Speed Tests: Gravel, MTB, and Road Frames on Zwift Dirt

In March, Zwift adjusted the performance of bike frames and wheels in the game, aligning them more closely with real-world performance differences between various bikes and wheel types. At the same time, they released the bike upgrade feature, allowing riders to put in work to make their bikes marginally faster.

Learn more about the performance changes >
Learn more about bike upgrades >

While I’ve spent a lot of time unpacking these changes on the road bike/tarmac side of things, I really hadn’t tested bikes on Zwift’s dirt surfaces until recent days. And the results surprised me! Let’s dig into how various bike types perform on Zwift dirt today.

First, a Wheel Important Note

The 1-hour time gap data below is based on the speeds of our baseline bike, which is the Zwift Carbon with 32mm Carbon wheels.

In Zwift, you can’t put the 32mm Carbon wheels on a gravel bike. Instead, you must choose between several gravel-specific wheelsets. The nice thing is, Zwift keeps it simple: all the gravel wheels currently perform the same.

When it comes to mountain bikes, there is just one wheelset you can use, named “Zwift Mountain”.

Because of how wheels work, for the data below, we paired each frame type with a specific wheelset so the comparisons would be useful:

• Gravel Bikes all used the Zwift Gravel wheels
• MTB all used the Zwift Mountain wheels
• Road bikes all used the ENVE 8.9 wheels (we tested a few top-performing wheelsets, and these turned in the fastest lap times)
• Zwift Concept Z1 (Tron bike) used the Zwift Concept wheels

Time Savings Over 1 Hour at 300W (Stage 0 vs Stage 5 Frames)

Let’s begin with a simple chart that clearly illustrates the performance delta between gravel, mountain, and road bikes on Zwift dirt. This chart illustrates the time difference between each bike and our baseline bike (Zwift Carbon with 32mm Carbon wheels) over 1 hour of riding on the Jungle Circuit at 300W (4 W/kg).

Use the toggle to switch between viewing the un-upgraded versions of each bike and the full-upgraded (stage 5) version.

Takeaways

First things first: there is a big performance gap between gravel bikes and MTB+road bikes on the dirt. This gap is bigger than it’s ever been, thanks to changes Zwift made in their March update.

In fact, the gap between gravel and road bike performance in the dirt is approximately twice what it used to be. (After Zwift made road bikes roll faster in the dirt in November 2023, road bikes were around 1 minute slower than gravel bikes across an hour of riding. Now that gap is more like 2 minutes.)

The performance gap between the fastest and slowest gravel bikes has also widened. Formerly, the difference between the fastest and slowest bikes was ~20 seconds. Now it is ~38 seconds. (This lines up with the changes Zwift made to road bikes, where they stretched out the bell curve of performance so there was a larger delta between the fastest and slowest bikes.)

Toggling between stage 0 and stage 5, we can see that fully upgrading a frame doesn’t change its performance relative to other frames of the same type (the fastest gravel bike remains the fastest gravel bike, etc.). But a few of the road bikes do overtake some mountain bikes, as the delta between MTB and road shrinks at stage 5.

Lastly, this data shows that mountain bikes are never the smart choice if you’re looking for the fastest setup in a Zwift ride. In the Jungle, mountain bikes are just barely faster than the road bikes (at stage 0 at least). But mountain bikes are significantly slower than road bikes on all other surfaces, and gravel bikes clearly outperform them on dirt. So the mountain bike has no home in Zwift currently, unless you’re looking to ride with a group and make the effort more challenging.

Time Savings Over 1 Hour at 150W (Stage 0 vs Stage 5 Frames)

This chart uses the same bikes as the first chart, but the tests were run at just 150W (2 W/kg) to see how performance deltas change at lower speeds.

Use the toggle to switch between viewing the un-upgraded versions of each bike and the full-upgraded (stage 5) version.

Takeaways

Wow! The performance deltas between each type of frame are much larger at 150W vs 300W. ~249 seconds separate the Cervelo Aspero from the S-Works Tarmac, almost twice the gap (~128 seconds) we saw at 300W.

The mountain bikes clearly outperform the road bikes at this power level as well, with the Scott Spark RC World Cup besting the S-Works Tarmac by ~83 seconds at 150W vs ~10 seconds at 300W.

If you weren’t sure about the advantage of a gravel setup on Zwift dirt, this chart makes it clear.

Overall Conclusions

The changes Zwift made to bike performance on dirt surfaces are quite substantial. And I think they’re good changes:

• Road bikes didn’t really get slower on the Jungle dirt, and that’s good – because nobody likes going slow on Zwift
• Gravel bikes got faster, making them a viable option in more scenarios. This adds a strategic bike choice element to certain Zwift races/rides.

Racers will want to consider the implications of Zwift’s updated dirt performance and polish up their mid-race bike swapping technique for courses that include significant dirt stretches.

What’s Next

Given the impressive performance of gravel bikes on dirt, I will conduct additional tests on key dirt sections to determine where using a gravel bike (or swapping mid-ride) makes sense. We’ll especially take a look at Makuri Island’s Temple KOM, which is a mostly dirt climb that forces key selections in races on that map.

I’ll also test how gravel bikes now perform on the gravel surface type, which currently only exists on the Sgurr Summit North in Scotland.

Stay tuned for results…

Your Thoughts

Do you have comments or questions about how Zwift bikes perform on dirt? Share below!