Free Motion Roller Power Loss

It's certainly possible that some energy is being spent moving the frame. Are these the same rollers (now mounted in a new frame), or a completely different set of rollers? If the latter, it seems far more likely that the difference you're seeing is just due to different bearings with different frictional resistance.

wiredued said:

Would a powertap be accurate on free motion rollers? Thanks

There is no reason I can think of why not.

They are the same rollers.

s288.photobucket.comkiwiwireOpen ↗

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They work alot like these home made FMRs

frenchyge said:

It's certainly possible that some energy is being spent moving the frame. Are these the same rollers (now mounted in a new frame), or a completely different set of rollers? If the latter, it seems far more likely that the difference you're seeing is just due to different bearings with different frictional resistance.

wiredued said:

The rollers I've been using gave me average speeds of around 19.6 to 20.6mph for a 3x20 but when I changed them to free motion rollers my one hour ride is about 17.4mph to 18.4mph. Is there power being spent moving the roller frame that is not showing up as speed? Would a powertap be accurate on free motion rollers? Thanks

Some possible explinations,
Something is now rubbig against one of the drums or belt.
Tire pressure is a little bit lower (it doesn't take much)
You're standing up more now that it's easier and during that time your speed drops thus lowering your average speed.

On the same rollers if all of the above are taken into account, i don't recall seeing more then a half point difference between averages before and after, the roller assembly really doesn't "eat" speed up, when you're in the saddle the assembly should barely be moving.

And if you're losing power? then you're just not pedaling hard enough. Losing speed and losing power are different statements, but they are both affected by the list above.

Ok, I gotcha. If the whole setup is moving back and forth a lot during the ride then there is definitely energy being expended flexing the bands -- similar to working against the suspension of a mountain bike.

As far as PT accuracy goes, I think you're asking whether the PT is still truly capturing your physical output correctly. IOW, whether the extra energy expenditure into the rubber bands is being counted by the PT or bypassing it? If that's truly the question, I think the answer depends on how you're riding, and is probably a combination of the two. Roughness in the pedal stroke itself which causes surges in wheel speed is probably handled by the PT. Bouncing due to movement of your body (if any) could represent effort that is not being captured by the PT. For example, if you were to sit on the bike without pedalling and just rock the bike seat forward and backward by contracting the abs/hips then there would be some work there that's not transmitting through the PT. My gut feel is that any rocking due to body motion is probably the smaller effect during seated motion (much larger during sprinting or pushing out of the saddle), but that's just a guess.