Unable to get over 400w even when sprinting

Hi everyone,

I’m really very new to Zwift and didn’t know how committed I was at first, so I bought a turbo trainer and added some speed and cadence sensors to it, and I have to say it’s working brilliantly, right up until I have to sprint.

I can throw absolutely everything at my bike, top gear, 120+rpm and I still can’t get above 400w, now I’ve seen someone on youtube using my exact setup get up to 800w in a sprint, so I’m having trouble believing that it is the turbo trainer, or the sensors.

My thoughts at the moment are aiming towards that my gearing is very low? but I have no idea, if you need any more information to help let me know, when it comes to bikes I’m not brilliant with the technical stuff but I’ll give it a go.

Trainer: Tacx Blue Matic (The smart one with the ANT+ Speed + Cadence sensors.

Thank you :slight_smile:

Zwift limits power to 400W, when power is calculated from speed sensor signals.

Oh brilliant, that’s just what I needed.

It does make me wonder how the guy on Youtube managed to get above that, probably using a different bit of kit, thank you for your response.

Not all classic trainers are limited to 400W, most of the supported classic trainers do have power curves well above 400W. https://zwift.com/hardware

What bike do you have on the trainer and how many teeth on you biggest chainring an on the smallest gear on the cassette?

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Thanks for your reply,

Ok so it was difficult to count, and since it’s a relitavely old bike I couldn’t find anything online.

I believe the largest one at the front has 51, and the smallest on the rear has 14.

I assume a road bike with 700c tires?

I did some calculations, so with a 55-14 @ 120RPM your rear wheel will turn at 55km/h looking at your trainer power curve it is just above 400w. (i used 700c tires) I could not remember what resistance setting is required by Zwift, I think it is level 3 (can you confirm)

Yes, level 3 resistance is what they recommend, and also yes 700c tires.

So from the sounds of it my bike is performing as it should, and the trainer is also displaying what it should. Would you say I just need (and forgive the lack of technical terms) a casette with a lower end? I’ve noticed in research that 14 seems quite high, whereas my chainring seems relitively normal. I could be wrong though.

I am completely useless. I just like riding.

I think a 11 tooth will be the best bang for your buck.

From below you will see your top wheel speed at 100rpm will increase with about 10km/h

I estimate you will get about 100W more.