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180lb rider on tri bike wattage @20mph?

AlexChejlykAlexChejlyk Posts: 2

I'm looking for some numbers to get an idea of how much to adjust my meter's multiplier.
I'm 5'8" (173cm) 180lbs (81Kg), ride a 2008 Cannondale Slice in aero position and have 50mm carbon wheels.
Are their riders who are a similar size willing to share their wattage numbers?

The situation:
I have a 4iii power meter that reads low. I know this because I train with my wife and she consistently has higher power numbers when riding at the same speeds. She weighs 55lbs less, has a newer bike (2016 QR PR6) with Zipp 404's and is more flexible, so she has a better riding position. We'll do a ride averaging 21mph, equal pulling efforts. I'll show 138 watts average, she'll show 139 watts.

My 4iii is consistent, just reads low. There is a multiplier in the app to help compensate so I do have a 'fix' once I know how much to compensate.



  • cougiecougie Posts: 22,512
    How do you know hers isn't high ?
  • cyclecliniccycleclinic Posts: 6,865
    maybe your wife is more powerful than you think. seriously though position is everything with power. you may actually be more aero than your wife. other riders numbers mean nothing without knowing the CdA.

    Also if a power meter is off you cant correct it. it may not be off. the way is to some testing in an indoor velodrome with a known good power meter and your current one.

    why not instead of trying to beat your wife at the power game just see your numbers as relative to you and your wife's relative to her. comparing power numbers is a pointless exercise in futility. it does not inform your training comparing to someone else. -wheel building and other stuff.
  • Perform a static slope calibration test on the meter. IOW validate the torque readings on the meter matches actual known applied torques.

    Comparisons to other rider's power output are mostly meaningless.
  • super_davosuper_davo Posts: 1,098
    I have a 4iii and I also think it reads low.

    When I use it on a bike on my Elite Direto I can be at 250 watts on that and it reads 200 on the 4iii. Part of that is a (known) leg imbalance, part is the 4iii reading low.

    Not a major issue if you're only using the 4iii, but a definite problem if you're following a plan with indoor / outdoor sessions (especially as the bike I normally use on the turbo doesn't use the 4iii).

    You can use the scale factor on the app to align but it doesn't necessarily need the same correction all the way through the power range e.g. you might be 10% out at 100 watts and 20% out at 200.

    I've aligned mine based on power at threshold as that seemed most sensible thing to do. But I've also decided the 4iii is not accurate enough for my needs and I'm looking at upgrading in the near future.

    My advice would be to borrow a direct drive smart trainer and use that to calibrate; it will be the only chance of getting it remotely correct. And even that isn't that important unless you're attempting to compare it vs something else.

    If you just want higher numbers then set the scale factor at 1.5 which is the highest it goes!
  • paul2718paul2718 Posts: 471
    We'll do a ride averaging 21mph, equal pulling efforts. I'll show 138 watts average, she'll show 139 watts.
    Numbers smell low to me, and are effectively the same.

    In the absence of other sanity checks, try riding up a reasonably steep hill at a constant average indicated power and do the physics based on ascent and weight. The power meter must read more than this lower bound, and the difference in required power between you and your wife will be much greater. You will probably need to do this a number of times to have any confidence in anything.
  • fenixfenix Posts: 5,437
    Way too low I think - but if you are drafting each other it's going to make them lower anyway.

    Just noticed OP hasn't been back since he posted.
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