Indoor FTP Vs Outdoor?

So I prefer to ride my structured < 1.5hr sessions indoors. Primary reason is that I can use ERG mode and remain on it the whole time. Anyhow, my workout today was 2 x 20 minute sweet spot interval with 2 x 15 mins tempo, but during the first SS interval I set a new threshold HR. Given I was at 230 watts and my FTP is 255 that is not right. I have a large fan and didn’t feel like I was overheating, but if I am setting new Threshold HR for SS workouts then I am working way too hard and risk overtraining?

Any advice appreciated.

What’s the outdoor bit of your question in the title? If the 255 W FTP was from an outside test then you have your answer right there.

Just trying to understand whether I should also be looking at HR too and saying to myself that if I’m setting new threshold HR values inside on the turbo with workouts way below threshold power then something is off. Or do you say “great higher HR for less power?”

I find it takes a good ~3 weeks of regular (3/4 a week) big effort rides/workouts on Zwift to get my heart rate and power figures up to outdoor stats, while drinking plenty of water and plenty of fan power, pre-heat adaption the lack of air movement is a killer indoors… Raising your heartrate and lowering your power thresholds.

the lack of air movement is a killer indoors… Raising your heartrate and lowering your power thresholds.

That would explain the higher HR and reduced power. Going to try putting the turbo in the shed as indoors it 20c and the fan whilst moving air means it’s still warm.

Could be stress or fatigue.   I’m current doing 2h 220w zone 2 sessions at the weekends.  Saturdays fasted session is at 154bpm, Sundays fuelled session is at a more normal 130bpm.

I put it down to my fasted state plus the weeks residual work stress.

There has been many an artical written on the indoor/outdoor discrepancy.

It’s mainly down to overheating, but also there is an element of the turbo itself. If you have an old wheel on turbo it feels fundamentally different when you pedal than outside, which is reflected in less power output. Better turbos with bigger flywheel apparently make the pedal action more ‘outdoor like’ so the power is closer.

I do alot of turbo work, on a top end turbo with lots of cooling, and my power outside is still about 10 watts more than indoors (3-4%)

Obviously everything above is only relevant if your power source is the same indoors and out. If you are taking power from the turbo indoors then there will always be a difference.

There’s often (but like lots of these things, it’s very individual) up to a 10% difference between indoor and outdoor FTP values, outdoor being the higher. That’s assuming you are using the same powermeter indoors and outdoors. Mostly it’s due to air flow, or lack of it, indoors. But there’s a lot of variables and just what triggers things is different for different folks.

You say you’ve a large fan, just how effective is it? I had a 40cm radial fan but now have a Cleva Vacmaster, it’s night and day difference but even so it’s still only a fraction of the airflow that I’d get outdoors. Fuelling and fluid intake is also important indoors, the latter mainly as a result of lack of air flow.

I did a workout yesterday, 5x10mins at threshold, when I started I was on the verge of shivering, by the third workout I was stripping off my top! HR got close to the max I’ve seen in recent years, might have been general tiredness. A couple of weeks ago I did a 3x15min sweetspot session and my HR got to top end Z3, there was just 30 seconds in Z4.

Do an FTP test indoors and use that indoors, leave the outdoor figure for riding outside.

when I started I was on the verge of shivering, by the third workout I was stripping off my top

I don’t think folks realise quite how hot you get on a turbo, as you say you start off freezing and end up sweltering.

Before I knew any better I used a turbo without a fan. I use to get through 4 pints of water in an hour, there was literally a puddle under the bike. After I finished I wouldn’t need to take a piss, i’d literally sweated out all 4 pints.

Oops! Meant to say “third interval” not workout!

I used to have a hub power meter and a wheel on turbo. I absolutely hated the turbo because I could see how low my power was and how much it hurt to reach my known outdoor numbers – and that was straight away so temperature and hydration wasn’t an issue. Even at low numbers. 220W was a stiff pace on that turbo but it was my steady comfortable 3hr pace outside.

Now I have a wheel off smart trainer but I don’t have a power meter. So some part of my ego is urging me to stick 15% on my Zwift numbers based on this 🙂

Based on experience and how strong I feel now, I think my power is better than what the turbo says, but it’s not 15% any more!

I find indoor training i am far stronger than riding outdoors. No idea why, just feel completely different on the bike.

Going to try putting the turbo in the shed as indoors it 20c and the fan whilst moving air means it’s still warm.

You’ll still need the fan – my turbo’s in the garage and at this time of year even with the door open I need a fan (after warming up – a remote control is a godsend here!)