Using Garmin Vector 3 Pedals to Troubleshoot a Bike Fitting Problem.

by Greg Pelican

Power meters have become a mainstream training tool for serious cyclists and triathletes.  The price has come down and there are many variations and manufacturers.  Garmin’s third generation Vector 3 pedals not only offers a great lightweight pedal and flexible solution for power, but also includes Garmin’s Cycling Dynamics which open up a whole new world of useable ride data.
 
This bog post explores the untapped potential of Garmin’s Cycling Dynamics.

As a techie, racer and bike fitter the potential use and application of Garmin's Cycling Dynamics fascinates me.  Yet when I search for relevant research from coaches of how this is being used I found next to nothing.  The truth is that the technology is still so new there is not much out there. 

Cycling Dynamics provide great info you can see real time on a ride or post ride:

• "PP" Power Phase Data: Power phase is the pedal stroke region (between the start crank angle and the end crank angle) where you produce positive power.  This also shows the left to right power ratio, and also left to right PP.
• "PCO" Platform Center Offset: Platform center offset is the location on the pedal platform where you apply force.
• Seated /Standing: The time spent seated verses the time standing.
  
  

In this blog post I want to share a real world example of how these new tools helped me to solve a Kona bound triathlete's bike fitting problem!

A member of our Segafredo-Trek Tri Team, Grace Plager, was advised by her coach to see me for a bike fitting after experiencing pain and loss of power in her left leg at Ironman UK.  Despite her bike issues Grace had a fantastic race and qualified for the World Championships in Kona this Fall!  I was excited to help her out.

I knew Grace from the club but never had worked with her as a bike fitter before.
When I put her Trek Speed Concept on the trainer I noticed that she had Garmin Vector 3 pedals.  This got me thinking... I asked her if she had her Garmin file from the Ironman race.  She did!  Grace even told me she noticed during the race that the "PPO" screen (Pedal Platform Offset) was way off.  Very interesting!  I was wondering about the left to right power balance as well.  When I reviewed the Garmin Connect file the average PPO for the left was +1.1 mm (towards outside of the pedal) and  for the right -4.1 mm (towards the inside) .  The average power data was also skewed at a 48/52 right bias.

When I dug deeper into the Garmin Connect file (see charts above) the actual data fluctuated a huge amount so the average didn't tell the whole story.  When I compared the PPO standard deviation from Grace's file to one of my own it was over 3X greater.  There were many points greater than 10mm off the center axis for both her left and right leg.  Her left to right power shifted much more than the average too, and the trend for both power balance and PPO got worse deeper in the race.

Next I had Grace ride on the trainer both and observed that her seat was very high and she was rocking her hips and reaching at the bottom of pedal stroke.  Motion capture and measuring with a goniometer confirmed that the seat was high.  We were able to replicate the PPO data from the race, and she felt pain in her left knee.

Now here is where it gets interesting...

I lowered the saddle to the correct height and had Grace pedal.  With the seat at normal height the PPO went to the center for both pedals!  After looking at the Garmin file, before seeing Grace ride,  I was suspected this might be a cleat position problem that could be solved by moving the cleat.  But clearly that wasn't the case or the solution!

When her seat was high Grace was rocking in the saddle which caused the uneven pressure to the pedal, and wide fluctuations.  It is likely that when she experienced pain in her left knee she shifted her position on the saddle to minimize the pain, and this also shifted her pedal platform offset.

This story has a happy ending!  The changes I made to Grace's bike setup resolved her pain and comfort issue and she is again training hard for Kona!  And for me I was able to use a new tool, Garmin Vector 3 and Cycling Metrics, to quickly pinpoint and resolve a fitting issue.  What was unique was to be able to use hours of race data to better understand the cause of the problem and get real time data feedback in the fitting studio to confirm the solution.

My brain is now wondering how oval Q rings effect the position and length of the Power Phase when pedaling.  But I digress, this has nothing to do with Grace, I'll save this for another blog!

In closing stop by one of our 8 stores and check out the new Garmin Vector 3 pedals.  I highly recommend them and Cycling Metrics as an excellent training and racing tool.

CONGRATS GRACE AND GOOD LUCK IN KONA!