I did a some tests on Zwift a couple of days ago to check how accurately their speed calculations match what would be expected in real life.

The protocol was to use the London Classique route which has the advantage that you zone into a couple of short sprints. One is uphill the other downhill which adds another useful variable.

I did 2 runs on each of the sprints at a number of different weights ranging from 45kg to 90kg incrementing in 5kg steps. I attempted to keep power constant for each run and started each run in the same place before the sprint start so as to build up speed before entering the sector.

I kept rider height constant at 1.70m.

I captured 2 variables

Time was that displayed on the screen as I crossed the line

Power came from Strava for the relevant sector (since I was doing a flying start and wanted to pedal through the finish I figured that was more accurate and consistent between runs than using the lap button)

Gear was fastest TT setup Cervelo P5x with Zipp 858/super 9 wheels.

The file below contains the raw results. There are two sheets, the first for the uphill sprint, the second for the downhill sprint.

Segment data is from Strava

Uphill is 0.19km at 1.1%

Downhill is 0.18km at -1.4%

(sample run here https://www.strava.com/activities/5057250842

Here is the data

https://drive.google.com/file/d/1VyX3f_8m7BtUu9jrWvgCU2MbaCa8ZeRq/view?usp=sharing

I have drawn my own conclusions from the data but do not wish to share them atm as Iâ€™d like to get some independent views just on the base data.

So hopefully there are some mathematicians and/or power geeks (hands up Iâ€™m one) who can take a look and say what they think.

The topics I am particularly interested in is how accurate is Zwift at estimating TT speed compared to real life and especially how does weight affect speed in Zwift TTs compared to real life?

Hope you can help and looking forward to hearing your conclusions