How Does Zwift Calculate Rider Speed?

How Does Zwift Calculate Rider Speed?

Your riding speed in Zwift’s virtual world is determined by several factors:

  1. Watts: this is the main factor determining your speed. The more power you’re putting into the pedals, the faster you will go.
  2. World: road gradient, draft effects, road surfaces, and air density values in Zwift’s virtual worlds all affect the speed of your avatar.
  3. Weight: lighter riders will go faster on flats and climbs than heavier riders if both are putting out the same wattage. Heavier riders will descend faster. Just like outdoors! Read “How Rider Weight Affects Speed” for specifics.
  4. Height: taller riders are less aerodynamic than short riders, so the shorter rider will go faster if two riders are holding the same wattage and everything else is equal (weight, frame/wheels, etc). Read “How Rider Height Affects Speed” for specifics.
  5. Virtual Bike Choice: the frame and wheelset you choose affects your speed, as each frame and wheelset has a weight and aero (CdA) value assigned to it. See our frame and wheel charts for a detailed breakdown of the performance of each frame and wheelset on Zwift.

So How Do I Get Faster?

You can’t exactly alter Zwift’s physics or your height, but here’s the fun part: you have control over the other factors listed above!

Are you overweight? You’ve come to the right place. Cycling is an incredibly effective low-impact exercise that lets you burn calories without beating up your body. Couple daily rides with a smart diet and you can shed weight safely and quickly while gaining fitness. (Ride Your Way Lean is a good read covering the fundamentals of weight loss for cyclists.)

Want the fastest virtual bike setup possible? We’ve got all the info you need, and then some.

The biggest speed factor, of course, is power. What kind of wattage can you put out, and for how long? Every body is unique, and we’re not going to dig into training plans and philosophies here. What we will do, though, is recommend the “Build Me Up” training plan in Zwift for anyone looking to gain fitness via a proven training program designed by an experienced coach.

And we’ll recommend these two books – the very best resources available for cyclists looking to train smart with power:

Notes on Speed Mismatches

Zwift speed doesn’t match your Garmin speed? Since Zwift uses a variety of factors to mirror real-world physics, pairing your bike computer to your power meter or smart trainer will return a very different distance number than Zwift’s – and that’s as it should be.

Zwift speed doesn’t match your outdoor speed? Zwift simulates outdoor cycling quite well, but no system can factor in every single outdoor riding variable (think potholes, rider posture, and group dynamics for starters). Because of this, some riders have observed that their speed on Zwift doesn’t match their outdoor speed. But there are plenty of sensible explanations for this!

“Keep Everyone Together” feeling slow? The physics of group workouts on Zwift are modified in order to keep all riders together. For most riders, this results in a Zwift ride that feels slower than normal. Similarly, the “Keep Everyone Together” option in Meetups uses some black magic to keep your group together, often resulting in some riders moving faster than normal, while others move slower.

Questions or Comments?

Share below!

About The Author

Eric Schlange

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

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John
John
11 months ago

I think a lot of the difference between outdoor speed and zwift is down to the fact you never stop on Zwift, no traffic lights, intersections to get through etc., slowing down and acceleration has a big impact, and of course wind !!!! on a calm day I find the flat and climbing speeds match pretty well

Dan Connelly
11 months ago
Reply to  Eric Schlange

Agree! But even so the CdA numbers used by Zwift are comparable to pro riders with their wind-tunnel-honed positions and their speed suits custom-fit to their bodies. The average century rider is a mess, with clothing flopping all over the place, in comparison. People underestimate the effect of this.

Mac Weelz
Mac Weelz (@wongsol)
11 months ago

“…lighter riders will go faster on flats… than heavier riders if both are putting out the same wattage.”

I’m assuming this is because the heaviest rider’s size/girth increases wind resistance? If riders were putting out the same w/kg—not pure watts—the heavier rider will go faster than the lighter rider on flats and downhills. For average C riders in a race:

50kg rider @ 3.5wkg = 175w
100kg rider @ 3.5wkg = 350w

Mac Weelz
Mac Weelz (@wongsol)
11 months ago
Reply to  Mac Weelz

I meant B riders. Sandbaggers ruin it for everyone.

I wish you could edit comments after the fact. /sigh

Aaron Lipton
Aaron Lipton
11 months ago
Reply to  Mac Weelz

At equal w/kg the heavier rider will always have the advantage. At equal watts, unless you’re going downhill the lighter rider will have the advantage.
This is why, as a lighter rider, I am not a fan of Zwift’s w/kg system since often it tends to put lighter riders at a disadvantage

Scott Ryan
Scott Ryan
11 months ago
Reply to  Aaron Lipton

Not entirely sure I agree with lighter riders being at a disadvantage – being a heavier/taller rider I have to put out more watts to have an equivalent W/kg. Climbing is also much harder on heavier riders. Don’t see many 80+kg riders winning races – although it amazes me how many 60kg and under riders there are on Zwift….

dan
dan
11 months ago
Reply to  Scott Ryan

lighter riders are at a disadvantage most of the time, unless its a hill the size of box hill or greater, shorter than that a heaveir rider pretty much can dominate on the flats, and downhills. 350+ races says so

Rich H
Rich H
11 months ago
Reply to  Scott Ryan

I totally agree.
At 6′ 7″ and 85kg, I obviously struggle to keep up with any lightweights on climbs, and then on the flat, I have to push a higher w/kg to stay in a group than any smaller riders because of their superior aerodynamics.

Rich H
Rich H
11 months ago
Reply to  Aaron Lipton

But it’s a lot easier for lighter riders to have a high w/kg.

MHolden
MHolden (@holdenadventures)
11 months ago

good article. thanks
how does Zwift and Zwift Power calculate placing for group rides?

  • I don’t think it’s ordered by whoever goes through the final arch way 1st
  • I don’t think its by sign-up or join order
rdcyclist (Mark Crane)
rdcyclist (Mark Crane) (@rdcyclist)
11 months ago
Reply to  Eric Schlange

I don’t think that’s the case for the timed rides. I’ve been several kilometers ahead of the leader and had him place in front of me. Same thing with a friend in an event: He was at least a click in front and placed 20 positions behind me.

rdcyclist (Mark Crane)
rdcyclist (Mark Crane) (@rdcyclist)
11 months ago
Reply to  MHolden

For timed group rides, it’s a complete and utter crapshoot so you don’t want to hang your hat on the results of those kind of events. The events over distance are the ones that are ordered by who goes under the banner (and it’s not always the banner you think it is) first.

Crankenstein
Crankenstein
11 months ago

Why in the world are you trying to race in timed group rides?

Mark C
Mark C (@rdcyclist)
11 months ago
Reply to  Crankenstein

I’m not. I was just answering M. Holden’s question about placing in group rides. Speaking for myself, I just found it interesting that Zwift couldn’t keep the finishing order for the timed group rides. Most times it has been comically incorrect.

Mirco
Mirco (@mircolup)
11 months ago

Basically low weight riders have disadvantage on zwift

B G
B G
11 months ago
Reply to  Mirco

Correct – not just it depends – given the W/KG system and the fact that the draft is less than real life. Holding onto someone doing 50 watts greater than you is much harder in Zwift than real life.

Rich H
Rich H
11 months ago
Reply to  Mirco

I think it’s the exact opposite.
I’m 85kg and if I were to do 3w/kg, I’d be putting out 255w.
Then if I were to ride with a 50kg rider, they would only have to put out 150w to get the same 3w/kg.

JennyT
JennyT
11 months ago
Reply to  Rich H

“Only?” For you but not for them. I’m 50kg. 150w is decent effort for me. Have you considered that we all have the same size bikes too, which we wouldn’t in real life?

D C
D C
11 months ago

I would love to see a chart which plotted w/kg vs. speed for flat courses on Zwift vs real-life. I think lighter riders go too fast for their power output at times in Zwift.

Kevin
Kevin
11 months ago
Reply to  D C

Yeah me too, it’s absolutely not a match at this moment. I get that Zwift uses a power meter to calculate speed, but it’s nowhere near the same speed at the same wattage outside. Never will I be able to make a 40km/h ride outside, but in Zwift it’s “no problem” using a Direct Drive.

KimS
KimS
11 months ago

There also appear to be spots on various routes where Zwift’s programmers (for reasons best known the themselves) have built in slow spots. There is no change in grade, no change in the type of road surface, but speed just gets reduced for an interval. This is very noticeable on a couple of the Watopia routes and in Richmond as well.

Mick Such
Mick Such
11 months ago
Reply to  Eric Schlange

Yeah Eric, if you mean the 1st hairpin bend on Box Hill, yeah I come to a virtual stop and spin out…. This has happened since London was created…. When are Zwift going to sort that out…. I’ve got the Full PRL to do this winter and that means 11 times up Box Hill. 😕 🤔🤔

slowridr
slowridr
11 months ago
Reply to  KimS

I wish it were possible – well, I suspect it is possible, but I don’t know how – to see the exact gradient that Zwift is applying and telling the trainer at each moment. I’ve long suspected that there’s more variation than the headline integer 0%, 1%, 2% etc, you can feel rolling ups and downs even on constant 0% sections. If the displayed gradient is an integer-rounded average over the next 10m or 2 seconds or something but the ‘steep bit’ is very brief that would explain the ‘slow spots’ – they often happen at junctions e.g. on Volcano… Read more »

Russ
Russ
11 months ago

Hi Eric, Your mention of ‘Air Density’ is something I’ve not seen before: “World: road gradient, draft effects, road surfaces, and air density values in Zwift’s virtual worlds all affect the speed of your avatar.” Do you know if air density is different on each World?

Viktor
Viktor (@viktor_icarus)
11 months ago
Reply to  Eric Schlange

I would assume that could be their way in a sense of creating a more realistic approach to the bigger climbs since the elevation would play a part in the real world?

Dan Connelly
11 months ago

I was hoping to see actual equations here… it seems from your rider weight tests up L’Alpe that Zwift isn’t solving the conventional power-speed equations, but rather uses some approximation, for example a linearization to avoid solving a cubic equation. In that test the % reduction in time exceeded the % reduction in body weight, which is inconsistent with the standard equations.

ShakeNBakeUK
ShakeNBakeUK (@bakeuk_2)
11 months ago

why do you claim in this article that lighter riders are faster on flats than heavier riders at the same w/kg, whereas in this article you claim the opposite..? https://zwiftinsider.com/wkg-tests/

ShakeNBakeUK
ShakeNBakeUK (@bakeuk_2)
11 months ago
Reply to  Eric Schlange

ah, bit confusing, i just assumed w/kg. oops!

Jim
Jim
11 months ago

Then there’s wind, which doesn’t exist in Zwift but plays a major factor outdoors, rarely helping but often hindering our speed. ‘

this is massive. They should simulate wind in Zwift

Jeroen van Bergen
Jeroen van Bergen
11 months ago
Reply to  Jim

This is indeed the major difference between riding in the real world and Zwift. I live in The Netherlands, near the cost, so I am quite used to riding against or with the wind. For training purposes I do not think implementing wind as a factor affecting speed would be useful. While just training it helps when circumstances are identical between rides so you can make proper comparisons. For racing (which I have not done on Zwift yet) it would add an interesting tactical element. Picking the right time to attempt to break away from a group will be harder,… Read more »

Mark Simnett
Mark Simnett
11 months ago

Any chance of doing some analysis into the acceleration of frames & wheels? Both from starting at zero; and also when alternating 180W to 220W continuously. In Real Life, a lighter bike is better on the flat in a group because aero advantage is less relevant – and the shifts in speed to hold position in the group is helped by faster acceleration – which is better on a lighter bike. So should be the same on Zwift… So fastest race bikes may not be the aero ones that do well on constant-effort, non-group rides…

Sven
Sven
10 months ago

ist that now an updated version because Zwift changed algos?
I recall heavier rider always wins at the same w/kg



James Kirkendall
James Kirkendall
10 months ago

I am new to Zwift, have completed about 20 rides and am midway through level 12 after the 1st month. I am a 5’5″, 132lb, 68 yo male who normally logs in about 4k miles per season outdoors. I am perplexed that I am consistently averaging 19-21 mph on Zwift routes, depending on elevation, and have only been able to achieve an average of 14-16 mph outdoors, again depending on the amount of elevation gain. I can’t believe that outdoor wind resistance has this much impact on my average speed. My budget limited me to a lower end Saris wheel… Read more »

James Kirkendall
James Kirkendall
10 months ago
Reply to  Eric Schlange

Thanks for the advice. I’ll check trainer calibration.

Niels
Niels
9 months ago

Hi guys,

I assume that the power/weight ratio is leading for rider speed.

When I do a race, sometimes I see people with a lower power to weight ratio higher in the race results. How is that possible?

Thanks!
Niels

SeaDoubleYou
SeaDoubleYou
9 months ago
Reply to  Niels

Hi guys, Interesting article – I’ve been using Zwift for just over a month now and have been very surprised by the speeds I have achieved… Typically I ride outdoors on the flat and average 19mph, but on Zwift I am often averaging over 20mph (which I guess is because I’m not having to slow down for corners, head into the wind etc) but I have done a group ride and a crit race when I averaged over 24mph!! I wish that were possible in real life! I’m using a wahoo Kickr and am impressed with the overall experience, just… Read more »

SeaDoubleYou
SeaDoubleYou
9 months ago
Reply to  Eric Schlange

Thanks for the reply Eric – I ride outdoors on my own all of the time so hadn’t particularly considered the effect of having a decent draft. This is a great site for a newcomer to Zwift such as myself by the way!

Robert
Robert
8 months ago

All else being equal, heavier riders do not descend faster in the real world, and I hope not in Zwift.

David
David
8 months ago

Maybe so, but why such a huge difference like 10km/hr on flat smooth pavement? Even when I do speed up, it is nothing close to what my “stationary/road” speedometer measures, and then can be up to 20 km/hr behind; it’s like I never even accelerated.

Howard Venning
Howard Venning
8 months ago

Regarding group rides; OK you want to keep riders together and therefore modify speeds accordingly, however how about disabling this when doing sprints. It adds a short competitive feature, and if the speed adjust was only during the sprint it would allow the slower riders to catch up and the faster riders time to recover. I did a group ride last night; London flat course; and did the Mall Sprint Reverse twice. My times for both segments were identical at 21s, however the power for the first was 169W (just warming up) the second 454W (close to max effort). Very… Read more »

Chas Ryan
Chas Ryan
8 months ago

Eric, I did a meetup yesterday for MegaPretzel and we started with 6 of us. We finished with 2. The last 50+ KM we were pegged at 46KPH on any flat or climb. For the descents, the speed would pick up only a few KPH. Ultimately, I “got the EPIC KOM” at 12:22 at a blistering 28.4 MPH. So, some kind of Zwift algorithm anomaly? What is your take on this? The RPE we had did align with our WPK but the speed was waaaay off.

Mark
Mark
7 months ago

Watts, cadence, gear ratio factor into how fast the rear tire revolves. Tire circumference determines how far you travel with each revolution. Those two variable produce your speed. Higher gears and bigger tires take more Watts to turn but it seems like we should know how fast the trainer is turning without having to estimate that from Watts.

Martin
Martin
2 months ago

All very interesting, thank you.

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