Speed and Cadence Revisited
19 May 2009

Speed and Cadence Revisited

Mid last year I purchased a Garmin GSC 10 Speed and Cadence sensor

19 May 2009

Mid last year I purchased a Garmin GSC 10 Speed and Cadence sensor which I mounted for a short time on my KH 29’er. A recent thread on ‘Quantifying the effect of unicycle gearing and crank length on speed‘ inspired me to fit the GSC 10 to my KH36 GUNI to learn more about my natural spin and what effect the 2 speed hub has on it.

As noted in my initial GSC 10 post, the design of the GSC 10 isn’t great leaving it overly prone to damage, imo anyway:

Garmin’s GSC 10 Speed and Cadence sensor unit is quite large. The mounting system – a rubber strip on the ‘back’ of the unit and zip ties – doesn’t stop the unit rotating around unicycle fork. There is also a longish reasonably fragile adjustable arm that comes out of the unit for the wheel/speed sensor. All up the design of the unit makes it prone to being damaged e.g. being bumped during a UPD and subsequently fed into the wheel. Due to the deep channeling in the back of KH Moment cranks, their Q factor and how the pedal/cadence magnet fits a home made spacer is needed

This time around I used a small rubber spacer underneath the cadence sensor positioned on the back face of the crank so it would pass close enough to the main sensor unit. I also used a dab of glue between the rubber pad on the unit and the fork, to hopefully help prevent the unit rotating around the fork and moving upwards and becoming loose due to how the fork tube narrows. Zip ties all round, job done!

To confirm everything is positioned correctly rotate the wheel. A small LED on the GSC 10 unit blinks red each time the crank magnet passes and green for the wheel magnet. Check! Though the Garmin 405 automatically detects the GSC 10 via ANT technology which works great all round, for any cadence data to be recorded during a ride the GSC 10 must be activated in the 405 menu system. It’s an easy thing to forget to do, or accidentally set to Off (DOH!). An additional icon appears at the bottom of the 405 screen during ‘Training’ to confirm the watch is set to receive data from the GSC 10.

So with GSC 10 fitted and the 405 watch  set to receive data it was time to head off on a short test ride.  The dirt loop I chose to ride is generally flat with a couple of gentle climbs and descents. It’s close to home and I ride it often, either as a warm up before a ride or cool down afterwards. I didn’t ride hard by any means, and kept within a comfortable… okay lazy … spin 🙂

It’s always interesting to see a ride presented as data. While the test ride was short and cruisey  (ok LAZY) the graph is typical of the pattern for the ride.

Cadence Speed Revisited

Cadence Speed Revisited

Laps of the loop in 1:1 gear were:

  • Significantly slower speed vs 1:1.5
  • Higher average cadence vs 1:1.5
  • Less variation in speed and cadence vs 1:1.5

Not especially surprising, and riding hard those differences would widen much further imo. What the graph doesn’t capture of course is the subjective experience of riding. I find it much more enjoyable to ride around the loop in 1:1.5 (though more challenging) vs spinning away in 1:1.

The only missing data from the story going forward is heart rate. In my MTB days I often wore a Polar Heart Monitor which ended up being sold years ago. Given the 405 watch already supports heart rate capture I might look into how much the chest strap costs.

The immediate mission with the GSC 10 is to use the data to help smooth out and speed up my riding and spinning. I might think they are improving, the data will let me see what is really happening. I hope to fit in some longer rides on the GUNI in the coming weeks, will be interesting to see the data!

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