Fast Dirt: Testing Zwift’s Rolling Resistance Changes

Zwift’s physics, like outdoor physics, are influenced by many factors including rider weight, virtual bike choice, power output, and virtual environment (gradient, air resistance, rolling resistance, etc).

Yesterday’s Zwift update to game version 1.52 included three notes about rolling resistance changes:

1. Reduced rolling resistance proportionally across road, gravel, and mountain bike wheelsets when riding on dirt road types.
2. Reduced rolling resistance for the ENVE G23 wheelsets to match other gravel wheelsets on gravel and dirt road types. 
3. Corrected the rolling resistance of the Zwift Mountain bike wheelset on brick road types.

The first change is the biggest news, but I’ll cover all three notes below. Let’s dive in!

Faster Rolling Dirt

Rolling resistance is known as “Crr” in the cycling world (read all about Crr on Zwift), and yesterday’s update significantly lowered the Crr of dirt surfaces throughout Zwift. Here is a table showing the old and new dirt Crr values for each of Zwift’s three main bike types:

* “Watt Reduction” represents how much less power riders will need in order to travel at 40kph with the new Crr values. This assumes a 75kg rider on a 7kg bike.

While this change has made the dirt roll faster for all bike types, the change isn’t as “proportional” as Zwift’s note may imply. As you can see, road bike riders are saving 80W with this change, while MTB and gravel riders are saving 36W.

Another way to look at it: if you’re on a road bike going all-out while climbing up the Jungle road (a regular occurrence in races), this change gives you back 80W that would have previously been used to overcome rolling resistance. That’s a lot of watts!

So, how much faster is the dirt? We ran some tests with our bots, using a 75kg rider holding 300W steady.

Our first test was on Makuri Islands’ Kappa Quest route, which features the map’s key dirt section (the Temple KOM climb) plus some tarmac. It’s a great test route to show how changes in rolling resistance affect particular sections and overall lap times on mixed-surface routes.

Old Kappa Quest Times

New Kappa Quest Times

A few notes on the results above:

• Previously, the Tron bike was 35 seconds slower up the Temple KOM compared to the Crux gravel bike. Now that gap has shrunk to just 12 seconds, which is right around how long it takes a well-trained rider to swap bikes in Zwift.
• The Tron bike essentially matches the gravel and MTB’s times on the descent, thanks to its superior aerodynamics and newly-reduced Crr.
• Zwift has updated their stock gravel wheels to match the name-brand gravel wheels, so all available gravel wheels perform identically. This is probably a good move. Less confusing!
• You may notice this week’s update also made the MTB faster on tarmac. More on that below.

Jungle Lap Times

Of course, the Mayan Jungle is where Zwifters encounter dirt most often. This is especially true now that Zwift has opened up their southern coast road! How did the dirt Crr change affect Jungle speeds? We did some test laps of the Jungle Circuit:

Wow! While all three bike types got faster, the road bike got much faster.

To Swap, or Not To Swap?

Prior to this week’s change, riders would often swap to a gravel or MTB when hitting key dirt sections like the Temple KOM or Jungle Circuit in a race. If you were able to swap quickly this was a smart move in many situations, since you could put a lot of time into your non-swapping competitors.

But given the results above, does it make sense anymore to swap from a road bike to a gravel or MTB when hitting the dirt?

Probably not. Certainly, if you’re in a situation where you’ll need to swap from road to gravel/MTB then back again, a swap no longer makes sense because you aren’t saving enough time swapping to make up for the cost of both swaps (approximately 25 seconds).

With that said, swapping may make sense if it’s a one-way swap. For example, if you’re in a Makuri Islands race that finishes atop the Temple KOM, it may make sense to swap to a gravel bike when you hit the dirt, since you can stay on that bike all the way to the finish line. (This would especially make sense if you’re going for a fast segment time and make the swap before the KOM start line).

ENVE G23 Fix

Zwift’s update 1.51 included a config error for the ENVE G23 gravel wheels – they didn’t get updated to roll faster on gravel like all the other gravel wheels. This week that error was fixed, so now the ENVE wheels match the performance of all other gravel wheels.

I already mentioned this above, but it’s worth noting again that Zwift also changed their Zwift-branded gravel wheels to match the performance of the name-brand gravel wheelsets, so all the gravel wheelsets now perform identically.

Faster MTB Wheels

Zwift says this week’s update “Corrected the rolling resistance of the Zwift Mountain bike wheelset on brick road types” but it would be more precise to say Zwift has made their MTB wheelset roll slightly faster on nearly all surfaces.

Along with the dirt change already noted above, this week’s change reduces the MTB wheels’ Crr from .01 to .009 on the following surfaces: Pavement, Sand, Brick, Wood, and Cobbles.

You still won’t be seeing many mountain bikes out there on Zwift roads, but at least they’ll be a bit faster.

Questions or Comments?

What do you think of Zwift making their dirt faster? Will you be doing any swapping in the future? Share below!