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This is prompted by curiosity, so a cheap and cheerful solution is desirable.

I'd like to measure my cadence, not just on my own bikes but on the heavy, clunky, undergeared, undersized rental bikes I sometimes use. I don't need realtime feedback if I can record.

So a sensor that goes on my ankle (or in a pocket, but I don't always have leg pockets) would be ideal, but does such a thing exist?

Chris H
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    Shopping questions are discouraged, you should know that, but here you go, It says you can connect it to your shoe https://www.wahoofitness.com/devices/bike-sensors/wahoo-rpm-cadence-sensor – Kibbee Dec 02 '20 at 18:53
  • @Kibbee a class of devices/solutions is more what I was looking for, but thanks. I probably could have been clearer on that point but wrote the Q in 2 stages – Chris H Dec 02 '20 at 19:03
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    No problem. I think the "no shopping" rule is kind of an odd one myself. This site has it's roots in computer stuff where things change every 3 months, so I can understand why they wouldn't want shopping questions which could quickly become outdated. But with bikes things change much less, and knowing which product to buy can often solve a problem. Is asking what tool to use a shopping question? It's really hard to say. – Kibbee Dec 02 '20 at 19:07
  • ... Though I must admit, a proper brand that should work reliably does sound good – Chris H Dec 02 '20 at 19:08
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    I think the pace of artificially induced change is probably faster with bikes these days than computers – thelawnet Dec 02 '20 at 19:26
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    Check your watch, count your pedal strokes for a period of time, then check your watch again. Do the math. – Daniel R Hicks Dec 02 '20 at 19:35
  • @Kibbee I think Wahoo might be the only company to make that type of shoe-mounted cadence sensor, but they don't need to be, so that would be a valid answer to me – Weiwen Ng Dec 02 '20 at 20:19
  • Re shopping - there's availability as well. The one jumps to mind is bike brands in India, which tend to be a completely different set from the rest of the world based on questions we've had before. – Criggie Dec 02 '20 at 22:07
  • Might be a good Meta question - something like "Does a product exist that fits these requirements" is that a shopping question? Vs "should I buy a X or a Y brand bike?" which is clearly shopping. The first has more long-term usefulness as a list of candidates, the second is a comparison of two things. – Criggie Dec 02 '20 at 22:09
  • @chrish do you have a head unit ? Or a phone that does sensors ? I know strava removed their native sensor support for "stability reasons" a couple years ago. – Criggie Dec 07 '20 at 02:15
  • @Criggie IPbike supports as many BLE sensors as anything else (though I've had trouble with a cheap junk speed/cadence sensor that wouldn't stay paired long enough to actually ride anywhere) – Chris H Dec 07 '20 at 11:55

6 Answers6

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The RPM Cadence Sensor from Wahoo can track your cadence based on the motion of your foot. On the product page it specifically mentions the following

The RPM can be worn on your shoe for spin classes or use with multiple bikes

Here's an article explaining how it can be used to track your GPS usage. It's important that it is mounted in the correct orientation.

I'm not sure if there are any other cadence sensors on the market that work solely off of motion as opposed to the traditional magnet based sensors.

EDIT:

I found that Garmin makes some accelerometer based candence and speed sensors that attach using rubber bands.

Here is a similar product from Saris

I found that the best way to find these products is search for "magnetless cadence sensor".

Kibbee
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    Decided to write this up as an answer so that it's more visible to people looking at this question in the future. – Kibbee Dec 02 '20 at 20:47
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    There are cheaper offers on ebay for some china-branded Bluetooth cadence and speed rpm sensors. They are two-in-one sensors which have a switch in the battery compartment where you tell it to measure speed or cadence. You buy two of those to measure both rpms. Wahoo is a good brand, but pretty expensive. All of these are easy to install and to remove. – Daniel F Dec 02 '20 at 21:15
  • Other magnet less sensors may rely on the sensor turning upside down with every rotation so may not work on the foot (although I suspect most use the same silicon chip / design and work the same) – mattnz Dec 02 '20 at 21:26
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    "Magnetless" sin't a word that would have occurred to me (as a word or to mean accelerometer-based) – Chris H Dec 02 '20 at 21:34
  • I think most ANT+ or Bluetooth cadence sensors are accelerometer based these days. The price of a MEMS accelerometer is cheaper than a magnet and reed switch. – Phil Frost Dec 03 '20 at 12:56
  • @PhilFrost looking around it seems that the majority of new cadence sensors do use accelerometers but I would posit that it's more likely due to them being easier to set up and they are more desirable to the end user. The parts are extemely cheap no matter which technology you are using. For instance, you can buy a reed switch for under $1 at retail, in single quantities. A company that manufacturers cadence sensors could probably acquire them for less than $0.25 a piece. The mark-up on these things is crazy. – Kibbee Dec 03 '20 at 21:28
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    @Kibbee The cheapest SMT reed switch I found is $0.89 for 1, or $594 for 1000. The cheapest accelerometer is $0.94 or $385. Not only is the accelerometer cheaper in quantity, but it doesn't require a magnet or the hardware to mount it. And while you can find cheaper leaded reed switches, now you have additional assembly costs. – Phil Frost Dec 03 '20 at 22:04
  • Alibaba lists a 3 axis accelerometer with BLE for $12 as a unit, $5 as a component, these could be used (with software) as bike speed/cadence sensors. BOM cost has nothing to do with what the likes of Wahoo and Garmin charge, – mattnz Dec 06 '20 at 22:01
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    @mattnz Alibaba also lists fully assembled magnet based speed an cadence sensors for $12 when purchased in quantity. I understand that the cost of these parts has very little to do with the final cost when they are sold by Garmin or Wahoo. It doesn't matter which technology they are using, be it accellerometers or magnets, they are all cheap. I think the prevalence of accellerometers based units is just that they are easier to market to people because they seem more advanced and are easier to set up. – Kibbee Dec 07 '20 at 13:47
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This is a somewhat alternative solution, but you can use music. Find a tune that has a similar speed to your cadence, and google for "BPM (song name artist name)"

https://tunebat.com/Info/The-Gambler-Kenny-Rogers/5KqldkCunQ2rWxruMEtGh0

So "The Gambler" by Kenny Rogers is 87 BPM, meaning you're pedalling at 87 RPM, or maybe at ~44 RPM if you're on the half-beat not the quarter beat.

This presumes you can listen to music while riding, that's another topic.

You can flip this around, and if there's a cadence you want to ride at, then find music which has a speed of the same, or double. You might want to practice at 100 RPM and so "Guns and Roses - Paradise City" is 200 BPM. Find close-enough matches with services like https://jog.fm/popular-workout-songs?bpm=200

Criggie
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    Bone conduction headphones do keep your ears clear, so that could be an option if a cyclist must listen to music. I can't recommend this in traffic, but people do listen to audio on long distance gravel rides - traffic is low. – Weiwen Ng Dec 02 '20 at 18:58
  • Interesting, more suited to the open road than the rental bike. To find the max sustainable cadence that way would take some fiddling, though on my own bikes a metronome app would work (on speaker even) – Chris H Dec 02 '20 at 19:06
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    Getting 38km/h on the rental requires thrash metal cadences, so that works for me, even if it looks like the soundtrack should be Benny Hill – Chris H Dec 02 '20 at 19:14
  • OK so I had no idea that was an actual thing. I was thinking of this or maybe this, rather than this, but whatever. – Chris H Dec 02 '20 at 21:47
  • @chrisH I was stomping into work this morning on a tailwind, and the song "I'm Just a Girl" was playing at 184 BPM Obvs I wasn't pedalling that fast, but ~92 was comfortable in the high 40 km/h's – Criggie Dec 02 '20 at 22:28
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    Or a metronome app that emits a simple "tic-tic-tic-tac" pattern as it's easier to adjust to a "target" bpm. Is not really necessary to use headphones: on quiet streets/roads you can use an arm band phone holder near the shoulder and the metronome will be audible. – Jahaziel Dec 02 '20 at 22:29
  • @WeiwenNg I'd like to get some bone conduction headphones, but can't see me wearing them where there's traffic. I've tried some very open conventional ones for audio navigation, but if they weren't too quiet to hear the directions, they were too loud to hear the traffic – Chris H Dec 03 '20 at 07:57
  • I've got some bone conduction headphones, and they're not great. Ideally your music would be a mono mix, not a stereo mix. This helps separate real-world noises with a "direction" from the tune. Frequency is poor too - with more mids and less bass and treble. So these bone conduction headphones are fantastic for voice/phones/audio books, and more like a cheap $10 transistor radio for music. Which is fine for background music - you're not expecting hi-fi sound on a bike. – Criggie Dec 03 '20 at 10:47
  • A metronome app is definitely usable! I use one when I run. I find that I can run the metronome and music over it. That way, I can listen to whatever music I want, but I've got a steady metronome undercurrent that keeps my run cadence pretty steady. – FreeMan Dec 03 '20 at 13:34
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The magnet less sensors such as Garmin and Wahoo that are designed to the crank, attached to your shoe, might work. These use accelerometers to determine cadence. The difference when attached to your shoe are they stay the same orientation, when attached to the crank they rotate upside down every revolution, so it might not work as well.

A comment posted here indicates the Wahoo sensor might work for you (but which one? they probably have many variations)

I change between riding three different bikes, this allows me to only need one cadence Sensor. Out of the four different cadence sensors I own, this is the only one that worked consistently while attached to my shoe.

It could get expensive and you might end up with a pile of sensors that do not work - As suggested in the comments, using one with an ORing to attach to the crank would be fairly quick and easy to put on different bikes. For me I suspect that would get expensive as I would forgot to remove it when returning the bike.

mattnz
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Tabulate it.

If you know the number of teeth for each gear, and the wheel diameters, you can calculate your cadence at any given speed.

Make a spreadsheet or table with your speed in the columns in steps of e.g. 3 Km/hr or 5 Km/hr, and on each row list your gears, and then calculate your cadence for each gear at each listed speed.

An online calculator such as this one at http://bikecalculator.com/ may help you.

Print off your table, laminate it to protect against the weather, and attach it somewhere to your bike where you can see it without it distracting your attention.

Now if you are riding at, say, 22 km/hr, and your table shows a cadence of 60 rpm at 20 km/hr in that particular gear, and 65 rpm @ 25 km/hr, then you know your cadence is roughly about 62 rpm.

Please Note:

  • Looking at tiny printed text in tables while riding is not a good idea. If you just have a small number of gears e.g. 5 or 7, you can make each row in the table sufficiently large to allow you to see the numbers without distracting you from the road.

  • The OP asked about measuring cadence; this method is not a measurement per se, but rather a rough means of determining your approximate cadence.

Alex Barber
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  • When I know my gearing, I do just that (knowing a few favourite gears for certain conditions). For one of my main use cases I have no idea of the gearing, and no way of finding out, just that it's low enough that moderate paces are good high-cadence training. In fact I wouldn't mind finding out just how low the gears are. – Chris H Dec 07 '20 at 07:14
  • Sheldon Brown's site can produce these tables very easily, just given the part information - it has a database with the actual cogs for a given cassette – Chris H Dec 07 '20 at 07:15
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Oh, measuring cadence is simple: Find a nice silent road where you can ride for a minute undisturbed, take some kind of clock that shows seconds, and then simply start counting when the seconds reach some set number (00 is perfect, but I find that 10, 20, etc. do just as well). Stop counting when that set number is reached again, and the number where you stopped counting is your RPM.

This works for counting heart rate (at rest, not on bike; most people can't easily count that fast) just as well as counting pedal strokes, and is precise to a single beat/stroke. You just need to be able to count while you have the second count in your sight.

A better alternative would be some app that plays a click exactly once a minute. Put that on your earphones, start counting on one click, stop counting on the next click. The advantage is that it leaves your sight unhindered, allowing you to do it with a low amount of traffic.

For counting cadence, it's advisable to count double strokes. That cuts the counting speed in half, and if you remember your pedal position on start/end, you can deduce the half-stroke count exactly.

cmaster - reinstate monica
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    You'd have to focus on the clock, counting the strokes, keeping an eye on the road and making a physical effort. Quite a lot of things, where your attention is going to suffer. Not a good thing to do in traffic. I'd rely on a one piece cadence sensor that attaches to a crank-arm with an O-ring and connects to a phone app via Bluetooth. Much safer imho.and easily transferable. – Carel Dec 02 '20 at 19:35
  • A good approach. It would take a special trip as it's not really compatible with sprinting for the lights, but that could be arranged. – Chris H Dec 02 '20 at 19:38
  • @Carel That's why I said "find a nice silent road". However, if you have a second count, it's perfectly doable: You glance at your clock from time to time, and you get an impression how long you can keep concentrating on the road. As the stop point comes closer, you'll look more often, and will have your eyes on the clock exactly when the stop point comes. – cmaster - reinstate monica Dec 02 '20 at 19:40
  • @Carel Also, once you know in which ballpark the result will be, you can basically forget the clock until your counting enters that range. – cmaster - reinstate monica Dec 02 '20 at 19:42
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a 3 axis walking pedometer placed in a sock works great. Needs no connection (powered by one internal AAA battery), but obviously must be manually removed from sock to read pace.

Many such pedometers are available via internet at prices around $20. I have used several different ones over 30 years of indoor and touring cycling, with all being extremely accurate at reporting total and average pedal revolutions.

fred landgraf
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  • I thought about pedometers, but none of the ones I've had (physical devices or apps) have had the ability to tell me the step rate at a given moment (that I could then tie up with my ride data) - I'd get the total number of pedal strokes from the ride, which would be slightly interesting on a singlespeed but less useful with multiple gears. – Chris H Dec 09 '20 at 16:15
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    @ChrisH I had a fitbit for a couple months, and that had "steps" which counted and even graphed. However it would read one bike as 10k steps per hour and a road bike at about 3k per hour (about reasonable) Plus they're silly-expensive. – Criggie Dec 09 '20 at 17:28