Battle of the cheap/inexpensive power meters: Sigeyi, Magene, Xcadey

Equipment
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-Left/right balance (kinda, see below)
-Many Shimano road cranks can’t read power from the (edit: drive side) crank accurately
-Some frames and cranks don’t have enough clearance
-Many SRAM MTB cranks can’t use a crank PM due to no flat surface for mounting
-Not buying another crank arm (or altering an existing one)
-Generally longer battery life and rechargeable (see many issues have with coin cells)
-Probably More aero

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Thanks for the answers. I guess I figured the spider would be more accurate. If you’re doubling a left power, any error is then doubled. Is that correct?

The 4iiii actually does look nice and I have an iPhone so Find My would be cool. I vaguely remember GP Lama showing the new PMs to be a little off though. Did they fix that?

Edit: Looks like Xcadey has a crankset/PM combo that’s designed to be a straight swap with Shimano. Looks nice but around $100 more expensive.

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  • AFAIK, all these spider-based meters offer is an estimate of L/R power. It is not as good as a proper dual power meter like dual PM pedals or double crank arm options. Noting that difference, it’s possible that an estimate may be better than none at all (left-side crank), but it’s not the same level as a proper dual-sided PM.
  • That is true when looking at the drive-side arms in particular. AFAIK, all the left-side power meters (4iiii & Stages specifically) are solid for their reporting (with the clear caveat that it’s one power value doubled).
  • Totally legit and the case with several of my bikes. MTB in particular may have wide chainstays for tire clearance that kill the L-S crank options.
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You’re right. It only affects the drive side. Edited

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From what I recall, it’s not a true left/right. But due to an accelerometer (to know the position of the crank arms), the PM can tell when the power is coming from the drive side vs non-drive. Does that sound right? Either way, it should be a truer reading of power throughout the full revolution of a pedal stroke vs reading and doubling one side.

Edit: Are the 4iiii dual sided PM on Shimano cranks accurate? Is it just the Shimano brand ones that are bad or all dual-sided on Shimano cranks?

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Huh. TIL. I just tested my Sigeyi by pedaling one legged and it was showing power from both sides just varying the split based on how much I pulled vs pushed. DC rainmaker says P2Max NGeco does the same.

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  • Yup, that is my understanding.
  • Yes, that is correct as well. These spider PM’s are what I call ‘Total Power’ as opposed to Single-Sided or Dual-Sided. The Total power is a true representation of power that does include any L/R delta, even it the data reported about L/R balance is not as accurate as a true Dual-Sided.
  • There may be an exception hiding here, but most of the ones that use the modern 4-arm asymmetric Shimano arms give flawed data. It has to do with how the drive-side crank arm deflects with inconsistency depending on loading conditions.
  • I do admit that I loosely remember Shane Miller showing that maybe one of the non-Shimano ones could be ok, but I’d suggest some research if you are at all interested in any Shimano DS PM option.
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Yup, the spider is just a fancy disc, connected to the drive side arm via the chainring bolts or direct-mount. It will read power no matter which leg is driving, even if it’s just one leg. That example shows why the L/R balance estimate should be taken with a decent bit of salt.

Still might be reasonably worthwhile within reason, but even with my true dual PowerTap pedals, I find L/R balance hardly useful beyond “hmmm, that’s interesting…”.

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Stages have found a way to make it work.

They have an Ultegra version too

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Cool, I thought there might be at least one decent example.

31

Agree with this. Though I know I have a L/R discrepancy which is why I’m leaning towards the spider over the left sided. Weirdly (perhaps), the L/R discrepancy changes indoors and outdoors. Indoors it can be as bad as 46/54, though usually around 48/52. But outdoors it’s almost always 50/50, sometimes 49/51. My only thought is that my trainer isn’t level, even though I’ve leveled it many times. Or the extra weight from the flywheel (on the left) makes the right pedal stroke ever so slightly needing more power. But this is why I want a spider. The discrepancy seems to change, which means any offset I add to the PM may not be true that day.

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Again for clarity, whether the balance data is worthwhile in review, it is irrelevant to the overall picture you describe. Total Power = Total Power, whether you look at L/R balance data or not.

  • The L/R balance data is a secondary bit of info and not used in any way to calculate the actual power data overall. The functional design of the spider is the key here, not balance data.
  • This will be superior to a single-sided power meter (doubled) because it is capturing full power data no matter how balanced or lopsided it may be (per the single foot driving example above).

So, even if you never bother to look at the balance data, this is better data overall because it is unlikely that anyone is 50/50 all the time. Hence that being the most common criticism of single-sided PM’s.

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I’m doing a new build with Sram Force and I’m going to buy the Sram/Quarq power meter spider. Full retail is $475 but I often see them for $375, sometimes less.

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Sorry, I should clarify what I meant. What I was saying is that I have Assioma Duos on another bike. This PM would be for the crit bike. I agree that looking at the L/R balance doesn’t offer much other than curiosity. But if I’m using a Left only, it’s going to underreport my true power in most cases, anywhere from 92-96%. Whether I care about that difference is another question (I personally do). That’s a fair amount. Now I can set an offset to multiply by 102% or something (4iiii has a calculator). But again, from past data, some days I don’t have a discrepancy, at which point I’m over reporting data. So with a left sided PM, my power readings could vary fairly substantially day to day.

So although I don’t care about L/R balance in that I’m not trying maintain a 50/50 split all the time, it does give me some data that can help me. If I was always 48/52 or always 46/54, I could probably be fine with a left sided PM and just calculate an offset. But since my personal data tells me that indoors I can be 46/54 and outdoors 48/52 or even 50/50, that’s going to change the accuracy of my PM day to day. A spider on the other hand will at least give me consistent numbers. Hope that makes sense.

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Plus the cost of a crankset and new bottom bracket though. If I was already on SRAM it wouldn’t be a bad deal.

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  • Yup, perfectly! :smiley:
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I picked up a new crankset for $200. One of the reasons I went with Force was the blowout deals on last year’s parts and the ability to get a matching top shelf Quarq power meter crankset for $600.