Need Help Configuring Kids Setup Using Only Speed Sensor

I’m looking for help and advice configuring my kids’ accounts, specifically the weight, wheel diameter, and trainer so that they have around 3.2 w/kg.

Both kids have their bikes on a DIY stand to elevate the rear wheel off of the ground. Neither has any resistance other than a poorly maintained drive train (bad dad moment). Both have a speed sensor on the rear wheel.

First setup is for a 9 year old riding a mountain bike with 20” IRL wheels. The 13 year old has 24” IRL wheels, also a mountain bike. Thanks.

With no resistance unit there is not power speed curve for Zwift to use to calculate power.

I would suggest using the unsupported trainer option.

Why do aim for 3.2w/kg?

This may help.

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The 3.2 w/kg matches me, but doesn’t have to be there. Thanks for the video!


If youse want to ride together, you can just create a meetup and use the “keep together” option.

Yes, we’ve done that and it works well. They also want to bike on their own, which is awesome, but I need to dial them down to avoid Zwift flagging them. Thanks!!

The video above did not exactly help with the setup I’m looking for. Still seeking advice for settings in Zwift for wheel size and trainer options to get to around 3.2 w/kg for each kid. Thanks!!

With no trainer and no resistance I dont think there is anyway zwift will be able to work. You can try a bunch of the supported trainers and experiment, but other than that who knows? The wheel must be going very fast with no resistance and will be very unrealistic.

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Hi Robert,

I am really interested in this. My 8 year old son has just got into this and I have tried a number of settings.

He is 27kg and riding a 24" MTB free wheeling as I dont have a direct drive.

At the moment i am using unspecified rollers with a 20" wheel to try and get his power down. I have no idea what actual power he produces. In his last couple of rides he is averaging around 130 watts which could be right I dont know. However thats nearly 5 Watts/kg and he can peak 8-9 so it is getting flagged for mechanical dopping.

I was going to try and up his weight to around 43kg to see what that does.

The next thing to try is maybe get him on actual rollers which should then give a real estimate of power and then change wheel size.

Would be keen to here what has worked for your kids.

Hi Robert.

I changed my sons weight in the companion app to 43kg. That seems to have make him not getting flagged as much. He still enjoys it that way.

We haven’t done a race together yet ar that setting we would be close. (Can’t let him beat me)

Until I get a direct drive trainer and put him on that, this will have to do.

I may have to increase his weight even more to reduce his w/kg.