I am currently seeing a massive gulf between inside and outdoor power numbers and I’m hoping you can help me work out what’s going on. I just started training with a power meter outdoors after a couple of years of using a smart trainer inside.
I did a TR ramp test the other day, and came out with a 243 FTP (according to my Wahoo Kickr Snap).
Then today I did a hilly club ride, quite staccato pacing - 3hr 30, avg 196 watts and TP gives me an NP of 267 watts. IF is supposedly 1.12 ( all this measured using single sided Favero Assioma pedals).
This two results seems mutually incompatible, right? Nobody’s physiology allows them to hold a NP 10% above FTP for 3.5 hrs.
I can think of two plausible causes:
One or other power meter is way off. They’re both calibrated but maybe one of them is just fundamentally broken.
I am absolutely terrible at testing FTP indoors
Have any of you ever experienced a gulf in numbers like this? Is there a way to test for what the problem is? If I have two power meters that disagree, how would I tell the accurate one?
Background to the numbers: I’m a tall guy, 92kg, 30 years old and moderately trained (12 years of endurance sport, mostly rowing and running, have dabbled in cycling on and off but only started training for it as my primary sport earlier this year).
A few issues, you didn’t do the same test indoors and out, you didn’t use the same power meter for both and both are estimations of ftp.
You can record both power sources and see if there is an offset and what that difference is.
Cooling makes a massive difference as well.
Do an ftp test using the same power source both indoors and out if you want to be sure that there is actually a difference is ability to perform inside vs outside.
I have an athlete that is similar size to you and has the same problem. His problem is two fold: he is using a different power source indoors. And he is extemely gifted anaerobically and not well trained aerobically. This leads to lots of power spikes and then coasting/sitting in that inflates NP in group rides outdoors.
The first thing I’d recommend is putting the assiomas on the bike indoors or using it as your source for zwift and see if that narrows the difference some.
Fwiw, most people will see some gains moving from indoors to outdoors even if using the same power source for a number of reasons (cooling, gravity, motivation, etc). If you track data very closely, you can use an indoors and outdoors ftp to keep things a bit more accurate.
What device/head unit are you using to record data from the assioma?
There are some settings to check in the app about doubling power on the Assiona UNO - depending on the device you link your pedals to then this needs to be either on or off.
Most devices take the single power reading and double it but some require the pedals to do the calc and send the doubled reading.
Could be that you have the setting set you “on” when it should be “off”.
There could be a lot of factors here, which could easily account for the difference:
You are using a one-sided power meter on the bike. If you have a large left/right imbalance, this alone can account for the difference. E. g. if your power is measured on the left side, a 55-45 imbalance means your power would be overestimated by 10 %.
You are using a Kickr Snap, which means its power numbers also depend on factors like tire pressure. Even direct drive trainers can become inaccurate over time. My Elite Suito’s power readings are markedly different from my Quarq DZero’s. Ideally, you want to use only a single power meter, i. e. I recommend you use Power Match (where TrainerRoad will use your Assiomas’ power numbers and ignore those of the Kickr Snap).
Cooling is another factor. If you only have a small fan, that’s definitely a limiting factor. Many people benefit from having two powerful fans.
Fueling can also be a factor.
What I would do is the following:
Use Power Match and forget about the Kickr Snap’s power meter. That also eliminates tire pressure as a variable.
If possible, upgrade your Assiomas to a dual-sided power meter. If you can’t do it now, I would aim for that.
Use threshold workout to validate your FTP. I would not go down the rabbit hole of FTP tests, IMHO it isn’t worth it. If you are right at your threshold, you will be able to feel it if you are going over a by just a few Watts. I’d try something like 4 x 10 minutes at threshold or over-unders. During the over bits, you should feel lactic acid accumulate in your legs. If you don’t, your FTP is set too low.
I have noticed something similar and have almost the exact same setup. The only difference is that my Assiomas (single sided power) are modified with SPD pedals as I ride XC exclusively outside. And my head unit is a Wahoo Roam. I’ve checked all the power doubling settings for my setup.
Here’s what happens. If I don’t bring my Assiomas to my trainer, the Kickr Snap is always significantly harder with lower power. Like so hard that 30 minute endurance rides feel like 30 minutes at threshold.
As mentioned by others, I simply swap my trainer pedal with my Assioma power pedal when I train. I calibrate before each ride (both in the Favero app and TR) and then power match. This effectively allows the Assioma reading to override the Kickr in terms of power (I think). Either way, my power numbers inside and outside match closely by doing this.
And when riding outside, I’m often with others that ride with power, and my numbers at different zones seems to match theirs, after accounting for weight differences. Basically my non-scientific observation from riding outside with others, along with race results, validated with bestbikesplit leads me to believe the Assioma power is accurate.
It also helps that the Assioma power readings make me feel better with a 3.1 w/kg FTP. I don’t even want to see what a ramp test on the Kickr would be. I’d probably just quit altogether at that point…the validation is a meaningless boost is all I’m saying.
It’s annoying to switch pedals, especially in the spring and fall when the weather dictates inside vs outside, but I’m hooked on riding with power.
I’m not sure why the readings are so different though. It isn’t the typical +/- x% for different power meters. It’s more like +/- 30%.
Rambling response.
TL/DR - Same problem, move your pedals to your trainer.
For some (many?) of us, our indoor power numbers (same power meter on the same bike) are always lower indoors than outdoors due to reduced cooling indoors (in spite of having Lasco-style blower fans and open windows), potentially combined with the effect of having different inertia of the trainer flywheel vs. biking outdoors.
