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I am a junior amateur cyclist and I have a road bike with a Shimano Sora groupset (shifters, crank, front and rear derailleur, cassette).

I am looking to step up my cycling to the next level and have since bought the Wahoo Bolt v2 including the speed and cadence sensors, but I could not find a decent budget power meter.

I have found a reasonable one from 4iiii that is crank based and just above my budget but it targets the Shimano 105 R7000 and the Shimano Ultegra R8000.

Is it possible to replace my crank with one these? If not, are there some that are compatible with the Bolt v2 and available in Canada?

I know there are some power meters that come with SPD pedals, but they are prone to break in case of an accident (which I got into not that long ago) and more expensive in my country (Canada).

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  • Do you intend on staying with this bike long term? (ie several more years)
    – Criggie ♦
    Commented Sep 20, 2022 at 23:46
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    Absolutely. I actually was planning to upgrade it piece by piece but I have had it for 6 months now and an upgrade this soon is beyond my budget right now.
    – Codingwiz
    Commented Sep 21, 2022 at 0:01
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    There are some "related" posts on the left which directly help. bicycles.stackexchange.com/questions/60248/… for example.
    – Criggie ♦
    Commented Sep 21, 2022 at 0:15
  • Pedal-based power meters are much tougher than you might expect. You can get some very high-quality pedal-based power meters these days for not too much money. The Assioma Favero comes to mind as a rock-solid, highly regarded power meter. And as Renaud mentions, you don't risk locking yourself into a particular set of components.
    – Will Vousden
    Commented Sep 21, 2022 at 8:53

3 Answers 3

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With the left (non-drive side) powermeters you do not have to have the left crank arm from the same groupset. It just needs to use a compatible interface and have the same length as the arm. For Hollowtech II cranks all the way from Claris and Sora through 105 to Dure Ace, you can attach and use any Hollowtech II left crank arm with a powermeter.

Do check the type of crank you have, though. Sora cranks are also being sold and mounted on new bikes in the Octalink R350 variant. The left crank arm would not be compatible.

Be aware that single sided powermeters have drawbacks in possible bias and even possibility of the rider beginning to push harder with one leg - that is bad for the riding and the muscle balances and everything related.

Pedal based powermeters are generally two-sided and better, but generally also much more expensive. I would not worry about them being fragile in a crash, there are other parts of the bike that might break earlier (frame, rims). They however may require occasional service and new bearings as any other pedals.

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  • Note that the Hollowtech II interface is also present on gravel (GRX) and some MTB groups (XT, etc.) in the Shimano offerings, and they can be fitted to a road group - HOWEVER - the GRX and the MTB groups have wider Q-factors than the road group, so there would be a potential issue with that for most people. A fellow rider actually had an XT left crank on their road group - so I have seen this happen. You might want to clarify your answer regarding this.
    – Ted Hohl
    Commented Sep 21, 2022 at 16:54
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    @TedHohl OK, thanks for the remark. I really only considered road cranksets (Claris to Dura-Ace). I own an old Hollowtech II Deorep-equipped MTB bike myself, but I really disregarded these as something else.
    – Vladimir F Героям слава
    Commented Sep 21, 2022 at 18:11
  • @TedHohl Most MTB cranks have a different sized HT2 interface than road cranks. They're generally not cross-compatible. The road cranks are usually a couple mm thinner (in the axis of the BB spindle) than their MTB counterparts.
    – MaplePanda
    Commented Sep 21, 2022 at 18:32
  • @MaplePanda I think you are correct that they are different. Now the fact that my riding buddy had an XT PM left crankarm on his 105 road crankset was still done. It is likely the retaining clip did not align among other things. Once I told him about the difference, he pulled it off.
    – Ted Hohl
    Commented Sep 21, 2022 at 23:57
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The pedals seems to be the best option to me (Wahoo makes some, they also sell a pair of pedals with the sensor fitted only on one pedal, which is less expensive), even if I understand your concern when crashing, although I doubt that quality pedals will the first destroyed component in a crash.

Pedals are one of the few components that are universal. With a budget is limited, there's another way to consider this question: if you upgrade/replace your bike, the pedals will be very easily transferred to a new bike, while another solution might be "lost" (whether it's a sensor mounted on a crank or a crank with a built-in sensor). I also have no doubt that pedals will be easier to sell than a crank with a power meter.

Power metering is considered an advanced feature, and if you want an crank with power meter, they will probably be for 11- or 12-speed groupsets. Changing such crank will require to upgrade the whole groupset. There are many questions about upgrades, it's not easy at is seems, especially on road bikes. You can't use a 11-speed/12-speed crank with a 9-speed system. Short version: you can basically easily upgrade pedals, saddle, seatpost and the wheels. The rest is not obvious, and it's very likely that you'll need to upgrade the whole groupset (transmission and brake system) in one operation if you want a significant upgrade.

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    I see no reason for a beginner on a cheap bike not to buy a power meter. Lots of useful information that will help there progress far more than other expenditure that is too often encouraged. Smart Trainers on work for people with space and desire to use them.
    – mattnz
    Commented Sep 21, 2022 at 8:09
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    @mattnz thx for the feedback, opinion removed.
    – Rеnаud
    Commented Sep 21, 2022 at 11:58
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    Stages left crank arm powermeters work with 9-speed without any issue. But it is on-sided and hence can be biased. Also, it is nicely upgradeable.
    – Vladimir F Героям слава
    Commented Sep 21, 2022 at 12:52
  • I use a Stages/Ultegra 11-speed power meter with a 10-speed shimano setup. Works well. Front derailleur is 105 10-speed, rear derailleur is Dura Ace 10-speed.
    – Christine
    Commented Sep 22, 2022 at 8:42
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Wiggle lists the 4iii cranks as being Hollowtech II compatible, which fits with everything else I have read on these. If your bike has Hollowtech II BB, then they will likely fit (I won't say certainly due potential frame clearance which I am uncertain what the risk is with road bikes and Hollowtech II, others can clarify if there is a chance of a problem). Your don't say how old you bike is, Hollowtech II was released 2 decades ago, so I expect it will use Hollowtech II BB if its less than about 15 years old.

If the bike does not have Hollowtech II, and you are buying both the cranks (not just the non-drive crank), the cost of a compatible BB to suit them will be small compared to the total cost, and well worth it. If you only want to install the left side crank, and you do not have Hollowtech II, it can still be done but you would have to source a Hollowtech right side crank and maybe new chainrings.

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  • It will fit, but will the shifting be compatible? Number of speeds does matter. A Sora bike might also use Octalink Sora FC-R350 even if the main line is Hollowtech II FC-R3000.
    – Vladimir F Героям слава
    Commented Sep 21, 2022 at 12:53
  • Ok, I now see it is a left arm the same way as Stages powermeters are. In that case my other comment about on-sided powermeters applies and the number of speed is not an issue. Only the Hollotech II vs. Octalink is.
    – Vladimir F Героям слава
    Commented Sep 21, 2022 at 12:57

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