You already know your weight setting in Zwift affects your speed–especially up hills!
And you probably also know that the bike frame and wheels you select will affect your speed.
But did you know your height setting also affects your speed? Zwift uses your height in its equations to calculate CdA, which is a measurement of how much resistance your body gives to the air as you ride. Just like outdoors where aero is everything, Zwift calculates taller riders as offering more wind resistance.
We’ve done a lot of automated test laps with various height/weight/equipment setups, and confirmed this: all other things being equal, the taller you are the slower you’ll go.
The test laps we’ve done in the 225-watt power range work out to ~30 seconds longer on a full Richmond lap for each 15cm (approximately 6″) of height added. Or to put it another way: a 5′ tall rider will be ~2 minutes faster than a 6′ tall rider for every hour of riding on a fairly flat course.
Another way to look at this is every 15cm removed from a rider’s height is like adding 5-10 watts of power in terms of speed increase. We can figure this out by looking at average Strava speeds at different heights, and plugging those numbers into BikeCalculator.com to look at power differences.
These numbers fluctuate depending on the wattage range you’re looking at, and what type of route we are riding–long, slow climbs won’t be as affected by height as much as a flats or downhill.
But it is worth noting that Zwift, in attempting to emulate real-world physics, does take your height into account (even if your avatar doesn’t get any shorter or taller).
Is the difference the same between a road frame and a TT frame in Zwift? It seems like CdA differences should be much less for TT frames.
Been a while since we’ve tested it, but I don’t think it makes any difference.
How about draft? It should be less behind little people.
According to Zwift, the draft IS less behind little people.
It’s incredible how Zwift penalizes tall riders. Using kreuzotter.de, in real life 15 cm would only make ~10s of a difference per Richmond Loop (at 225 W). From my estimates I suppose that Zwift simply scales the cda with the height squared, which assumes all the body and bike proportions scale up and down linearly (including head size and all the bike parts).
The height “bug” pisses me off actually. I have been considering just putting my height at absolute minimum because of this. There is no real world example where height would incur a penalty like this. They should have stuck with weight only for cda calculations.
I think this explains why shorter riders dominate the TT’s in Zwift, even if they are putting out much less power in a flat TT. It is completely counter-intuitive to how real world flat TT’s work.