This may be a stupid question, I completed the 20 minute ramp test and determined my FTP. I realized my settings for crank length were set at 170 mm rather then the 155 mm cranks which I am using.
I reset my pedal settings to 155 mm, my question is my FTP accurate or do I need to re do the ramp test?
No, your FTP will not be accurate with your current info.
- The crank length setting is critical to calculating power correctly.
Someone here may be able to run some math for you to estimate what it really is with the correct crank length. Or you will have to simply retest with the correct settings.
Your power numbers will be inflated by the ratio of 170/155 or 9.7%. To get to what it should be multiply your FTP by 155/170 or 0.912.
No need to redo the test.
Mike
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Ok cool, Thanks
So my FTP was 246, now my adjusted and more accurate FTP will be roughly 225?
My workouts will be substantially easier. Not sure if that’s a good thing.
Assuming you had a proper Ramp Test execution, it’s a very good thing. You may well have been looking at (and experiencing) workouts that were too hard and not in the proper training zones.
So “easier” is relative when you consider you were likely overdoing it (again, assuming that you tested at the 170mm length and then swapped to the 155mm length after the Ramp).
Great Thanks!
I have been making steady progress and just made the adjustment a couple weeks ago.
I love the program ! !
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Looks like one group mulitplied vs divided… since we effectively have 0.9 and 1.1 as “answers” for the adjustment amount for the test FTP. No idea which is right, but it should be reconciled.
We ran the numbers and to switch between the 170mm and 155mm cranks and you just need to multiply your earned FTP by 1.1.
(Edit to add @Bryce, so we can keep this in one “world”… TR)
I just noticed that
So which one is correct?
One would give me an FTP of 270 and the other would be 225. Pretty big swing.
I don’t know (and it’s the reason I didn’t run the math myself).
It might help to restate the inputs, so we can validate the calculations.
- Crank Length on the Physical Bike: 155mm
- Crank Length in the Pedals Setting: 170mm
So, you were pedaling with LESS length than the pedals used in their power calculation.
Does this summary sound correct?
Yes that is correct
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Given that the pedal knows the force and the cadence but has an inflated value for the lever arm, it must be calculating a torque value that is too high. As such it must be reporting the power as too high.
Mike
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Hey everyone!
Sorry for the confusion, I’d like to clear things up. When we ran the numbers yesterday, there was a miscommunication between me and Corey, our Senior Support Agent who worked out the conversion. We ran it again today, and the factor is indeed 0.912. Corey was nice enough to share all the reasoning behind it for those who are interested:
Sorry again for the mixup.
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How are crank length settings stored? I have the ability to change the crank length in my wahoo elemnt companion app or the powertap app. Is it then stored in the pedal? So if I connect the pedals to one phone and set crank length is that value stored so that when I connect it to another device (the one running TR) it will use the previously set value? Or does it go back to some default?
The length is stored in the pedals. That setting is retained until it is changed by any device with that ability.
One thing I found and Wahoo has yet to fix, is the Companion app only goes as low as 165mm. So if you have cranks that are shorter I’m guessing the reading on your Wahoo computer is going to be off.
I may well be wrong, but as long as you stay out of that setting page on your Wahoo computer, it should use whatever setting is applied to the pedals in a different app.
Meaning, if you set them at 155mm in the PowerTap app, it should keep and use that setting on the Wahoo.
I think that’s true even if you can’t make that change using the Wahoo device.
That would be good.
For now Wahoo has instructed me to set the companion app at 165mm. Not sure what the default setting was probably 170 or 175. They never said what effect it would have on the reading from the computer.