Distance / Speed with Tacx Flux

I’ve been looking at other forum topics to see if I could find an answer, but I haven’t found anything conclusive (I know there’s another topic of an user with a Tacx Flux S, but there’s no fix apparently).

I’ve switched from Zwift to Trainerroad and I see a difference in speed or distance. For example, a flat ride at 170-180w (64kg) Zwift for an hour would clock around 28-30km, while in Trainerroad for a similar workout, the distance covered sits somewhere around 20km.

If it helps, I have a Tacx Flux and selected the default wheel circumference (2096mm).

I’m aware that at the end of the day it is a “vanity metric” and mostly useless for our purposes, but if you have gone through the same issues or have any idea how to correct this, I would be really thankful.

1 Like

Same experience here but I just accepted it as two different pieces of software making potentially different assumptions to give a purely indicative output.

Doesn’t using ERG mean that distance is totally irrelevant though? i.e. regardless of gearing you are only doing Y watts, therefore a calculated ‘wheel’ speed could vary hugely for same input given gearing and RPM and is genuinely meaningless.

1 Like

Official TR info on Speed / Distance:

In short:

  1. In Zwift, all of your riding speed and distance are determined via calculations using your power in conjunction with the road grade, your weight & height, and in-game bike/wheels. This is an estimate that somewhat parallels riding outside in concept.

  2. In TR, whether in ERG or Resistance mode, your speed and distance are determined via calculations from the trainer/bike wheel speed and the wheel circumference entered in the settings. It is a “simple” calculation of wheel revolutions times the wheel circumference, nothing more & nothing less.

This different approach leads the TR speed and distance to be impacted heavily by the gearing (and resulting wheel speed) that the rider is using. In ERG specifically, you can do the same workout in your low (34/28) or your high (50x11) gearing. Each will return VASTLY DIFFERENT speed and distance.

Essentially, speed and distance in training are garbage and not representative of the actual effort applied. People can manipulate that speed and distance via gear selection as shown above, which makes it highly subjective, and just short of useless.

If you care, and are using ERG, you can simply change your gearing up or down to get the speed and distance you want.


Thank you very much for your kind and quick response, Chad. 100% understood!

I agree that those two are useless metrics, but since they are there when the ride syncs with TPeaks I was wondering if I could “optimize” that aspect as well.

Thanks once again and congrats for the great work, really loving it so far. Huge fan of your work here in Spain! :slight_smile:


Since last month I’m often doing TR + Zwift at the same time - TR controls the trainer in Erg mode, Zwift provides the eye candy. The speed and distance never match, for the reasons @mcneese.chad linked. Same would happen if you recorded a Zwift session with a Garmin head unit or watch. Example: Ericsson +1, 75 mins, 26.1 km on TR, 32.2 km on Zwift. Just ignore it.


If one were to pair a Bluetooth speed/cadence sensor, would those numbers more accurately reflect speed/distance in the workout summary the “road” equivalent?

I only have ANT+, but would upgrade if it did.

I don’t think ANT+ vs BLE is an issue unless you have interference or dropouts resulting in data loss.

Besides that, not sure how you would mount the speed sensor to a Flux trainer. Not much exposed to be the “rear wheel”.

Sorry, I’ve got a wheel-on Flow. I’m realizing that I’m limited to 2 BLU for connection with my Apple setup, so even if I did it probably would connect without a workaround.

1 Like

An on-bike speed sensor measures wheel rotation speed, and multiplies it by circumference to calculate speed. A wheel-on trainer measures roller rotation speed, and multiplies it by roller circumference to calculate speed. A wheel-off trainer measure spindle rotation speed, and multiplies it by wheel circumference to calculate speed. If all three are set correctly, all three will report the same result.

1 Like

I would like it if TR was able to calculate a logical speed based on your power output, weight and height. What bothers me (as vain as it is) is that my buddies spend time on zwift and that mileage is added to their annual total while I spend an equal amount of time on TR and only get half the mileage for more work put in. Just to be clear I ride in my small chainring in ERG mode because I like how that feels.

1 Like

So the problem is your fake miles aren’t worth as much as their fake miles? :wink:

  • That takes the problems of comparing any outside mileage to any other rider and amplifies it to a silly degree. Mileage is a shallow metric devoid of much useful purpose other than possibly tracking equipment wear.

A hack that you could employ is to increase the wheel size entered into the TR app, so you get more “distance” from each revolution of your rear axle. I’ve suggested it in the past so people can fake whatever mileage makes them feel better based on their ERG mode gearing preference.

It’s not the solution you mention, and TR is apparently considering a simulation of sorts, but even if that happens in the future, you have a hack that you can employ right now.

@mcneese.chad I appreciate the information but not your condescending tone. My point is that I don’t want fake miles. I want miles representative of my effort on the bike.

1 Like

Sorry, not meant to be condescending. I made a mistake by including my opinion in the overall picture.

It seems as if the circumference doesn’t affect the data the smart trainer is generating (I use a tacx Neo) in ERG mode.

I increased it doesn’t do anything for distance (and speed).

I was looking for a way to increase distance a bit as I use the counters in Strava for my equipment as reminders for maintenance. For sound reasons I use the small blade in front and a big blade in the back in ERG, hence a relatively low flywheel speed.

Depending on the power level in the training therefore the trainer underestimates distance bij 35-50% or so. That difference will add up if you do 4-5 hours a week on the trainer.

And it is a bit annoying you cannot disable distance in Strava at all: then you could decide to just remove all distance data for indoor (ERG) riders and I wouldn’t have to go all out on a two hour trainer ride to average 19k/h.

Bottomline: either it would be nice if you can disable distance and speed data at all, so it doesn’t generates this unrealistic number. Or, it would be nice if there is some sort of algorithm that generates a fictional distance taking into account power and weight (pretty much what Zwift does).

If both those options are not available then as a last resort the function of increasing wheel circumference would help. But I have no idea how to do that for the tacx neo.

1 Like