Zwift’s physics model includes varied rolling resistance of virtual wheels across different surfaces. Smart racers think strategically when choosing frames and wheels for unpaved or mixed-surface routes like Road to Ruins and Two Village Loop.
Here’s a complete rundown of all the rolling resistance numbers and resulting wattage effects for Zwift wheelsets.
(Note: we update this page as new wheelsets are released–see the changelog at the bottom for a list of changes.)
Zwift’s Road Surfaces
Zwift worlds use several different road surfaces. Here’s the complete list from fastest to slowest:
- Sand (introduced in the Urukazi expansion of Makuri Islands)
- Brick (example: part of downtown Innsbruck just before the Leg Snapper)
- Cobbles (example: Italian Villas)
- Wood (examples: Watopia fishing village piers and bridges)
- Ice/Snow (found only on the Radio Tower climb, as far as we know)
- Dirt (examples: Mayan Jungle, Yumezi’s Temple KOM)
- Grass (found only on Repack Ridge, as far as we know)
Zwift has built the game so each wheelset can have its own Crr (rolling resistance) value for each road surface type. So a set of TT disc wheels may roll super fast on pavement, but terribly on dirt. Just like you’d expect outside.
When the Crr increases, two things happen in game: your speed drops, and resistance increases on your smart trainer.
Zwift Wheel Categories
Right now, there are three categories of wheelsets in Zwift:
- Gravel: includes the “Zwift Gravel” wheelset plus some name-brand wheels which (oddly) perform better on dirt than the Zwift Gravel wheels
- Mountain: includes only the “Zwift Mountain” wheelset
- Road: includes all other wheelsets (40 at the time of this posting)
Generally speaking, each of the three wheel categories above has its own Crr values for each surface in Zwift. This makes each type of wheel perform differently across different surfaces.
Example: on pavement, Road wheels have a Crr of .004 while Gravel wheels have a Crr of .008 and Mountain wheels have a Crr of .01. This means Mountain wheels will roll slower than Gravel wheels which roll slower than Road wheels.
The only exception is gravel wheels. Here, Zwift chose to do something different and make all the newer name-brand wheelsets roll faster on dirt than the Zwift Gravel wheelset, giving them a dirt Crr of .016 while the Zwift Gravel wheels have a dirt Crr of .018.
Wheelset Crr Values
We’ve done some testing to determine the Crr of all the wheelsets on each of Zwift’s surface types. Here are the current numbers:
|Surface||Road Crr||MTB Crr||Gravel Crr (Namebrand)||Zwift Gravel Crr|
You can see why the jungle dirt feels much tougher on a road bike than a mountain bike. Because it is! The rolling resistance is nearly double!
It’s also worth noting that the Crr value for road tires on pavement (.004) is quite low. We’re virtually rolling quality tires on fresh tarmac. Living the dream!
If you know the Crr value of a particular tire/wheel, you can extrapolate the wattage required to overcome the rolling resistance at a particular speed. This is commonly done outdoors, and in our tests, it seems to work with Zwift’s physics as well (nice work, Zwift programmers).
Doing this tells us how much of our power is going toward overcoming rolling resistance. In turn, this tells us how many watts we can save just by moving to a wheelset with lower rolling resistance.
Here are those values, assuming a 75kg rider on a 7kg bike traveling at 40kmh (24.9mph).
|Surface||Road||MTB||Gravel (Namebrand)||Zwift Gravel|
Now things are getting interesting. So if you’re in a race on Watopia tarmac traveling at 40kmh, and you’re on a road bike while the guy next to you is on the Gravel bike using the Zwift Gravel wheels, he has to put out 72-36=36 watts more than you just to overcome rolling resistance.
But if we move to the Jungle Circuit, suddenly that Gravel rider has the advantage, able to keep up with you while doing 223-161=62 fewer watts! (Of course, in the jungle nowadays we don’t usually go as fast as 40kmh, so this difference would decrease a bit.)
The numbers will get wild once we have more wheelsets with different Crr’s available. Pull out your calculators, kids!
Note: the wattage numbers in these examples don’t take into account additional differences that could occur based on varying rider weights, heights, drafting status, bike frame used, etc.
Of course, rolling resistance isn’t the only thing you’re feeling on your smart trainer. In fact, it’s typically the least of the three factors which determine overall trainer resistance. Just like outdoors, we know that wind resistance and/or gravitational force are usually the biggest things slowing our avatars down on Zwift.
- Nov 10, 2022: added sand surface data, and explained how newer namebrand gravel wheels have a different Crr than Zwift’s original gravel wheels
- Dec 8, 2019: added gravel wheelset numbers to the tables