I know there have been numerous explanations in these forums explaining that the speed on Zwift will be different than on your trainer. However, I am experiencing extreme differences. For example, I will be going very hard and showing 20+ mph on my trainer (Tacx) and/or my Garmin Fenix 8 but only 4 or 5 MPH on Zwift. This can persist for extended periods of time. Then, all of a sudden, when I am only going about 12 or 14 on my trainer and/or Garmin, I am going 35+ mph on Zwift. This has occurred on my current Tacx trainer and in the past on a mechanical trainer with a Garmin speed and cadence monitor. (FWIW - my trainer and Garmin are always very close.) I am not really interested in detailed explanations; all I want to know is how to fix it. Any help? Thanks in advance!
The other applications are assuming you’re on a flat road. Depending on what route you’re riding on Zwift, you might be going uphill at 15%+, and that’s why you’re going slower.
There’s nothing to fix. If you want to go faster, just choose a flat route.
Hopefully this isn’t too detailed.
What sort of Tacx trainer do you have? And how are you transmitting power to Zwift?
My guess would be that you have a wheel-on trainer, in which case the speed of your rear wheel and your speed in Zwift will not have much correlation. Speed on a wheel–on trainer is based on how fast the rear wheel is spinning, while speed in Zwift is calculated based on the amount of power you are putting out, your weight, your height, and the gradient on which you are riding.
So, if you’re going up a steep hill, you might be putting out enough power for your rear wheel to be spinning at a speed of 20+ mph, but that would be on the flats. But since you’re on a hill, and having to fight gravity, your in-game avatar isn’t going that fast.
That’s a quick explanation, but I hope that helps.
Thanks for the reply. I am aware that elevation changes will impact speed on Zwift, but most of the courses I have done are flat or flattish, yet the speed differences persist. I also really notice it with other riders who either fly past me or whom I fly past. I don’t care about the speed per se, but I worry about the training/data impact especially when I am doing an FTP test. I am actually scheduled to do another FTP tonight which is why I brought this up today. Thanks.
Appreciate the response. As noted in my other reply, I am mostly on the flats. I have never done a group ride or anything like that; I only use Zwift for training. That said, your explanation for the hilly courses makes complete sense and I will keep that in mind on the rare occasion I do one. Thanks.
Hi @Brett_Rufkahr.
Welcome to forums, this is Haziel part of the Zwift Support team, I highly recommend you confirm that your trainer is calibrated and updated based on the manufacturer’s instructions, to confirm is not related to power readings.
If the issue persists please contact us here.
Which trainer do you have exactly? A Tacx what?
Garmin Tacx Neo 2T Smart Trainer purchased in December of 2023, so a little over a year ago. Thanks.
Thanks - I will definitely double check that! Hopefully, that will fix the issue.
I went to Garmin to learn how to calibrate my trainer. Here is what the Garmin site says:
"The NEO Smart measures your power with incredible precision, making sure you that your data is accurate and reliable. This Smart trainer is the only trainer that doesn’t require a calibration process. The NEO Smart measures your power with a maximum deviation of 1%.
The NEO Smart is designed that it doesn’t have any internal wearing parts, transmission or parts that are influenced by temperature, meaning that the power accuracy will not drift over time."
Consequently, that does not seem to be the issue.
FYI: A Tacx Neo 2T should not require any calibration. Are you in SIM mode, or in ERG mode? I have noted in your activities that you have done several workouts lately, which might be in ERG mode. In ERG mode the trainer will automatically adjust the resistance to compensate for your gear and cadence in order to keep you are the correct target wattage for the interval. So, if you just keep pedaling faster and faster, your watch (connected to the trainer ‘wheel’) will show that you are going faster and faster (because the flywheel keeps going faster), but Zwift shouldn’t show any (appreciable) change in speed, because it would be lowering the amount of resistance on the trainer to keep you ‘in the zone’.
But something is wrong.
The pictures of your last workout show that the power targets are not being met by the trainer.
Example1: trainer should hold you at 155W for 3 minutes, but you are doing 206W
Example2: trainer should hold you at 170W for 2 minutes, but you are doing 150W
I also don’t see any cadence values, but that shouldn’t be the problem right now.
When selecting a WO, is the ERG mode button selected?
Can you please take a screenshot of your pairing screen.
You can’t fix it.
In SIM mode, for any given power output, your speed on Zwift will be influenced by height, weight, draft, drag, surface, gradient, bike choice, wheel choice. The trainer has no knowledge of most of those variables. You cannot possibly expect the trainer speed and distance to match your Zwift speed all the time and for every eventuality.
In workout mode, with erg on (or external erg control outside a workout), your (fly)wheel speed can cover a very broad range for any given power output, depending on gear choice. Granny gearing will give painfully slow trainer speed, even with big power output. TT gearing will give the opposite, with potentially crazy fast trainer speed at modest power output.
In short, trainer speed is a product of cadence and gearing, completely unrelated to power. Zwift speed is very much related to power, plus a load of other variables, and has sod all to do with how fast your flywheel is spinning.
If you want something approaching parity then ride Tempus Fugit all day on an entry level TT bike, without erg, and set wheel circumference to 2133 mm for the trainer. That should get you in the right ballpark.
p.s. group workouts or rubber banded group rides will add another complication, creating even more separation between the real and virtual worlds.