Garmin Speed / Cadence Sensor Review

I bought myself a new gadget the other day, a Garmin Speed / Cadence Sensor for my Forerunner 305. I didn’t really NEED one but new toys are always a good motivator.

When out on my bike in the real world the GPS on the Forerunner obviously tracks my speed and distance and works flawlessly. When on the Tacx Flow Turbo Trainer however I’m not actually going anywhere so the GPS doesn’t record my speed and distance. The computer on the Turbo Trainer does record both my speed and distance and also my cadence and power output, so I was able to see these things. The problem, if you can call it a problem, was that the Tacx Flow doesn’t interface with my computer. So, when I upload my turbo training sessions to Garmin Connect or any other fitness training software I get the data from my Forerunner but have to manually enter the distance, average speed, max speed, and power output data and don’t get to see anything about my cadence.

This is where the Speed / Cadence Sensor comes to the rescue. The gadget consists of a wireless sensor that fits to your chainstay and two magnets – one for the crank arm to measure cadence and one for the wheel to measure speed and distance. Fitting was a simple affair, just pop the sensor on the chainstay and fix with two zip ties, screw the wheel magnet onto a spoke making sure it aligns with the sensor and attach the crank magnet to the crank arm with the provided sticky pad and a zip tie, again making sure it aligns with the sensor.

As I was using this on my Turbo Trainer I already had the cadence sensor from the turbo trainer attached to the bike but the Garmin one is fairly adjustable so it was easy enough to get everything aligned. To make it even easier, the Garmin sensor has a little LED that flashes each time it picks up a passing magnet. It flashes red for the cadence sensor and green for the speed sensor so making sure everything was working before tightening the zip ties was a doddle. The magnets are just magnets so it would probably have been possible to use the existing crank arm magnet from the Tacx Flow for both the Turbo Trainer Sensor and the Garmin sensor but in the end I used a separate magnet for each.

Of course, once it was all attached I just had to give it a go so I jumped on and did a relatively easy workout. As usual I could see my various readouts on the Tacx Flow computer but now could also see corresponding values on my Garmin Forerunner.

The Tacx Flow computer only shows 2 values at any one time (plus the overall time) and I usually have these set to show speed and cadence. Reassuringly the speed and cadence on the turbo trainer readout matched those on the Garmin. I therefore soon changed the display on the turbo trainer to show Power and Cadence, whilst my Garmin (which can show up to 4 parameters at any one time ) was set to display Distance, Speed, and Heart Rate.

Everything worked beautifully and the figures all matched up. Best of all, once I’d finished I was able to connect my Garmin Foreunner to my computer as usual and upload the workout to both Ascent and Garmin Connect. All of the usual data was there (normally just time and heart rate data) but now it also had speed, distance and cadence data.

Here’s the graph of my workout from Ascent showing:
Red – Heart Rate
Purple – Cadence
Green – Speed
Brown – Power (It isn’t recording this but Ascent makes a best guess – which wasn’t too far out! Although it doesn’t know what resistance / slope settings I’m using so it isn’t that accurate. )

Garmin Sensor Readouts

Read outs from Garmin Speed / Cadence Sensor

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Alan Cole

Alan is a Freelance Website Designer, Sports & Exercise Science Lab Technician and full time Dad & husband with far too many hobbies: Triathlete, Swimming, Cycling, Running, MTBing, Surfing, Windsurfing, SUPing, Gardening, Photography.... The list goes on.

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