3-4 % is within the margin of error probably. Assuming you calibrated both PM's you could just have to live with it.

Make sure you have the right crank length in the P1 set up. 2.5mm difference would give you about a 5% error.

Seems about right considering drive train power losses and the measurement accuracy of both platforms.

That is incredibly close and within margin of error.

They key is to always test FTP on the same device. I used my Tacx Vortex for FTP until I got the Powertap hub. Now I use the hub reading for FTP. The hub is way more accurate. That said, the Vortex IS consistent. So as long as you train on the same device and it is consistent with itself, yo can use the data to your advantage.

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"If it costs you 30 minutes at Maryland so what" -dwreal

That's not a big difference at all!

My Stages vs Neo during a 20 min test and any intervals over 180 is 20-30w off. For example, intervals at 220w on Neo, Stages will be around 190w.

So is this sort of how your two legs match up?

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Genetics load the gun, lifestyle pulls the trigger.

I'm in a similar boat with myVector 2s (left side only)

I can calibrate both and recalibrate both after a good warming up period

The Tacx will ready 30-60 watts higher than my Vectors. It reads closer to where my old Quarq probably did. The vectors have always read low, and I've just learned my new lower zones

Funny that I thought I would move pedals from bike to bike. Yet to happen...

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Merge Multisport Founder & Head Coach
USAT Level 2 - Short & Long Course
Ironman Certified
Brevard, NC

As stated before, 3-4% is pretty good. I know Tacx claims a lower error for the Neo, but consider:

• The PT pedals also have a stated error in the low single digit percentage range. Therefore, it is possible both are within 1.5-2% of actual power, which is right between your two displayed value ranges.
• The pedals are 'upstream', so they are reading your power before drivetrain losses. I have no idea if Tacx calibrates the neo to compensate for that or not, but on the surface, you would expect power read at the hub to be lower than when read at the pedals.

Cool, congrats, your system works. You have two well regarded power meters agreeing with each other close enough.

Your second question - Yes, I calibrate my pedals before every ride. The Garmin automatically prompts for it, so it literally takes 5 seconds to do. The number varies between 32-36, with a mode likely 33. If it is not in the 30s, I probably had some weight on the pedals, so I'll repeat a few times to double check. Dig a little and you might discover whether that is an off-set, thus varying about 4 Watts. Or, it could be a multiplier. If so, calibrating may mean a >10% difference if it has 32 saved and on that day it should actually be 36.

I've got power tap pedals and stages crank arm. Pedals in tri bike and stages on road. I have been mostly on road bike over the winter on trainer. FTP up to 257. Got on tri bike and power was way lower. Decided to take pedals off and place them on road bike and compare the two. 2.5 hour ride and my pedals were 17 watts lower for the ride. It was interval based as well. Some of my z3 intervals were as much as 21 watts off(pedals being lower). I've called power tap about it and they said it's not a big deal...I dunno. Seems like a pretty big gap to me.

Thanks for the responses. I am of course not worried about the minor discrepancy, rather I am trying to gauge if this is a consistent difference that I can expect to see when I ride outside. I did a 20 minute power test on my TACX in JAN which was 329 watts. I did an outdoor 20 minute power test on a warm weather trip on my powertap pedals at 351 watts. When I got back I was having difficulty managing the new power zones suggested by my outdoor power test. I chalked it up to a sickness, indoor cooling problems and switching to my TT bike, but I foolishly forgot that it could be mostly equipment related!

I will be riding outside again soon, so I guess we will see what happens.

Mostly likely the issue is INDOORS vs OUTDOORS. Many people have difficulty generating the same power indoors vs out. For that reason... they have 2 FTP's (in/out).

351 is damn good BTW :)