How will my Weightloss affect my Zwift Speed?

I just updated my weight from 96kg to 93.8kg… I am just wondering if and how this will affect my speed on Zwift?  Will such a small weightloss even show in my average speed?  What is the math on this… just wondering how fast I will ride if I reach my weight goal.


My weight was approx 108 two months ago… I imagine that would have affected the speed in which I <crawl> up the Zwift Hills…

It will certainly affect your speed going up hill - but effectively not on the flat. The steeper the hill, the more difference it will make…

Zwift seems to be pretty realistic in the way it models climbs - in other words, if it takes you a certain amount of time to climb a hill with an average gradient of X in Zwift, it should take you about the same amount of time to climb a hill of the same gradient in “real life”, providing your power output is the same and you have entered your weight correctly.

The place to go to do cycling maths of this sort is the Analytic Cycling website (google it). If you select static forces / speed given power you can work out your speed up a hill of a given gradient. There are a whole bunch of assumptions and if you are interested I can give you a good set of defaults to enter, but the critical ones are slope (a 4% gradient (as in the Zwift Watopia epic KOM) = a slope of 0.04), weight (including bike, rider, all gear etc) and power. Oh, and the answer is in meters per second, so there is a bit of maths involved… :wink:

To cut a long story short, when I use this to calculate what my time should be for a 5.8 mile hill of average 4% gradient using my average power (260 W) from my best attempt on the Zwift epic KOM it gives me 23 minutes 54s, which is pretty close to my actual time on Zwift of 23m 16s. Doubtless I could realistically tweak the parameters to get it spot on. As you may have guessed I’m pretty light at 63kg, and when I do the sums on Analytic Cycling I enter 72kg, which is 63kg plus the weight of my best bike, clothing and equipment in real life. Zwift must do something similar and calculate a total weight for bike + rider etc by adding a few kilos to the rider weight entered.

Anyway - to answer your question - if I do the sums for myself and add an extra 2 kilos, it adds about 20 seconds to my theoretical time. So your weight loss from 96kg to 93.8kg can probably be expected to save you about that amount of time on that climb. It might not sound like a lot, but it is really when you think about it. E.g. 3kg weight loss would gain you about half a minute, which is a big margin at the competitive end of things, even for amateurs/mortals…

Obviously your weight loss from 108kg will have gained you much more time (maybe about 2 or 3 minutes?). And it’s worth pointing out that a 4% average climb is not very steep - on a really steep climb of 12% or so the time saved would be several times more!

Awesome… thanks

I am not sure how much faster I got by losing the weight… never cycled in my life, bought a bike a couple months ago, which is why I am losing the weight.  I have a lot to learn

The great thing is that the more you ride your bike the more your power output will increase as well as the more weight you will lose… and these things will act together to make you faster than either would on their own…

As a general rule, the more power you can produce the faster you will go, with the proviso that when you are going uphill weight becomes more and more important the steeper the slope. On the flat, aero becomes more and more important the faster you go…

I am a lightweight rider 61k and do 3.8 w/kg and just can’t keep up to heavier guys doing 3.5 w/kg over the course of a race - say 30 k or so.  Unfortunately, I think that is the way it is in real life.  Little guys get crushed in the crits. 

Yeah, crits aren’t great for lightweights like us… You need to be fitter and more skillful than the bigger riders to stand a chance. And unfortunately in most places it’s difficult to find competitive events for amateurs that hinge on long climbs…

I am learning a lot from you guys… I thought I may lose power as I lose my weight (less fat on my legs pushing down on my pedals hehehe).  Also, I thought that the lighter rider had all the advantage, and the heavier riders were the underdogs vs the light guys.

Will the power really come up on its own the more I ride?  Or should I be doing something special?

You won’t lose power by losing fat… :wink: There comes a point when weight loss will reduce power, but that’s only a worry for the seriously skinny folks… And even then, it could be advantageous if you are a climbing specialist and power to weight ratio is more important than power alone. On the flat, raw power is more important, but any excess weight that doesn’t contribute towards power (fat, basically) is still disadvantageous as it will reduce your ability to make quick accelerations and also make you less aero (more surface area).

In general, the more you ride the more powerful you will get, but the fitter you get the more difficult it becomes to make further gains - the graph starts to flatten off towards a theoretical maximum (that you will never reach as an amateur…).

But importantly, there are different types of cycling fitness/power. If you train a lot at sprinting you will get more powerful over short intervals, whereas if you train at maximum efforts over 20mins or an hour you will get better over those periods.

I’m 111kilos around 245 lbs and 6’4" 1.93m tall. That’s heavy on a bike. I’ve been riding in the real world solo for  8 years to lose 112lbs to get to this weight even! It was only when I got to the point where I could even consider riding with a group that I realized just how far I still have to go. Compared to just about every other rider I am MUCH heavier and the little guys leave me for dead on the climbs, in a group ride they are slower than me on the downhills and I have to hang back into the hills rather than attack then they shoot up them while i lose my momentum and grind up slowly running out of gears (even on my 11-32) . I’d always assumed the little guys had every advantage therefore. So it’s interesting to read above about heavy riders having the edge in ‘crits’. I’m pretty powerful in the legs (gotta be to carry the weight) but the only way I can lose weight via diet is to eat smaller salads lol! I’m at a plateaux, so all I can do is ride more (and Im out every day pretty much anyway) …sorry…long post…short repy is that I notice every single gram of weight loss/gain on a bike instantly lol!

Just to be clear, the comments about bigger guys having the edge in crits etc. only really apply if you are comparing people with similar body compositions. So a 6ft, slightly more muscular guy would likely have the edge over a skinny 5ft 7" if they were both of similar fitness and with similar body fat percentages, whereas the opposite might apply on hiils. This is because the bigger guy has more raw power but the skinny guy has a larger power to weight ratio. But unfortunately weight from fat is only ever going to be a disadvantage, and excess muscle mass is also likely to be disadvantageous, in the upper body at least.

yes, it’s all upper body blubber lol!