So read the big thread in here. Had a look on the website. Seems great. But, I don’t get how the virtual power works?

I use a tacx sattori (which is supported). How does the software know what resistance level I have set the turbo to, or what gear I’m spinning? Wouldn’t both be needed to calc power?

Apologies if this is a dumb question!

It has different settings for different turbo resistance levels. You can’t really change level mid workout (well you can by selecting a different setting.)

Gear is irrelevant, it’s all based on wheel speed.

There’s a known curve for your trainer that’s stored in the software database. At any given speed for a specific setting (specified by you in settings, level 2 or 3 etc) it will generate a power value associated to that curve.

As mrblobby said, gear is irrelevant. Changing down and spinning faster can give you the same output…

Ah okay so you just leave it at the same resistance. I quite often have to switch up and down resistance levels, so maybe I’ll have to use the front derailer and shift to the granny ring during intervals then.

yeah, adjusting the resistance during workouts would render the virtual power useless.

Having trained on HR last year, and starting to use Trainer road and virtual power this autumn i realise I NEED a power meter 🙂

You do NEED a power meter. Though once you have one you will realise you need one for all your bikes 🙂

The thing about a PM that you lack in TrainerRoad is both the consistency (resistance of a turbo does vary quite a bit from cold to warm, and there’s loads of other variables at play e.g. clamping force, tyre pressure, tyre wear, etc.) and a measure of the power you use when you accelerate (it goes by wheel speed but doesn’t factor in the additional power you need to increase the wheel speed, so for short hard intervals your virtual power is likely to be quite a lot lower than your actual power.)

BTW, I think you can stop a workout and change the trainer type, so you should be able to change the resistance level if you really need to, bit of a pain though. I’ve got a PM but the only time I really change resistance levels is if I’m doing some low cadence high resistance blocks with some easy recovery in between.

My turbo bike is also my winter bike, doesn’t seem right to spend so much on it…

your virtual power is likely to be quite a lot lower than your actual power.)

This is the best news I’ve had for ages.

your virtual power is likely to be quite a lot lower than your actual power.)

Where as everyone told me it was higher….

You need the speed/cadence sensor for it I believe. Don’t treat the numbers as real just as a measuring stick.

when you read Wiggins can hold 470w for an hour, anyone that says virtual power is reading low is an instant friend of mine.

your virtual power is likely to be quite a lot lower than your actual power

This is the best news I’ve had for ages.

That’s this weeks motivation sorted…

This is the best news I’ve had for ages.

Only for very short hard intervals where the acceleration is a significant factor as it’s not measuring the burst of power you use to get up to the speed of the interval, so it depends on how hard you accelerate (oh and conversely it’ll measure a higher wattage than you are actually generating when you are decelerating.) For example, it’d probably be way off if you were measuring your best 10 second sprint, but for longer intervals where you build the power more gradually I doubt it makes much difference.

It generally smooths things out quite a bit too, so you lose a lot of the peaks and troughs. I suspect it mostly evens out in the end though so don’t get too excited 😉 The downside really is that you just don’t get to see some of the details.

Edit… just look at some of the rides in the ride feed on TR, it’s easy to spot the ones that are using a PM and ones that are using virtual power. The PM ones usually have a peak and a trough at the start and end of an interval that the virtual power ones miss.

Having just bought a stages and tried it once – it seems I can be in zone 2 heart rate but yet (based on virtual power ftp) at perhaps zone 4 power on the stages.

However, a quick google suggests trainerroad virtual power gives a higher figure than a stages….

However, a quick google suggests trainerroad virtual power gives a higher figure than a stages….

All depends on how accurate the power curve is for your turbo (and there’s loads of other variables that can make virtual power less consistent too.) Stages should be more accurate and consistent.

I just work zones from power. Over time you’ll probably see changes in you HR when working in different power ranges (loads of things can cause HR differences.) Power is far more consistent.

HR can be an useful indicator of overtraining or tiredness but for training power is much better.

My comments about HR were mostly related to the fact that its what I’ve been using out on the open road – for steady endurance rides. The stages is a very recent thing.

Indoors I was using virtual power.

Trying to get a feel for what my FTP would be for the stages without having to do a horrible horrible FTP test for the second time in two weeks (the first one using virtual power).

Can you not just stick the bike with the stages onto the turbo and see how the stages power compares to virtual power? Just ride at a few specific power values and build up a table so you can see what the variability is.

One thing to watch out for is that tyre pressure and roller tension can have a huge difference on resistance, and thus virtual power figures. My tacx trainer has a calibration feature which does a “roll down” test. By adjusting the tension and pressure so that you get the same calibration number, you should get pretty consistent virtual power figures, although it’s best to get the trainer warmed up as resistance drops as the temperature increases.

resistance drops as the temperature increases.

I really hope not!

And I think my original FTP must have been a little too low, cos since I’ve redone it, I’m really really struggling on work outs. They used to be tough. Now I feel like I need to go and have a little sit down in a corner on my own.

MrBlobby, yeah, that’s the plan, but I’ve just been waitng on getting the right length of chainset for the bike which is on the turbo. Then I’ll just fit the stages on the non-drive side. That way the turbo set up is identical with respect to what I measured my FTP with.

resistance drops as the temperature increases.

Sadly, that’s certainly my experience on the two Tacx turbos I have. If you re-cal after an hour it’s moved by about 4 points which equates to a reading of about 10% (yes, 10%) less power !

Ok, so having compared Trainerroad virtual power with Stages….

It seems that Virtual Power gives me 50-55 watts less than the Stages when comparing average power and normalized power.

Would it be a fair approximation to then say that my FTP on the Stages would be ~50watts higher too?

That would take my FTP up to 4.18W/kg…..does that seem reasonable for someone in 3rd cat who kept getting dropped??? Or was I either not trying hard enough in the races or poor positioning perhaps?

Seems a little high to me, based on some of the previous posts giving FTP ranges for different levels of cyclist?

That would take my FTP up to 4.18W/kg…..does that seem reasonable for someone in 3rd cat who kept getting dropped???

Not unless you have absolutely zero race craft! That’s fairly similar to mine, and I’ve placed in a number of 3rd cat races and can sit in E/1/2s.

Wow. I need to borrow a power meter…

Kryton – yep, the best Watts per £ upgrade you can buy clearly 😉

I think I did have a bit to learn in races but only got up to 3rd cat towards the end of the season, didn’t get chance to do any E123s etc.

Some courses seemed to suit better than others.

Perhaps I need to embrace another FTP test on the turbo 🙁