Lack of outside stimulation make the same power more taxing mentally.
Less air flow means less evaporative cooling means you'll be hotter, thus less power made.

You are right, it does not matter how tight you crank down the wheel.

Same with me. I can never maintain same watts numbers inside as outside. I simply work with different lower watt number inside for the same perceived efforts. Still with the lower numbers inside I suffer a lot....Florida also, Quarq PM.

One theory is something clever and sciencey to do with inertia and the microaccelerations required coming out of the low torque phases of the pedal stroke to maintain your cadence which do not happen to the same extent on a flattish bit of road. Outside you have the inertia resulting from the mass of you + your bike and your speed. It's more like riding uphill, where your mass and the effect of gravity are deccelerating you through the "dead spots" in your stroke, if you go for that kind of thing. Why isn't a watt simply a watt in this case? I guess it is like the difference between AP and NP, but on a tiny, transient time scale.

Some folks find it easier to hold their watts with a heavier flywheel, like you can get on the Kurt Kinetic. And then it matches outdoor riding more closely. The heavier flywheel holds more kinetic energy.

But this is only one theory, and not mine. But my outdoor FTP is a good 20W better than indoor, and I take that into account through testing indoors and outdoors seperately, and setting power targets for my races based on the outdoor numbers and the race simulation rides I do.

Many athletes put out a little less power indoors. A whole zone off is about right for me too although the gap between the two seems to be narrowing with each passing year. I stopped worrying about it years ago.

Tell us about the cooling fan/s you're using indoors. The very best box fans only generate ~ a 12mph breeze when set on high while an excellent hassock fan may yield 16 mph right at the grill and less farther away. The upshot is most folks are getting vastly less convective evaporative cooling on their trainer than they receive riding outdoors at a noodling pace. Once your core temperature exceeds 103F it becomes nearly impossible to make yourself continue to work hard.

Advice- stronger fans.....more fans.....turn the AC down in your trainer room.

YMMV,

Hugh

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Genetics load the gun, lifestyle pulls the trigger.

I'm not worried about it. A good workout is a good workout, regardless of the numbers. I'm just curious as to why.

I get what you are saying, but the difference in the power required is noticeable within a few seconds after starting. Core temp doesn't go up to that point within the first minute.

I don't think it's a mental issue. I think if you connect a machine to the pedal that applies a constant force riding on trainer or riding outside, the power readings inside would be lower.

I propose the following experiment to test this matter:

Do a series of workouts outdoors and indoors, to establish baseline "indoor" and "outdoor" FTP's.

Then, put your bike on a trainer, and the bike and trainer on a platform that can be driven around town. Make the platform drive at the same speed at which you typically ride outside, and then compare power numbers to your typical outdoor ones.

Alternatively, you could put a box around you and your bike, with a cut-out in the bottom, and ride around outside. The box would simulate the conditions of riding inside.

Please update us with your findings soon!

I detect a little attempt at humor here. Hmmm.
I have my outdoor 20 min FTP at 235, unadjusted.
I'll do an indoor one once I recover from IMFL to compare.

This has been discussed ad nauseam. The basic findings every time someone brings this up is better cooling = better power. Get a fan and try harder.

For a data point, here are my best 20 min power indoors vs. outdoors this year (I used 20 min due to the inherent variability with riding outdoors in a city - 20 min is about the longest steady interval I can ride without hitting lights, traffic, intersections, etc.)

Indoor: 336
Outdoor: 318

FTP is based on an hour, not 20 minutes.

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On the internet, you can be anything you want. It is a pity so many people choose to be stupid.

I typically have a NP in the 160s on the trainer. Last week I did an outdoor ride and NP was in the 180s. First time I've ever seen an NP outside of the 160s over an hour, and the perceived effort was on par or slightly easier than some of my more difficult trainer rides.

I know. But there are 20 min tests to approximate it too.

The OP stated that he noticed a difference at his normal zone 2 pace/power. You don't need better or more fans to put out 145 watts for 10 or 20 minutes.

FTP correlates well with either, but is neither.

Read this: http://www.joefrielsblog.com/...ike-performance.html

Inertia makes a big difference as well as cooling.

I appreciate I was nit-picking a little, but unless I am massively mistaken (along with a fair percentage of this site), FTP is based on an hour.

Care to clarify why you think it is not as all the references I can find say it is, and there are quite a few.

I am genuinely curious.

Thanks

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On the internet, you can be anything you want. It is a pity so many people choose to be stupid.

It is a mental issue if your equipment is OK. If you get the adequate cooling there isn't any good reason why indoor/outdoor power should be much different. <5% difference. My 2x20 power on the rollers has been within 5-10 watts of the same workout all uphill.

Did you ensure to calibrate your powermeter? What kind of power meter do you have? Did you re-calibrate after a small bit to ensure temperature has no effect?

There is a good reason why indoor sustainable power output on a trainer should be different to outdoor power - inertia. It is very common for some people to have considerably less power on a turbo despite adequate cooling. It affects some more than others. Even trainers with different inertia qualities make a difference to sustainable power output.

This study disagrees. I'll concede that if you only train outdoors and then jump on a cheap mag trainer you will have some muscular coordination issues. After a bit of adaptation you should be able to get up to outdoors powers levels.

As a thought experiment: If a rider only rode indoors on a cheap mag trainer. Lets also say this rider was well motivated and became well trained. On his first outside ride I wouldn't expect him to have dramatically higher power just because he now has more inertia.

We also don't know what kind of trainer the OP has. Could be a fluid2 or kurt kenetic. If so, then inertia is not a problem as these trainers have enough.

I find no difference at all. Just mentally, it's a hell of a lot harder to do things like a 90 minute tempo ride on tired legs indoors, compared to outdoor. Accelerating form a stop sign, I'll see 500 Watts easy, but you won't see that type of power spike indoors.

Coincidentally, I have a very cheap magnetic trainer with little flywheel weight.

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