FTP difference between trainer and outside

I find that my FTP (and pretty much all of my training zones above Z2) to be lower indoors that outdoors.

What kind of variance are others seeing? I think I could be 10-12% different. I use a smart trainer, 2xfans (front and rear), ample fluids, and my trainer room tends to be nice and cool.

Obviously the remedy is more trainer sessions.

Why is it that some seem to lose little or no power indoors?

I still have the difference but after I gave up of ERG and moved to big chainring and add second vent it looks smaller (cca 5%)

There are many variables here. I wouldn’t mind too much and just see it as a different modality with its own ftp.

Just to make sure we are comparing the same power inside and out ? same meter ?

Have you ever done any flat outdoor time trial testing versus hill climbing testing, same duration same bike?

Do you stand more outside (might affect the numbers if you are looking at normalize power.

The flat and uphill test is something I like to do and get an idea of how close the two are. I like to see them within 3%. The uphill is usually better.

If the discrepancy is higher than this I add more time under tension, low cadence work on flat terrain.

Some do a better job of working against the resistance and some can generate the power through pedal stroke and maintaining tension.

If you can get a video of your chain, along the top above the chain stay between the front chainring and rear cassette.

Do this at a tempo pace. The chain should always maintain tension, no dropping or slack with each stroke. If it is then there is an opportunity to decrease the size of your deadspot.

Fast Talk has a good podcast on why there are differences between trainer wattage and outside wattage. Some research was done at a Canadian university. Can’t remember what the episode was called. it was a couple of years ago. Never really understood the Why of the difference. could be related to the nuances of how the bike moves more outside and allows the rider to be more mechanically efficient. Perhaps that accounts for some of the increased power outside vs. trainer riding.

My take home was to respect each the wattage for what it is. if you’re guiding workouts by FTP then use your trainer FTP if you’re working out on your trainer. Use your outside FTP if you’re doing workouts outside.

We could probably do uphill, flat and rolling FTP tests to, and use those depending on where we’re doing the workout.

We can also overlay HR and RPE to get more meaning out of the workout. To do this, i’d imagine we’d need all the test and then consider what the RPE of the wattage felt like. From there we could make some good associations. We’d probably need to consider training status when overlaying HR data, as HR response to exercise changes with training status. I’d guess if we really were diligent and motivated to track this, we could make even more nuanced associations and really dial training in.