What Is It Wednesdays Sensor Edition

Speed, cadence, power, heart rate – these are just a few things you can track while riding. It seems more and more we’re a data driven society. Data is no longer facts and figures relegated to analysts stuck in basement offices crunching numbers. Anymore we can just look at our phone or even our wrists to see just how many steps we’ve taken, calories burned, distance traversed and much more. Bike computers aren’t exactly new, but now more than ever they are more easily accessible to the masses. With that in mind, I’m sure plenty of you have asked exactly what are those number crunching devices and what are they doing – and hey, do I need one? So allow me to take you on a brief tour of the main sensors you will come across and hopefully answer some of those questions for you.


Credit: Trek/Bontrager

Whether you measure in kilometers or miles per hour, a speed sensor is going to give you information about how fast you’re going (or not going in the case of that monster hill you dread, just me?). It’s taking your distance divided by the elapsed time that has passed. There’s a few ways you can measure your speed including dedicated sensors or computers,and apps like Strava, MapMyRide, and Wahoo.

If you opt for a sensor setup then what you will typically see is a magnet that attaches to a spoke on your rear wheel and a receiver mounted on the chainstay. Models can either be wireless or wired and may work with either a display mounted to your handlebars, or synced to an app on your phone. Personally I use the Bontrager Interchange (pictured above) which measures my speed and cadence, paired with my phone (via Bluetooth/Ant+) which I keep mounted to my stem while running Strava. This setup works for my rides at the moment, but one day I plan on upgraded to a full on bike computer, more on that and Ant+/Bluetooth later.

If you plan on utilizing your phone’s GPS to display that info instead of a dedicated system, no worries, it will give you a great estimate. One word of advice just from my own experiences, the GPS available in most phones will just draw a straight line between two points as it pings the satellite with your location meaning it can over or undershoot your distance. In areas with spotty GPS this can provide unreliable stats. For example, I was once going 3,200 mph on my bike, now I know I like to think of myself as Wonder Woman but I had left my invisible jet home that day. I’ve also missed out on many miles that were cutout because of the finicky GPS in my phone.


Credit: Cateye

Often you will find speed and cadence paired together on sensors, not always but typically if the unit cost $25 or more it’s going to have both. Cadence is the number of times you pedal within a given amount of time, with the standard being rotations per minute or RPM. If you wish to measure cadence then you will have to have a dedicated sensor as your phone will not be able to measure this on its own. Same setup as a speed sensor – a magnet on a rear wheel spoke that connects to a receiver every time it passes during the wheel’s rotation. The Bontrager model that I showed in the section above also tracks cadence, but I thought I would also show a model that is built into a dedicated bike computer such as Cateye’s Strada 430. You can see the cadence displayed at the bottom right.

Don’t be mistaken with cadence, the higher the RPM doesn’t always equate to faster speeds ESPECIALLY when multiple gears are involved. When going up a hill I will shift to a lower gear in order to pick up my cadence and maintain a fairly level rate of perceived exertion (RPE). In English that means that while I am going up a hill, something that is more difficult that riding on a flat surface, I will drop my gear so that I can pedal faster but with significantly less resistance so that my legs don’t feel like murder jello later, saving energy so I can ride longer.


Credit: Garmin

This one I had to do a little of research on because while I have heard of them and seen a few, I don’t have any personal experience using one. Power meters measure how much effort you put into moving you and your bicycle over a distance in a measurable amount of time. Power meters will display in watts which translates to the amount of energy it took to do what I just broke down. Power meters come in a few styles and can be found on the crank, pedal, hub, and less common as a footpod you can put in your shoe. The one pictured here is a pedal based unit from Garmin Vector. As you can imagine, the calculations that go into interpreting this data are much more complex than cadence and speed.

Power meters allow you to see just how hard you’re working because speed and cadence don’t always give the full picture (hello fast down hills!). A great combo to analyze is actually the power you’re outputting in conjunction with your heart rate to understand if you can push harder or if you’re running out of juice.

Heart Rate

Credit: Polar

The last sensor we’ll discuss is the humble and handy heart rate monitor or HRM. HRMs come either as the traditional chest strap model or less accurate optical sensors on some watches and fitness bands. HRMs are measuring how fast your heart is beating over the course of a minute represented as beats per minute or BPM. Some bike computers can pair with HRMs otherwise you can use one that displays on a watchface like the Polar A300 pictured.

As I mentioned in the power section, measuring your heart rate can give you insight on how hard you’re training. Once you figure out your max heart rate and target heart rate range then you’ll know if you can kick it up or notch or need to take it a bit easier. If you’re interested in learning more about target and max heart rates, let me know and I can make that a What Is It Wednesday one of these Wednesdays.

Ant+ and Bluetooth

I am going to keep this section brief. If you have a smartphone or tablet then likely you are already familiar with Bluetooth, it’s a method of pairing devices together so that can work hand in hand to perform a task (phone + Bluetooth speaker = jamming out while meal prepping for the week). Ant+ isn’t new but it’s not as big of a name as Bluetooth. It serves a similar purpose – allowing two devices to communicate with each other wirelessly. Newer phones are coming with built-in Ant+ more increasingly. If your phone, or computer, doesn’t have Ant+ built in you can still use it, you’ll just need to purchase a separate Ant+ stick to plug it in to your device. I am actually going to be signing up for Zwift soon and need to replace my Ant+ stick, maybe I’ll do a review 🙂

So whether you need any of these is really up to you. My recommendation is that if you’re a casual rider then you’re not likely going to benefit and can likely take a pass on these. However if you ride as a means of training then try using what is already built into your phone/apps as a test run before dropping some cash on a device and when you’re ready to make that step – do your research! Find out what will work for your riding style, where you ride, and how you plan on keeping tabs on all of this information. Alrighty folks, this concludes another What Is It Wednesday, see you in a week, hope you learned something!