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 â€śtronâ€ť concept bikes.

And obviously, the weight of your girlfriendâ€™s bicycle (which youâ€™ve not identified), is a much larger percentage of her body mass than yours.

This concept has been coined â€śtrue W/kigâ€ť. A full understanding of TRUE W/KGâ€¦ may be obtained here, with kudos to the author.

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

Hereâ€™s a useful excerpt (thanks, @Eric_Schlange_ZwftIn

Q.

HEAVY WINS

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, actuallyâ€“but one big reason is what weâ€™ll call â€ś**true w/kg**â€ťâ€“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 letâ€™s say theyâ€™re on 9kg bikes. If you add that bike weight to the riderâ€™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 youâ€™re climbing straight up (which is impossible), your effort isnâ€™t only lifting you up the hillâ€“itâ€™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 â€śTrue W/kgâ€ť but rather only account for the weight of the rider. Apples and oranges comparison.