Drivetrain loss - n=1 study!

As part of transparency for Zwift racing, I’ve started dual recording power data for my rides. I use a Tacx Neo that doesn’t require any calibration and Powertap P1S pedal. Initial recordings below showed that the P1S read a good bit higher than the Neo, which I found unusual as DCR used these two as his gold standard for comparing powermeters:

Powertap ride #1
Neo ride #1

I fully degreased my chain, cleaned up my cassette and lubed with Finish Line Ceramic Wax lube. Here’s the second set of data after cleaning up the drivechain:

Powertap race #1
Neo race #1

Average power on both the pedals and Neo were pretty much identical over the race distance.

I’m pretty meticulous about keeping my bikes clean, but as my trainer bike doesn’t go outside the chain doesn’t get the same love as my road bike. Moral of the story? If you’re using a trainer as your power source, pay attention to your drivetrain. The losses can be significant.

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TL;DR: freshened up chain on trainer was good for 15 watts. Good to know…

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Interesting, I only use the Hammer (since I have a powertap hub on the road) so maybe I should be more diligent with the drivetrain. Maybe those 120% vo2 intervals are really higher, or at least I can tell myself that when I stink at the 2.5-3min versions lol

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While DCR clearly relies on P1 pedals for comparing against other power meters quite a bit, his stance on single-sided power meters of any variety leans more toward “it’s tough to recommend the left-only approach with other options in the same price ballpark that fully capture all power.” I agree, for analysis of this kind I’d want to see real “complete” power at both ends of the drive train compared.

Looking at your first ride, for example, I see a lot of differences that look like they could simply be inaccuracies of a single-sided power meter; I also see a lot of stuff that’s hard to eyeball. I wonder if you could try throwing in the data files for these rides into the DCR Analyzer to make for a more direct, second-by-second visual comparison.

I’m not saying the drivetrain cleanliness/lubrication doesn’t matter, just… this comparison leaves a lot of questions.

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Absolutely granted there’s probably a lot more to it than just the drivechain. Reason I posted this was lots of people talk about drivechain losses with measuring power at the hub. Only thing I did different was really thoroughly clean the drivechain. I’ll be recording all my races on two sources from now on. I’ll post some other rides in time👍

There is a measurable difference. I ride with P1’s and powertap hub outside and I see up to a 10% drop in power when measured at the hub. Below are the 2 recordings of the same ride. You can see each HC climb I did, the difference in power kept increasing and really increased after the 3rd. I was using a completely cleaned and degreased KMC chain with squirt lube.

Dual sided P1’s
Powertap GS hub