Tandem Cycling - Tandem Power Measurement

Any info out there in BF land on options available for tandem power measurement (wireless) that would be compatible with a Garmin (ANT+)? I looked on the Saris website and nothing jumped out that appeared to be compatible with a rear-disc equipped, 145mm spacing tandem.

I have not tried it, but it seems the iBike Power meter should work with your Garmin 705 Edge. The following link might be useful.
http://www.worldcycles.com/index.html?lang=en-us&target=d184.html

rdtompki,

andyman is correct, we use the iBike with a 705 for the stoker to see realtime power, the set up works great.

Any info out there in BF land on options available for tandem power measurement (wireless) that would be compatible with a Garmin (ANT+)? I looked on the Saris website and nothing jumped out that appeared to be compatible with a rear-disc equipped, 145mm spacing tandem.

Cinqo(s) could probably be rigged up.

I don't think anyone in the TdF is using an iBike to measure power. SRM, Cinqo, and Powertap are the only real options for those guys.

Cinqo(s) could probably be rigged up.

I don't think anyone in the TdF is using an iBike to measure power. SRM, Cinqo, and Powertap are the only real options for those guys.

I don't see any tandems on the tour. Rick is asking about options for a tandem. We actually have experience with all types of power meters and we found that the iBike works without having it "rigged up" plus the iBike is about half the cost and not just "probalily" may work, we know it works on a tandem.

Both my wife and I train and race with power on our single bikes. We considered the Ibike a couple of years ago and passed. We use both the Quarq Cinqo and PowerTap with a Garmin 705. I thought about using the Ibike for the tandem. Since we have not been riding the tandem much this summer it fell off the radar screen. I think everyone is familiar with Ibike's shortcomings. I can see how it could be of some value on the tandem. Speaking for myself, once you train with power, one gets good at estimating power based upon perceived effort. Obviously, not very accurate and on a tandem there are two people coordinating their effort. I can see how an Ibike feeding both Garmin 705s could add some value.

There is a new power meter coming out next year. Here are some details.

"Clark Foy of San Jose Bike Club has invented a new powermeter. It's
a bunch of accelerometers, stuffed into the hollow pedal spindle of a
Speedplay pedal. Not only does it yield power information measured
directly, it also measures left/right, and in each of the pedal circle
quadrants, so that feedback can be incorporated to improve
efficiency. It's wireless, and communicates to existing "head" units
which use the ANT protocol, which most use. Garmin is one such unit;
there are close to 10 brands that could work.

There are computer chips inside which are electrically reprogrammable,
so as the algorithms improve, the pedals can get "software upgraded".

Retail price will be something like $899, which includes the pedals
($200 retail price). You'll need to purchase one of the head units
separately, like a Garmin.

Product will be launched at Interbike, early production late Q4'09,
broader distribution in Q1'10."

This looks interesting for the tandem. When I first heard about this, I thought tandem and track. Speedplays are fine for tandem but I would not use them on the track.

I can see it now. Go out for a tandem ride and then download the individual power data to Training Peaks and let the discussion begin.:D

I have a Powertap (that doesn't see much use these days) and a Quarq/705 setup for my single bikes.

One problem with riding the tandem a lot, without a power meter is that it throws off tracking the cummulative matrices in Cycling Peaks. Hence, I would love a power meter that gives the power for both riders on the Tandem.

We thought about the I Bike, but in addition to the setup, and extrapolation issues, it wouldn't solve my problem of getting the Captain's only power.

Perhaps a Quarq for the captain, and a I bike? You'd need a crank, with a removable spider. I don't see an intrinsic reason you couldn't run an FSA Team issue, set up backwards, with some locktite on the pedal threads.

Also, there was a guy on here that had a tandem set up with dual SRM's. Rather pricey, but it was for a study presumably supported by a grant.

There is a new power meter coming out next year. Here are some details.

"Clark Foy of San Jose Bike Club has invented a new powermeter. It's
a bunch of accelerometers, stuffed into the hollow pedal spindle of a
Speedplay pedal. Not only does it yield power information measured
directly, it also measures left/right, and in each of the pedal circle
quadrants, so that feedback can be incorporated to improve
efficiency. It's wireless, and communicates to existing "head" units
which use the ANT protocol, which most use. Garmin is one such unit;
there are close to 10 brands that could work.

There are computer chips inside which are electrically reprogrammable,
so as the algorithms improve, the pedals can get "software upgraded".

Retail price will be something like $899, which includes the pedals
($200 retail price). You'll need to purchase one of the head units
separately, like a Garmin.

Product will be launched at Interbike, early production late Q4'09,
broader distribution in Q1'10."




This sounds similar in concept to the Brim Brothers shoe based system. http://www.brimbrothers.com/

However, they've had trouble apparently with working it all out.

One problem would appear to be how the meter measures force in the up stroke, which would likely be a similar problem for the pedal based system.

I hope the Speedplay system makes it to production.

[Edit] actually reading it, it appears its a different system based on acceleromaters, not, pressure on the pedals.

Both my wife and I train and race with power on our single bikes. We considered the Ibike a couple of years ago and passed. We use both the Quarq Cinqo and PowerTap with a Garmin 705. I thought about using the Ibike for the tandem. Since we have not been riding the tandem much this summer it fell off the radar screen. I think everyone is familiar with Ibike's shortcomings. I can see how it could be of some value on the tandem. Speaking for myself, once you train with power, one gets good at estimating power based upon perceived effort. Obviously, not very accurate and on a tandem there are two people coordinating their effort. I can see how an Ibike feeding both Garmin 705s could add some value.

There is a new power meter coming out next year. Here are some details.

"Clark Foy of San Jose Bike Club has invented a new powermeter. It's
a bunch of accelerometers, stuffed into the hollow pedal spindle of a
Speedplay pedal. Not only does it yield power information measured
directly, it also measures left/right, and in each of the pedal circle
quadrants, so that feedback can be incorporated to improve
efficiency. It's wireless, and communicates to existing "head" units
which use the ANT protocol, which most use. Garmin is one such unit;
there are close to 10 brands that could work.

There are computer chips inside which are electrically reprogrammable,
so as the algorithms improve, the pedals can get "software upgraded".

Retail price will be something like $899, which includes the pedals
($200 retail price). You'll need to purchase one of the head units
separately, like a Garmin.

Product will be launched at Interbike, early production late Q4'09,
broader distribution in Q1'10."

This looks interesting for the tandem. When I first heard about this, I thought tandem and track. Speedplays are fine for tandem but I would not use them on the track.

I can see it now. Go out for a tandem ride and then download the individual power data to Training Peaks and let the discussion begin.:D

Hermes, you should give the iBike a try on your tandem, we also ride and train with power on our singles, and we've compared the numbers with the power tap and the Gen 3 iBike, the power numbers are almost identical! (the iBike of 2 years ago is not at all as good as the new Gen 3) You'll be surprise how much you can use power on the tandem, as you mentioned one gets good at estimating power based upon perceived effort, so we know how endurance power zone feels on our single and is not different on the tandem, all of our training on the tandem is with power and it really works. We have a combined FTP for the tandem, we got it by doing FTP tests and the numbers came almost identical to our individually FTP numbers (Adding the FTP of the two of us).

I don't see any tandems on the tour. Rick is asking about options for a tandem. We actually have experience with all types of power meters and we found that the iBike works without having it "rigged up" plus the iBike is about half the cost and not just "probalily" may work, we know it works on a tandem.

You missed the point. I think crank-based power meter options are probably possible on a tandem, and if so would be a superior solution to an iBike (assuming $$ not an issue for you). Of course you would need two head units too, maybe pair captain with stoker power, and stoker with captain, to have some fun!

On our Davinci we would need identical crank-based power measurement units each of which needs to support a single, 36t chainring (on the left side). This is probably too expensive a solution given we're never going to race, but intriguing nevertheless. A better solution might be a Powetap hub for our single bikes which have identical 12-27 cassettes. I will look into the iBike as well. It appears it may develop useful information at a reasonable price, but I certainly wish the website were more forthcoming about the nature of the algorithms used short of revealing any of their precious IP.

Hermes, you should give the iBike a try on your tandem, we also ride and train with power on our singles, and we've compared the numbers with the power tap and the Gen 3 iBike, the power numbers are almost identical! (the iBike of 2 years ago is not at all as good as the new Gen 3) You'll be surprise how much you can use power on the tandem, as you mentioned one gets good at estimating power based upon perceived effort, so we know how endurance power zone feels on our single and is not different on the tandem, all of our training on the tandem is with power and it really works. We have a combined FTP for the tandem, we got it by doing FTP tests and the numbers came almost identical to our individually FTP numbers (Adding the FTP of the two of us).

Thanks for the info. We will look into it.

On our Davinci we would need identical crank-based power measurement units each of which needs to support a single, 36t chainring (on the left side). This is probably too expensive a solution given we're never going to race, but intriguing nevertheless. A better solution might be a Powetap hub for our single bikes which have identical 12-27 cassettes. I will look into the iBike as well. It appears it may develop useful information at a reasonable price, but I certainly wish the website were more forthcoming about the nature of the algorithms used short of revealing any of their precious IP.

While it may be somewhat out of date, they do have several patents, which, by their very nature, reveal their "precious IP". If you look up the company name at the bottom of the web site, then go look for patents with that assignee name, there are only three hits (possibly more applications not yet issued, I didn't look). Now the patent describes what they were envisioning when the patent was written, and not necessarily what they wound up doing, but it would appear that they use a MEMS accelerometer and calculated acceleration (from the wheel sensor) to compute actual acceleration and tilt. They also use two air pressure sensors, one with a port facing forward and another to the side to measure wind speed (this isn't right, but the error could probably be calibrated out). The main remaining input is cadence, measured conventionally. Optional other measurements include altitude and temperature, which appear to be used either to improve accuracy in other measurements or to fine tune things. A roll-down calibration followed by a curve fit allows a measurement of rolling resistance and air resistance. Pretty much the rest is a matter of math.

To the original question, as far as I can tell, since there's no crank or pedal based pressure sensor, you can only get total power, so if you're looking for something tandem-specific, you're not really getting it here. You can compute the total power, but you can't separate captain from stoker. If that's what you're looking for.

...but it would appear that they use a MEMS accelerometer and calculated acceleration (from the wheel sensor) to compute actual acceleration and tilt. They also use two air pressure sensors, one with a port facing forward and another to the side to measure wind speed (this isn't right, but the error could probably be calibrated out). The main remaining input is cadence, measured conventionally. Optional other measurements include altitude and temperature, which appear to be used either to improve accuracy in other measurements or to fine tune things. A roll-down calibration followed by a curve fit allows a measurement of rolling resistance and air resistance. ...

Thanks for the information. You're describing what I would envision their approach. Devil is in the details in terms of how the various measurements are combined, weighted, filtered ,etc. It's surprising that their website is more of the "trust me" variety. When I get some time I'll look up the patents; might be interesting.

If you have some extra cash laying around you could try this out.

SRM Dura Ace (http://www.excelsports.com/new.asp?page=8&description=Dura-Ace%20Wired%20PowerControl%20V%20175mm%20USED&vendorCode=SRM&major=3&minor=15)

If you have some extra cash laying around you could try this out.

SRM Dura Ace (http://www.excelsports.com/new.asp?page=8&description=Dura-Ace%20Wired%20PowerControl%20V%20175mm%20USED&vendorCode=SRM&major=3&minor=15)

Cash is always and issue but the SRM solution is not that straight forward. You need a timing chain on the captain and stoker cranks and typically a triple. I suppose one could be motivated and have some special work done on the SRMs to make it work.

I think the Ibike is great or hopefully a pedal based system that will still be expensive but will also work on the road bikes.

And if I were going to use a crank based system and figure out a way to "make it work", I would use the Quarq. We have this technology on road bikes and it works well for less money than an SRM.

Cash is always and issue but the SRM solution is not that straight forward. You need a timing chain on the captain and stoker cranks and typically a triple. I suppose one could be motivated and have some special work done on the SRMs to make it work.

I think the Ibike is great or hopefully a pedal based system that will still be expensive but will also work on the road bikes.

And if I were going to use a crank based system and figure out a way to "make it work", I would use the Quarq. We have this technology on road bikes and it works well for less money than an SRM.

I posted more for the gee whiz of look how much this stuff costs. I was pretty sure that cheaper solutions were available.

I like seeing the power output from other people. I know my power will be similar and I get that information for about zero cost :thumb: :)

Good luck with it. I'd like to see progression numbers over a training season.

This was a good read (http://www.saris.com/t-powerBasics.aspx) on the subject.

I posted more for the gee whiz of look how much this stuff costs. I was pretty sure that cheaper solutions were available.

I like seeing the power output from other people. I know my power will be similar and I get that information for about zero cost :thumb: :)

Good luck with it. I'd like to see progression numbers over a training season.

This was a good read (http://www.saris.com/t-powerBasics.aspx) on the subject.

A better read is Training and Racing with a Power Meter by Allen and Coggan. Training with power is much more than "knowing" your power or being able to say I produce X watts. It is about hitting power numbers that are meaningful to you over discreet periods of time to improve VO2 Max and Threshold Power as well as others. Downloading individual power numbers into Training Peaks Software and tracking progress becomes very meaningful and motivating. Post ride analysis leads to incite on how to increase performance. This benefit even makes the SRM cost justifiable. The question becomes how many power meters can one have and which bikes to equip to have it make sense when you are paying the cost. For us, we do not ride the tandem enough to justify yet another power meter solution.

If a pedal based power solution becomes available that will work for the track, I would get two setups. Then I could easily swap pedals to the tandem and effectively set up the equivalent of four bikes with power. And BTW, the current SRM solution for a track bike is 3700 Euros if you are looking for a gee whiz factor.:rolleyes:

And BTW, the current SRM solution for a track bike is 3700 Euros if you are looking for a gee whiz factor.:rolleyes:

That is significantly more than the ~$3800 for the NIB Dura-Ace (http://www.excelsports.com/new.asp?page=7&major=3&minor=15).

I'll just leech for the next decade or so :innocent: :)

And if I were going to use a crank based system and figure out a way to "make it work", I would use the Quarq. We have this technology on road bikes and it works well for less money than an SRM.

I sent an email to Quarq, and asked if they were aware of any tandem compatible cranks that would work with a Quarq. I haven't gotten a response yet.

I'm betting you could use any of the Quarq cranks now available turned backwards for the captain's crank, and etiher get the pedal threads redone, or use locktite.

Stoker's crank might be more problematic.

A better read is Training and Racing with a Power Meter by Allen and Coggan. Training with power is much more than "knowing" your power or being able to say I produce X watts. It is about hitting power numbers that are meaningful to you over discreet periods of time to improve VO2 Max and Threshold Power as well as others. Downloading individual power numbers into Training Peaks Software and tracking progress becomes very meaningful and motivating. Post ride analysis leads to incite on how to increase performance. This benefit even makes the SRM cost justifiable. The question becomes how many power meters can one have and which bikes to equip to have it make sense when you are paying the cost. For us, we do not ride the tandem enough to justify yet another power meter solution.

If a pedal based power solution becomes available that will work for the track, I would get two setups. Then I could easily swap pedals to the tandem and effectively set up the equivalent of four bikes with power. And BTW, the current SRM solution for a track bike is 3700 Euros if you are looking for a gee whiz factor.:rolleyes:

Hermes, You are perfectly correct. Most people believes that a power meter is just used to do your workouts or just see your power during the ride, but as most of us that really train with power know that one of the most important aspects of power is the ability to analyze you ride after and keep a real track of your efforts and the amount of stress your body is enduring day by day, week by week and over a whole season, allowing you to train and recover correctly, also the ability to measure your fitness and build a power profile over time. Having a power meter on our tandem stills allow us to get TSS and IF for the rides that we do on tandem, this keeps our data power data without gaps on TSS and IF and really allows us to maximize our training. One of the things we've learned on a tandem is that you are only as good as you are as a team (the two of you). So having the ability to see individual power on the tandem is good, but you are still connected and it is really is one machine with two engines that need to ride as one and at the end of the ride combined power still is going to be super important.

That is significantly more than the ~$3800 for the NIB Dura-Ace (http://www.excelsports.com/new.asp?page=7&major=3&minor=15).

I'll just leech for the next decade or so :innocent: :)

That is because the track market is small and SRM only makes their "top of the line" Scientific version for fixed gear.

I would guess the cinqo/SRM would have to be specially calibrated to work with the reverse torque.

Yes, reverse torque is important, particularly on the track.

IIRC I have heard that you can't use an ordinary bike powermeter backwards on the tandem because powermeters are set up to read zero when they see reverse power. For example if you freewheel down a hill then pedal backwards really fast you should see 5 or 10 Watts negative power. My bet is that you don't because it would look confusing so easier to drop the data.

Pedal based power meter...pics from Interbike courtesy of Google wattage group.

Some photos from the pre-Interbike open house:

Information sheet, page 1:
http://www.flickr.com/photos/djconnel/3930884632/

Information sheet, page 2:
http://www.flickr.com/photos/djconnel/3931039857/

Blow-up from wall poster:
http://www.flickr.com/photos/djconnel/3930768660/

Souvenir water bottles :):
http://www.flickr.com/photos/djconnel/3930768710/

Pedal based power meter...pics from Interbike courtesy of Google wattage group.

Some photos from the pre-Interbike open house:

Information sheet, page 1:
http://www.flickr.com/photos/djconnel/3930884632/

Information sheet, page 2:
http://www.flickr.com/photos/djconnel/3931039857/

Blow-up from wall poster:
http://www.flickr.com/photos/djconnel/3930768660/

Souvenir water bottles :):
http://www.flickr.com/photos/djconnel/3930768710/

Wow that looks very good! that looks like a great option for tandem. Any idea of price?

:D :love:

I hope it works well.

I may end up selling a few pairs of Keos :innocent:


Pedal based power meter...pics from Interbike courtesy of Google wattage group.

Some photos from the pre-Interbike open house:

Information sheet, page 1:
http://www.flickr.com/photos/djconnel/3930884632/

Information sheet, page 2:
http://www.flickr.com/photos/djconnel/3931039857/

Blow-up from wall poster:
http://www.flickr.com/photos/djconnel/3930768660/

Souvenir water bottles :):
http://www.flickr.com/photos/djconnel/3930768710/

Wow that looks very good! that looks like a great option for tandem. Any idea of price?

$800 including pedals is what I remember.

Why not the Polar chain-pickup system? That's what I'm thinking about. One pickup for the timing chain to get captain's power, another for the chainstay to get combined power off the stoker's HRM. Subtract for stoker power. The Polar recording HRMs move from bike to bike, so all you need is multiple pickups. Riders I know using the Polar power setup say they work +- about 5% compared with SRM.

Why not the Polar chain-pickup system? That's what I'm thinking about. One pickup for the timing chain to get captain's power, another for the chainstay.

Because it won't work with a belt:)

I agree: Vector appears the most promising solution, especially if they release a Frog version (Speedplay road pedals being more oriented towards competition than rest stops). Frogs share the same spindles as X-series and Zeros, but it's a matter of Metrigear devoting the resources to calibrating frogs. In due time , I am sure.

The negative torque discussion is quite interesting. I'd never considered that before: only the stoker drive-side spider never sees negative torque. Vector will have no issues handling negative torque. And with the Quarq Qollector, you should be able to collect captain & stoker synchronized data, alleviating the challenge of aligning independently recorded ride files on two separate head units.

BTW you no longer need to rely on my flickr shots: it's now all on the Metrigear web site (http://www.metrigear.com/).

I sent an email to Quarq, and asked if they were aware of any tandem compatible cranks that would work with a Quarq. I haven't gotten a response yet.

I'm betting you could use any of the Quarq cranks now available turned backwards for the captain's crank, and etiher get the pedal threads redone, or use locktite.

Stoker's crank might be more problematic.

Well, Quarq is coming out with a CinQo for the Lightning...

Interbike 2009 - New Quarq Power Meter Crankset Options (http://www.bikerumor.com/2009/09/24/interbike-2009-new-quarq-power-meter-crankset-options/)



INTERBIKE 2009 - Quarq has been busy putting together powermeter rings for lots of crankset brands, with models for the following manufacturers coming out within the next two months:

* Rotor Agilis 3G
* Rotor 3D
* SRAM S975
* Cannondale Hollowgram SI / SL
* Lightning Carbon
* TA Specialties Carmina

All of these are pictured above or after the break, along with a prototype Collector data retrieval “black box” for cyclists that don’t want or use a big cycling computer on their bike (think track cyclists) but still want to collect power data.


http://www.bikerumor.com/wp-content/uploads/2009/09/quarq-power-meter-cranks-interbike09-02-600x362.jpg

...and Lightning is coming out with a tandem crankset.


http://gallery.roadbikereview.com/data/roadbike/701/DSC_0632.jpg

Okay..... let me make sure I understand the problem with each position:
Captain crankset: supports captain power only; supports negative torque, so must be a track version of a Quarq or SRM to operate correctly. Negative torque may occur when captain applies negative torque but the stoker applies a positive torque of greater magnitude such that the net drivetrain experiences positive torque and therefore the freehub does not disengage. Stoker crankset, timing chain: same as captain crankset, minus drivetrain losses in timing drivetrain. Stoker crankset, drive side: supports captain + stoker power - timing chain drivetrain losses, so can be used for total power. However, a triple crankset seems to be the preferred solution here, and I don't believe there's any sets which work with triple cranksets. Rear hub (PowerTap): reports total power - total drivetrain losses

The negative torque issue is a big one. For example, the Polar estimates power by estimating chain tension from the primary mode of chain vibrations. But this doesn't work if the monitored segment of chain (the top part) is slack. It also hasn't been calibrated to belt drives.

SRM makes a track version (http://www.cyclepowermeters.com/srm-track-system-428-p.asp) ($$$$$) and Quarq has one in development. So then perhaps you have a PowerTap for total power (- drivetrain losses), SRM track for captain power. But to display the difference would require a very clever head unit, and none are available yet (Qranium might do it; I'm not sure). Post-processing Qollector data would work, but that's not visible on the bike.

Metrigear Vector (http://www.metrigear.com/) is the most promising solution, but may end up delayed from its '00Q1 release projection, especially if mountain bike pedals are to be used (Speedplay Frogs are not part of the Q1 projection). Brim Brothers (http://www.brimbrothers.com) (cleat system) is another possibility, as is the pedal system revealed at Eurobike. But I don't know if it works with mountain bike shoes, or for which pedal systems it is designed. There's another system which is designed to measure crank arm bending, and that would also be similar, but I really really doubt it's available for tandems.

Very interesting discussion. I don't have a negative torque issue on the Davinci of course. Our stoker crankset is to say the least a bit unusual for crankset solutions might be out. A pedal-based solution could be very interesting if SPDs were supported. iBike might be entertaining, but in the absence of wind I could estimate power output myself and I'm very suspicious of the ability of a $700 device to accurately measure relative wind direction and velocity and calculate its effect. In any event wouldn't take a tandem into account (or does it). A pure headwind isn't too bad, but 30 degrees one way or the other and we feel like two 1/2 bikes.

You could run a full right-side-drive system with the existing technology, I think.

Or put your Cinqo/SRM on the left side of the stoker crank - no reverse torque. But the crank would be turning backwards, so I don't think a stock Cinqo would work. I don't know if the SRM knows which direction it is turning.

Okay..... let me make sure I understand the problem with each position:
Captain crankset: supports captain power only; supports negative torque, so must be a track version of a Quarq or SRM to operate correctly. Negative torque may occur when captain applies negative torque but the stoker applies a positive torque of greater magnitude such that the net drivetrain experiences positive torque and therefore the freehub does not disengage. Stoker crankset, timing chain: same as captain crankset, minus drivetrain losses in timing drivetrain. Stoker crankset, drive side: supports captain + stoker power - timing chain drivetrain losses, so can be used for total power. However, a triple crankset seems to be the preferred solution here, and I don't believe there's any sets which work with triple cranksets. Rear hub (PowerTap): reports total power - total drivetrain losses

The negative torque issue is a big one. For example, the Polar estimates power by estimating chain tension from the primary mode of chain vibrations. But this doesn't work if the monitored segment of chain (the top part) is slack. It also hasn't been calibrated to belt drives.

SRM makes a track version (http://www.cyclepowermeters.com/srm-track-system-428-p.asp) ($$$$$) and Quarq has one in development. So then perhaps you have a PowerTap for total power (- drivetrain losses), SRM track for captain power. But to display the difference would require a very clever head unit, and none are available yet (Qranium might do it; I'm not sure). Post-processing Qollector data would work, but that's not visible on the bike.

Metrigear Vector (http://www.metrigear.com/) is the most promising solution, but may end up delayed from its '00Q1 release projection, especially if mountain bike pedals are to be used (Speedplay Frogs are not part of the Q1 projection). Brim Brothers (http://www.brimbrothers.com) (cleat system) is another possibility, as is the pedal system revealed at Eurobike. But I don't know if it works with mountain bike shoes, or for which pedal systems it is designed. There's another system which is designed to measure crank arm bending, and that would also be similar, but I really really doubt it's available for tandems.

THe Metrigear solution is ANT+ technology so a Garmin 705 will work. The captain and the stoker each have a 705 that is coded to each set of pedals so that each on measures individually. IMO, experienced riders will be able to use that data effectively. Garmin would have to make a firmware solution that would allow totalized power for the the captain and stoker which is possible if they elected to do it. I also think it may be possible to feed information from one Garmin to another but I have not done it.

If I were Metrigear, I would focus on Shimano and Look pedals next. I am not sure why they picked Speedplay first other than Speedplay probably made an investment in the company. I am interested in a Metrigear solution for Shimano so that I can put power on my track bike without spending 3700 Euros.

Metrigear Vector (http://www.metrigear.com/) is the most promising solution, but may end up delayed from its '00Q1 release projection, especially if mountain bike pedals are to be used (Speedplay Frogs are not part of the Q1 projection). But I don't know if it works with mountain bike shoes, or for which pedal systems it is designed.

Speedplay has displayed a new mountain pedal protoype, the SYZR (http://bikehugger.com/2009/09/speedplay-syzr-pedal-prototype.html#more). So if Metrigear was inclined to work on a Speedplay mountain pedal, it would more likely be on the upcoming SYZR rather than the Frog.

http://bikehugger.com/images/blog/SYZR%20pedal%2001.jpg

http://bikehugger.com/images/blog/SYZR%20pedal%2002.jpg

If I were Metrigear, I would focus on Shimano and Look pedals next. I am not sure why they picked Speedplay first other than Speedplay probably made an investment in the company. I am interested in a Metrigear solution for Shimano so that I can put power on my track bike without spending 3700 Euros.

I think they picked Speedplay because it was easier to work with their spindles (axles).

As far as the Vector system on a tandem, I think you could get away with one set, and two headunits (or the cool Qollector for just post ride analysis). Left pedal for stoker, and right pedal for captain. Of course if you have some significant difference in power between L&R then the reading based on one side will not be as accurate.

we have characterized the power at each position during stationary tandem cycling and we have some data on the open road as well.

briefly, we used an srm at each postion and ran a right side only setup with the inner ring serving as the timing chain. we also had a powertap on the rear wheel.

check out some video at: www.pedalingforparkinsons.org

we have did a fair amount of testing to ensure accurate and consistent readings at both positions. at some point i may write it up and submit to a journal..though not too sure if there would be interest.

jay

I think they picked Speedplay because it was easier to work with their spindles (axles).

Speedplay seems to have a whole lot longer axles than Look, Shimano...

Nothing new, just an interview with a Metrigear rep at Interbike.

MetriGear Interview (http://www.youtube.com/v/Em3vwGKlna8&color1=0xb1b1b1&color2=0xcfcfcf&feature=player_embedded&fs=1)

MTBR Interbike Interviews:
MTBR Virtual Booths (http://reviews.mtbr.com/interbike/)

RoadBikeReview at Interbike:
RoadBikeReview Youtube Channel (http://www.youtube.com/roadbikereview)

Clark Foy of Metrigear has been testing the Vector at the Low-Key Hillclimbs (http://lowkeyhillclimbs.com/2009/). He posted some of his data on their blog (http://www.metrigear.com/blog/). As you can see, it's still prototype at this stage: some algorithm tuning is still occurring.

Algorithms are non-trivial. The naive approach would be to assume power = F · v. But if I push forward on both pedals and pull back on the handlebars while the bike is coasting, F · v > 0 while the bike is not being propelled, and muscles are doing no work. It's all Newton's Third Law. So the pedal needs to isolate the rotational velocity. This is just my wild speculation, but it seems to me from the data since they showed force data and not velocity data, the velocity data is the one for which algorithms are being tuned.

The data are very cool, though.

He was back at the next week's Low-Key Hillclimb, as well, this time with two pedals working together: Clark's on the outside in this photo (http://www.mudncrud.com/gallery/main.php?g2_itemId=35460&g2_imageViewsIndex=1) going into the steep section.

It looks like the Metrigear will also record cadence as well according to the article.
http://www.bikeradar.com/news/article/interbike-new-vector-power-meter-from-metrigear-23513
I wonder how this will fit with the cadence/speed sensor that already comes with the Garmin 705. You will have two pickups for cadence displayed on the 705 unit, unless you use just the Metrigear cadence and the GarminGPS for speed

Has anyone run power measurement of both cranks and also the rear wheel to see how it all adds up. I am just wondering what the inefficiencies of a tandem are and what may be done to reduce them.
I noticed it when I did a race with a stoker of similar ability to myself. On solo bikes we can hill climb at very similar speeds to each other. When we raced on the tandem we were noticably slower climbing than when solo even though the power to weight ratio is the same. So I can only assume that power is being lost somewhere.

Dean,
I assume you and your stoker have similar climbing cadences. Did you experiment with OOP? Are your respective HR in the same zone were you to be climbing solo? It seems possible that either differences in cadence or in where in the pedal stroke power is being applied could cause some inefficiency. How big a difference in climbing speed did you experience?

It looks like the Metrigear will also record cadence as well according to the article.
http://www.bikeradar.com/news/article/interbike-new-vector-power-meter-from-metrigear-23513
I wonder how this will fit with the cadence/speed sensor that already comes with the Garmin 705. You will have two pickups for cadence displayed on the 705 unit, unless you use just the Metrigear cadence and the GarminGPS for speed

I have the Quarq and Power Tap wireless ANT+ with the Garmin 705. I have the Garmin 705 speed/cadence sensor on the bike as well. The reason for the sensor is that I had it prior to getting power. Both the Quarq and Powertap provide cadence info. The firmware in the Garmin prioritizes Quarq and PT cadence over cadence from the Garmin sensor.

Dean,
I assume you and your stoker have similar climbing cadences. Did you experiment with OOP? Are your respective HR in the same zone were you to be climbing solo? It seems possible that either differences in cadence or in where in the pedal stroke power is being applied could cause some inefficiency. How big a difference in climbing speed did you experience?

We do have similar climbing cadence, but in saying that I do tend to spin faster climbing on the tandem than solo. Haven't tryed OOP and weren't using HR moniters, all I know is that we were being dropped on the hills by guys we could keep up with normally. I have to say that I used to use HR and power meters years ago when I was racing more competitively. But now that I am riding and racing more for fitness and enjoyment I do not bother with it anymore. I like riding more without these things telling me what to do, and reminding me of how slow I am compared to 20yrs ago.

But now that I am riding and racing more for fitness and enjoyment I do not bother with it anymore. I like riding more without these things telling me what to do, and reminding me of how slow I am compared to 20yrs ago.

+100

Bill J.

Some climbing data....


Brian and Janet (http://www.illumixstudios.com/Sports/Low-Key-Hill-Climb-09/Low-Key-Hill-Climb-Mount/10322473_BWsfC#715774450_6j7Jm) on Mt Diablo in the Low-Key Hillclimbs: 110.3% (http://www.lowkeyhillclimbs.com/2009/week7/results.html) of the male single median speed.
Janet (http://www.illumixstudios.com/Sports/Low-Key-Hill-Climb-09/Low-Key-Hill-Climb-Alba-Road/10404208_SUJFt#720801696_rZdRs) on Alba in the Low-Key Hillclimbs: 81.3% (http://www.lowkeyhillclimbs.com/2009/week8/results.html) of male single median speed.
Brian (http://www.illumixstudios.com/Sports/Low-Key-Hill-Climb-09/Low-Key-Hill-Climb-2009-OLH/9950329_MEAhP#679268319_qFBuo) on Old La Honda at Low-Key Hillclimbs: 131.8% (http://www.lowkeyhillclimbs.com/2009/week2/results.html) of median single male speed.

Okay: I'll assume the ratio of masses of Brian to Janet is 4:3. Then I should weight their speeds (roughly proportional to power:mass) proportionately. Doing this, using their individual speeds normalized to the median male single speeds, I get 110.2% for the predicted tandem speed. As a tandem they were 110.3%.

Not bad, all things considered.

I was interested to see how out of phase their cranks were: 90°:

http://lh4.ggpht.com/_bkV80B63wT8/Sv8_4ElE-4I/AAAAAAAAAz0/N4qxK_PZrVI/IMG_2873.JPG (http://picasaweb.google.com/rbrunner1/LowKeyHillclimbsWeek7Diablo#5404108310402366338)

For anyone still tracking this thread, we've successfully implemented two independent power meters on our daVinci tandem. The DV drivetrain "made it easy" - no math needed, just some metalwork on behalf of our dealer to mate the Quarq units to the DV cranks. No need to flip the pedals (we ride Look, so it'd be messy to reverse them), and Quarq was able to program them to read power in the opposite direction. Unfortunately it's not a solution for standard tandem drivetrains. :(