Garmin Vector 2 and Tacx Vortex

trainer
power-meter

#1

Hi everyone

I’m just wondering if anyone has noticed differences in reported power with Garmin vectors and Tacx smart trainers

I’ve only just bought the Tacx and have been very impressed so far but today I thought I’d compare the wattages during a workout.

The Garmins were running a higher wattage by about 15-20 watts consistently across the workout.

Is this to be expected with smart turbos and therefore should I have an FTP for outdoors Using the Garmin and one indoors for the Tacx

Both were correctly calibrated and torqued prior to ride


#2

I literally just got my Vortex in the mail this afternoon! I’ve been riding the vectors for 2 seasons so far.

I think generally they power differences are there between power meters and smart trainers. Some of the difference can be the fact that the trainer measures at the wheels while the PM measures at the pedal (or the crank, crank arm, spider, hub… depends on the PM).

Another thing can also be if you have the 2s version that is single-sided only then that could account for some of the difference.

I’ve heard the guys on the podcast say that it really doesn’t matter if it’s accurate as long as it’s consistent. So the difference between 200w and 210w is really a big deal as long as that power output is consistently reported one way or the other and not constantly switching between 200w and 210w.

One thing that can help is enabling Powermatch. That way TR takes the power from your PowerMeter and adjusts the trainers resistance so that your PM numbers are where they should be for the interval. That way you have a consistent number indoors and outdoors.


#3

Hi ntdeck

I hope you like the vortex, I’ve been quite impressed. Espiecially in erg mode

I’m probably just going to keep the power from the vortex and not worry about my vectors, they’ll likely be going onto my outdoor bike with my other bike sitting on the turbo permanently. Obviously switching bikes depending on seasons

It’d be interesting to see if yours reads similar wattage discrepancies though?


#4

My vortex and Assiomas do show differences in power but its dependent on many things.

As it’s a wheel on trainer tyre pressure and tension of the roller on the tyre can make a big difference, although calibration should account for that. The other factor is warm up time. At the start of a ride there’s a big difference between the power readings from the pedals and the trainer. If the calibration is done when the trainer is warmed up this goes away as I get into the ride. A lot of these variations go away with a direct drive trainer.

The other thing I’ve noticed is that the power discrepancy depends on power level. At 1-200 W the trainer reads about 20W higher than the pedals and they get closer as the power increases.

Definitely look into powermatch though:

Some users don’t like it or have problems getting it to work well, but I’ve had no issues do far with my setup even for short intervals. Personally I use the Assiomas as my source of power no matter which bike I’m on and whether I’m indoors or outdoors for consistency.


#5

The difference in power between the Vortex and the Vectors will vary, depending on tire pressure, how hard the roller presses against the tire and temperature. If you like, you can fiddle with the roller tension to get them to align pretty well.

One reason using Power Match could be a good idea, is temperature drift. As the trainer warms up, the displayed watts can change by up to 20 watts in a normal room temperature. If you work out in a colder room, it can be even more. Last winter, I did a 2 x 8 min FTP test in my cold shed (around freezing) and it gave me a FTP of 316. Looking at other ride data, my FTP at the time was around 250, maybe closing in on 260, but certainly not anywhere near 316!


#6

I noticed a big difference between the power readings from my PM’s and the Vortex Smart, the bigger concern to me was that the slope wasn’t constant (i.e - the readings were closer at lower power and further apart at higher power). I am lucky enough to have differnet PM’s on my bikes, so I could check against Powertap, Vector 2 (dual sided) and Quarq - all gave similar differences. The nice thing is that the difference was constant (i.e always 25W at FTP), so once I knew it, I could use the Vortex OK. I’ve attached a picture showing the differences I was getting

The tyre pressure and contact makes a big difference to any wheel-on trainer, so it is important to calibrate every ride, or at least once per week.

Ultimately, I always used my PM with the smart trainer. That way, I knew that the readings I was getting outside were the same as the readings inside.

On a light-humoured note, it’s really easy to Zwift dope with the Tacx Vortex… :-):joy::joy:


#7

Did my first ride on it and it worked great! I’m glad I got it :slight_smile:

like the other guys mentioned (and I had forgotten) the tire pressure, how tight the trainer is, and to some extent even the cold can affect the readings.

I checked at a few points today. I had power match going on TR so it was reading my PM numbers and adjusting the trainer resistance to match. I also calibrated both PM and trainer before the ride. I used the Tacx Utility app to check what the trainer was actually reporting for my power. It was generally around 10% high but towards the end it started reading up to 15% higher than my PM. I was doing VO2max intervals so I know there was a lot of heat being generated that would affect the tire pressure. It was also very cool in my garage at the start.


#8

So after reading these responses I’ve just realised that I have a TACX Flux and not a Vortex!

Doh! Suppose it is new, like a new girlfriend it’s sometimes hard to remember her name :slight_smile:


#9

Interesting that there are lots of happy Vortex users. I’m getting rid of mine, I have zero confidence in its reported watts and this had led to inflated FTPs, failed workouts, and ridiculously easy (and likely worthless) workouts.
Powermatch lags really badly, I’m better at power matching compared to TR+Vortex+Vector3. This makes ERG mode virtual useless except in situations where intervals are long and continuous.
Its accuracy is supposed to be <5% so I guess I’ve nothing to complain about if my FTP is 300w one day and 315w the next.