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PostPosted: Thu Apr 10, 2014 1:05 pm 
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Joined: Wed Mar 17, 2010 12:04 am
Posts: 95
Hi,

I've got a powertap that I switch between two bikes, my training bike and my race bike.

I commute on my training bike and use cheap SPD pedals and heavy shoes. It dawned on me the other day that my power readings might be different between bikes as power is being measured at the hub, and there are fairly significant differences between the shoes / pedals / drivechain on both bikes.

My SPD shoes are over 300g each heavier than my race shoes, and the weight difference between my bottom of the range SPDs and my Dura-Ace's must also be significant.

But then I also have the weight advantage on the down stroke......

I know this is going to be marginal, but thought it would be interesting to discuss whether there is an impact?


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Posted: Thu Apr 10, 2014 1:05 pm 


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PostPosted: Thu Apr 10, 2014 1:16 pm 
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Joined: Tue Sep 20, 2011 12:54 pm
Posts: 387
Location: Haines, AK - Temporarily
I think you could easily have a different drive train loss between the two bikes that could account for an equal/more loss.


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PostPosted: Thu Apr 10, 2014 6:32 pm 
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Joined: Thu Feb 27, 2014 8:59 pm
Posts: 91
Location: Kingston, Ontario, Canada
Your race bike likely takes less energy to ride at the same pace.
While it is a torque reading and im not sure how cycling systems use it, you will need as much energy to pull the heavy pedals up as it (the weight) helps going down.


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PostPosted: Thu Apr 10, 2014 6:44 pm 
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Joined: Sat Aug 29, 2009 4:30 pm
Posts: 1530
Heavy shoes can really increase your output power, but only if you take your foot off the pedal during each "upstroke", So the weight of the upstroking shoe doesn't work against the gravity pulling down the downstroking side. Then you have to switch feet really fast for the next half of the crank rotation.

It takes skillful coordination.


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PostPosted: Sat Apr 12, 2014 2:17 pm 
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Joined: Tue Aug 03, 2010 6:29 pm
Posts: 589
I've noticed, although I can't say with 100% certainty, but I had about a 5 Watt difference in 20 min power when switching between shoes.

The lower reading came with a pair of Sidi Energy, heavy, nylon sole etc etc and the higher power output with a pair of DMT Radial, so, stiffer, carbon sole, lighter.

I don't think the weight had anything to do with it, probably the stiffness, if anything. I'm using a Quarq though, so I wouldn't see any drivetrain losses which are probably relevant in your case as well.

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