Lighter v Heavier Riders

ZwiftHQ … I know that you want to believe in your Algos that determine Zwift rider speed, but please keep in mind that those math equations gave you a result with DRAFTING that was (and may still be despite a recent dampening) WAY too beneficial to ridersAn especially in big groups and even moreso descending, SO THERE COULD ALSO BE SOMETHING IN NEED OF A TWEAK IN YOUR CALCS OF THE IMPACT OF RIDER WEIGHT ON RIDER SPEEDS.

Is it possible that this could be the source of why heavy riders do not seem to have more benefit on descents versus the lighter ones?

As for the lighter vs heavier rider debate … I have a theory … We KNOW there are no winds on Zwift … I wonder if the Zwift Algo may also ignore the self generated wind/wind resistance from riders going 40kph? If the algo ignores or miscalculates that drag, then the lighter rider does not have to fight that drag as much as one should. We know lighter riders struggle to fight regular or self created headwinds more than a heavy one, so that might explain some lighter rider outperformance on descents … Could you please share your thoughts ZwiftHQ?  Thanks.  #Rideon #zwiftΔriding 

They have factored in heavier performance, I am a light rider (56-57kg) and often can’t keep up with others who freewheel past me downhill - I can’t catch them even with 500w of effort!

My Last Ride.

Rider 99kg Zwift - Richmond, VA 12/22/2015

TT BIKE 12.4km 211W 35.0Kph 21:25

vs Bike calculator

Position Hood = 12.4km 211w 31.52kph 23.60
Position Droop = 12.4km 211w 34.07kph 21.84
Position Aero = 12.4km 211w 36.74kph 20.25

I’ve now done about 10 rides in Zwift. I am 6’9" and 300+lbs (down about 90lbs from when I started a year and a half ago), so I’ve certainly a fringe use case here.

Going up hills is torturous and I get passed by dozens of riders. Meanwhile, going down hills, I can essentially coast and recoup.

Though close, the performance is a bit exaggerated.

What I mean is in the physical world, it’s not nearly as hard to go up hills. Yet in Zwift I absolutely CRAWL uphill while consistently putting out ~200w to 250w. Honestly, I dread the hills in Zwift more than in real life.

Meanwhile on many of the long downhills in Zwift, I can essentially coast down @~30mph. Now, with my mass, I can certainly do a lot of coasting in real life, but not at such high speeds for extended periods.

Here’s a screen cap from Strava from my last ride:

Going up in the 10% grade I’m outputting 500-600w for 6mph. Going downhill at -7% grade I’m coasting at 0w and 35mph

…Just some feedback for the product team. Let me know if there’s any way I can help to tweak and improve the product.

As a heavier rider (6’5" 250lbs), I find maintaining speed downhill to be reasonably easy, just as it is in real life.  The thing that seems odd to me is that applying power downhill does absolutely nothing.   I can be cruising downhill at 27mph, and apply 500w of power at 110 RPM, and it basically does nothing.  I can’t seem to get over 30mph now matter how hard/fast I pedal.


I was in spectator mode watching a race the other day.  Going downhills, some riders were trying to break away, dramatically increasing their power on the descent, and they were still going exactly the same speed as the other riders in the group who were applying half the power (watching their Watts/Kg on the rider list).


Note to Self:  If racing, don’t bother wasting energy trying to make up speed on the downhills.  It doesn’ t work.  Save the energy for the climbs.

+1 The resultant errors due to inaccurate estimation algorithms are also quite apparent for Heavier Riders.

I’ve made some more observations regarding power output and road gradient in Zwift compared to real-world riding (I have a power meter on my road bike).

Ignoring wind resistance as best as possible, I have to conclude that there is something not quite right with how my speed in Zwift is affected by reasonably large power output (ie 4-5+w/kg) on the downhill sections.

On a 8-10% downhill gradient (sheltered and minimal headwind) I can apply ±500w for 10 seconds or so and accelerate from 25mph freewheeling to about 45mph.

I cannot reproduce this in Zwift (using a Wattbike).

Yep. I am 103 kgs right now. I hammer up the hills at 350 w average in 3 minutes. Its harder than real life. On the downhill though it doesn’t matter if I push it over 1000 w, I struggle to hit 40 mph, and rarely exceed 41. Again, not like real life.

I am satisfied its the penalty I pay for being old and heavy, and not really a candidate for the KOMs. And I do recognize that some of this is purely mathematically magical.