Incorrect distance

I always just care about how fast I travelled a certain distance to prep for an event. So how quick for a sprint Tri segment on the bike, or Olympic distance etc.

With running, the general best metrics they have access to are speed, distance and heart rate. Power for them is new, under development and in need of more time to learn how they can use it.

For cycling, we have power, that is generally a superior metric to speed, distance, time and heart rate. Power (and it’s related metrics) take into account more of the actual demand on the body than any of the other metrics can really do.

If you do 10 miles on the trainer in 30 minutes vs 1 hour, you are getting much different stress. Sure, you can add the speed component to that and figure out some relative differences. But can you really put anything notable to the differences in terms of stress on the body?

That is what Power, TSS, IF and others offer. They are more direct to the actual loading on the body. Adding in Heart Rate to that can fill out a wider picture. But speed and distance are relatively useless metrics in comparison to those.

The advent of Virtual Power for the trainer makes inside riding and access to estimated power cheap and easy. Even when it’s not “perfect” match to real power, it is still superior to speed and distance.

Yes, see the linked article above for greater details.

Depending on the trainer, your weight, aero drag, bike / wheel / tire setup, speed and distance on the trainer may be WAY OFF. This is especially true if you are performing workouts via ERG mode in TR. There is a pure calculation of rear wheel revolutions per minute and the circumference of the wheel in the app.

The reality is that ignores the real power in play, and that can be HUGELY different in low gearing vs high gearing in ERG mode. Again, read the info above that covers this.

The only way to estimate your rolling speed in a real condition is to use something like Zwift or similar app that takes into account rider size, weight, related equipment and such. Even with that, there are notable differences between real results and Zwift results in speed and distance.

The info you want to know can really only be learned by actual use outside. You will have to deal with real conditions, including wind (that is totally lacking in all simulations we have now) so you can get a guess as to your power in play outside and covering real ground.


Just drop 20 kg off the weight you input and away you go!

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I’m not sure exactly how to explain this, but I’m gonna try anyway. Let’s say you currently cover a 40k bike leg of an Olympic tri in 1 hour 15 minutes. Let’s say it takes approx 200 watts NP to do this.

On the trainer, if your 1 hr 15 min NP is greater than 200 watts, that would yield a 40k bike leg faster than 1 hr 15 min…correct?

Forget about what “distance” you recorded on the 1 hr 15 min trainer session…and focus on the watts. THAT will tell you that you will go faster outside.


Yeah, your right. I would put this in same category as messing with the calibration of your trainer. And you would be specifically trying to do it. In TR I’m not sure you could say your distance is ever correct. And many folks shift their gears and unknowingly effect their distance.

My original statement still holds true. Once your beyond the inputs of weight and power, there is nothing you can do to modify zwift speed.

  • Are you including equipment choice within the game?

Wheels and bike do have an impact on speed. Some are very minor differences, but best to worst case can actually matter depending on how much you care about “speed” in the game.

This may be a beer infused ramble that seems logical at the time I posted it but distance doesn’t really matter outside either does it?

What I’m thinking is that your time to complete to a flat 40k is going to be different from your time to complete a 40k in the mountains. Add in a headwind or tailwind and that will also effect your times as well.

Yup, distance and speed (related to time) are relative metrics and give some info, but far from full context of a ride. Without power (or even with heart rate), it takes coupling of several data points to form a picture of effort and relate it to other future efforts.

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I think we are losing the original context of what I was talking about. Yes, there are a lot of configurable options in zwift. None will give you a drastically incorrect speed unless you modify the power or weight data going into the zwift algorithm. You have to be specifically trying to cheat the system. In TR the speed posted to strava is never correct, and it is drastically off for even those not trying to cheat.

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Well, the ITU Course Marshall’s might have something to say about that…

Turbo trainer is for training, you want to simulate the race.

Funnily enough, I was/am doing exactly that for my Olympic race prep, I’m doing London this year, maybe Eastbourne and/or Dartford Bridge.

I haven’t done an Olympic race for years, and the courses are either very hilly or have many dead turns. So an idea of your/my performance over 40km from the turbo isn’t going to be terribly accurate.

I’m using the TR Olympic Low Volume Triathlon Plan at the moment, will shift to Mid volume in May.

As the weather is terrible here (BTW I’ve just bailed on the Tunbridge Wells Half Marathon due to Storm Dennis) I do race simulations on Zwift occasionally. 40km on a virtual flat course, avg power 220W I covered in 1h05. On a virtual course with the same elevation gain as Eastbourne, 227W and it took me 1h13.

This was kind of reassuring as it fit my targets, but there’s no way to know how you sit on the bike, how aerodynamic you are, what tyres you use, the road surface quality, the heat, the wind, of race day.

At the end of the day I still need to put in the training and push for a higher FTP before race day.