The ANT+ Bike Speed/Cadence Sensor: Everything you ever wanted to know

After the popular ‘everything you ever wanted to know’ post I did back this winter on the footpod, I decided it was time to continue the series with the Speed/Cadence sensor.  Thankfully, the speed/cadence sensor is actually a bit less mysterious than the footpod, primarily because it’s a very mathematically simple device (unlike the footpod which calculates distance based on a number of calibrated factors).

So let’s start out – what exactly is it?

Well, there’s actually three different ANT+ sensor types related to this area, which align to the three different official ANT+ sensor device profiles for speed & cadence sensors.  You have:

1) Speed Only Sensor: This unit uses a wheel sensor and magnet that’s mounted on the frame with a magnet on the rear wheel to measure speed and distance.  Because the wheel circumference is known (manually entered, or calibrated via GPS), each time the magnet passes the sensor a simple mathematical calculation can be made to determine overall speed and distance.

2) Cadence Only Sensor: This unit uses a cadence sensor on your frame and a magnet on your crank to measure cadence.  The crank is the arm that the pedal connects to (and in turn, your cleat then shoe then foot). Each time your crank arm passes the sensor a single revolution is recorded.

3) Speed/Cadence Combo Sensor: This is by far the most popular type. This unit type sends both speed and cadence information wirelessly to the head unit, and does so usually using a single device (either one piece physically or two small pieces connected via wire)  mounted near the rear wheel.  It’s simply a combination of the first two unit types I noted.

Each of these different devices uses a different ANT+ ‘profile’ type, which means that just because a device supports one profile type, doesn’t mean it’ll support the other types.  The combo sensor type was the oldest, and is the most widely supported.  I know of no ANT+ devices that fail to support it.  Meanwhile, the speed-only and cadence-only sensor types are newer and far less supported.  For example, the Garmin FR305 doesn’t support these newer ANT+ profiles.

What do I mean by ANT+ profiles/device types?  Well, every ANT+ device has a profile, think of it like a ‘classification’.  There are ANT+ Heart Rate Straps (HRM Device Profile), Power Meters (PWR Meter device profile) and others.  There are even new profiles coming for data streams like Skin Surface Temperature and Electric Bikes (LEV).  Each of these is simply a standard identifying a device, as without standards ANT+ as a ecosystem wouldn’t work too well.

Speed/Cadence Sensors:

For most folks, the most common Speed/Cadence sensor is the $35 Garmin GSC-10.  Without question it’s the Microsoft Office of the ANT+ world – almost everyone has it.  This simply has three pieces.  The first is the spoke magnet (seen left), then the cadence magnet (seen right), and finally the electronics pod mounted to your frame that has two magnet sensors capturing both speed (upper moving arm off unit) and cadence (lower right side of unit).

But there are others that have created Speed/Cadence combo sensors as well, most with slightly differing designs.  Some of these designs are meant to solve certain bike frame configurations where the GSC-10 doesn’t work well by using a small wire to bridge a separate pieces for the speed and cadence data.  This gives more flexible installation options Ultimately the unit combines the data together though so it shows up at an ANT+ combo sensor.  For example, below is the Wahoo Fitness combo sensor:

I suppose the above picture probably deserves some explanation (I generally feel any photos with cutting devices probably do).  The Wahoo sensor is in the middle about to get snipped, as I was redoing the cabling to play around the idea of extending the short cable in the middle to accommodate a recumbent bike.  I never did get a bike to test with, though conceptually it’s pretty simple and worked just fine on my desk (albeit in a very non-weatherproofed sorta way):

Speed Only and Cadence Only Sensors:

Next we have those units that are either speed sensors or cadence sensors…but not both.  These sensors are dedicating to delivering either speed data, or cadence data.  They can’t do both, and can only measure what they are designed for (meaning, you can’t use a speed sensor to measure cadence).  The most common reason people by these sensors over combo sensors is if their bike has a specific configuration that the combo sensor won’t fit.  In particular, these are more popular with unique bikes like recumbent and tandem bikes.

Here for example, is a speed-only sensor from Bontrager:

Bontrager also makes a speed sensor that mounts directly into the fork as well, similar to the frame mounted sensors noted below in the next section.

Bontrager also makes a cadence-only sensor, though, these are generally harder to find simply because the demand is so low for them.

In both of these situations these singular-function sensors require that the ANT+ head unit supports the single-function device profiles.

Newer bike computers like the Edge 500 and Edge 800 do – but many older units do not, so it’s something to keep in mind.

Frame Integrated Speed/Cadence Sensors:

The last category of speed/cadence sensors out there is the frame integrated sensors.  Technically from an ANT+ standpoint this is merely a speed/cadence combo sensor.  And today, only one company makes them – Bontrager – as part of their Duotrap line.  And further, today only one bike frame vendor  support these – Trek.

That said, for those that have these bikes – these are awesome.  The pod simply fits right into the bike.  I installed one of these on The Girl’s back this past winter…really cool stuff.

Here’s what it looks like installed into a Trek Speed Concept:

As you can see above, the design is incredibly streamlined – and perhaps more importantly, not susceptible to getting bumped out of alignment.

Power Meter Speed/Cadence Information:

Finally, it should be mentioned that most cycling power meters will include either speed information, cadence information, or both.

The type of data gathered by these power meters will vary based on how the specific power meter measures its power data.  That in turn drives whether or not speed or cadence data is determined – and if so – whether it’s measured or calculated (estimated).

Take for example crank based power meters (like Quarq and SRM).

These power meters use magnets to determine cadence – it simply measures each revolution of your crank (the thing your foot ultimately connects to).  Here’s an example of a Quarq Power Meter, with the magnet visible below, attached to a small metal ring near the bottom bracket (taken looking straight down onto the crank & chain rings from above):

Then you’ve got other crank power meters like Power2Max, which doesn’t actually use magnets at all – but rather uses mathematical equations to determine your cadence based on other known variables.  In this case, these calculations are usually given a specific cadence range they are accurate to.  For example, the Power2Max is specified as 30 to 180 RPM.

And finally, you’ve got hub based power meters, like the PowerTap, which can do both speed and cadence.  In the case of speed it can measure that directly since it knows revolutions based on hub rotation.  But for cadence, it actually calculates that mathematically.  This is generally pretty accurate, though like the Power2Max it has known ranges or fringe scenarios where it doesn’t work quite as well (really high cadence work).  But for typical everyday use, it’s absolutely more than sufficient.

In most head unit configurations (that’s the display unit), cadence information from a power meter will always override cadence information from a separate standalone sensor.

Why do you want cadence or speed data anyway?

Well, it depends.  Let’s start with cadence.  There’s actually been quite a bit of research on both sides of the cadence coin.  One side says that a higher cadence – such as 90-95RPM is ideal, while the other side says that a ‘self selected’ cadence is most efficient.  Many folks do high cadence drills though to be able to spin at higher RPM’s in the event it’s required – without taking as large a hit heart-rate wise simply to spin the cranks faster if required (i.e. a sprint to a finish).

Virtually all ANT+ cycling head units will display cadence information in real time on the bike, such as below (see as CAD):

During the ride the data is recorded for later access, easily viewable in charts/graphs:

Looking at the speed side of the equation, most folks tend to use speed sensors indoors on trainers.  This allows them to gather both speed and distance data when inside.  And while speed and distance while on a trainer is purely a function of your gearing combination and resistance applied by the trainer (meaning, by changing gears and resistance you can dramatically change speed without changing effort) – it can still be an interesting metric for some.

Afterwards, like cadence, you can view the speed and distance information in charts/graphs:

For mountain bikers a speed sensor can be more accurate than GPS in determining distance – as the speed sensor measures speed purely based on revolutions of the wheel and isn’t dependent on GPS correctly tracking on quick switchbacks in forests.

And finally, the same can also be said of indoor track cyclists, who are looking for data in places where GPS isn’t going to work well.

Wrap Up:

As you can see, speed and cadence sensors are both quite common – but also pretty integral to many cyclists.  The good news is that they are pretty cheap, with most ANT+ units costing about $35 – well within the budget of most folks.


To the left are a few different ANT+ speed/cadence sensors that I’ve used and have no problems with.  At this point, I generally recommend some of the quick release variants.  Bontrager came out with the first variant, but it’s been widely rebranded by others, including Motorola.  You can find the Motorola branded one on Amazon.  I use the Bontrager one on my bike day to day and it works perfect (the Motorola branded one is identical).

Garmin GSC-10 ANT+ Speed/Cadence Sensor
Motorola ANT+ Quick Release Speed/Cadence Sensor [Review here for Bontrager branded variant]
Bontrager DuoTrap ANT+ Speed/Cadence Sensor

If you purchase through Clever Training or Amazon you help support the site.  And, with Clever Training you’ll get 10% off your shopping basket.

Hopefully I’ve covered everything you ever wanted to know about speed and cadence sensors – but if not, feel free to drop a note below and I’ll compile it into a Q&A and update the post – similar to what I’ve done on the footpod post.

Thanks for reading!

(Note: I’m currently away on my honeymoon, but due to the magic of automated publishing, you’ll be enjoying content in the meantime.  Thanks for reading!)

DC Rainmaker :

View Comments (235)

  • I've recently upgraded from a Garmin Edge 305 to a Garmin 500 Bundle. I'm trying to use my previous ANT+ Bike Speed/Cadence Sensor on my commuter bike and my new ANT+ Bike Speed/Cadence Sensor on my road bike. I don't get any speed or distance reading on my 500 for my commuter bike setup. I've physically remove the ANT+ Bike Speed/Cadence Sensor from my commuter bike the speed and distance are properly displayed and seem accurate.

    Advise would be greatly appreciated. Thx

  • I have read your page already and gotten many information about bike details. I have some information about Recumbent bicycle and Recumbent Bike. I'm trying to use the Garmin 910xt but the Spd/Cad sensor is Not connected. Thanks for shearing this page.

  • Hi, very good post!
    I am new to those wireless technologies in the bike. I still use a bike computer with wires for speed and cadence. But it is gettin old and sometimes it stops working in the middle of the ride and that makes me really mad!

    I am currently looking for a new computer and there are many different options available. And I will also use it for running.
    But I find it hard to get one to be used in the bike and in the wrist. I mean, the Garnin 310XT or the Suunt Ambit for example are very good for bike and running (swimming also) but I don´t want to keep looking at my wrist to see speed and cadence while I´m on the bike.
    also I have two main questions:
    1- Which receiver would you suggest to use for running and cycling that can be easily taken of from the wrist and put in the handlebar of the bike?
    2- If there is no good option for the question 1, than the solution would be to use a watch and a cycle computer. Can an ANT+ transmitter (HR, Cadence) be paired at the same time to 2 different receivers (watch and bike computer)?

    thanks for the helpful post!
    Ricardo

    • Ricardo, try the Garmin 920XT. You can add a quick release kit to move it from your wrist to the bike. DCR has a great write up on this device here.

  • Hi Ray,

    thanks for these informative and through reviews. Thumbs up!

    I recently bought the Forerunner 920xt and now I am looking for a speed/cadence sensor. I've read both of your posts, this one about the Garmin GSC 10 combo or the new magnet-less speed and cadence sensor, reviewed here https://www.dcrainmaker.com/2014/05/garmins-spd-cad-magnetless-sensors.html. The price for the GSC 10 is almost the half of the new ones.
    Also, how relievable is the GPS speed sensor on the 920xt since I will be riding 99% of the times outdoors. If the reliability is good then I could just go for the new magnet-less cadence sensor only?

    I've been through all the comments here but I couldn't find any related answers. I apologize though if there is some but I missed them.

    Thanks a lot!

    Bruno

  • Any comments regarding the Giant RideSense? I just got a 2016 Defy Advanced Pro 2 and it comes with this, is it worth to use it? I'm planning on getting a Garmin 520 bundle which comes with the cadence sensor, so should I just stick with the garmin unit and remove the ridesense? Any apps that will connect directly to this ridesense or definitely need a garmin u other units to track it? Thanks

  • What happen if i wanted to wash my bike? Should i take the sensor off first? or can i wash it without ejecting it? tks

  • Thank you for the informative article &comments. I recently purchased a tadpole trike and have a Garmin 405cx paired with a gsc 10 unit. I do not have the speed sensor set up because cranks and wheels are separated and I'm fine with that because I am using it for cadence training. My problem is, the cadence is displaying at 1/2 its actual value (ie I am pedaling at 90, but the unit is displaying a cadence of 45). Any suggestions?

  • Hi
    I am using a Wahoo Blue SC speed/cadence sensor with an Edge 520 (also own FR305 for running and edge 500 for mtb); I have never had a problem with a Garmin device.

    I am getting ghost (error) speeds very often with the wahoo sensor [which are killing my videos].

    I have been contacting their customer support and I have received some emails back but I suspect that, no matter what they say; they are still behind Garmin in terms of quality and reliability. They adviced to do the trivial: replace battery and get sensor closer to magnet; did that and still same results

    I will be ditching the wahoo sensor and will be buying a Garmin speed / cadence sensor. I need a stable and reliable speed sensor [to be installed in look 695].

    Do you recommend the Garmin magnet less sensors or the bullet proof [though bulky] GSC 10?

    Thank you

  • Hello Ray,

    Excellent site, please keep up the great work!

    I have been doing some aerodynamic testing on bicycles and logging the speed through a speed and cadence sensor. One interesting thing is that the old Garmin GSC 10 unit sends a signal at every magnet sensing event, whereas the Bontrager DuoTrap / Motorola style send an update every second.

    The ANT+ protocol for speed/cadence meters give the time of the last event and cumulative revolutions. So at 25mph there will often be about 4-5 updates on the Garmin unit, there will be 1 on the Bontrager. The speed is calculated with the equation:

    speed = change in wheel revolutions x wheel circumference / change in time

    At constant speed, both should be equally accurate, however for fine measurements while accelerating or decelerating, the old Garmin GSC 10 gives a better data read out. The quicker update also leads to a nicer real time display.

    As Garmin has changed there speed detection method to the accelerometer style which seems less accurate, it would be interesting to know if anyone is still making an ANT+ magnet sensor that updates on a per event cycle rather than the constant 1hz.

  • Hi there,
    I have the Suunto Ambit 3 watch and I understand many of the cadence /speed sensors aren't compatible. Are there any wireless ones compatible that you've come across since the release of the Ambit3? I want to use on my bike for indoor use and of course outdoor (to the extent the watch doesn't have a feature).

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