Power way lower outside

Hi all

I’ve recently come back to consistent riding after a bit of a break (personal issues and work just meant I couldn’t ride as consistently as I used to). At my peak I hit an FTP of 275W at 74kg. I knew this was pretty accurate as I managed to do a 70.3 bike leg at 213w and run well afterwards.

Anyway, I have just started riding consistently again and did a ramp test that produced a result of 235 watts. I was surprised, this was quite a bit higher than I thought my FTP would be.

I have then done a couple of rides outside. These were purely ‘fun’ rides with no training intention. Just riding for the joy of it. On each one I did a bit of an effort, just to see where I was at, and I was finding it very difficult to hold 200watts. I managed a 12 minute effort at 200 watts with a very high heart rate. It felt like a threshold effort (for reference, I’ve been using TR for over 5 years and have done a lot a training, so am used to feeling what threshold and sweetspot feel like). As such, at a guess, I’d guess my FTP outside is in the 200 region.

I am at a loss as to how to explain this. This wasn’t fatigue, i’ve ridden outside 3 times since the ramp test with the same kind of result.

I have always found it easier to put power down on a trainer, contrary to most, but this is just silly.

Has anyone got any thoughts on what could be going on? The last thing I want is to train for a race and go into thinking my FTP is x and then find out that, outside, it’s actually x - 15%!

Thanks in advance

First question: How exactly are you measuring power (same exact device inside / outside)?


Your 12min 200w effort is essentially a sweet-spot interval.
12mins at 85% FTP is a hard effort, even more if you are not accustomed to feeling the effort level.
Id just crack-on with the training and see what happens after a few weeks.

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Hi Chad

Sorry, I should have said that!!

Yes, exactly the same. It’s my stages gen 3 on my Scott Foil. I use the same bike on the trainer.

My trainer is a Tacx Flux

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Hi Jon

Thanks for the reply.

I would agree but on the trainer I can do the same wattage for 20 minutes at about 15-20 bpm lower and feeling like it’s not too taxing. If I did 200 watts on my trainer it’d feel pretty comfortable for a long time. Outside it felt pretty difficulty pretty quickly.

I also find it a lot harder to hold a decent cadence outside. On a trainer I am happy anywhere between 85 and 95 rpm. Outside I find myself going to the lower end of that range…

Presumably you are using Power Match in TR, and ERG mode?

  • If so, what gearing are you using on the trainer?
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I’m not… :frowning:

I find the Flux is just terrible in ERG mode with power match. Genuinely awful. The resistance floor is stupid low - in my smallest gear it generates too much power for the recovery intervals - and it is very hit and miss as to whether it decides to change power for the interval. I just use it in normal mode and change gear like a loser :wink:

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OK, so Resistance mode, but still using the power meter paired, so TR will use that power data over the trainer data.

One key difference that may exist is the pure “inertia” variation between inside and outside. Some people have a tendency to perform better with high or low inertia, and there may well be enough difference between the training inside and your rides outside.

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Thanks for coming back so quickly.

Yes, TR is using the data from my power meter rather than the trainer (my god the Flux is inaccurate - the other day my PM was reading 135 and the Flux was bobbing along at 95).

That’s the only thing I can think of - perhaps I am better with low inertia. Maybe I should be a mountain bike rider! Or even a fat bike rider…

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This is so interesting! Every obvious explanation has been ruled out already. But have you tried riding outside again and doing an “effort”? Maybe you were just having a crap day? Happens to me sometimes when I don’t get enough sleep or food, or just for no apparent reason. I’m sure you know what I’m talking about.

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What was the terrain like that you were riding? It’s much less cognitive load to just focus on a number on a trainer than keep your eyes on the road, your head on a swivel for cars, AND keep peeking at that PM to stay in range. That could account for part of it.

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I have a hard time pushing the same watts outside compared to my trainer, BUT only on flat roads. I can push more watts on climbs compared to the trainer though…

Were your efforts outside on flat roads? I know there is some science to explain why with some are better or worse climbing vs flat.

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I had the same issues (also with the Flux…) with trouble to keep wattage up on flat roads, with my road bike. TT-legs where awful.
When I did hills or when I switched to the mountain bike (switvched over power pedals) i was able to hold SS and treshold wattages over time. Clearly a inertia thing for me. This winter I am doing some of my SS intervals in the big ring to try to combat this.

The wattage floor on the flux was annoying but acceptable as i had a gearing range to get by for at least the intervals longer than 3-4 minutes. Power match also did good. My flux had pretty good accuracy vs my power meter. A “bonus salary” just in time for black Friday made me take a loss on the Flux and go for a kickr Core. The Inertia on the core feels more like the Flux in big ring, but now I wont have to cjhange gears along the way. I wonder how this will affect my tempo-legs come summertime

Hi Kajet

I did wonder that, and will try again over the weekend, but it was consistent over three rides so I would be surprised if that was the case…

Now that’s a really good pint. The roads were flat, there’s not much in the way of hills around by me, well, nothing more than 2 minutes.

I do find that I can hold a much better power on hills so that would perhaps support Chad’s thinking that maybe i’m better at lower inertia riding

Hi Stefan

I am starting to believe that it’s an inertia thing. I just need to work out how to deal with that as I don’t train to get better at FTP tests! I want to get better at riding outside and this is definitely holding me back!

I’d be tempted to dual record an indoor ride on both trainerroad and whatever head unit you are using outside just to make sure nothing weird is going on with either setup.

it’s all about adjusting to the new environment, mentally. if the PM is the same indoors and outdoors, then your body is capable of doing the same work in both environments.

if it’s lower outdoors:

  • work on keeping even pressure on the pedals, erg mode does this for you – your CNS has to do the work outside (one reason I don’t like erg modes).

  • don’t coast

  • learn how to keep the pressure on the pedals and the watts up with a tailwind or a slight downhill.

  • if it’s hilly, look at NP for the session rather than AP.

For what it’s worth, I used to have a similar problem adjusting between indoor and outdoor – from '07-'15 I did my winter training on e-motion rollers. For the first couple of years, I could do Hour or Power numbers 20+w above what I could do outdoors. It was an eye opener as to what I was capable of doing, and it just took doing the work on the road to eventually get indoor and outdoor power to match.

Here is the article I was thinking of that I read a few years ago. The science may be a little thin, but it’s something to think about. https://cyclingtips.com/2013/09/climbing-and-time-trialling-how-power-outputs-are-affected/