Are Zwift’s Tarmac Speeds Realistic?

When you compare your Zwift speeds to outdoor speeds, which is faster?

Zwifters tend to find their speed in-game is faster than their speed outdoors, typically by a margin of 1-4km/hr for solo rides. This can be disconcerting since many riders set fitness goals based on miles ridden per week.

There are several possible reasons why your outdoor speeds could be slower than your Zwift speeds:

• Zwift’s algorithms for calculating speed are incorrect.
• Zwift’s calculations include assumptions (such as your position on the handlebars or the condition of the road) that do not reflect your outdoor rides.
• Outdoor rides are slowed in ways Zwift rides are not.
• Zwift gives you more opportunities to draft.
• Your power readings in Zwift are not accurate, leading to unrealistically high speeds. (This is a separate topic which we won’t deal with here.)

Let’s look at these possibilities in detail and figure out what’s really happening.

Possibility #1: Zwift’s Algorithms for Calculating Speed are Incorrect

Formulas for calculating bike speed are well-established and reliable (see some details about that here). Zwift simply feeds a variety of variables in such as:

• Rider and bike weight
• Rider CdA
• Aero settings for equipment
• Tire rolling resistance
• Gradient
• Air density

into an established equation for speed, and the correct speed gets spit out.

I highly doubt ZwiftHQ’s game physics programmers have made any major errors in this area, so I’m going to dismiss this as an issue.

Possibility #2: Zwift’s Calculations Include Assumptions Which Do Not Reflect Your Outdoor Rides

Do you spend most of your time on the flats, on the hoods, or in the drops? How high is your seat, and how tucked in are your elbows, knees, and head? How smooth is the pavement?

There are other factors that affect your speed apart from the basics of road grade, power, and rider weight and height. Zwift has to make some assumptions here, and it’s fair to say those assumptions are quite generous.

One example: all Zwift tarmac has the Crr of new tarmac. How often do we get to ride on new pavement outdoors? It rolls fast.

We ran some speed tests on the Fuego Flats forward sprint with different rider weight and watt variables. (No, we didn’t run the numbers for climbs or group rides–we wanted to keep it simple.) Rider height was set to 175cm, the average male height in the US. We used timings from a basic Zwift Carbon frame/32mm wheels setup as well as a very fast setup of the Specialized Venge S-Works frame/Zipp 858 wheels.

We compared those numbers to two different online bike calculators, setting them to 25 degrees Celsius, 50m elevation, 8kg bike weight, riding in the drops, and default values otherwise. Here are the results:

• 300 watts, 100kg rider
  Zwift Carbon, 32mm carbon wheels: 38kph
  Specialized Venge S-Works, Zipp 858 wheels: 38.9kph
  BikeCalculator.com: 39.16kph
  Kreuzotter.de result: 37.1kph
• 225 watts, 75kg rider
  Zwift Carbon, 32mm carbon wheels: 35.8kph
  Specialized Venge S-Works, Zipp 858 wheels: 37.2kph
  BikeCalculator.com: 35.77kph
  Kreuzotter.de result: 34.8kph
• 150 watts, 75kg rider
  Zwift Carbon, 32mm carbon wheels: 30.8kph
  Specialized Venge S-Works, Zipp 858 wheels: 31.4kph
  BikeCalculator.com: 30.55kph
  Kreuzotter.de result: 30kph
• 150 watts, 50kg rider
  Zwift Carbon, 32mm carbon wheels: 33.7kph
  Specialized Venge S-Works, Zipp 858 wheels: 34.4kph
  BikeCalculator.com: 31.44kph
  Kreuzotter.de result: 31.7kph

As you can see, Zwift speeds are generally within 2kph of the bike calculators, with the greatest difference being at the 150 watts/50kg rider test where the difference between one calculator and our fast test setup was 2.96kph.

It’s worth noting that small changes in the bike calculators (such as using tubulars instead of clinchers, or a slightly improved CdA, or a higher elevation or temperature) are enough to equalize the speeds.

Additionally, the bike calculators don’t let you set which bike frame or wheelset you’re using, and we know those impact speed outdoors just like they do in Zwift!

Overall, I think it’s safe to say Zwift makes some slightly generous assumptions about your posture and environment which do not reflect a typical outdoor ride experience. The difference these assumptions make in speed is reflected in the numbers above.

Possibility #3: Outdoor Rides are Slowed in Ways Zwift Rides are Not

Stopping at traffic lights, braking to avoid vehicles or other obstacles, slowing into turns on steep descents–these are all are common occurrences outdoors which never happen in Zwift.

Then there’s wind, which doesn’t exist in Zwift but plays a major factor outdoors, rarely helping but often hindering our speed. And there’s coasting, which we do all the time outdoors, but rarely on Zwift.

Consequently, your Zwift average speeds will logically always be higher, even for similar effort levels.

Possibility #4: Zwift Gives You More Opportunities to Draft

Drafting in Zwift, like drafting outdoors, results in a power savings of ~25% or more. If you are comparing your outdoor solo ride speeds with Zwift speeds, the draft effect alone will make a noticeable difference since you often benefit from some draft effect in Zwift even if you’re not taking part in a group ride.

Conclusion

While a Zwift ride will generally be faster than an outdoor ride of similar effort, the differences are minimal and not enough to invalidate including Zwift miles in your training metrics.

Pro tip: if you’re really looking to take your fitness to the next level, start training with power and TSS, with less focus on distance. Here are two top books on this subject:

All About Zwift’s Cannondale SuperSix EVO Frame

Zwift added the Cannondale SuperSix EVO bike frame to the Drop Shop this week, and Cannondale fans have been justifiably pestering us with messages ever since. “It’s the only bike in Zwift with 4 stars for weight and 3 for aero! It must be fast… how does it perform?”

We’ve been hard at work putting test data together. It hasn’t been easy, because much of past test data was invalidated when Zwift modified the rolling resistance of various surfaces, making it so we can’t compare new test runs to old. But we still made it happen… for science!

Fast On the Flats, Faster Up the Climbs

The SuperSix EVO is billed as an “aero climbing bike”–that is, Cannondale is trying to find the holy grail of cycling–a stiff, fast aero bike that is also featherlight so it climbs well. Some say they’ve achieved that with the newest SuperSix EVO, rolled out in the summer of 2019.

Kudos to Zwift, who have set the bike up in-game to perform the way Cannondale intended–it’s fast on the flats, and faster up the climbs.

Seeing Stars

And it is the only frame in the Drop Shop combining a 4-star weight rating (the best possible) with a 3-star aero rating. You may think this would make the SuperSix EVO the fastest climbing frame, since the other top climbers are rated 4 stars for weight and only 2 for aero.

But you’d be wrong.

Test Results

While the SuperSix EVO slots in at #6 on the list of best climbing frames, it is still 8 seconds behind the King of the Alpe, the Specialized Tarmac Pro, on a ~50-minute climbing effort. So it’s a strong climber, but not the strongest.

And while it’s pretty fast on flat roads, it is still ~8 seconds behind the four fastest frames over a ~1-hour effort. (Those four fast frames are the Tron, Felt AR, Cervelo S5, and Specialized Venge S-Works.)

This is a perfect illustration of how Zwift’s 4-star grading scale, while simple, falls short in certain instances.

For example, the Cannondale EVO frame is rated 4-stars for weight and 2 for aero, so you would think it would be slower up the Alpe than the new SuperSix EVO. But no! If we were able to look at the precise numbers Zwift has used for these frames’ weight and CdA, we would see that the SuperSix EVO is slightly heavier than the standard EVO, even though both are rated at 4 stars.

Chameleon Paint Scheme

You can unlock the EF Education First Pro Cycling Team paint scheme if you finish the Giro de Rigo. But what about the default paint on this frame? To be honest, we’re still trying to figure out how it works, because it’s unlike any other colorway on Zwift! We can’t figure out if it’s a wacky bug, or a crazy sort of reflective paint. Check out these in-game shots, where the frame is clearly “mimicking” its surroundings:

The Verdict

If you don’t want to mess around with a “climbing rig” and an “aero rig,” you could do worse than having the Cannondale SuperSix EVO as your only frame.

Keep in mind you’ll need to be at level 36+ and have at least 816,500 Drops available to make the purchase.

The SuperSix EVO won’t beat the “specialized” rigs on their own turf, but it’s pretty darn close. If you’re looking for an all-around frame with a bent towards climbing, this is a smart choice.

Your Thoughts

Have you picked up the SuperSix EVO yet? What other frames would you like to see in game?

Important note: this post contains speed test results for Zwift frames or wheels. These results may change over time, and a bike's performance relative to others may also change. We don't always revise posts when performance rankings change, but we do keep current, master versions of our speed test results which are always available. See the frame charts, wheel charts, and Tron vs Top Performers for current performance data.