Newbie very confused

I’m trying to help my son set up his bike with Zwift. He has a mountain bike with Garmin sensors. His bike has 29" tires. How do we tell Zwift that his tires are 29"? It seems like all Zwift has are smaller tire diameters. He also has a Garmin 520 Edge that is set up correctly with the right wheel size. Can Zwift talk to his Garmin 530 Edge or does it have to talk to the sensor.

Thank you so much for any help. I hate to waste your bandwidth with our newbie questions.

29" is same size as 700. Just pick something like 700x32.

Zwift must talk to the sensors.

A snobby Mountain bike tire on a wheel-on Trainer is not a good idea.
Try to get an extra rear wheel with a road bike tire or a special trainer tire.

Hi, would you answer a few questions so we can help troubleshoot?

  1. Are your Garmin sensors on this list of supported devices? Which one is it?

  2. Is your trainer the type where you leave the rear wheel on, or is it a “smart trainer” where you take the rear wheel off?

  3. What computer OS (PC / Mac) / mobile device (Android / iphone / iPad) / smart TV is running the Zwift game app?

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He has the new Garmin Speed Sensor II and Cadence Sensor II. They aren’t exactly on that page but I expect they are very similar to the Garmin on that list of supported devices.

He leaves the rear wheel on. It is a Speedback Sports Omnium which has rollers on the back and holds the front wheel in place.

He is using his Iphone XS although he would also like to use his Windows 10 computer.

I guess what was really confusing us was that we did the conversion to MM and got 737 mm from 29 inches rather than 700 mm for the wheel size. I guess the power and speed are way off and he’s sad that it looks like he won’t be able to do Zwift. It appears that the sensors have connected to the game on his Iphone but the numbers are too far off.


700C and 29" have the same size rims. 700C doesn’t refer to the size.

What do you mean the power and speed are way off? Make sure the Omnium is selected in the Speed menu. Also, how old is your son? Zwift is based on watts/kg so maybe he’s too light?

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One other thing, your Zwift speed wont match the garmin cycling computer. Zwift take your weight and the the road terrain into account when they calculate speed. The garmin head unit only know your wheel speed.

FRiC is correct. 700c and 29" tires share the same rim diameter, but mountain bike tires are fatter and taller than road tires (broadly speaking). The larger circumference of a mountain bike tire means it will roll farther than a road bike tire for every pedal revolution. This is what’s throwing off your speed numbers in-game.

At this time, the fattest tire option available to select when using a classic wheel-on trainer is 700 x 38c which is more typical IRL for a gravel bike. We recognize the desire to broaden those selections for Zwifters riding bikes with even fatter tires, and we’re having internal conversations to make those available in future game updates.

In the meantime, we recommend you select the largest available 700c tire size. In a workout, you can tweak the FTP bias +/- 10% to further bring the game experience closer to what it’d be in the real world.

Thank you for letting us know where to up our game! We appreciate your feedback.

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Thanks so much everyone! I have passed all this on to my son and hopefully it will help. I’m very grateful for your time.

Let us know if he got it all working and if you have more questions please ask, here are many eager users that want to help.

Ride On!

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