Managing Indoor vs. Outdoor FTP for TrainerRoad Workouts on Garmin

Training
1

Hi,
I’m a new TrainerRoad user, and I’m a bit confused about how to execute workouts outdoors. My indoor FTP is 270, while my outdoor FTP is 302. A couple of days ago, I did “Glassy -3” outdoors, which is a sweet spot workout, but my heart rate stayed in Zone 2. After a while, I stopped the workout and switched to an endurance ride for the remaining time.

What is the best way to adjust the workout targets before sending them to my Garmin for an outdoor ride? ChatGPT suggested that I manually set my outdoor FTP first, send the workout to Garmin, and then restore the indoor FTP. While I can do that, it seems like there should be a more efficient solution. Is there a better way to handle this?

2

How do you measure power outdoors and indoors? A 32w difference is extremely big (at least in my eyes) and would likely occur due to inaccurate powerreadings (either outdoors or indoors or both).

I get that doing the same workout outdoors feels easier than indoors (I have the same thing, probably due to better cooling and being less static on the bike), but the feel should still be relatively close.

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3

Indoors, I’ve been using a Tacx Neo 1, while outdoors I use a 4iiii power meter on the left crank. From what I understand, the difference between indoor and outdoor power can vary by 8-10%, depending on the athlete. In my case, it’s 11.8%, so I don’t think it’s extreme.
However, this is the situation I need to manage. :blush:
I’m also unsure if TrainNow or Adaptive Training will properly account for the two different FTP values.

4

The only way to adjust your workout targets for outdoor rides would be to manually change your FTP each time you want to send a workout to your Garmin. However, I agree with @christiaanvanos above – ideally, your indoor and outdoor FTP should be fairly similar. A 32-watt difference is quite significant.

I noticed you’re using a Tacx trainer indoors and a 4iiii power meter outdoors. If you’re on the same bike, make sure PowerMatch is enabled. PowerMatch ensures that the power data in TrainerRoad comes from your 4iiii power meter while still allowing the Tacx to control resistance in ERG mode. This way, your power readings will be consistent between indoor and outdoor sessions.

Also, how is your cooling setup for indoor training? Having proper airflow is crucial. Many athletes struggle more indoors because they underestimate the need for cooling. If you don’t already have a powerful fan, we’d recommend investing in one – blower fans, for example, are very effective at keeping you cool during tough trainer sessions.

Frequent manual FTP changes could also interfere with Adaptive Training and your Progression Levels. Your FTP and Progression Levels (PLs) are closely linked, so changing your FTP regularly (and artificially) could lead to inaccurate PLs. This could result in workouts that are either too easy or too hard for your current fitness level.

Additionally, if you’re manually adjusting your FTP by ~30 watts between indoor and outdoor rides, AI FTP Detection might not function accurately, as the shifting data would likely confuse the algorithm.

For these reasons, we’d recommend avoiding manual FTP changes for different workout environments. Your actual FTP doesn’t change based on whether you’re indoors or outdoors, but factors like cooling and equipment differences (e.g., different power meters) can affect how your FTP is expressed.

By improving your cooling setup and using PowerMatch, you can make your indoor trainer rides feel more like your outdoor sessions.

Hope this helps! Feel free to let us know if you have any additional questions.

2 Likes
5

No, indoor and outdoor FTP should not be different, provided that you are in roughly the same position on the bike. An exception would be if e. g. you are on a TT bike indoors and a regular road bike outdoors, then the difference in body position implies you may not be able to put out as much power on the TT bike (in a TT position) than on a road bike. Another factor could be cooling, but then it isn’t your FTP that is different, but you are limited by whatever cooling you have.

An 8–10 % difference is way too large. However, the fact that you are using two different power meters, and one of them being single-sided, is the much more likely explanation. E. g. I am left-leg dominant, sometimes by 5 %. That means if I were to compute my power = 2 x left leg power, it’d overestimate my power output by 10 %. (The actual number fluctuates and typically lies between 57:43 and 52:48.)

The second issue is that not all power meters, including the one in your Tacx Neo, need not be accurate. My Elite Suito and Quarq DZero disagree by about 10 % now after initially being within margin of error. Both measure total power, so this is not a leg imbalance issue.

I have solved this issue for me by ignoring my Suito’s power numbers and using my Quarq power meter (using PowerMatch).

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6

I use rollers for indoor training so use the same bike and power meter for outdoor and indoor workouts. I find it so much harder to maintain higher power outdoors than indoors despite the equipment all being the same.

When I used a smart trainer and a second bike I found a big difference in power between the 2 different setups. Im glad that rollers have elimated one different factor.

7

Another factor to take into account is cadence and the inertia carried by the flywheel or rear wheel. If you do your threshold intervals outdoors on an incline at lower rpm, it might feel better (or just different) than doing it at 90–100 rpm at high inertia on the trainer.

8

Although I don’t enjoy fitness tests that much, I just completed another one using the Powermatch feature with my 4iiii power meter. Guess what? The result was the same: 270W! :blush:
So, both the Neo and the 4iiii are measuring similar numbers, which means something about riding outdoors is boosting my FTP.
Fortunately, I found a solution by using the “scale” feature on the 4iiii power meter, which I’ve set to 0.9 instead of 1. This means it will scale down the outdoor values by 10%. Indoors, I plan to turn off Powermatch and stick with the numbers from the Neo.