How Does Zwift Determine My Speed?

How Does Zwift Determine My Speed?

For Wheel-on Classic Trainers:
Zwift takes the wheel speed broadcast by your speed sensor and the power curve (see example below) of the trainer you select on the Pairing Screen and converts that to virtual watts, also known as “zPower”.

Your in-game speed is determined by:
• zPower watts
• Your weight and height
• In-game bike frame and wheel set
• In-game drafting (Tri and TT bikes get no drafting boost)
• In-game road surface (Mountain bikes are fastest on dirt roads, but slowest on pavement)
• In-game virtual elevation changes.

Activating a Power Up such as the Truck (draft boost), Feather (weight reduction), or Helmet (aero boost) can further alter your in-game speed for a short duration.
powercurve
This is not a real trainer curve, only to demonstrate the concept.

Example: Your wheel turns at 40 km/h then Zwift will use the curve and determine your Power as 200w. Using a set of complex equations taking your weight, height, road incline, rolling resistance and other factors in to account Zwift will calculate your virtual Speed.
So that 200w can be 45km/h on a flat road or 12km/h on a hill.

For Smart Trainers and Power Meters:
Your in-game speed is determined by:
• The power/watts broadcast by your trainer/power meter
• Your weight and height entered
• In-game bike frame and wheel set
• In-game drafting (Tri and TT bikes get no drafting boost)
• In-game road surface (Mountain bikes are fastest on dirt roads, but slowest on pavement)
• In-game virtual elevation changes

Activating a Power Up such as the Truck (draft boost), Feather (weight reduction), or Helmet (aero boost) can further alter your in-game speed for a short duration.

*****Also note that there are no stop signs, cars, or wind, and you don’t need to slow down for curves within Zwift.

Thanks to @Gerrie_Delport and @Mike_Rowe_PBR for all the help in putting this together.

Ride On!

Having trouble with speed
Output wattage seems too low
Climbing on non-smart trainer
Garmin Edge and Zwift data difference
Zwift New User - Game or Real Life Simulation
Speed/distance inaccurate
Why I am Too slow
Resistance connection troubles!
Very low speed with Wahoo Speed Sensor
Help Needed to Understand my Metrics
Totally new to Zwift and exercise bike riding
Speed & Kilometers inaccurate
Very low power
Why does it ask for my wheel circumference on a direct drive trainer?
Kurt Kinetic reports incorrect cadence
Speed on hills
Wrong KPH displayed
Cannot climb the Volcano
Pairing Garmin Speed and Cadence Sensor 2
How to record actual mph
Assistance with Wahoo Kickr
Too Slow in Zwift
Power reading
Getting a spin bike - where do I start?
Dumb trainer with speed and cadence sensors
New to Zwift (Hub), trouble with MTB setup and resistance
Real axiom ct 2015 trainer Low watt after update
Rodillo normal
Very large speed difference from trainer and zwift
Very large speed difference from trainer and zwift
Speed to slow
Add an inline speed skater animation
Having trouble with speed
Speed determination in Zwift
SCOTT Week 2020
Nube: how to calibrate a dumb Trainer
Why is my Zwift saying I am going so slow?
Are there some 'boosting' coefficient for women in zwift? Some discrepancies between FTP in Zwif and ZwiftPower
Wahoo speed sensor on spin bike
Help A Noob With Kickr Snap & Zwift Understand If I’m Doing Something Wrong Or Not
Discrepancy between my wahoo bolt and Zwift Kickr data
New to Zwift and finding Garmin miles and zwift miles inconsistent
Slow Speed
Cycle-Ops Jet Fluid Pro Trainer
Speed not accurate during training program
Error when pair speed sensor
Heart rate v leg strength
ZWIFT Spin Bike Help
New to Zwift - Very slow speed
Zwift speed unrealistically fast
Cyclotron Fluid ST?
Inaccurate with wahoo kickr
Titanium Strength TS2 Indoor Bike
Closest to elderly Tacx Satori Blue
Classic Trainer Speed Difference
Getting the most out of a 'dumb' trainer
Cannondale CAAD12 - compatible?
Speed on Zwift is too fast
My tyre size not available as an option
Tips for New Rider on Keiser M3i?
Speed not accurate and no draft
Speed dropping off during climbs
How is Zwift calculating speed
Trainer selection?
Distance not correct
Quick Hello & noobie first question
Advice please
Speed sensor pairs, in game speed low
Speed issues & setup
Sensores wahoo y velocidad
Speed readings to high on Elite Power Mag Smart B+
Velocidade/ Speed no Zwift
Spin bike, not enough Watts, everyone passes
Cycling slow in the Zwift world
Which Tire Size Should I Pick?
New to Zwift, getting differing results
Watts and speed too slow
Speed doesn't match outdoor speed
Actual speed
Routes how do speed & gradient work
What would be a typical speed at
Getting dropped even if im riding harder
Spinning Bowflex C6 Help
Is there anything to explain how Zwift works?
Zwift biker slow on hills
Zwift shows half speed
Speed drops dramatically
Schwinn 510 U
Avg watts vs max watts
Zwift wat
First time user questions
Accessing ride-stats?
The cyclist (me) doesn't move
Slow Speed

2 posts were split to a new topic: Custom Zwift speed

Is there a calculator somewhere where I can put in the data and see what the watts should be? My spouse is on a kickrSnap and we can’t ride together because he is sooo slow. He’s not like that on the road.

He calibrates every time he rides.