More Power!

FarEast

Maximum Pace
May 25, 2009
5,528
538
193
Yokohama
#1
Well it looks like there are more power meters are hitting the market:

http://www.bikeradar.com/news/article/stages-cycling-stageone-power-meter-interbike-2012-35270/

For those not wanting to read the whole lot here is the complete model and pricing run-down is as follows, based on crank manufacturer:

Cannondale BB30: Price TBD
•Hollowgram SI SL (pre-2012, road/mtn power meter only)
•Hollowgram SI SL2 road
•Hollowgram SI SL2 mountain
•Hollowgram SI road
•Hollowgram SI mountain

Shimano:
•Dura-Ace 9000, $949 power meter; $1,349 complete crankset
•Dura-Ace 7900, $899 power meter; $1,299 complete crankset
•Ultegra 6700, $799 power meter; $1,099 complete crankset
•105 5700, $699 power meter
•Dura-Ace Track, $899 power meter
•XTR, $899 power meter
•XT, $799 power meter
•Saint, $899 power meter
•DXR, $899

SRAM/Truvativ:
•X9 GXP, $699 power meter; $899 complete crankset (Compatible with X7, X9, X0, XX [166mm Q model], and many other Truvativ
•X9 BB30, $699 power meter; $949 complete crankset
•Rival OCT GXP, $699 power meter; $899 complete crankset (Compatible with Apex, Rival, Force, Red, Truvativ Omnium (track), and many other Truvativ models)
 

FarEast

Maximum Pace
May 25, 2009
5,528
538
193
Yokohama
#3
The thing I love about it is that you only need to purchase the left crank arm, the prices they have on complete cranks are also very competitive as the cheapest I found a DuraAce 7900 crankset for is about 43,000 JPY so you only end up paying about 60,000 JPY for the power meter and in my eyes thats a bloody good deal.
 

jdd

Maximum Pace
Hardest Crash
Jul 26, 2008
2,497
628
133
Kanazawa
#4
Probably a dumb question, but is the meter only metering the left side? How does the left crank (sensor?) monitor both sides?
 

joewein

Maximum Pace
Oct 25, 2011
2,424
862
133
Setagaya, Tokyo
joewein.net
#6
Metering only the left side is probably a cost-cutting measure. By incorporating it into the left crank arm, that (relatively inexpensive) part is the only part to replace to install it. No changes to the right crank and the chain rings, no changes to the bottom bracket.

For people mostly interested in comparing with their own data on different training rides any left/right imbalance in power output of their legs is not really important to measure, as long as all the left leg data can be compared over time.
 

FarEast

Maximum Pace
May 25, 2009
5,528
538
193
Yokohama
#7
Probably a dumb question, but is the meter only metering the left side? How does the left crank (sensor?) monitor both sides?
Probably in exactly the same way all the others do - right now only the, Polar, Gar-Vapourware-min and Pana-ziptie-sonic has left and right strain gauges.

It will be a complex peice of voodoo buit in to the software.
 

GSAstuto

Maximum Pace
Oct 11, 2009
945
242
103
tokyo
www.roadfixie.com
#8
The Polar Rube Goldberg Arrangement is insane. Part acoustics and part who-knows-what. Plus it's not ANT. This strain-gauge only version makes perfect engineering sense. As long as you have a cadence (TDC) input and relevant strain differential, you can calculate the force vs time and with a couple other parameters you'll have reasonably accurate power readings. Would be interested to see how accurate this is compared to a torque shell gauge system like the PT which is measuring power delivered right to the wheel. Meaning - I wonder about the compensation for everything up to the wheel? Are all bikes the same? I have no clue, actually, haven't looked into this - but for example - losses in frame flex - you could be putting out 300w at the pedal but only 270 at the wheel (per rotation). And this value would be non-linear based on riding position (in saddle, out, sprinting, etc). Whereas the PT will give you accurate reading at the wheel with only the losses in the wheel itself not being fully accounted for.
 

Yamabushi

Maximum Pace
Jun 1, 2010
2,335
188
1,083
Tokyo (Nezu)
fudoushin.com
#9
The Polar Rube Goldberg Arrangement is insane. Part acoustics and part who-knows-what. Plus it's not ANT. This strain-gauge only version makes perfect engineering sense. As long as you have a cadence (TDC) input and relevant strain differential, you can calculate the force vs time and with a couple other parameters you'll have reasonably accurate power readings. Would be interested to see how accurate this is compared to a torque shell gauge system like the PT which is measuring power delivered right to the wheel. Meaning - I wonder about the compensation for everything up to the wheel? Are all bikes the same? I have no clue, actually, haven't looked into this - but for example - losses in frame flex - you could be putting out 300w at the pedal but only 270 at the wheel (per rotation). And this value would be non-linear based on riding position (in saddle, out, sprinting, etc). Whereas the PT will give you accurate reading at the wheel with only the losses in the wheel itself not being fully accounted for.
Well do you want to measure what the cyclist is outputting or do you want to measure what is reaching the rear hub? If you are wanting to measure the cyclist's output, which would definitely be my preference, then you want the sensors as directly connected to the cyclist as possible. Pedal > Crank > Rear Hub
 

GSAstuto

Maximum Pace
Oct 11, 2009
945
242
103
tokyo
www.roadfixie.com
#10
Exactly - actually - <what> you are measuring doesn't really matter as long as you can compare it to previous and expected results consistently. So - measuring at the crank makes good sense as it does take most of the machine itself out of the equation. However - if you are interested in bringing the machine into the loop - then you need to have measurement at the road - and closest you can get right now is the hub itself. Or - put the bike on a dyno and calibrate the power meter according to a variety of conditions. Then just add a saddle sensor, chainstay straingauge and perhaps bar straingauge. Maybe even a differential straingauge at the tire sidewall, too.
 

Yamabushi

Maximum Pace
Jun 1, 2010
2,335
188
1,083
Tokyo (Nezu)
fudoushin.com
#11
Basically, I agree, Tim. The location isn't that critical, consistency is the key. The actual mechanical loss even at the rear hub is very small. Last weekend I was telling Tim about a John Hopkins study regarding the mechanical efficiency of modern bicycles. They found that with un-lubed chains in a clean environment modern bikes were about 98.6% efficient. I have to say I was surprised how efficient our machines have become.

All that being said, given equal reliability, which isn't currently the case, I'd most prefer to have a pedal based system. In the world as it exists today, given what's available right now, and money not being a big consideration, I'd choose the crank based SRM. As it stands however, I unfortunately, currently own none of the above. :)
 

GSAstuto

Maximum Pace
Oct 11, 2009
945
242
103
tokyo
www.roadfixie.com
#12
The chaindrive, itself, is quite efficient. However the frame is not. Everytime you apply force, the frame flexes, the material will absorb that energy and return only a fraction. So - you need to consider how much of your work effort is going into flexing the frame (and other bits) as well as through the actual chainsystem itself. Including the wheels, which must 'wind up' on every stroke, then compress and decompress the rubber layers and rim itself deforms slightly, then reforms on a cyclical basis. A really great Power Meter would let you calibrate against a dynometer or dynometer-like device - say, something you put on a set of rollers , and then you can get all sorts of input data from which to optimize your power through selection of frame, wheels, etc as well as best riding position under any circumstance. And of course from there you need to optimize according to wind resistance - so you should definitely get yourself tested in a low speed wind tunnel. And while you're at it - how about a realtime bio-monitor? Simple heart rate is so arcane. Better is VO, Bood Glucose and ATP levels, sterol levels, core temp, etc etc .