Power Meters for Sub-compact Cranks

20 replies · 2,903 views

bobknh
794 posts
#1Oct 12, 2018, 12:30 PM
I've been riding with Stages power meters for many years. Why I use and recommend direct read power meters, is a topic I could write a book on; but other cycling coaches and experts have already done that! My Stages units are Shimano Ultegra left side crank arms compatible with any Shimano 24mm Hollow-tech crank set and bottom bracket. I'm currently running 2 sets -- a 6800 46/36 on my road bike, and a 46/34 (a mashup of a 46/36 with an after market 34). Unfortunately, while these gear sets work well enough with 11-36 11 speed cassettes, I would much prefer to run something like a 42/30 with a 12-32 cassette. There are some crank sets like the White Industries VBC, or Compass Cycles that offer these sub-compact cranksets. The problem is that Stages and other popular power meter manufactures don't make a compatible crank arm power meters for these crank sets. Here is a DIY power meter that you can install on any metal crank arm: https://watteam.com .
While you do have to spend an hour or so to install these, it appears that you can install them on almost any alloy crank arm, and save a bundle of money over the cost of more popular units like Stages. Does anyone have any experience with these?
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barturtle
49 posts
#2Oct 12, 2018, 1:29 PM
Those are only for hollow aluminum cranksets: Shimano, Campy, Cannondale are the ones they list as compatible.
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drwelby
531 posts
#3Oct 12, 2018, 1:48 PMedited
You could run one of the Stages SRAM mountain cranks with the NSB 104 bcd spider, assuming the wider Q-factor is OK. That would get you to a 32-42.
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clarksonxc
358 posts
#4Oct 12, 2018, 3:11 PM
Another option would be to get a Stages XTR or XT crank arm and use a mountain crankset. I think the XTR ones go up to a 44 or 42T big ring with a 2x setup. This will result in a wider Q-factor but it will fit in a road BB with spacers.
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bobknh
794 posts
#5Oct 12, 2018, 7:08 PMedited
barturtle wrote:Those are only for hollow aluminum cranksets: Shimano, Campy, Cannondale are the ones they list as compatible.

Thanks for the info. Another burst bubble.
Some of the suggestions for Shimano XT or XTR crank sets also wont work well for me. Even if Q-factor wasn't an issue, I'm not even sure if they will fit with my road width BSA BB shell designed for narrower road crank axles.
The ideal solution would be a pedal based system. Unfortunately, all the pedal based systems available require 3 hole road cleats and shoes. I much prefer my 2 hole mountain bike shoes for gravel and even road riding these days.
One promising crankset was the Praxis Zayante M30 which allows the use of a 32T inner chainring. The Zayante even has an attractively priced power meter option using 4iiii crank arm system. Unfortunately, the only sub-compact chainring combination they offer is a 48/32. If you want anything else like a 46/32, or a 42/30 you are SOL. Very frustrating.
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Volsung
878 posts
#6Oct 13, 2018, 3:45 AM
Easton has one but your lower limit is 46/30.
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bobknh
794 posts
#7Oct 13, 2018, 9:13 AM
Volsung wrote:Easton has one but your lower limit is 46/30.

Looks interesting. Not cheap though. About $900+ for the power meter/ crankset, plus $$$$ for the direct mount chainring pair. And as you point out, 46/30 is the only sub compact option. Considering that there are pedal based, and crank arm based power meters that cost under $300, which are easy to move from bike to bike. These are one sided systems, like the Stages meters I'm using; but for most of us, I'd argue that these systems are good enough.
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drwelby
531 posts
#8Oct 13, 2018, 10:22 AM
bobknh wrote:
Some of the suggestions for Shimano XT or XTR crank sets also wont work well for me. Even if Q-factor wasn't an issue, I'm not even sure if they will fit with my road width BSA BB shell designed for narrower road crank axles.

They work fine with a 68mm BSA shell, the bottom bracket includes spacers. You could possibly run the XTR triple and toss the small ring to get a 30/40. I don't think there any larger aftermarket chainrings that aren't narrow-wide. But the Shimano Metrea crank is sold as a 32/46 and 42 single and also uses the assymetrical 96mm BCD so you might be able to use one of those, assuming no weird cross-compatibility BS. So you might be able to rig up an XTR crank in 30/42 or 30/46.

Someone in the Gravel Gearing thread posted a Stages-equipped FSA Energy 386 Adventure 46/30 setup, so that's another close-but-not-quite option.

Another option is to stick to 34/46 and run a 11-40 cassette, throwing out the 11 tooth cog and adding in a 14 to the second position. A 30/42 12-36 is about the same as a 34/46 13-40. You then shift the problem to how to shift to the 40, but that's better understood than mixing and matching Shimano commuter group chainrings with XTR.
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bobknh
794 posts
#9Oct 14, 2018, 11:45 AM
drwelby wrote:

They work fine with a 68mm BSA shell, the bottom bracket includes spacers. You could possibly run the XTR triple and toss the small ring to get a 30/40. I don't think there any larger aftermarket chainrings that aren't narrow-wide. But the Shimano Metrea crank is sold as a 32/46 and 42 single and also uses the assymetrical 96mm BCD so you might be able to use one of those, assuming no weird cross-compatibility BS. So you might be able to rig up an XTR crank in 30/42 or 30/46.

Someone in the Gravel Gearing thread posted a Stages-equipped FSA Energy 386 Adventure 46/30 setup, so that's another close-but-not-quite option.

Another option is to stick to 34/46 and run a 11-40 cassette, throwing out the 11 tooth cog and adding in a 14 to the second position. A 30/42 12-36 is about the same as a 34/46 13-40. You then shift the problem to how to shift to the 40, but that's better understood than mixing and matching Shimano commuter group chainrings with XTR.

FSA makes a gravel oriented SLK carbon crankset that is competitively priced. Here is a review from JOM at Gravel Cyclist: http://www.gravelcyclist.com/?s=FSA. I believe 4iiii power meters will factory retro fit their crank based power meter on the left SLK crank arm for about $400. The only chain ring choices are 46/30 or 48/32. These use proprietary FSA direct mount rings. You are dependent on FSA for replacements. Although I prefer a smaller chain ring tooth gap eg. 42/30, I can live with the 46/30 and a standard 11-32 cog set. The 16 tooth chainring gap and the 21 tooth cassette gap, will put me at the upper limit of my SRAM eTap wifli rear derailleur capacity. Since I can continue using my Stages power meter with the XT or XTR cranks, this is probably a better solution. The XTR system will also give a wider choice of chainrings. When all is said and done, I don't think the Q-factor is that big a deal for me.

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simplemind
71 posts
#10Oct 15, 2018, 8:00 AM
bobknh, you do seem to have a high level of power knowledge, so I'd like to segway to "why not use a pedal power meter" such as a Garmin Vector 3? Sure eliminates the issue you're having with compatibility, but I'm sure it might introduce other issues, I just don't have that knowledge.

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brando
47 posts
#11Oct 15, 2018, 8:42 AM
drwelby wrote:

Someone in the Gravel Gearing thread posted a Stages-equipped FSA Energy 386 Adventure 46/30 setup, so that's another close-but-not-quite option.

Hey, that's me! I am really liking this setup. I have a Stages 6800 on my road bike so having the same left-crank power has been good going from one to the other. I also happened to get this at a time when the Gen2 Stages were still available at really good closeout, which helped. Now the only 386 I see is the Gen3 Carbon crank, which would be fine, but I'd pair with the SL-K which is more money too.

I also suspect that within the next few years there will be additional options available in sub-compact. With Shimano's new Ultegra RX rear derailleur, I am hoping they come out with this.

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bobknh
794 posts
#12Oct 15, 2018, 10:02 AMedited
simplemind wrote:bobknh, you do seem to have a high level of power knowledge, so I'd like to segway to "why not use a pedal power meter" such as a Garmin Vector 3? Sure eliminates the issue you're having with compatibility, but I'm sure it might introduce other issues, I just don't have that knowledge.

Not so sure about my "power" expertise - I would suggest folks like Andrew Coggin as the real experts - but my main objection to pedal based power meters is the fact that all of the current models are designed to use road shoes with 3 hole Look style plastic cleats. After I quit racing about 10 years ago I've switched over to 2 hole SPD style mountain bike shoes and pedals. I'm currently running Crankbrother eggbeaters on all of my bikes. While I still have a pair ultralight custom Rocket7 road shoes, which I could use with Look style pedals, I much prefer my very comfortable Shimano mountain bike shoes for the occasional hike-a-bike on my gravel routes, as well as regular visits to the local cafe's and coffee shops.
While the current generation of pedal based power measurement are getting good marks from experts like DCRAINMAKER, they are still relatively expensive. And, in my case, I already own 2 Stages Ultegra left cranks. Of all the solutions suggested, the most economical and best fit to my needs would be an XT, or XTR 2x crankset paired with my Ultegra Stages left side crank arm.
OTOH -- If you haven't already invested in a direct power measurement system, and prefer 3 hole road style shoes and pedals, then a pedal based system would be a great choice for use with any crankset and gear set you may want to use.
BTW, there are some rumors about the development of pedal based systems that can be used with any pedal --- but don't hold your breath for anything soon.
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bobknh
794 posts
#13Oct 15, 2018, 10:19 AM
brando wrote:

Hey, that's me! I am really liking this setup. I have a Stages 6800 on my road bike so having the same left-crank power has been good going from one to the other. I also happened to get this at a time when the Gen2 Stages were still available at really good closeout, which helped. Now the only 386 I see is the Gen3 Carbon crank, which would be fine, but I'd pair with the SL-K which is more money too.

I also suspect that within the next few years there will be additional options available in sub-compact. With Shimano's new Ultegra RX rear derailleur, I am hoping they come out with this.

Yup - if I hadn't already invested in my 2 Stages Shimano Ultegra meters , this or the the FSA SLK gravel would be a good choice.
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drwelby
531 posts
#14Oct 15, 2018, 10:57 AM
Another crazy option would be to find an older Ultegra 6700 right crankarm in 130mm BCD and then run a TA Alize 42t tripleizer on the inside position with whichever sized granny ring. The main concern would be frame clearance with this setup. It would also look a little weird without an outside chainring. It's also technically a 10 speed chainring so I don't know how well it would shift with an 11sp chain.
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brando
47 posts
#15Oct 15, 2018, 11:11 AMedited
Another option (a little out there) would be the Absolute Black ovalized 46/30 chainrings for Shimano 110 BCD 4 bolt:

https://absoluteblack.cc/oval-road-chainrings-30-46-and-32-48-for-110-4bcd/

I don't know if Stages works with ovalized chainrings, though Froome has ridden oval Stages the past few years I think?

ETA: looks like Stages says "yes, but will read 4-5% higher": https://support.stagescycling.com/en/support/solutions/articles/1000158537-can-i-use-the-stages-power-meter-with-oval-or-osymetric-chain-rings-

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clarksonxc
358 posts
#16Oct 15, 2018, 1:46 PM
bobknh wrote:
Not so sure about my "power" expertise - I would suggest folks like Andrew Coggin as the real experts - but my main objection to pedal based power meters is the fact that all of the current models are designed to use road shoes with 3 hole Look style plastic cleats. After I quit racing about 10 years ago I've switched over to 2 hole SPD style mountain bike shoes and pedals. I'm currently running Crankbrother eggbeaters on all of my bikes. While I still have a pair ultralight custom Rocket7 road shoes, which I could use with Look style pedals, I much prefer my very comfortable Shimano mountain bike shoes for the occasional hike-a-bike on my gravel routes, as well as regular visits to the local cafe's and coffee shops.
While the current generation of pedal based power measurement are getting good marks from experts like DCRAINMAKER, they are still relatively expensive. And, in my case, I already own 2 Stages Ultegra left cranks. Of all the solutions suggested, the most economical and best fit to my needs would be an XT, or XTR 2x crankset paired with my Ultegra Stages left side crank arm.
OTOH -- If you haven't already invested in a direct power measurement system, and prefer 3 hole road style shoes and pedals, then a pedal based system would be a great choice for use with any crankset and gear set you may want to use.
BTW, there are some rumors about the development of pedal based systems that can be used with any pedal --- but don't hold your breath for anything soon.

Be careful mixing the Shimano road/mountain cranskets and crank arms. The Q factor would be different between your left and right leg! The XTR/XT Stages meters can be found relatively cheap if you hit the sale at the right time.
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bobknh
794 posts
#17Oct 15, 2018, 3:13 PM
clarksonxc wrote:

Be careful mixing the Shimano road/mountain cranskets and crank arms. The Q factor would be different between your left and right leg! The XTR/XT Stages meters can be found relatively cheap if you hit the sale at the right time.

Thanks for the heads up. I'm not at all familiar with mountain bike components- specifically XT/XTR cranks. I assume your comment means that the XT/XTR crank arms have a different geometry than straight Ultegra arms. Seems like every direction we discuss has unpleasant complications. Hopefully, one day Shimano will wake up and realize that there is a demand for 2x sub-compact Ultegra grade cranksets for gravel bikes.
1
bobknh
794 posts
#18Oct 25, 2018, 3:18 PMedited
The new Powertap G3 disc hub, may a good solution to power measurement with sub compact gearing as it will allow you to use any crankset or gear set you fancy: https://www.velonews.com/2018/06/bikes-and-tech/first-look-powertap-g3-disc-hub-power-meter_467768
O f course, you do have to build up a wheel to go with the hub. But then you get to chose 24 or 28 spoke count, and any rim, spokes, nipples and build you like. I've built several wheels myself, and prefer to use an experienced wheel builder like Dustin Gaddis at Southern Wheel Works. If you DIY, you can probably build a damn good wheel for a total cost of under $800. If you use a custom builder, depending on your choice of rim, spokes and nip's, I would expect the total cost, including hub, to be a few hunded more.
As far as the PT wireless hub is concerned, this tech. has been around for a long time. The folks at PT have had many years to perfect and improve it.
One possible hiccup with this hub however, is that due to the electronics in the hub, it uses a proprietary 160 mm rotor. You can't use a direct mount or standard 6 bolt rotor. While PT supplies the rotor and includes it in the cost of the hub, personally, I'm uncomfortable with notion of having to source a part like a rotor which wears, or can be easily damaged, from only one manufacturer. I just checked -- the PT rotor is only available from PT and costs $99.99 plus shipping!
Bike John
34 posts
#19Nov 15, 2018, 3:51 AMedited
bobknh wrote:One possible hiccup with this hub however, is that due to the electronics in the hub, it uses a proprietary 160 mm rotor. You can't use a direct mount or standard 6 bolt rotor. While PT supplies the rotor and includes it in the cost of the hub, personally, I'm uncomfortable with notion of having to source a like a rotor which wears, or can be easily damaged, from only one manufacturer. I just checked -- the PT rotor is only available from PT and costs $99.99 plus shipping!

At this year’s (2018) Eurobike, PowerTap showed off a demo wheel with their new *G4* disc-based rear hub that will use standard Centerlock rotors and have compatibility with “142 thru, 148 Boost thru and QR axles to work with any type of disc brake bike – road, mountain, cyclocross or gravel.” Instead of coin cell batteries this will have some sort of sealed magnetic charging port and support for normal Shimano freehubs, XD-R drivers, and (future) Shimano MicroSpline. Availability is “early 2019”, whatever that actually means.

https://bikerumor.com/2018/07/10/eb18-cycleops-floating-trainer-platform-plus-new-trainers-powertap-g4-disc-hub/
(scroll halfway down)

TBH, I’m potentially more interested in Quarq’s (unannounced) new power meter with one-piece direct mount chain rings, provided they have some sort of ~ 46/30T option.

Assuming they continue to support GXP and BB90 bottom brackets.

https://cyclingtips.com/2018/11/2019-sram-red-etap-goes-12-speed/
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bobknh
794 posts
#20Nov 15, 2018, 6:54 AM
Bike John wrote:
At this year’s (2018) Eurobike, PowerTap showed off a demo wheel with their new *G4* disc-based rear hub that will use standard Centerlock rotors and have compatibility with “142 thru, 148 Boost thru and QR axles to work with any type of disc brake bike – road, mountain, cyclocross or gravel.” Instead of coin cell batteries this will have some sort of sealed magnetic charging port and support for normal Shimano freehubs, XD-R drivers, and (future) Shimano MicroSpline. Availability is “early 2019”, whatever that actually means.

https://bikerumor.com/2018/07/10/eb18-cycleops-floating-trainer-platform-plus-new-trainers-powertap-g4-disc-hub/
(scroll halfway down)

TBH, I’m potentially more interested in Quarq’s (unannounced) new power meter with one-piece direct mount chain rings, provided they have some sort of ~ 46/30T option.

Assuming they continue to support GXP and BB90 bottom brackets.

https://cyclingtips.com/2018/11/2019-sram-red-etap-goes-12-speed/

Thanks for the post. Looks like PT has addressed all of my issues. Very interesting. Let's see how long it takes them to go into production.
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