your power measurement will be lower. Based on that, can you tell that you are having a good day? Is you partner having a good day? A bad day? Are you pedaling down hill? What does your power measurement tell you if you don't know how the system (captain + Stoker) are performing.

The data you get is meaningless unless you can reference it to something tangible. If you can pedal stroke correlate it between captain and stoker, then you have a meaningful comparison. If you measure total power applied to the hub, then you can tell how you are performing as a team. Beyond that, a power graph that is modulated by your partner is just a pretty graph to look at.

It would be interesting to hear from anyone who has used a pedal or crank meter on a tandem.

Dean V

If you are both serious about training by power obviously independent power measurement is the only way. We are not that serious and are quite happy with just the single measurement at the wheel.

agriskman

My assumption was that a pedal power meter measures power by force on the pedal so that should not be influenced by my stoker (who has no interest in power training). One advantage of the tandem is that I can train as hard as I want for my single races while my stoker can ride however hard or easy as she feels like. This is why I am potentially interested in an individual power meter, not a team one.

bradcycles

I have no interest in a combined power meter. Both my stoker and I ride with power meters on our single bikes and are often curious as to our actual performance on the tandem on any single day. As others have said, my understanding is that the pedal power meters will accurately reflect the power output of each individual rider. If my stoker puts in a hard effort on a couple pedal strokes so that i do not have to exert as much force, that means that i will have greater ability to go harder on later pedal strokes.

I thought i read someone who said they had problems with the garmin vector working with their lightning cranks on the tandem.

Team Fab

Just because your partner pedals harder does not mean that you do not, what it means is that if your pedal the same you are accelerating.

Alcanbrad

Any force applied to the pedals results in acceleration. In addition to the forces applied to the pedals, you just have to consider all the force vectors (rolling resistance, air resistance, gravity, bearing friction, drive train losses, static and rotational inertia, frame flex, ...) to determine the actual acceleration

agriskman said:

My assumption was that a pedal power meter measures power by force on the pedal so that should not be influenced by my stoker (who has no interest in power training). One advantage of the tandem is that I can train as hard as I want for my single races while my stoker can ride however hard or easy as she feels like. This is why I am potentially interested in an individual power meter, not a team one.

This is why I am questioning the value of single power meter on a tandem. When you apply power to pedals, the pedals push back and you can feel that push back in your feet. The power meter measures that "push back". Muscle cells only know on and off, what your body does is modulate how many muscle cells are told to contract. So when you decide to apply power to a stroke you instruct the muscles to contract a certain amount. Now consider your partner pedaling harder for a few strokes, or pedaling with an uneven power stroke. Can you feel it? If your power applied to pedals was constant, you could not feel anything your partner was doing. That change in feeling is directly measured as a change in power by the strain gauges in whatever set up you have. If your partner had a perfect power stroke, then you would get an accurate reading of what you are putting into the pedals, otherwise the power curves you are looking at for yourself are not accurate as to what your body is producing. Power meters help you determine your sustainable power and how to develop a smooth power stroke in both legs.

If what you are looking for is what the pedal see's, then any product should be fine, otherwise I would save my money.

I am kinda feeling like Don Quixote here, so time to shut up and go for a bike ride

twocicle

Alcanbrad, most of those concerns are inconsequential. Pedal power meters will record the wattage effort YOU apply to the pedals regardless of whatever the stoker does, and does not measure power applied to the drivetrain as a whole. Sure the stoker input level could make it easier or harder for you to maintain a certain speed, but there is nothing to stop you from adjusting your effort level accordingly.

Team Fab

I agree to the above and would add.

If the stoker applies 10 watts more in a giant burst of energy, unless the rear tire spins the pedals are not going to jump away from the captain. The pedals will accelerate at a speed that the captain will easily compensate for in a split second. Probably faster than a 1/4 turn of the pedal. I don't think that will even register on the power meters display.

I actually think that shifting will cause more of a blip on the recording of power than that.

twocicle

For independent power measures, any meter that measures upstream of the spider should work. Crankarm based (ROTOR, Infocrank, Pioneer, Watteam, 4iiii), or pedals (Garmin, Polar, Xpedo), or cleats (Brim Brothers).

FWIW, there has been a big price drop across most power meters over the last couple weeks.

Power Meter Pricing Wars: Let The Games Begin | DC Rainmaker

For my purposes (mostly single bike / training & racing) I'm near pulling the trigger for either a Power2Max or Specialized/Quarq spider based meter for my S-Works FACT cranks on that bike. Possibly, though I'm not sure, this same spider may fit on Lightning cranks, so if we do move to those cranks there is the chance of porting this spider over to the tandem as well (for combined rider, total powertrain readings). I'll probably give Lightning a call to inquire if they know whether or not either of these meters will fit their cranks.

--

update regarding Lightning vs Specialized spider compatibility:

Lightning spiders are offset some 5mm to the inside, while spiders for Specialized FACT cranks are offset some 5mm to the outside. Net diff is 10mm between the two, which would mess up the chainline on the Lightning cranks if a Specialized type spider were used, plus unknown if there would be sufficient clearance from big ring to the crankarm. Lightning can mfr a compatible crank to make the Specialized power meter spiders work, but otherwise it seems a no-go.

merlinextraligh

This. I've been training with power for 10 years now, and 2 years on the tandem. I've used a powertap and Quarqs on single bikes, and Look Power pedals and Garmin Vectors on the tandem.

Any interference in one rider's power reading from the other rider's efforts I believe is deminimis. I base this on a couple of things. If I pedal at a constant effort and my stoker unclips, my power remains pretty much constant (although speed drops). If I unclip, and my stoker continues to pedal, my power meter will show some power, typically 0-3 watts. So there's a tiny influence. Additionally, the readings appear pretty consistent with perceived effort.

I do find that my power is lower on the tandem than on the single bike. However, I don't believe this is from interference from the stoker. I think its more a function of difference in calibration of the different meters, subtle position differences, and just the dynamic of riding a tandem.

And what's most significant is that the Garmin on the tandem is consistent and repeatable. So, even if it reads lower than the Quarq on the single, it does so consistently. And the key point for training with power is consistency, which is more important than absolute accuracy.

merlinextraligh

As for Powertap pedals vs Vector,

3 things I dislike about Vector:

1) the pod. It's a bit ugly, and its fragile. They break easily if you don't follow the installation instructions precisely. I broke one installing it, even following the instructions (Garmin did replace it under warranty) and we broke another lifting the bike over a curb. They won't break riding, but its likely at some point you may break them leaning the bike against a curb, putting in a car,rack, etc.

2) the need for a torque wrench. To properly install them you need a torque wrench with a special claw foot, and need to tighten precisely to 25nm. This may not be a huge issue given that they appear to be accurate if you tighten them to at least 25nm, without having to hit 25nm exactly.

3) you have to use Look style cleats. (really wish they would have stayed with Speedplay)

Powertap potentially solves the first two issues.

Negatives I see for PT: 1) 48 gram weight penalty;

2) the battery on the bottom looks ugly and clunky, and may hurt cornering clearence.


Personally, I wouldn't buy the Powertap Pedal now. Every power meter that has come to the market has had startup problems with various glitches needing to be ironed out. Vector is a bit ahead of the Powertap Pedal in that process.

Team Fab

The 0-3 watts could be caused by the pedal rotating as the crank arms go around**********???

merlinextraligh

that's my assumption.

bradcycles

We are getting our calfee tandem built now with lightning cranks. are there any crank based power meter spiders that can be used? I would prefer a crank based system since i use speedplay pedals and woukd orefer to stick with those.

twocicle

thought you might

The only crank or spider power meter I can think of that could be Lightning compatible is the Power2Max "Type S" or the Quark (or Specialized S-Works) since these use the same spider mount pattern as Lightning. I was told they could do something regarding the spider offset differences. Crank arm clearance might be another thing. It would be an interesting experiment and if I were the mfr (ie Lightning) it is something I would have already mocked up as proof of concept for my customers. These spider based power meters are now under $1000, and sort of venturing into the affordable category. Other crank or spider power meters are either preinstalled or compatible with a limited variety of cranks and nothing for Lightning available.

Other than pedal based meters, Brim Brothers are still working on delivering their "Zone" Speedplay compatible cleat-based power meter, which should be shipping this year. I am on the pre-order email list and as yet my number has not come up. Hopefully DCRainmaker will do another validation of the final product w/latest software against other meters. From his last post (link below) the Zone power readings were not great, but there is supposed to be a sw upgrade coming to fix that.
https://www.dcrainmaker.com/2014/09/b...roduction.html
https://velonews.competitor.com/2014/...r-meter_345153

bradcycles

DC Rainmaker's first ride with the P1 Pedals seem to have produced data that closely tracks the power from the Powertap G3 hub. Good early sign! And, it sounds like the pedals will be released in early June:

First rides with the PowerTap P1 Pedals & PowerTap C1 Chainring?and more | DC Rainmaker