How do your zwift numbers compare to real world?

(Emil Holland) #1

Hi folks, just did my first ride today, a great feeling. I did notice, however, that my average speed came out lower than for similar ‘real world’ rides even though I went very hard. Have you noticed anything similar or had the need to calibrate, and if so, how to approach this?

I have a vortex smart, and do not have a separate speed censor…



(Flores Carlos (C)) #2

Speed in Zwift is calculated in a different, it will always be different than in the real world, I know you talking about avg, check the zwift FAQ they explain more about how speed is measured. 


(Lauren Rubin) #3

My Zwift numbers always come out a bit higher than real world. I bet it comes down to what equipment you’re using as much as the software itself.

(Duane Gran [Vision]) #4

My outdoor rides tend to be around the 30-34kmh speed and in Zwift they tend to be around 33-38kmh, so a bit higher.  Compared to my locale, Zwift has these advantages speed-wise:

  1. As far as I can tell, there is no wind in Zwift.  There is air resistance at speed modelled, but outdoors a bit of wind will hinder three out of four directions your ride.
  2. My local terrain is more hilly. I get about 500m rise per hour while on Zwift it is closer to 400m on Watopia and 300m on Richmond.
  3. While I ride solo a lot in Zwift I’m often picking up a bit of draft passing or being passed by others, so it probably lifts the speed just a bit.
  4. It’s probably easier for me ride a firm and steady pace on the trainer.  I don’t need to dial back for turns or any real life scenarios.  I just put out the planned power.  It sort of explains why an hour on the turbo is so much harder than outdoors to me.
  5. Try as I may, I haven’t found a power up in the real world.

So Zwift seems a little faster even accounting for these things.

(Stuart Davis) #5

I tend to find my Zwift average speed quite close to an average real world ride, except normally the amount of climbing I do is 2-3x what I “do” in Zwift.

I use a Wattbike so the power figures should be bang on, however my average power for an indoor session is usually about 10-15% less than I get outdoors, yet the speed in Zwift is similar, so I agree overall Zwift seems a bit quick.

Then there are the persistent 15+w/kg flyers… lol

(Noel Nunkovich *USMES*) #6

My numbers are pretty close. My average speed in Zwift tends to be just a touch lower but I live in a really flat area. I don’t generally do much climbing in the real world so my average speeds are a little higher.

(Martha Frost) #7

I’m not sure how the “difficulty” slider works as far as the climbing bit…but my numbers look pretty similar to what I get outside too. Assuming no wind, no stops, none of that stuff. 

(Matt Robinson Westbury Wheelers) #8

I’m slower on Zwift for the same power output than IRL, by quite a bit.  Both on the hills and on the flat.  I’m pretty aero tho.


Of course, there is no way to enter your CdA.  I guess if you could, everyone would put themselves down as super slippy and you’d be back to square one.

(Michael Henasey) #9

Remember, there’s no headwind in Zwift!


(Eric Schlange [ZwftInsdr] B) #10

I find my numbers compare pretty closely between Zwift and the real world.

Emil–did you calibrate your Vortex using the Tacx utility? If you’ve got it too tight that might explain why it was harder than it should be…

(Stuart Davis) #11

My average speed in Zwift tonight was 21.3mph, on Strava. On the totally unrelated Wattbike computer it was 21.6mph.

Pretty damn close!

(Emil Holland) #12

Thanks for all the responses.

Eric, do I need another speed measuring device to calibrate? I don’t have any unfortunately… In terms of tightness, I set it tight enough that I don’t hear the tyre slipping, but not too much tighter than that…



(Noel Nunkovich *USMES*) #13

@Emil Holland

All you need to calibrate your Vortex Smart is the Tacx app on a compatible Android or Apple smart phone. I have a Vortex Smart as well, and in my experience calibration is an absolute requirement if you don’t have a separate power meter. I’ve compared my Vortex power to my crank-based power meter and gotten some pretty big differences. The Vortex is pretty sensitive to trainer tension. A little bit of difference in tension can make for a pretty big swing in measured wattage, which could really affect your Zwift experience.

(Eric Schlange [ZwftInsdr] B) #14

What Noel said! I don’t have separate power meters to compare my Vortex power readings to, but I calibrate it using the Tacx app and try to get it right in the middle of the good zone. 

Then I check it every few rides to see if I’m still in the right spot. So far it’s held pretty steady.

(Eric Schlange [ZwftInsdr] B) #15

Forgot to mention–you’ll need to enable bluetooth on your phone and pair it with your trainer (using the Tacx app) to do the calibration.

Once the calibration is done, turn off bluetooth (or at least turn off the Tacx app) so you’re not paired to the trainer anymore. Apparently Zwift doesn’t work well with smart trainers if they’re already paired via bluetooth–I had this happen when I first started–noticed it wasn’t really changing resistance on hills and such. Unpaired it and that fixed it.

(Noel Nunkovich *USMES*) #16

Hah, yeah. What @Eric said. My first ride or two I had all kinds of weird stuff happening until I realized I had my phone, my Garmin Edge 520, and Zwift all fighting over control of the trainer. So now the Garmin has the Vortex “sensor” disabled unless I’m using it specifically. I always start the Tacx app, connect to the trainer, calibrate, disconnect from the trainer, then start Zwift on the PC.

One last thing: make sure your rear tire pressure is consistent as that makes it easier to get a consistent calibration.

Based on my comparisons with both Power2Max power meter on my road bike and Quarq on my TT bike, the Vortex power readings are pretty spot-on as long as the calibration bar is very close to dead center in the app.

(malcolm may (WCC) C) #17

I’m researching this question also. I did my first ride today. On a dumb trainer - lemond revolution. Similar to the kikr I suspect but without the electronic. I busted my ass for 43 minutes so its a great workout.

Though my zwift says I averaged 14.9 mph and my joule says 19.6 mph. Apparently as lemond doesn’t seem to be recognized it caps me at 400 watts and I usually pull over 1400. So if the watts are part of the speed calculation then I can see why it will take me til eternity over the hills and forever in the sprint. 


(Eric Schlange [ZwftInsdr] B) #18

Top pro riders don’t even pull over 1400 watts… I think your numbers may be off.

(malcolm may (WCC) C) #19

Nah. Not so. These are just blip watts. 5 sec spots. Top riders pull over 1800 in a sprint. The track guys over 2000. Cav nearly 1700 in a sprint. 

You need to look a little deeper into the use of power. My powertap is calibrated and accurate. Upgraded and has a history. And pushing big watts has little to do with much other than its part of the algorithm.  Max watts are not the same as the FTP or the ave watts in a ride. 

Big people push big watt. Little people not so much. Next you’ll be saying 140 cadence is impossible

(Eric Schlange [ZwftInsdr] B) #20

mal may–I thought you were saying you were hitting 1400 watts for an extended period of time, not for a short blip. Sorry for the misunderstanding.