New Bike/New Ergomo + Old bike/Old Ergomo = Inconsistent Data

Discussion in 'Power Training' started by Geoff2010, Feb 6, 2007.

  1. Geoff2010

    Geoff2010 New Member

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    Greetings everyone,
    I just got a new bike, and with the bike I ordered a second Ergomo
    BB. My old Ergomo BB will be used in my TT bike, while the new one is
    for my road bike. Currently both bikes are built up, so I decided to
    do a quick test to make sure both units were giving consistent data
    readouts.

    My test protocol was as follows:
    1 min @ 90RPM in 39/25 (record avg power)
    1 min @ 90RPM in 39/23 (record avg power)
    ...
    1 min @ 90RPM in 39/13 (record avg power)

    I did the exact protocol on both bikes and came out with VERY
    different numbers.

    Code:
    TT Bike (old ergomo)
    Gear    Cadence Power
    39/25   91      94
    39/23   91      114
    39/21   90      131
    39/19   91      155
    39/17   90      196
    39/16   91      221
    39/15   90      235
    39/14   91      261
    39/13   90      292
    
    Road Bike (new ergomo)
    Gear    Cadence Power
    39/25   90      117
    39/23   91      123
    39/21   90      141
    39/19   91      200
    39/17   90      227
    39/16   90      260
    39/15   91      291
    39/14   91      315
    39/13   90      336
    
    Difference:
    Watts   Percentage
    23      19.66%
    9       7.32%
    10      7.09%
    45      22.50%
    31      13.66%
    39      15.00%
    56      19.24%
    54      17.14%
    44      13.10%
    
    The guys who installed my new BB followed all the instructions
    including the wire exit angle, torque specs, refacing shell, etc. The
    BB on my TT bike has been taken out and put back in a couple of
    times...the wires are coming out properly, but I am not sure how
    smoothly the BB screwed in last time.

    In a perfect world I would like to know my actual power, but I am not
    overly concerned with it. I am more concerned with having my TT and
    my Road bike give me consistent data for training purposes. I suppose
    my question is two part:

    1 - how do I know which bike is giving the "accurate" readout?

    2 - how do I manually adjust the incorrect unit so it provides good
    data?

    Thanks in advance.
    Geoff

    P.S. I know most people use a PT for calibration purposes, but I do
    not currently have access to one.
     
    Tags:


  2. bikeguy

    bikeguy New Member

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    Where did you test the bike? Actually riding, or on rollers (stationary)?

    -bikeguy
     
  3. Geoff2010

    Geoff2010 New Member

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    I performed the test on my Blackburn trainer, using the same wheel/tire on both bikes with the same number of "screws" of the resistance unit.

    -Geoff
     
  4. MiSzA

    MiSzA New Member

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    I assume that you set the Bike1 and Bike2 thingy- correct?

    Because each BB has it's own Calibration Number (printed on the BB) you need to input it in the computer unit under "Settings" / "Bike" - K-factor.

    The manual also suggests that you do the offset procedure each time when switching from Bike1 / Bike2 - also I suggest you do the sw upgrade.
     
  5. Geoff2010

    Geoff2010 New Member

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    Yes, bike 1 and bike 2 are both set up with their factory supplied k-factors. I have also done the offset test for both bike 1 and bike 2. The firmware I am running was downloaded from the Ergomo website yesterday.

    I convinced one of my buddies to hook me up with his PT for the night, so I'll hopefully have "accurate" numbers on both my bikes by morning.

    One side question: If the install on one (or both) the bikes isn't quite right, and that is the cause of the bad data, is it possible that there may be some shift or something that will cause the manual K-Factor adjustment to eventually drift from accuracy? Am I going to need to borrow someones PT once a month to make sure my Ergomo isn't wrong???
     
  6. jetnjeff

    jetnjeff New Member

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    Which Blackburn?

    The Ball unit resistance drops dramatically as it heats up and I have no idea if it ever levels off. It also picks up quickly if you let up a bit and it cools even a fraction.
     
  7. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Good deal, that's much better than trusting trainer calibration tables. Take the time to do a weighted torque test (stomp test) on the PT and manually zero the torque before each test ride. That way you'll have a reliable measure of the PT accuracy and can really dial in your Ergomo power. Here's a link to the PT stomp test: http://midweekclub.ca/powerFAQ.htm#Q23

    If you've got a funky Ergomo install and it isn't changing with time(e.g. loose cups) then I wouldn't expect it to drift with time. What I'd worry about are nonlinearities across it's power measurement range. IOW I'd worry that a bad install puts unintended torque on the Ergomo BB causing it to read differently at different power levels. If that's the case then tweaking the K factor for one power level won't correct power across the board and may even cause more problems at one end of the range or another.

    I started power training with an Ergomo Pro but eventually switched to PT after scoring some screaming deals on race and training wheels. But I ran both side by side for a few weeks and the displayed power differences(they tracked nicely, but the Ergomo always read 10 - 20 watts higher as expected) didn't change during that period.

    I'd put on the PT wheel, zero the torque, stomp test it (static weights are better, but you might not have 50 pound weights lying around) and figure out the PT error. For the stomp test I just strap a toe strap very tightly around the rear brake clamping the brake shut and locking off the rear wheel, that frees me up to balance on the pedal without having to hang onto the brake for dear life. Then test each Ergomo bike (repeating the PT setup each time) at several different power levels for a minute or so at each level (the Ergomo has built in 5 second rolling averaging, the PT is selectable and should be set to 5 seconds for comparison sake but a mid interval average from a minute long steady block should agree). Take into account the PT error from the stomp test and if the offset stays the same at low, mid and high power settings then I'd adjust the Ergomo K factor accordingly.

    If one or both Ergomos read very differently at different power levels I'd try a reinstall or contact Ergomo about repairs.

    Good luck,
    -Dave
    P.S. FWIW the original Ergomo instructions placed the acceptable wire exit angle from ~8:00 - ~11:00 when viewed from the left side. They've since revised that to exactly 9:00, if your LBS followed the older instructions there could still be some error there.
     
  8. Geoff2010

    Geoff2010 New Member

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    Thanks for that great post. I used the PT to calibrate my Ergomo. I think they are pretty accurate, but I am seeing some weird stuff. The Ergomo and the PT line up nicely until about 320W. Then the Ergomo seems to fade off a bit from the PT... I have two theories:

    1 - What you stated - the weird install is causing non-linear power readings.

    2 - I am slightly right leg biased when the going really gets tough... I am right handed, so this is a definite possibility, right?

    If it still feels "off" when I am training I'll have the LBS re-seat the BB to see if perhaps it was a bad install. If that still doesn't fix it, i'll send the unit back to Ergomo.

    -Geoff
     
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