New to Zwift and on the 7 day trial. Did a Watopia after updating all my settings correctly (tyre size etc), and found that my garmin says 17.6 miles and Zwift reports 20.1 miles, way off. Anyone else experienced this? I’m a stickler for my data being correct so if this is a flaw I’ll be disappointed.
My key concern is that Zwift is showing me as being way faster than I know I am. I trust what my Garmin tells me when I use it independently. If I compare them as 2 stand alone activities they seem way off and that bothers me. I hope that makes sense.
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You cannot compare the speed or distance between Zwift and Garmin. The Garmin does not know anything about the virtual elevation changes.
Speed within Zwift for your setup is calculated but taking the rear wheel speed, the power curve of the trainer you selected and that is converted to watts. With those watts, weight entered, height entered, ingame bike, ingame drafting and virtual elevation changes your speed is determined.
As long as you enter the correct info your ingame speed should be close to accurate.
Another thing to remember is that within Zwift you don’t slow down for corners, no stop signs and nothing else that would make you break or slow down.
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Hi Susan,
your post does make sense.
I think this may have something to do with the way Zwift translates
your power output and converts it to the game. I believe there is a
line of thought that inside miles may be harder than outside miles
partly due to the inability to coast (i.e. down hill) and possibly also
due to cycling indoors with no natural cooling effect. Therefore you
get more for your money so to speak.
Basically the two figures you get will not be the same. I had the
same issue when I first used Zwift and was using my rollers with
a Garmin speed sensor.
Now that I have started using a rear wheel off trainer I only have
Zwifts distance calculation. I don’t think you should worry about
it too much although I understand your concerns. Zwift is a great
place to keep fit. You just have to decide which distance to record,
Zwift or Garmin.
I’d go Zwift. I’m sure more is better, isn’t it? LOL
"Ride On "
What trainer are you using? and are the trainer on the correct setting.
If you ride up the mountain in zwift then your garmin will show faster but when you ride down than Zwift will show slower times.
There is definitely something inconsistent with Garmin. I too record on my “Indoor Bike” setting on my Garmin and my observations are that when I am on a workout Garmin shows much higher distance than Zwift. This makes sense since Zwift will adjust the speed for the terrain that I ride but at the same time, Garmin calculates the distance correctly. Correct me if I am wrong, but since in a workout I stay in the same gear (I prefer 50/14), then the average cadence will translate to the distance covered using appropriate conversion tables (for example: BikeCalc.com - Speed at all Cadences for any Gear and Wheel).
When I am in free ride, Garmin gives me a much shorter distance than Zwift.
I think that Zwift is more consistent but not sure if it is more accurate. Garmin has an issue that I cannot figure out when it translates power so much differently in workout and free ride modes for similar power output.
The attached screenshot of my Garmin speed trace will show you what I mean. The first 90 minutes are a workout and the last ~8 minutes are straight after when I continued a little longer in a free ride. Obviously my power fluctuates but on average it is not too dissimilar to the power I was holding during the workout yet the speed is substantially lower…
Unfortunately it does not work like that. I your garmin only know how fast your wheel are going. So to calculate speed it use the magnet on your back wheel. Zwift use the your power number and calculate your speed taking into account the wind, your weight your height and the road (up or down).
So your garmin and Zwift won’t match it may for one specific condition but in general it wont.
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Not sure I agree. If the bike had a wheel on, for a given cadence the wheel would turn a certain times per minute at a given (fixed) gear. This is a fixed number locked between the pedals and the wheel. In reality, your cadence fluctuates with the terrain and you also switch gears but if you could hold the same cadence at the same gear along a course, the speed would be fixed irrespective of incline. The difference would be that with inclines, the resulting power would be very small downhill and very big uphill.
I don’t really care, to be honest. I just record the biggest number! 
Yes this is true, but you don’t take into account the power needed to turn the pedals at a constant speed.
what trainer do you use?
Here is a small test.
-
Put your bike on the trainer and put it in the biggest gear in the front and the smallest at the back, don’t let the trainer roller make contact the wheel, now pedal at 90 rpm and record how difficult it was, your speed and power (if you have a power meter)
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Now let the trainer make contact with the wheel and set it on its most difficult setting and pedal at 90rpm recording difficult it was, your speed and power (if you have a power meter).
you will find with no resistance it was easy to pedal and you generated 0w (power) and with resistance it was very hard to pedal and you did the same speed as test 1 but now you generated a lot more power.
Your garmin did not know you were working hard to generate that power but Zwift know you did and use that power to calculate your virtual speed.
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I think that we are saying the same (similar) thing but you said it a bit more clearly.
Cheers!
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Then what on Earth is the point in Zwift using your speed sensor if it’s not going to use it for what it’s for…measuring speed based on the circumference of your wheel. It’s farcical!
The point of the speed sensor is to let Zwift try and measure your power output, so that it can translate that into your in-game speed, taking into account your weight, your height, your in-game frame and wheels, the gradient, the road surface and so on.
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Please read this: How Does Zwift Determine My Speed?
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I get the utilisation of speed for their power algorithm but why not keep things simple and measure distance the good old fashioned way…Distance =Speed x Time. Since when has power ever come into that simple equation. Why do they have to over-engineer it lol. Your car doesn’t measure speed using the horsepower of the engine or aerodynamics…it takes the circumference of the wheel and uses the rpm as a factor and proxy for speed.
Then what is the point of having a trainer with resistance, your wheel will spin much faster if you remove the resistance roller from the wheel.
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But it does take more power to go up an incline.
While pedaling if you keep the same amount of power when hitting an incline your speed will drop, this goes for cars as well.
If Zwift just used your wheel speed and matched it to in-game speed you would be doing unrealistic speeds going up incline within Zwift. You would also have a very unfair advantage going against users using a power meter or smart trainer. This is why Zwift levels the playing field by using power to calculate speed. It is more or less far for everyone.
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Because Zwift isn’t just travelling on the flat all the time. You don’t keep the same speed when you hit an uphill slope unless you push harder, right?
Yes, but your car’s wheel is travelling in a single world and your car slows down on an uphill slope unless you press the accelerator down further. Your bike’s wheel is in one world but your avatar is moving in another.
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