On the workout screen, when set to imperial units, the speed and distance are displayed as the metric value with an imperial label.
As much as I wish 136 W would get me to 27.8 mph, unfortunately it doesn’t. It should be 17.2 mph (which is 27.8 kph). Same goes for the distance, it’s displaying the kilometer distance with a miles label (it should be 19.65 miles which is 31.6 km).
Yes this is fixed in our next version. Thanks for reporting it though.
Apparently it extends to all measurement units because the app thinks I’m almost 400 pounds (180 kg) instead of 180 pounds. Updating it does nothing, it just reverts back to the imperial equivalent of the metric value.
It shows correctly on the website, so hopefully it’s calculating my “speed” and “distance” correctly still.
I’m seeing wildly inaccurate speed/distance value from last nights spin vs that reported by Garmin.
While they both may be wrong, I’m more inclined to believe that the Garmin is closer to true, since I’m recovering from achilles surgery 10 weeks ago, and definitely not putting out enough power to be averaging 29km/h
Android, T/D app updated 3 apr 2025 v 5.2.5
using
Not sure if related or different to this ticket but seemed to be similar
Neither is inaccurate/right/wrong…
Speed and distance on a trainer without an elevation profile is BS. Doing exactly the same effort with a low and high resistance setting gives you totally different speed/distance.
On a virtual ride with elevation profile, you can expect to be ‘in the ballpark’, that’s it. There’s still nothing accounting for wind speed.
Use power on a trainer (or use a speed/power conversion profile adapted to your specific trainer.
Thats not correct. Speed and distance are simple calculations based on number of revolutions of the wheel, which is measured using a rotating sensor on the rear wheel;
distance= revolutions x times the circumference of the wheel. A 700x23 tyre has a circumference of ~210cm (https://www.cateye.com/data/resources/Tire_size_chart_ENG_151106.pdf)
and speed is simply distance/time taken.
Elevation has little to nothing to do with this calculation except perhaps to differentiate between 2-d flat distance on a map, and actual distance cycled on the road due to hills/descents - essentially 2 sides of a triangle being longer than the third.
Regardless of the absolute accuracy of the distance/speed, given that my garmin and trainerday are using the exact same sensors, on the exact same resistance, on the exact same bike/turbo/environmental conditions, thus both have access to the exact same data, they should both show the same distance and speed - incorrect as it might well be - like they do for heartrate, cadence and power.
What med tech CD Is trying to say is that a certain effort that you put into the bike let’s call that power is going to produce a certain speed or emulate that speed. Outdoors that depends on factors like your body weight the type of tires that you’re using on your bike, the wind, Your aerodynamics and well as well as if you’re going uphill or downhill. When you try to estimate indoor speed, you shouldn’t just look at wheel speed.
Basically all smart trainers, you can shift to a small gear, which normally would be easy/slow or switch to a bigger gear, which will ultimately change the speed of your wheel, but it won’t change your effort. So wheel speed is a very poor indicator for indoor speed, especially in ERG mode and something like Zwift where you’re dealing with slopes wheel speed could be used.
So what we do is we ignore wheel speed because it is so Inaccurate, And we convert power to speed this has the potential to be extremely accurate, but it needs to factor in your weight your aerodynamics, and an estimate estimated elevation.
so in our profile settings on the website, you can actually change your aerodynamics or your CDA and change the relationship between power and the speed that you go so you can fine-tune it the way that you would like. If ours seems too fast, just increase your aerodynamic drag your CDA and if ours seems too slow, just decrease it we assume like a .5% elevation grade. As I said this method is extremely accurate if you get those parameters correct and we speed is completely inaccurate depending on what gear you’re in for ERG mode.
So what you seem to be saying is that even though I’ve added my speed/distance sensor to the TD app, it is totally ignored? So I should just not bother registering it?
If this is the case then what purpose does it serve in letting it be registered?
and I must play with that drag value until i get figures which seem to match the garmin? when I get that figure matching, what effect will changing gears on the bike have, or changing the resistance setting on the turbo?
Can you tell me what trainer you are using? But generally no we do not take speed from speed sensor. There is something called virtual power for people that don’t have any power meter but that’s something different.
I’m on a Tacx T1435 Sirius Soft Gel Trainer, with the already mentioned sensors:
also one I forgot to mention
All paired with both the TD app and also with Garmin 540
That´s not correct. You were on a stationary trainer and moved exactly 0m…
You have a true Power meter. Use that and forget about distance/speed on a trainer. You could just as well pedal without your wheel touching the trainer roller and with a high enough gear do 80kph during 2 hours without fatiguing.
It only makes some sense if you do a virtual ride.
Oh yes, Assioma pedals for power converted to speed is much more accurate than speed from speed/cadence device in this case. Just need to dial in our CdA to match your expectations.
If you ride outdoors you have an idea of how many watts produce how much speed on flat ground.
This calculator compares power to speed for example
With your devices you can change resistance and gearing to produce different combinations of wheel speed with the same amount of power. On outdoor bikes you don’t have a resistance knob other than hills and wind…
And yes to MedTechCD’s point, indoors you did not move so speed and distance = 0. But yes many of us like to track virtual miles like real miles…
unfortunately I’m way down on “normal” power output, due to recovering from achilles surgery, so i think nothing from my historical data is relevant- especially since I never really ride on the flat, usually straight up into the mountains.
I just assumed that a wheel-on turbo would be almost as accurate as an real road ride, since it counts actual wheel revolutions, which directly translates into distance, regardless of power delivered; obviously a direct mount trainer is different as there’s no wheel to count rotations of.
anyway, I’ll try playing with that value, but do I move it initial by .2 or .0000002? how severe is it as an adjustment?
You are missing the point. If you could turn resistance to 0 you might be able to pedal at 70kph indoors or even 100kph with big enough gearing… The problem is the trainer’s resistance does not know your weight, what kind of bike your ride so it has no idea how to set the right resistance to match what you would feel outdoors for a give speed.
Tip your bike upside down and pedal with your hands. I bet you could make your wheel go a lot faster than you could if you were riding on flat ground outdoors with your hands. Now it is possible some resistance value on your trainer would be closer to matching your outdoor speed for a specific speed. Realize resistance is linear but speed is not 100w does not produce 2 times the speed 50w does on flat ground. So one specific resistance is not accurate for different intensity levels.
Changing from .6 to .5 likely gives you about a 10-20% difference depending on the power you are producing.
i dont think i am. one revolution of my (700x23)bike wheel is 210cm. that doesnt change with how much power i put out, or what gear i’m in or what the resistance setting on the turbo is, nor wind, friction etc. if the wheel turns 10 times, thats 20.1 metres. what does change is the power required to make the wheel turn 10 times, and that depends on the gear I’m in and the resistance of the trainer, but that power is being measured (accurately, hopefully) by the pedals. very low resistance means less power needed, high resistance more power
of course this is only valid when i have a way of counting the wheel revolutions to measure the distance, which i do with the wheel-on turbo, and which i assume the garmin uses to measure distance, since the gps will not give it any useful data
We should probably give up on this. 
Yes it’s easy to calculate the distance on your wheel. That’s not the problem, the problem is it’s too inaccurate compared to outdoor effort vs speed. Some times when you get lucky Garmin will give you a speed/distance you like indoors using a speed sensor and other times it will be grossly off. Once you set ours it should stay reasonably accurate.
There are endless discussions of this problem on the internet.
Fair enough, Thanks for the discussion - and for the product also; I was only trying to get an understanding of why the divergence between the two platforms for the same event. When I get cleared to go back on the real bike I’ll give them another comparison in ‘real world’ and see if they are closer then. In the meantime I’ll just twiddle the dial until I get close enough! Cheers
TD uses Power to calculate what the outdoor speed would look like on a fairly flat road (0.5% grade), for someone with your weight.
Measuring wheel speed on a trainer is only of interest if you don’t have any power device. The wheel speed can be used to calculate power from a speed/power curve that is valid for a certain resistance setting and/or trainer type. That calculated power (from wheel speed) can then again be translated to a speed that will reasonably match outdoor speed for a certain given grade and your weight.
If you simply use wheel speed, a 1 hour 100W effort can result in 5k or 50k distance depending on the resistance setting. That’s why I say (and I’m only one of the many saying that) that speed/distance measured by wheel speed on a trainer is meaningless. You need to measure Power if you can and that will fairly well translate to an acceptable outdoor speed.
If you don’t have power, use duration and HR to get a feel for effort given.
What you’re saying is similar to:
‘I rode 65kph for 20 minutes’ without saying that you didn’t even pedal because it was a long fast downhill section. That makes no sense from a training POV.
