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My current crank arm is 175 cm. I have a Giant Contend 3 with the following parts:

  • Rear Derailleur- Shimano Claris
  • Front Derailleur - Shimano Claris
  • Crank - FSA Tempo, 34/50
  • Bottom Bracket - cartridge

What characteristics or model should I buy for a stages left arm power meter?

Does the material have to match what material I have on the bike currently? Must my current crankset brand and model match the stages advertised one? I do not mind about the matching - I only care that it works correctly and wont cause imbalance when pedaling.

The available models for GEN 3 STAGES POWER L:

  • Shimano ULTEGRA R8000 POWER METER
  • XT M8100 / M8120 POWER METER
  • GRX RX810 POWER METER
  • Shimano DURA-ACE R9200 POWER METER
  • Shimano DURA-ACE 7710 TRACK POWER METER
  • Shimano SAINT M820 POWER METER
  • Shimano DXR MX71 POWER METER
  • Shimano XT M8000 POWER METER
  • FSA SL-K BB30 POWER METER
  • CAMPAGNOLO RECORD 11s POWER METER
  • CAMPAGNOLO SUPER RECORD 11s POWER METER
  • CAMPAGNOLO H11 POWER METER
  • CAMPAGNOLO SUPER RECORD 12s POWER METER
  • SHIMANO XTR M9100 / M9120 POWER METER
  • CANNONDALE SI POWER METER
  • STAGES CARBON POWER METER FOR 30MM - SRAM, RACE FACE NEXT SL, & FSA 386EVO
  • STAGES CARBON SRAM MTB GXP POWER METER
  • Shimano 105 R7000 POWER METER
  • Shimano XTR M9000 OR M9020 POWER METER
  • 105 5800 Power Meter
  • Shimano ULTEGRA 6800 POWER METER
  • Shimano DURA-ACE R9000 POWER METER
  • Shimano ULTEGRA R8100 POWER METER
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  • 1
    Some background - CLARIS is a shimano groupset "level" - several positions "down the tree" from 105 which is the lowest listed groupset with a power meter. A pro would ride Dura Ace, or perhaps train on Ultegra but not Claris (8 speed) Perhaps you might consider a bike upgrade before a PM, or perhaps a new bike with a PM. I'm not trying to pick holes in your bike, but realistically it would be termed "entry level" That said, I still ride one seven-speed road bike and do quite well on it, but my performance measure is strava segment times not power.
    – Criggie ♦
    Dec 31, 2021 at 2:07
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    Putting a $300 power meter on an $860 bike seems a little questionable.
    – whatsisname
    Dec 31, 2021 at 2:41
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    @whatsisname: Having a power meter is always good. The improvements in your training quality can result in much better gains than investing the same money in a more expensive bike.
    – Michael
    Dec 31, 2021 at 14:39

4 Answers 4

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I hate to say it, but none of these will work with what you've got

The first thing you need to take into account is the crankarm's interface with the bottom-bracket spindle. Your FSA Tempo crank uses a "square taper" interface, which is extremely common, but has fallen out of favor in higher-end components; instead, they typically have the spindle permanently connected to one crankarm, and a bigger, more convoluted interface with the other crankarm--see, for example, the opening on the one FSA crankarm Stages does offer.

Power meters are fairly high-end items, so it's no surprise power-meter makers are going after the high end of the market. As far as I know, there are no PM cranks that fit square-taper spindles.

Another thing to consider is Q-factor: how wide-set your feet are. Cranks will be designed so that each foot should be equidistant from the bike's centerline, but I can easily imagine that if you were mixing-and-matching, you would wind up one crankarm putting that foot closer to the centerline than the other, which could cause biomechanical problems.

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4

As Adam pointed out, none of those options are compatible with your setup.

To get something workable you would have to change your crankset. The cheapest option is the main line Claris FC-R2000 with the appropriate bottom bracket like BB-RS500 (BSA). Then the 105 left crankarm with a powermeter would be compatible. Or the Ultegra one, but it is just more expensive without any real benefit (in this combination). A Sora (FC-R3000) crankset would also work in practice, but introduces some small incompatibility for no reason. The higher speeds (10+) cranksets are not compatible at all, even if they might work in some way for some people.

For the left crankarm it does not really matter too much if it is Claris or Ultegra, as long it is road, Hollowtech II and the right length. Of course, the stiffness differs, but it probably won't matter at all.

Make sure to maintain the same effort with both legs when using on-sided powermeters.

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None of the Stages power meters will work with your current crankset. Further, you might upgrade your bike later and you might or might not be able to take whatever power meter crank you get with you. It might be worth considering an alternative: left-only pedals. The most cost-effective one would be the Favero Assioma Uno, which uses the Exustar version of Look Keo cleats (and can be upgraded to dual sided later on). Favero is a well-regarded manufacturer. All the alternative pedals I’m aware of are more expensive. Pedals can be easily transferred from bike to bike.

The downside is that if you aren’t on Look pedals, you would have to change to them. Most of the road pedals are based on the Look Keo cleat system. Favero sell the Assioma Duo Shi, which is designed to retrofit to Spd-SL pedals, but it adds a lot of stance width, and it is dual sided only. Garmin’s Rally pedals have SPD and SPD-SL versions and are available single-sided, but they are pricier than Faveros.

An admittedly less satisfactory alternative would be to pace your intervals with heart rate. Even without heart rate, you can do hill repeats for intervals; a GPS computer will enable you to monitor your lap times nicely.

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  • OP might go for a pair of pedals, for a two-sided solution and not having to deal with subtly different pedal feel from different models/brands.
    – Criggie ♦
    Dec 31, 2021 at 1:59
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    @Criggie to clarify, a single sided power meter pedal is actually a pair of pedals. The PM circuits are in the spindle. With this arrangement, the PM manufacturer will just sell a dummy right pedal. If you upgrade, they sell you a right spindle, and you transfer the pedal body over (Favero’s bodies are probably made by Xpedo)
    – Weiwen Ng
    Dec 31, 2021 at 2:14
  • Nowadays you may even get pedal-based powermeters, single or double sided where you may switch the pedal body, just keep the axle(s), the active part, to switch beween two roadbike (Look or Shimano) cleat systems and one MTB (Shimano) system. If you start with the single-sided device you may upgrade to double by buying a right active axle.
    – Carel
    Jan 3, 2022 at 18:52
  • @Carel that discussion mainly applies to Garmin's Rally pedals right now, although you can informally do the same thing to Favero's Assiomas.
    – Weiwen Ng
    Jan 3, 2022 at 19:09
  • @WeiwenNg: You're right, but I didn't mention the brand because I think that this may as well be available from other companies in future times.
    – Carel
    Jan 4, 2022 at 14:13
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If you do not want change the drivetrain of your bike and you have an Android smartphone, you may wish to consider my app which estimates power. https://www.cykelstrom.com It does not depend on the crank type and adding a cadence sensor gives good results and is a lot cheaper.

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  • I'm assuming this works off of calculated speed and change in altitude? But it wouldn't know about weather, riding in pack, aerodynamics, etc.? If you're going to suggest an alternative approach you should be clear about the drawbacks. Also, why this particular app?
    – DavidW
    May 7, 2022 at 20:20
  • Speed is measured using GPS or external speed sensor. The app knows the weather through a free data service at the coordinates throughout the ride. The app uses a tuned algorithm using the inertial measurement unit in the smartphone. I suggest visiting cykelstrom.com for detailed information including accuracy and correlation metrics. I suggest my app as a solution as it appears the original poster may find it difficult to outfit their current square drive bottom bracket with a crank type power meter. I am happy to answer any other questions.
    – OshkoshBiker
    May 8, 2022 at 2:25

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