Yet another call for the ability to account for wheel circumference...

(Tim Abbott) #1

Absolutely ludicrous that Zwift won’t take differences in wheel circumference into concern. My trainer bike is an old 26er mtb, so, due to Zwift’s inexplicable assumption that we all ride 700c road wheels, I pass you actual roadie punks like you’re standing still while putting out some fraction of your power. Makes it totally unrealistic and unfair for all. Seems like a really basic thing to account for, but I guess it’s platforms like TrainerRoad and whatnot for me until this feature is implemented.

(chip tonkin) #2

I just started my 14 day trial and discovered this “feature”. This would be a trivial fix for developers and is obviously a commonly requested feature (and would make it so much more accessible for those of us that want to semi-realistically use non-standard equipment). I am happy to pay $10/month if this is implemented otherwise I will go elsewhere.

(Kim Lodro Dawa (Drivo)) #3

Dont under stand the request. The power output is the same if you have made the setup to your trainer correctly. This have nothing to do with Zwift, but something to do with your Turbo Trainer. Having 26" wheel or pram wheels even, should have no difference in the power output if you have set up your trainer to the wheel size. If the trainer doesnt support different wheel sizes, its maybe time to get a new Trainer or try talk with the manufactor of the brand of the Trainer you are using. Seriously, makes no sense what so ever to incoperate wheel circumference into Zwift!!!

(chip tonkin) #4

You are correct that the power output is the same, but people with perfectly good “old school” trainers don’t have an (inexpensive) way to push that power amount into Zwift. These folks are able to ride in Zwift using just a speed sensor and the game calculates a rough power level based on the type of trainer you use (yeah this will never be perfect, but it let people participate and see if it is worth investing real dollars to make it more realistic).

I have a trainer I like a lot and I can use a Wahoo speed sensor with it, but now because the game simply assumes 700c wheels, my speed in the game is wildly off (to the point of not even being fun - I just blaze past everyone in the game). Every single head unit and phone software that I am aware of that utilizes these types of sensors have the ability to enter in wheel size in order to produce reasonably accurate speed estimates - why would Zwift not do this if it is going to accept speed as the sole input? 

(chip tonkin) #5

Oh - and please allow us to enter in a custom value (and not just a drop down list of common wheel sizes) so riders could use this method to calibrate a wider variety of trainers including some spinners and other exercise bikes to create semi-realistic speeds while in the game. You could certainly label these riders differently and disqualify us from being able to win lap times, etc. because obviously this method could be used to cheat.

(Tim Abbott) #6


Charles explained it perfectly, but I would add that even were we to add an actual power meter to our setup, the in-game experience would still suffer greatly without the ability to add a custom circumference.  Because Zwift inexplicably assumes that all speed data is coming from a 700c wheel, people running smaller wheels will literally blow by people with 700c wheels putting out the same effort. In one revolution, a 700c wheel will cover 9.4 inches greater distance than a 26" wheel (tire sizes/pressures being equal).  So with every turn of my 26" wheel, I’m receiving a 9.4 inch distance traveled bonus that is being erroneously translated into a much greater speed.  For instance, 20mph on the 26" wheel translates into 15,514 revolutions in one hour.  Add 9.4 inches to each one of those revolutions, and Zwift assumes that I’ve traveled an extra 12,153 feet in that hour, for a 2.3 mph bonus.  So, again, 20 mph actual on my trainer is interpreted as 22.3 mph in Zwift.  Not very fair to everybody running 700c wheels, especially when you think of how simple a fix it really is.  I’ve not come across another “training” program as obstinate as Zwift is when it comes to trying to get it right.

(Kim Lodro Dawa (Drivo)) #7

Then the problem is at the Wahoo speed sensor as there you should be able to put in the right circumference and then the Wahoo speed sensor should be able to calculate what speed you go at.

Even 700c wheels doesnt have the same circumference. A 23mm Vittoria tyre compared to a 23mm Continental tyre with same pressure doesnt even have the same circumference. Then the difference is even bigger if you use a 28mm tyre compared to a 23mm, and then the air pressure in the tyres and all of them are 700c wheels.!!!

To get the exact speed from that or as close as possible you manually have to measure. Not even the charts being put up is exact.

Have you ever done any kind of software programming before???

Do you really have any clue whatsoever what it would take to get these things implemented??? Are you aware about the amounts of dfferent wheel sizes and circumferences that are out there???

A simple fix…are you totally out of your mind???

Even a fairly good trainer you can get for little more than 100 Euro…and then you want Zwift to use months of work to get that implemented.!!!

Seriously, it makes no sense what so ever to have that massive work done for so few people and it would never be a good job done anyway, impossible!!!. Go get a proper trainer that are able to handle your mtb wheels, pram wheels or what ever you are using. I dont see nothing on Zwift other than road racing bikes with normal 700c wheels, so IMHO Zwift should never implement it using other wheel sizes. Let that be up to people to buy some proper trainers.


The one obstinate here is for sure not Zwift. Think you have to look at yourself.! Sorry dude.

(Tim Abbott) #8

“Even 700c wheels doesnt have the same circumference. A 23mm Vittoria tyre compared to a 23mm Continental tyre with same pressure doesnt even have the same circumference. Then the difference is even bigger if you use a 28mm tyre compared to a 23mm, and then the air pressure in the tyres and all of them are 700c wheels.!!!”

Yup.  Exactly my point.  That’s why every application along these lines allows to enter a custom circumference.  Accuracy, ya know?  You may have even noticed “tire sizes/pressures being equal” in my response.  I’m gonna give you the benefit of the doubt and just write you off as a troll.  And yes, it’s a simple fix - just look at TrainerRoad, Garmin, and basically every other $5 cyclocomputer out there.  If you’re not a troll, however, I’m beginning to understand from your responses why simple concepts may be beyond your comprehension…

(Kim Lodro Dawa (Drivo)) #9

Tim, you still didnt seem to get the point.!!!

Zwift is a road racing game. Go get some proper gear so we can get over the circumferences that we have used since my childhood (more than 40 years ago) to calculate speed, its horrible inaccurate and then you want accuracy…!!! Troll…??? No dude, I am a human being. Where on earth do you come from??

Go buy a proper trainer. They are cheap now a days.

Zwift are fairly new, they dont have resources to do silly requests like that and I hope they never will do. It will cause a lot of problems in the long run.

Please be reasonable and please stop the negativity. Its seriously childish what you two are up to.!!!

(Tim Abbott) #10

Ok.  You’re right.

(chip tonkin) #11

Wow - I just don’t get the rabid response. FYI - “speed” sensors do not measure speed. They directly measure RPM, and speed is calculated in software by multiplying by a wheel circumference. In every instance I am aware of this number is user supplied whereas Zwift just assumes 700c. Implementing this as a variable would certainly not be a significant programming challenge, but if for whatever reason Zwift doesn’t want to their product to be useable by people like me (or they just want me to dominate all races), then by all means, keep it the way it is.

(Kim Lodro Dawa (Drivo)) #12


It could seem like a game, it looks like a game, but its only a game if you participate on equal base. The reason why they ask people to be honest when they have to put in their weight.!!!

For us who are serious, we would go get some proper gear. For me you can do 10 laps while I manage to do one, I really couldnt care less. For me Zwift is helping me with my training, Zwift is fun with others who also are honest and do some effort to get some useful gear if they not already have it. I get to meet new people from all over the world and so many other benefits

If you want to be a negative dude, who cant be bothered to get some proper gear or have it setup up as exact as possible, like cheating with your weight etc…your call. You are screwing up yourself. Cheating is easy on Zwift if you really want. But doing that is nothing but acting like an imbecile!!!

If you think you win races or dominate races by using improper gear, you have just not got a clue what Zwift is or how it should NOT be used. You are not winning anything and the only thing you dominate is your own disturbing emotions. So amazingly childish behavior. Then you say…oh then its trainerroad or other until blah blah…Well, I sure will not miss you :wink: and dont think others will either LMAO

(chip tonkin) #13

Kim - this will have to be my last post responding to you, but I am giving it one last try in hopes that maybe your misunderstanding of my request is also shared by others. And perhaps those same people are responsible for deciding on potential features. So in that spirit:

Damn - I want the exact same thing you do. I don’t want to blaze past people - I want it to make my speed in the “game” relative to the power I am producing in my basement. It simply does not do that now and the feature that I requested would make that happen for me. To repeat, in order for me to get honest results in the “game” with the gear I have, I need this feature. I simply don’t understand why you would not want me and others to have that ability.

Regarding getting new gear - two things: 

1) I don’t have unlimited funds

2) the affordable gear has all sorts of problems in my situation with noise being the biggest. It is simply a deal breaker for me. The indoor bike I have is whisper quiet, setup identical to my bike, and the manual magnetic resistance gives me a great approximation of the wide variety of inclines that I train for (and frankly when calibrated does a pretty good job with power estimate, but it just has no way of feeding that info to Zwift). So if I can get an accurate speed into Zwift, then it turns my Keiser M3 into an incredible training platform for me. And I suspect many others as well. 

So having said all that, whether I have convinced you or not, hopefully someone out there is listening as I would really like to make use of this game and so far can’t figure any way to make it work without this feature being added (other than perhaps spending $600 on a pedal power meter)


(Kim Lodro Dawa (Drivo)) #14
  1. Only few people in the world have unlimited funds. You can even buy a used trainer for way less than 100 USD.

  2. As more and more people are changing their old stuff to the newest, its also possible to get used power meters.

  3. I saved up for several month to buy the trainer I have now. Its just a socalled “dumb” trainer. However, it gives me a power output. I would like to have a better trainer and I will get it even I have to eat porridge for a year. Why, because I have a great passion for cycling, in Denmark we have cold, wet and windy weather more or less 6 months a year and its very expensive to buy proper clothing, way more expensive than to buy a new quiet trainer. I am among the people that are considered poor here in Denmark, so no unlimited funds here.

  4. If there is something we as humans really want, we sure will find way to get it.

  5. Only among the most poor people in India and Nepal I have met people who really couldnt afford anything else than food and shelter. They didnt have a phone or a computer either. You are on the internet, you already have stuff, you are willing to pay 10 USD per month to get on Zwift. I am certain that you easy could find the money needed one way or the other to get some useful gear that would meet your requirement. If not, you will not be able to pay for being on Zwift anyway.

  6. You act immature and childish when saying you gladly pay $10 per month if it gets implementet or else you will go elsewhere. No one takes bs like that serious!

  7. I certainly hope that Zwift will totally remove the option to connect unless you have some sort of powermeter. Maybe I should make that request :wink: Or they could make a seperate server for people without.

  8. You put it up as Zwift should solve your economic issues.

(Kim Lodro Dawa (Drivo)) #15
  1. Get a used bike, a racing bike with 700c wheels. You might even get it for free, then you dont have to buy a powermeter :wink: It will still be quiet. You will get the sense of how it is to be on a racer instead of the MTB. So you do have plenty of options to your situation. Though, as you are already riding a mtb, you are obviously already spending money on new chain, casette, wahoo speed sensor etc etc…

  2. A Keiser M3 is not something cheap! How on earth did you manage to get that and then you cant afford to get something with a power meter.??? It just doesnt make any sense what so ever. You could sell it and get both an entry level racer plus a turbo trainer!!!

  3. Dear Charles Tonkin or what ever your real name is, you really dont get any support from me what so ever in your request. Keiser M3…will take me a couple of years to save up for a thing like that.!!! you cant afford…pppffffffffffffffffffff

(Alan Stewart) #16

+1 for tyre size/circumference input.

Not interested in debate above.

My bike has 700x25c, my trainer wheel is 700x23c

My friends road bikes are 700x25c and don’t have the luxury of a dedicated spare wheel. Changing a tyre is a PITA just to change it back an hour later to go outside.

We all use supported classic trainers and garmin speed/cadence sensors.

(Tim Villa) #17

Kim is behaving like someone who just got smoked by a 26er.

(Kevin Lail ZTR(B)) #18

Plus 1 for the wheel diameter option.  I use a stages power meter, but my wife is really small.  155 crank with 650c wheels, which makes power meter options a somewhat limited.

(Val Usatoff) #19

I would also echo the call for the ability to set the wheel circumference.  My reasons are unusual but I’m sure not unique.  I have attached a Bluetooth Speed/Cadence sensor to an old gym/spin bike but the flywheel is small so I need to use a different circumference to better estimate the speed.  Thanks.

(Kevin West) #20

Seems like a sane enough suggestion to me. If zwift are going to allow speed sensors to control zwift then they should do it as well as they can and that means taking into account wheel size. I’d be surprised if they aren’t already working on it.

There could be an argument for letting people with smart trainers “block” people just using speed sensors but I’m not sure that I would bother to do so.