Garmin GSC 10 Speed/Cadence Bike Sensor

Another handy piece of equipment from Garmin!

This kit comes in three basic parts; a sensor unit, which is about the size of a matchbox, and two magnets about the size of your pinky nail. Several zip-ties are included for mounting purposes; the entire kit weighs at most a couple of ounces.

Installation is pretty straightforward, but do follow the directions carefully and don’t snug down the zip-ties until you’re sure you’ve got all three components just where you want them and have tested the system!

The sensor mounts to the left chain stay with a pair of zip-ties. Garmin thoughtfully added a piece of rubber padding to the bottom of the sensor unit, so it won’t rough up your fancy carbon frame or your paint job

A single zip-tie attaches the crank magnet to the crank, although I had to use a large (3/4″) shim on my FSA crank (which has a curved profile and a hollow back) to place the crank magnet in the proper position for the sensor to “see” it. The spoke magnet clamp has both a round hole and a square hole; make sure you use the right hole for your spoke profile! I mounted mine on a spoke directly opposite the tire valve, just to help keep the wheel in balance.

The sensor unit must be positioned along the chain stay such that it can “see” both the crank magnet as it passes by the cadence sensor (the round part on the side of the sensor unit), and the spoke magnet as it passes the speed sensor (the part that looks like a lever in the picture).

Testing is accomplished by pressing a small button on the sensor unit, which prompts it to flash a red LED, then a green one to indicate that testing is started. As pointed out by another reviewer, the LEDs are hard to see in bright ambient light; I’d recommend testing in a garage if possible. Hi-intensity LEDs would have solved this problem, although I suspect these LEDs were chosen for their low power consumption, so maybe it’s a smart design decision after all.

Once the test button is pressed, the next 60 revolutions of the crank should cause the red LED to flash when the crank magnet passes the sensor, while the spoke magnet passing the sensor should generate a green LED flash. If you saw the red/green flash when the button was pressed, but don’t see a flash as each magnet passes the sensor, chances are one or both magnets are not properly aligned with the sensor (there are alignment lines on the sensor and both magnets), or the magnets are passing too far from the sensor (this is the problem I encountered and solved with a shim).

When you’re sure everything is in the right places, snug the zip-ties and cut them flush. Then set up a screen (typically the Biking screen) on your 305 to display Cadence in one of the data fields, and go ride!

The handlebar mount and cadence and speed sensors went on quickly and worked flawlessly. However, when I first received the package in the mail, I was concerned I had ordered the wrong item. I have a Forerunner 305 wrist-mounted GPS, and all of the packaging for this product references the Edge GPS sensor, so I didn’t know whether or not this would even work with the Forerunner. There are very slight differences in navigating the menus to set up the cadence sensor between the Forerunner and the Edge, but the cadence sensor does indeed work very well with the Forerunner, so Forerunner owners order without fear!

The design could be improved upon as you need to have a magnet on both the crank arm and the spoke within 5mm of the sensor. This makes id difficult and may require some minor modifications on some bicycles (I needed to add a spacer between the crank arm and the magnet). Too much tilt towards the crank, risks having the arm of the sensor being caught in the spokes after a large bump on the trails or raod. I have known of other people being able to purchase a larger magnet to the inside of the pedal screw which allows the sensor to be farther appart. Other than that, it works great with the Edge.

It has worked flawlessly on my TT and road bike. I use one Edge 305 and switch between bikes. When switching, you must go to the “Accessories” menu and rescan for the sensor. You must set this up exactly according to the directions and check the LED’s in a dark room. You can not see them in a room with normal lighting. I do a fair amount of cadence based training and this cadence sensor has proved flawless.

What a great training tool! I did not have a computer for my bike, but have been using my Garmin Forerunner 305 while running for some time now. I decided to purchase the cadence sensor, and am glad I did, what a great training tool and it has helped me improve my riding significantly. Highly recommended if you are serious about riding.

I bought the Edge 305 w/o the cadence sensor thinking I don’t need it but I was wrong. Once you realize what the Edge can give you for information and you start to plot everything ( I use SportTracks )you became addicted and you want cadence chart too !!!

Furthermore, the sensor allows you to get speed even when there’s no GPS signal ( tunnel, cities, etc). A fact that overlooked.

Easy to install and the red/green light tells you if the unit senses the magnets which have to run pretty close to the unit. I would suggest you test the unit on your bike in a rather dark area to make it easier to look at the ligth on the unit.

I purchased this item and, based on the reviews I had read, I also purchased a battery for it because Customers had complained that the Garmins were being shipped with batteries that did not contain a charge anymore. However, to my surprise, the battery worked fin and I really enjoy having the extra cadence information when I download my workout histories. Works great with my ForeRunner 305. I highly recommend it.

Unlike the Polar speed/cadence units, the Garmin is made to work from the rear wheel (great if you ride an indoor trainer) and its creative design allows it to catch both speed and cadence from a single unit. Impressive. Just be sure to get a new battery – mine, like others, came shipped with a dead battery.

Installed cadence sensor for my edge 305. all went well until I got to the wheel sensor which is supposed to attach to the spokes with a threaded shaft and a plastic “nut” to tighten onto the spokes. I have a super light krysium wheel which have flat spokes. I could not attach the sensor because the spoke was too wide. my solution was to drill a hole in the spoke slightly smaller than the shaft of the magnetic sensor and thread the sensor on. I also could have drilled a slightly larger hole and used their plastic nut reversed on the back to hold the sensor on. Be advised.