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    ReferenceRoutes & MapsSpeed Tests

    Crr and Watt Savings of Zwift Wheel Types

    Eric Schlange
    By Eric Schlange
    December 11, 2019
    19

    Zwift introduced varied rolling resistance in October 2019, adding a new level of variation to the performance of virtual wheels across various riding surfaces. Smart racers should take care to think strategically when choosing frames and wheels for mixed surface routes like Road to Ruins.

    Here’s a complete rundown of all the rolling resistance numbers and resulting wattage affects 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:

    • Pavement
    • 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 (example: Mayan Jungle)
    • 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 only the “Zwift Gravel” wheelset
    • Mountain: includes only the “Zwift Mountain” wheelset
    • Road: includes all wheelsets except the “Zwift Gravel” and “Zwift Mountain” wheels

    See the full list of Zwift wheelsets >

    Each of the wheel categories 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.

    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:

    SurfaceRoad Wheels CrrMTB Wheels CrrGravel Wheels Crr
    Pavement.004.01.008
    Brick.0055.01.008
    Wood.0065.01.008
    Cobbles.0065.01.008
    Ice/Snow.0075.014.018
    Dirt.025.014.018
    Grass.042

    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!

    Wheelset Wattage

    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).

    SurfaceRoad Wheels Wattage at 40kmhMTB Wheels Wattage at 40kmhGravel Wheels Wattage at 40kmh
    Pavement36
    8972
    Brick498972
    Wood588972
    Cobbles588972
    Ice/Snow67125161
    Dirt223125161
    Grass375

    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, 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.

    Fighting Resistance

    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.


    Changelog

    • Dec 8, 2019: added gravel wheelset numbers to the tables

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      Eric Schlange
      Eric Schlangehttp://www.zwiftinsider.com
      Eric runs Zwift Insider in his spare time when he isn't on the bike or managing various business interests. He lives in Northern California with his beautiful wife, two kids and dog. Follow on Strava

      19 COMMENTS

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      Peter Ricc
      Peter Ricc
      2 years ago

      Great information. Thanks for the work.

      0
      Reply
      Sammy Knockaert
      Sammy Knockaert
      2 years ago

      Is this correct that a gravel bike needs almost 100W extra over road bike on the ice/snow surface? Zwift physics are just stupid 🙂 I would like to see this irl where the road bike hits the ground even before he can reach 40kmh 🙂

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Sammy Knockaert

      It’s correct, BUT keep in mind the only ice/snow surface in Zwift is the radio tower climb, which nobody will do at 40kmh. At a much lower kmh, that wattage difference is also much lower.

      2
      Reply
      M4rk0
      M4rk0
      2 years ago

      Is it just me or does Zwift need a complete overhaul of their 1 to 4 star ratings for frames and wheels? The information provided adds no value.

      4
      Reply
      Weasel
      Weasel
      2 years ago

      So why would anyone choose to drop 400,000+ drops on a gravel bike? Surely Zwift needs to correct this.

      1
      Reply
      Pat
      Pat
      2 years ago

      How about NYC’s glass roads? CRR = 0.0001?

      6
      Reply
      Daniel Wood
      Daniel Wood
      2 years ago

      Great information. Now I’d love to know the additional wattage needed to overcome the Tacx Neo roadfeel! 🙂

      1
      Reply
      Jan Pryds
      Member
      Jan Pryds(@jan)
      2 years ago

      Does it mean that vEveresting on RadioTower are too hard/to long time compared with old records??

      1
      Reply
      Rémi Guyomarch
      Rémi Guyomarch
      2 years ago

      In real life rolling resistance decrease when tire size increase, not the other way around.
      So gravel tires (with small threads) should get lower Crr values than road tires.

      But at the same time, CdA (effective drag area) increase, and by a significant margin.
      Combined with the less aggressive geometry of gravel bikes, resulting again in CdA increase, means typical gravel setups are slower than pure road setups at high speed (ie on tarmac), simply due to aerodynamics.

      So either Eric’s calculations are wrong or Zwift physics model is wrong.

      1
      Reply
      Andrew
      Andrew
      5 months ago
      Reply to  Rémi Guyomarch

      While true that rolling resistance generally decreases as tire size increases, it assumes that tire construction is the same and pressure is held constant. But in real life, usually neither tire construction nor typical pressure is the same between road and gravel tires — gravel tires typically have knobs, thicker sidewalls, and are run at much lower pressures, all which increase crr. Disregarding Rene Herse tires.

      0
      Reply
      Stephen Thompson
      Stephen Thompson
      1 year ago

      Thank you for the information, very good intel. I assume a MTN bike is then the best choice for TDZ stage 7, correct? The bike weighs more but pros outweigh the cons with rolling resistance. Thank you.

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      1 year ago
      Reply to  Stephen Thompson

      For sure MTB on stage 7! The events might even force it, not sure…

      0
      Reply
      Rich
      Rich
      1 year ago
      Reply to  Eric Schlange

      Wish I’d read this before stage 7 😱
      Thanks Eric for all the brilliant tips.

      1
      Reply
      Ron
      Ron
      1 year ago

      I always thought 0.0032-0.004 represented a range of Crr’s for smooth asphalt. Which is what it seems to be in Zwift.

      0
      Reply
      Andrew Schneider
      Andrew Schneider
      1 year ago

      What road surface is the cracked looking road around the volcano. Is the cracking purely just cosmetic or does that get considered as a different road surface>

      0
      Reply
      Tobias
      Tobias
      4 months ago

      Hi Eric, do you have any information regarding the dependencies of rider weight to roling resistance, meaning if a 60kg rider rides up e.g. Castle KOM @Makuri with 5W/kg and so does a 70kg rider with respectively higher Watts but same W/kg – is the roling resistance increased for the 70kg rider? Or are they on the same resistance – if it would not be the same roling resistance, the heavier rider would have an advantage because the roling resistance would have a lower percentage of his reletavily higher power compared to the 60kg rider…

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      4 months ago
      Reply to  Tobias

      Crr is a constant based on the tire… so that doesn’t change with weight. BUT the actual drag from your tires is a product of both Crr and body weight (and gravitational acceleration, too, but that’s a constant).

      So the answer you’re really looking for is yes – a 70kg rider has to put out more force (read: watts) to overcome rolling resistance than a 60kg rider. If both riders are going the same speed, the 70kg rider is having to overcome more drag force from his tires than the 60kg rider.

      0
      Reply
      Mark Baker
      Mark Baker
      2 months ago

      Thanks for this Eric. I’ve always been curious about the dried up lava or dirt on the volcano roads. Does it have the same Crr as pavement?

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 months ago
      Reply to  Mark Baker

      Yes, it does.

      0
      Reply
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