FTP in turbo trainer

javidr

Hi

I have heard that turbo trainer FTP is around 20% lower than the real FTP on the road.

How accurate is that? I have a TACX Flow and my FTP is 200w, which i consider much lower than what i usually do on the road

Thanks

fat daddy

You can definately produce more power on the road and I dont get why ... perhaps the edition of the wind pushing back on you at 25+ mph is enough for the body to recruit more muscle in to the job as the glutes and lower back activate ?

napoleond

About the same for me.

However. Pin a number on my back and that's a different story.
My peak 20 min in one ~2hr hilly TT was higher than I've ever done in a standalone 20min FTP test.

cougie

Everyone is different. It's just a guide.

markhewitt1978

An FTP test done properly is your aerobic fitness only, whereas 20 minute efforts on the road will often be more because you're drawing on anerobic efforts for part of it.

All the same output being lower indoors is a common thing, something to do with inertia.

javidr

Is there any estimation on what is the expected FTP on the road based on turbo trainer results? I am expecting it near 20%, but its just my guessing

fenix

Thats all it is - just guessing.

Its probably harder to hit true FTP inside as its always going to be sweatier indoors (at least in the UK) but I dont think thats so much of an issue if you use it for your inside training.

Alex99

20% seems rather a lot. Joe Friel suggests 5%, which is close to my experience. But, there is quite a variation. Apparently some people can match their best efforts on the Turbo.

MiddleRinger

Are you using the same powermeter for your indoor and outdoor measurements?

javidr

Nop, indoor i use turbo trainer meter

Grantmk

Another factor is the surface your trainer is on, I have a small rug that I use(d) to absorb noise when using the turbo. I noticed my road figure seemed a lot higher. A quick experiment on the turbo showed a 10 - 15% difference when the turbo was on a hard service compared to the thin rug I was using.

Dave_P1

Do you use a power meter when on the road because because if you don't you have no way of telling

AK_jnr

And if you are just hoping you can add 20% to tell your mates on the cafe ride, dont bother. Lol.

Saying that though, I cant get near my outdoor 20 min power on a turbo. Oddly my 5min PB is on a turbo which is strange considering I couldnt wrestle the bike about to squeeze more power out.
Both measured using the same PM.

MiddleRinger

My 20-minute power (not ftp) on the turbo is about 5% less

javidr

Hi

Today i have tried to put a bit more of pressure on the tyre (around 85psi) and my power is much higher (around 30w higher) than what it was with a 70 psi tyre

Does it make sense that the tyre makes such a difference?

antsmithmk

Your tire makes no difference at all to the power you are producing

Man Of Lard

antsmithmk wrote:

Your tire makes no difference at all to the power you are producing

Agreed but it might make a difference to the measured power if the change in pressure improves the contact and thus transfer of power if the power is being measured on the trainer (rather than the bike)

MiddleRinger

JaviDR wrote:

Today i have tried to put a bit more of pressure on the tyre (around 85psi) and my power is much higher (around 30w higher) than what it was with a 70 psi tyre

Does it make sense that the tyre makes such a difference?

Tyre could have been slipping beforehand. How are you measuring the power? Meter in the actual turbo or Zwift zPower calculation? I believe changes in setup such as tyre pressure and roller clamp force can affect that.

In other news, my trainer FTP is now higher than my road FTP (same powermeter). Probably need to do another test out on the road.

javidr

Hi

Its zwift power calculation, which i thought was read from the trainer isnt it?

I havent changed anything so it doesnt make any sense

Maybe i have improved that much this week?

markhewitt1978

JaviDR wrote:

Hi

Its zwift power calculation, which i thought was read from the trainer isnt it?

I havent changed anything so it doesnt make any sense

Maybe i have improved that much this week?

If you change your tyre pressure then the trainer will need recalibrating.

nicklong

If you don't have a proper power meter, then whatever FTP you've measured is only correct against the test protocol you used. So, if it is based upon recorded turbo trainer resistance * your tire pressure * your particular setup * whatever batch variability the turbo manufacturer accepted during production, then your FTP is correct so long as all of the above are recreated outside.

This is the main benefit of training with a true power meter - it measures what happens at the point of torque (pedal, chainring, crank arm) which CAN be recreated outside. It is also broadly comparable to other people using accurate calibrated power meters.

An example - imagine trying to measure your age based upon number of lightbulbs that you've had to replace in your lifetime. So long as you use the same brand of lightbulbs and you light your house up in the same manner, you might be able to do a decent estimate based upon expected average bulb life. But you can't compare the number of bulbs you've used it you move house, or with anyone else without knowing exactly what bulbs they buy etc.

A power meter would be like everyone having a stopwatch given to them at birth

MiddleRinger

nicklong wrote:

A power meter would be like everyone having a stopwatch given to them at birth

Haha I love that! Only some people were given slightly less accurate stopwatches and some poor fools were even given stopwatches that only measured half of the time and just doubled the number.... :P