Garmin GSC 10 Speed/Cadence Bike Sensor

• Cycling speed sensor for select Garmin wrist-mounted personal trainers and cycling computers
• Self-calibrating, wireless design measures both cycle speed and cadence in pedaling strokes per minute
• Provides up-to-the-minute feedback or captures results for later workout analysis
• Compatible with Garmin Edge 305, Edge 305CAD, and Forerunner 305
• Attaches easily to any bicycle; 1-year warranty

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!

Buy Garmin GSC 10 Speed/Cadence Bike Sensor Now

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!

Read Best Reviews of Garmin GSC 10 Speed/Cadence Bike Sensor Here

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.

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I'm a big fan of Garmin computers, and especially the mapping features of the 705. If there were any other computer that did what theirs does, the GSC-10's sensitivity to water would be an unacceptable design flaw. It's supplied with zip-ties (requiring a cutting tool to remove it), yet it won't tolerate even a small amount of water such as from washing one's bicycle or riding in light rain for over an hour. Garmin is honorable and will replace drowned GSC-10's under warranty. (I'm on my third one.) But it's really unacceptable to have to remove the sensor any time I wash my bike and any time rain is anticipated, and to have to do without it for a couple of weeks, or longer, any time I get rained on unexpectedly. They're replacing so many of these that, after a wet spring in the eastern USA, my last warranty replacement was backordered for five weeks.

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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.