Group workouts - different watt/kgs

Was checking workout group plan for us home.

My girlfriend has ftp 108 - 66 kg- and has to cycle 130 watt, i. E. 1,96 watt per kg

I have ftp 200 - 108 kg and have to cycle the same moment 240 watt, i.e. 2.22 watt per kg.

Everybody should drive same speed.

Why is there such a birg difference.

It would make sence for me to drive at 211 watt (108 kg x 1,96 watt per kg as fron my girlfriend(

Am i correct ?

Hi @Frank_Jager, I’m not understanding your question, sorry, can you elaborate?

Are you two doing a group workout event with “keep everyone together” enabled? Or are you comparing the exact same workout between your two accounts with different FTP’s?

I was comparing on each of our mobil phones same workout and found the difference i cannot understand. Thought that both should drive same watt/kg to drive same speed for the workout.

Hi @Frank_Jager

w/kg is not that relevant on roads flatter than about 5% incline. On flatter routes raw power will go faster.

Workouts are based off of percentage of FTP so they will be different. An interval at 95% of FTP will yield different numbers.

for example:
Girlfriend FTP 108, 95% is 102.6 watts, w/kg = 1.55
Your FTP 200, 95% is 190 watts, w/kg = 1.76

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Do you have an idea about my yesterdays race. Copy attached. For me there is no system on how speed will be calculated. I know less weight much faster but seems to be unrealistic. Is there a basic to calc how much i have to ride in watt to reach the top ten for example


Sorry no attachements possible. Could you check at my activities if you have time.

Thx in advance


Hi Frank,

I asume you’re from the Netherlands. I’m too. Please send me an email at and maybe I can help you with your question, because I can’t interpret your post the way you wrote it down.



workouts are based on a % of ur FTP, so riders with different FTP’s will have different power requirements for each section of the workout.
i.e. the fitter you are, the harder it’s gonna be for you, otherwise no point (:

If these are two separate workouts (doing the same workout), then:

Your girlfriend is doing 130/108 = 120% of FTP.
You are doing 240/200 = 120% of FTP.

So it sounds right. You were both doing a section targeting 120% of FTP.

Your weight is irrelevant in a workout usually, since the workout is based on your wattage.

Weight will alter your speed to a degree, especially on slopes, but the main issue here is how hard you’re working, not how fast you’re going. If both your FTPs are accurate then you will have both been working similarly hard.

Keep in mind that you are not just propelling your own body weight, but also the weight of your equipment selection (which may be as much as 7 kilograms difference between frames available on Zwift). Reference: https: // zwiftinsider. com/ rider-weight-speed/ This aspect is often overlooked in the world of professional cyclists, as any conversation about W/kg will always have inherent the assumption that their equipment will ALWAYS be at the UCI minimum legal mass.

Factors such as these become VERY obvious to cyclists on Zwift. Last evening, for example, I passed nearly 100 riders in the Tour of Watopia Stage 4 (Double Dirt - Serpentine 8 course) who were putting out much higher power than I could manage. Why? I was on a MTB and they were on various Road Bike selections, especially including notably slow “tron” concept bikes.

And obviously, the weight of your girlfriend’s bicycle (which you’ve not identified), is a much larger percentage of her body mass than yours.

This concept has been coined “true W/kig”. A full understanding of TRUE W/KG… may be obtained here, with kudos to the author.

https: // zwiftinsider. com/ wkg-tests/

Here’s a useful excerpt (thanks, @Eric_Schlange_ZwftIn


But why is it that when two riders are holding the same w/kg, the heavier rider will always be faster? There are multiple reasons, actually–but one big reason is what we’ll call “true w/kg”–that is, including the weight of the bike in our w/kg number.

Suppose we have two riders, 100kg and 50kg, both riding at 3w/kg. But let’s say they’re on 9kg bikes. If you add that bike weight to the rider’s weight and calculate the true w/kg, you get this:

100kg rider + 9kg bike @ 300 watts = 2.75w/kg
50kg rider + 9kg bike @150 watts = 2.54w/kg

So even though both riders are holding 3w/kg, the heavier rider is holding a higher true w/kg.

Another reason heavier riders go faster is that, unless you’re climbing straight up (which is impossible), your effort isn’t only lifting you up the hill–it’s also driving you forward by overcoming the forces of air and rolling resistance. Heavier riders are putting out more pure [nominal] watts than lighter riders, meaning (in simple terms) there are more watts available to overcome air and rolling resistance after the lifting is done.
uq # # #

The W/kg metrics displayed in Zwift are NOT “True W/kg” but rather only account for the weight of the rider. Apples and oranges comparison.