Kids racing on Zwift

My son is 8 and uses Zwift… He really likes racing the Crit city race… I put him in D cat as he has no concept of tactics and can only average about 150-180w for the whole race. (He has been racing triathlon since he was 4 and last year was beating kids in u12 AG). Today he got flagged saying something to the effect of you missed your calling as pro cyclist… he was really upset and quit the race. I think it happened because his watts per kg were too high… I have him down as 30kg I think… But he is likely closer to 22… He is using my Kurt kinetic road machine trainer which I have ridden with my PM to see how accurate it is and I always found Zpower reading about 10W lower than both my stages and 4iiii power meters. His max power over the course of the ride was low 500s when I told him to use the leaf and sprint through the rollers section and that is when the warning popped up… Anyway, any thoughts on a way around this other than increasing his weight as that isn’t really fair to him… I will try him in cat C but I don’t think that will fix this problem… Perhaps if it also took actual power into consideration as opposed to W/kg… Not complaining, as his account is free, but I hate to see him discouraged, and don’t want to tell him that he isn’t allowed to sprint during races … Thoughts?

Zwift don’t use w/kg in calculating speed, most speed calculations does not use w/kg in their formulas. it does use weight and power but not in the power/weight format.

There are may things that goes into the calculation like as below. (I found this one it is easy use)

Zwift also have a minimum weight of 45kg even if you put a lower weight.

Also 500w for a 8year old sound a bit high, are you sure there was not a power spike in the Bluethooth connection.

Thanks for the quick response… Do you have any recommendations on how to keep him from getting that thing from popping up? His max power was only 523 for the whole ride, and it was right around when he hit that that the warning popped up. He was just really upset about it.


There is no way to disable that message, Zwift has markers and timed sections that will trigger that message if a rider goes faster than the max speed set buy the Pro riders.

I would suggest to check his setup for wheel slip and make sure everything is calibrated.

for a 8 year old? :frowning: :muscle:

Thanks… Just checked and he wasn’t changing tire size from 700-23… His is 24"… So that would mean a speed difference of about 17%… I will fix it and see how much of a difference that makes.

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So after changing tire size, he did another race and his average power was down 20-30W from previous races… I looked at the previous races and they were generally 165-180 avg… this one was 152. Thanks for the tips.

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I recognize the problem. My 7 year old also is riding. She can also spike up to 500 watt. Don’t ask me how but she does. Yesterday she had average of 140, but after one of those spikes she got the “uh oh” message and she was removed from our meetup ( 2 rounds volcano together…just us 2).
It really discouraged her.
Will it help to upsize her wheelsize? Currently 24”

500 w is massive (I’d say there are adults that can’t do that). What trainer is she on? When pairing are you telling zwift that type of trainer or a different one? Is the wheel size on the bike the same as entered in zwift?

@Ben_Brawn she is in a Tacx Santori with wahoo speedmeter and 24 inch wheels. And yes it is set to that. I know it is nuts. But they do make these spikes. They don’t keep it very long, but they do reach it. I know more kids have similar issues. I just don’t know how to fix it.

She is not racing, but they get discouraged when they can not continue in group or meet up.
At 21 kg she is pretty athletic, but mostly in playing outside and fieldhockey. She likes zwifting with mum and dad.

What setting on the resistance is it set to? Zwift should indicate what level to put it at and then you need to leave it there. Also, was the warning she got due to tire slippage or was it because of the power spikes?

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Make sure the tyre is inflated to 110psi. Warm up the trainer and tyre then do a calibration before doing a ride.

On a few websites I’ve seen people claim it’s not very accurate, others say you just have to do the above, eg Is a Tacx satori smart trainer accurate?

I think it’s just fair to say that the Zwift algorithms work well for adults, but not for kids., particularly now that they’ve allowed lower weights. My 8yo is the same - constantly getting flagged when he gets over-excited as he can spike quite high for a few seconds. It’s a tough balance between setting it up so that he doesn’t get flagged and not handicapping him such that he gets dropped (as he’s still a bit erratic).

What trainer does your kids use?

My kid? Just a generic “RavX” magnetic dumb-trainer with Wahoo cadence and speed sensors. He probably just needs the resistance screwed up a bit, but it’s not exactly scientific (any tips for a dumbtrainer spindown using Z power?) and I’m trying not to put him right off. If it’s accurate, great, but if I just keeping turning the screw until he’s slow, I’m helping nobody. I wasn’t that interested in Zwift myself until he was, but he loves the game aspects (collecting badges and kit). But if I make it a chore, he likely won’t ride and his exercise drops back to zero.

Hi, my 9yo has just got into zwift last week with the Zwift kids race (very well organised FYI) and would like to participate more in upcoming kids zwift events…is there a way to find out when these kids events are on as I can’t locate searching through Companion