Power output differences on different bikes

VS1 · #1 08-18.-2007

Hi,

I am using a polar power output on both a carbon road bike, and on an aluminum CX bike with slick tires;

The road bike setup is full dura ace 10 spd with Ksyrium SSC SL wheels while the CX (using slick tires for this purpose) setup is: 9 speeds, XT or Ultegra cassette, ATR rear der. crank-brothers egg beater pedals (using shimano mtb shous);

I use this power system rotationally on these 2 bikes and C o n s i s t e n t l y I get higher power readings on the road bike (like when trying to go for power max, or 30sec highest avg.)

Any idea what can be the reason for that difference? I thought that naybe the diference between the KEO carbon and the Eggs/heavier shoes may contribute, and maybe the drivetrain on the cx is not as efficient as the 10spd D/A..

Will be happy to get an explanation to that. Thanks.

jbvcoaching · #2 08-18.-2007

Did you weigh each chain?

VS1 · #3 08-18.-2007

Sure. both bikes accurate details are set in 'bike 1' and 'bike2' (chain weights, length and chainstay length)

jbvcoaching · #4 08-19.-2007

I always look at measurement issues first, especially with different PM's (different power units, chainstays, chains, etc).

Could be the flexier (presumably) MTB shoe/pedal system. How do power numbers compare for more moderate power levels, 5 minute intervals, 20 minute intervals, NP for 2+ hour training rides? I would expect the MTB shoe/pedal issue to be exacerbated at sprint power levels, but that's just a WAG based on my own experience (and I don't even use a PM on my 'cross bikes).

VS1 · #5 08-19.-2007

Thanks; Well I notice this diff. issue on those sprints so maybe there is some losses there; I can feel the noises and little movements of the cleats in the ckrank-brothers pedals (which might not be in very good shape too)

the mtb shoes are with carbon soles too but the pedaling with the KEO is certainly smoother and more efficient.

These by themselves don't quiet seem to me as as complete explanation for this phenomena nut maybe part of it.Thanks again

p.s. shouldn;t be a problem with measurement units

lanierb · #6 08-19.-2007

Quote:

Originally Posted by VS1

Hi,

I am using a polar power output on both a carbon road bike, and on an aluminum CX bike with slick tires;

The road bike setup is full dura ace 10 spd with Ksyrium SSC SL wheels while the CX (using slick tires for this purpose) setup is: 9 speeds, XT or Ultegra cassette, ATR rear der. crank-brothers egg beater pedals (using shimano mtb shous);

I use this power system rotationally on these 2 bikes and C o n s i s t e n t l y I get higher power readings on the road bike (like when trying to go for power max, or 30sec highest avg.)

Any idea what can be the reason for that difference? I thought that naybe the diference between the KEO carbon and the Eggs/heavier shoes may contribute, and maybe the drivetrain on the cx is not as efficient as the 10spd D/A..

Will be happy to get an explanation to that. Thanks.

As a former polar power user, the obvious answer to this is that the Polar is super inaccurate in practice.

VS1 · #7 08-20.-2007

I agree that it is not highly accurate* but a one-direction deviation must have additional explanation..</SPAN>

lanierb · #8 08-20.-2007

Quote:

Originally Posted by VS1

I agree that it is not highly accurate* but a one-direction deviation must have additional explanation..</SPAN>

The additional explanation is probably something to do with the polar installations on the two bikes. These things can be really hard to troubleshoot though. I tried over and over on one of my bikes before finally giving up. If it's consistent then you could always just apply an adjustment from one bike to the other. If it's different only in some gears, then your best option is probably to fiddle with the installation and chain settings etc. I highly doubt the difference is anything real.

VS1 · #9 08-20.-2007

Thanks.

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