Thanks Kurt. Why do you say indoor trainer speed is inaccurate? Isn’t it measured off the wheel speed sensor??
Sure, if you have a speed sensor on your rear wheel, it’s measuring speed in the same way as it would outdoors. The issue is the resistance. If you’re running a wheel-on trainer, the speed isn’t accurate compared to outdoors because the resistance isn’t what it’ll be in the real world. For example, when you were putting out 50 watts and showing 14mph, the resistance on your trainer was probably very low. Speed will change relative to power each ride if unless you keep the exact same resistance on the trainer.
If you’re running a direct-drive trainer (Kickr, Hammer, Neo, etc.), the speed sensor on the trainer should be disregarded as it is based on a whole host of different inputs, none of which translate well to actual speed outdoors.
In summary, indoor trainer speed is mostly useless for any kind of practical application. The only “real” data you’ve discussed in this thread thus far is what your Vectors are giving you, so you should be trusting those. As @mcneese.chad said, you need to do another test using the Vectors as your power source and train based on those numbers going forward. There’s a good chance your real power will be lower than your Virtual Power, but that’s nothing but mind games. If your virtual FTP is 400W or 200W, none of it was “real” anyway. Now you can know where you truly stand and can build from there. Ride on!
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But the math is done on sensors that are measuring a speed sensor on a system that has many unmeasured variables.l (fluid viscosity, wheel tension, tire wear, tire PSI, etc…)
Power meters can vary from each other and certainly from smart trainers but they “should” nearly always be more consistent and used (when available) rather than virtual power.
Thank you for all this info. Does anyone know why the V3s would read more accurately outdoors than indoors on the trainer?
- What makes you think inside vs outside data is different in the first place?
The power meter pedals are measuring force and velocity, and outputting a power value based on the known variables and calibration applied in the factory. Assuming normal use with a proper zero offset applied at the start of each ride, there is no reason to expect different power data inside or outside.
They measure the input from the rider and give power data. Nothing more, nothing less.
There is a fundamental problem is trying to use the power meter data against the Virtual Power meter data that should be ignored and avoided. VP is not a practical tool to use with respect to a real power meter.
They don’t, and it seems you are not grasping the point here. There is no valid comparison between the Vectors and Virtual Power. Virtual Power is a guess, an estimate. Vectors are actual power data. The two are apples and oranges and should not be compared for “accuracy.”
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I guess what I am trying to say is, using only the V3s for power data 100w inside on the trainer has a much different RPE than 100w outside on the road. Or maybe I am just crazy.
Inside perceived exertion is almost always higher than outside. Lots of reasons: cooling and motivation chief among them. It’s not uncommon for new indoor riders to experience significant differences between indoor and outdoor perceived exertion, particularly if they haven’t addressed cooling indoors.
What type of trainer are you on?
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OK, RPE at a similar value is a VERY different discussion.
This is the whole inside vs outside issue. These are not concrete, but touch on the main issues:
- Cooling
- Motivation
- Bike vs Trainer Motion (or lack there of)
- Momentum and Inertia differences
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You so fancy. 
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HA, I try 
Just trying to give more depth and use existing references when possible.
This is what I get for responding on my iPad or iPhone while, er… “recovering” on the couch all the time.
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Hey, we are on the very same page and I appreciate your thoughts here and elsewhere. Always great to be able to rely on the great knowledge and support from so many of the forum members. Gotta love this place 
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Thanks for the help guys.
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My experience with virtual power. I started TR in Nov. 2019 using a Cyclops Fluid 2 dumb trainer with wahoo speed and cadence sensors. The first ramp test FTP was 217 which I thought was pretty low as I had been using Sufferfest prior and their virtual power had me in the 250’s. Knowing that virtual power was not real power, and only really concerned about setting proper training zones, I just accepted that and went forward with the mid-volume plan via plan builder. Fast forward to August of 2020 and I was setting at a VP of 242. In early September I was able to afford a Saris H3 smart trainer with legit power. I immediately thought it was way easier at the 242 FTP and per a Zwift race calculation, I raised it to manually to 251. Today I did another ramp test after completing another round of SS base and my FTP is 277. I realize the difference between VP and real power, but I am still surprised at the amount of difference. I can’t believe it was a 35-watt difference from the 242. Bottom line if you can afford it get a smart trainer with good power numbers or a power meter. Virtual power will make you think you are weaker than everyone else and it will eat at you!! At least if you are using the Fluid 2. Thank you, TR!!