Probable old question, but does anybody know what AVERAGE wattage is lost in the direct drive vs a dual crank measurement . I’ve heard that when going from the Tacx Neo to a crank based power measured in a bike it’s about 10 watts due to the drivetrain loss.?
Any powermeter is different so to say there is an average difference is difficult . I recorder the same ride with my stages and tacx Neo and found virtually No difference except in sprints Where the stages Goes up quicker. My suggestion is to compare the same ride with Dc rainmakers analyzer tool than you know the difference beteren your powermeter and the neo.
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I’m just looking for a average watteage lost due to drivetrain. I know it dependes on lots of things , chainline, condition, lubricants, derailures etc. but due to the method and where the power is measured,I was thinking lots of folks ride the Neo, and have power meters on their cranks so I’m looking for feedback from those folks, if they noticed any measurable difference. That’s all. Splitting hairs I know.
I see . My stages Measured 2 W higher on a 200w average ride So not a big difference
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I have a Stages left only power meter which appeared to measure a consistent 15-20W LOWER than my Tacx Neo. From conversations with a much more knowledgable friend this is a pretty common discrepancy. I would’t use two different power meters to measure the efficiency loss between two points in a system unless you’re sure that they are calibrated together and have matching power curves.
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My Assioma’s read the same as my Neo. (Within a one or two watts)
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One of them has to be off.
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My Quarq PM’s are very close with my Tacx Neo - usually with a watt or two.
I’m planning to put my mountain bike with a Stages single arm PM on it sometime later this season, so it will be interesting to see how close it is.
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Same for my Assiomas and Drivo II.
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My Stages is miles off and all over the place over and under, havent checked it lately as I now have a aero Garmin mount on road/trainer bike and it wont broadcast past the stem, so dont use it anymore.
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Dura Ace SRM PM, Praxis Ceramic BB. Ceramic speed pulley, Dura Ace chain. Ultegra cs. Squirt chain lube. Vs Tacx Neo-1 DSC_0073_BURST20190311194156548|281x500]
(upload://8q1c0jTKht3f2hLkkZ8RY0UI0WP.jpeg)
Same here - Neo and Assioma agree almost exactly. I did have a Stages left side only that read 10% less than the Neo but subsequent tests with Vectors and now Assioma revealed this to be due to leg imbalance.
Pure visual comparison, but I got very close results from my new Neo 2 against my P1 pedals. Maybe 4w separation around 180w (2-3% difference with Neo 2 higher). So I think they are close.
Performed a ramp test on Friday and was curious about this topic as well when looking at the results. Power2Max crank power meter and Tacx Neo were separated by 2.5% during the highest recorded 1 minute step, 10 watt difference, the P2M reading higher than the Neo. Does anyone have thoughts on if this is a dependable method to determine improvements/degradations in drivetrain efficiency?
Well, as I said above, my Neo 2 reads HIGHER than my P1 pedals (maybe 2-3% based on simple comparison). Moderate clean chain with good lube. So it’s not really and solid conclusion, but opposite direction of variation.
Just out of curiosity, what are you going to do with the numbers? You could argue the best place to measure power is after the drivetrain? Thinking about it in a different way - HP vs BHP? A manufacturer might quote HP as the figure will be higher and more attractive to the coonsumer but what really matters is BHP, ie the power at the wheels…
I have a Neo and two different Power2Max Type-S power meters. Sometimes the numbers are the same, but in general they are within 3%. The Neo is usually the higher number, but oddly not always.
Let’s go with 3%. At 100W, that is 3W (i.e., 100W vs 103W). At 300W, that is close to 10W (i.e., 300W vs 310W)
That said, if someone say their power meters differ by 10W, you need some context. 10W sound like a lot, but in the context of the stated accuracy by the power meter manufacturer it may be well within spec. Is it 10W at 100W which is really bad? or is it 10W at 400W?
Another thing to consider is single sided power meter offerings such as Stages, 4iiii, Pioneer, etc… I believe the single sided meters are always left only (L). Power is measured and then doubled on that side. If that leg is stronger or weaker by say 3%, then after doubling you have 6%. At 200W, that is +/- 12W. At 300W, that becomes +/-18W.
Many riders find when going from single-sided power to dual-sided that their FTP changes substantially. It is probably like going from a dumb trainer using an estimated power based on the trainer’s power curve to a Neo. The change is big and usually downwards. 
Think of it as a reality check?
BUT in the context of TR, FTP is a number to help you set your workout levels. Do not get hung up on the actual number. Use the same power meter for your workouts that you used for your FTP test. If you have a smart trainer and a power meter on your bike, go w/the on bike power meter. Then, your inside numbers and outside numbers will have the same meaning to you.
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Difference in percent measured could indicate an improvement in friction losses due to equipment choices, for example a waxed race day prepped chain etc. If it could be reliably measured to the individuals setup trainer/powermeter. As you state yourself to more closely align BHP and HP.