4iiii Precision crank arm power meter for 400 dollars

4iiii has dropped the cost of entry to power measurement to an all time low of just $399 while promising incredible accuracy.

Their new 4iiii Precosion Power Meter sticks onto the back of your left side crank arm, similar to Stages’ units, except it’s smaller and can be installed by the end user. It comes with a pod and calibration kit, and if you want a second pod (or third or fourth or fifth), those are $350 each. That allows you to add a second one to your crankset and get true left/right, or just add them to other bikes and use the original calibration kit. Or, if you have a bunch of friends or a friendly bike shop, you really only need one calibration kit.

Power through for more on the tech…

4iiii Precision crank arm power meter

Inside each pod are eight strain gauge grids, but they’re wired into two systems. Those two different strain measurement systems, and they’re very different than each other in the way they measure forces. Those competing measurements are compared and contrasted by the software to end up with a more accurate reading.

You calibrate it by putting a spindle into your pedal hole on the crank. It has a a spindle with grooves and a hook, then you simply hang anything on it that’s more than 10 pounds. Put the cranks horizontally, hold the rear brake and the load cell in the spindle tells the pod how much weight is being placed on the system, then it calibrates itself. The accelerometer in the pod knows if it’s level enough to calibrate, otherwise it’ll reject it and you try again. A warning of the calibration settings will show up on their smartphone app or common cycling computers.

4iiii Precision crank arm power meter

Once it’s set up, it transmits by ANT+ and Bluetooth LE simultaneously. They’re using a Nordic chip, so when BT 4.1 comes online, it’ll be a simple over the air update. In fact, all updates for the system will be over the air through their app. That update to the newer BT standard will allow it to transmit to multiple Bluetooth devices at once.

The pod itself sticks to the crank arm with a two-part epoxy. It comes with a template guide to help get it lined up and properly aligned. They say it only takes about 10-15 minutes to install and then a six hour cure time. It weighs just 10g with the battery.

It runs on a standard 2032 coin cell battery for 200 hours. It’ll be available by the end of the year. Final production units will be just a bit shorter and thinner than these, and they should fit well between Shimano’s new 4-arm cranks and the chainrings and many other models, too.



  1. @Everyone–what is with the proliferation of power meters, I see they’re mounted on pedals, shoes, spiders, crank arms, not trying to be snide but is this really a major accessory people are clamoring for? Other than racers of course.

  2. DC Rainmaker had a pretty favorable review of this. It was a pre-production model and he only got to use it for a while, but he seemed impressed. Exciting times in the power meter world.

  3. @pile-on Anyone who wants to improve their training would find a power meter useful. It doesn’t have to just be those who race, but yeah, it probably is a majority of racers. And there are a lot of them in the world, from Cat 4s to Pros.

  4. @pile-on

    No. There is almost zero market for them. Like 12 guys/girls total want them. The entire market is competing for one dozen people world wide.

  5. Do they expect people to pay $400 for that product? I understand development costs and time on the back-end, but that right there? The tangible product? They could have spent some more time making it look like it was worth more than $5.

  6. Bikerumor!!! You guys need to answer the million (err 400) dollar question that’s already been asked twice… Will this work on a carbon crank?

    It would almost be too good to be true if it does. Bur if it does it’s gonna sell like crazy!

  7. I think it’s great and I’m definitely interested in power meter choices. It seems like this sort of competition is a long time coming. If this meter works as advertised, my question would be where does this leave all the other makers? Further, when they partner up with a crank maker like Shimano and sell stock cranksets with power meters for just a couple hundred bucks more, will that be the end of the $1500+ power meter?

  8. I doubt it will work with carbon cranks; the following from their website –

    “Precision requires a flat crank. The following are compatible cranks.
    Shimano:The last 3 generations of cranks:105, Ultegra and Dura-Ace, mountain bikes: Deore XT SRAM:Rival OCT mountain bikes: X9 FSA:Energy”

  9. chessclubloser – On DCR, according to 4iiii it will/does work with carbon cranks. The slight issue is that carbon cranks behave differently to metal ones, so will need more regular calibration (and that is now in the process of being determined).

    Also, a single ‘pod’ can be fitted to the drive side crank.

    The bigger issue is that cranks need to have a flat surface for the ‘pod’ to be mounted on.

  10. Gotta assume on carbon/not flat, that it won’t be difficult to make a housing that is specific to a crank profile. Just a matter of time.

    If these work and prove durable, they will sell a boat-load.


  11. @pile-on ; when i’m doing my long rides (6 hours and more), i’d like to monitor the power i’m pushing to the pedals, just to be spot on and not to be completely exhausted at the end of the ride . The heart rate monitor is not completely reliable. I’m sixty and like the pros, i want to improve ! I’m OK to spend 400$ into this, even with 95% accuracy.

  12. The strain response in a metal is uniform in each direction, making strain gage application easy and predictable. With carbon, the response is largely dependent on the fiber direction and layup schedule, not to mention the layers of resin and epoxy covering the actual fibers. I’d be interested to see how it performs on carbon, especially with the end user applying the strain gage.

  13. @ pile-on – seemingly every company @ IB is selling a freaking FATBIKE, and the potential market for power meters draws your focus?

  14. I just had my best-ever finish by a large margin in a 50 mile MTB race that I rode with less fitness this year than in years past. I can attribute a large percentage of my improvement to pacing against 30 second average power rather than heart rate.

  15. Suddenly, a PM on each bike looks a lot more doable!

    FWIW, for those who haven’t ridden a bike with a PM, it is arguably the best single training gadget you can get. As a secondary benefit, it is also the best (and only consistent) way to tell how many calories you actually burned on a ride, making it a tool for non-racers who are riding for weight loss or general fitness.

  16. @david, @BeeJay, @frogg, thanks for the feedback–I was just a little shocked at how many variants were coming out, and why there are so many.
    @Tommy Rodgers, I’m a bit ambivalent towards fatbikes too, they look fun though.
    @HI, you seem nice.

  17. @pile-on Once you ride with a power meter up a climb or trail, you will appreciate what a powerful pacing tool it really is.

    I don’t even have a racing license anymore but at 37, am fitter than I was as a 25 year old racing in Belgium. Why? Cos power meters show me how to go hard in an effort or go easy on a easy ride.

    I also run 34×32 Condator gearing now that I understand the importance of cadence.

    I don’t have a coach, don’t follow a rigid training program. I just ride and once a week go hit 6w/kg for a minute or 10. Doesnt matter what the wind or weather is doing, I just ride to wattage and cadence. 🙂

  18. My riding buddy has gone through three stages arms now, with the same problem on each. Mid ride, it just fell off the crank arm. They’ve said there’s new epoxies and all that, and I will say they warrantied and shipped him replacements ASAP, but there’s a difference between “Here’s the arm your piece fell off” and “It fell off, and yes I was the one that glued it on, I couldn’t find it”, I suspect.

    When someone takes this same tech and sticks it INSIDE a hollow crank arm (with a way to replace the battery), It’ll be a game changer. Until then, a stray rock, repeated stress, and the elements don’t leave me to trust glue on strain gauges yet.

  19. Next task for DCrainmaker: Setup a bike with the Pioneer DA crank, Stages on left arm, 4iiii on right arm, one Vector S pedal, one Keo Power pedal, and a Powertap hub. Because… data.

  20. I have seen a LOT of stages power meter sold (now with less issues than others) so the power meter market is certainly opening up. I am excited for when the smoke settles and some impressive power meters emerge at very competitive prices.

  21. Why not include a hole in it to be zip tied? Or you could just zip tie it yourself. Would this effect the strain gauges? Seems it would be a bit more secure this way. Great idea and I am enjoying all the new PMs driving the costs down.

  22. @cracked-frame

    I find the ambiguous name at least mildly irritating. My guess is “Four Eyes.” It would be nice to hear if there is any meaning behind all the “i”s – or maybe the owner wears glasses? I dunno. This company also produced the “Sportiiiis” cycling ‘HUD’ – which isn’t a HUD so much as some distracting LEDs blinking in your peripheral vision. That one is pronounced “sport eyes” so…. four eyes it is.

  23. I spoke to the guys in the booth, one being the engineer and he confirmed it will be compatible with carbon cranks. It will need to calibrated once a year if using carbon cranks using the supplied calibration kit. A 5-10 minute process according to him. The production unit will be 25% smaller than what is pictured.

  24. pile-on – I am a little late to the discussion, but if someone is watching, a power meter is not only useful for performance training, but helpful for older or less-experienced riders. Older riders have limited maximum heart rates. The power meter is your first indicator of effort, and with a little practice the rider can see when their level of exertion is going to cause them to go anaerobic, and exceed their maximum sustainable heartrate. This is particularly useful for high racer recumbent riders on a long uphill grade, because if you crapout, you have to unclip and get a foot down in a hurry. Better to shift up a cog or two and spin to the top of the hill a bit slower. Over time, the rider can watch their maximum sustainable power output increase.

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