zPower improvement idea - Dual spoke magnet setup


(Marc-Andre Savage) #1

I wonder if the Zwift team has considered having the option of using two wheel magnets (mounted at opposite ends of the wheel) to double the speed sampling rate. This would go a long way in improving power output lag and resolution, especially at low wheel speed. 


(Eric C. (Zwift HQ)) #2

This seems like it would require us to either develop our own speed sensor or build in time to support people who’d have such a thing (most likely a small percentage).

Does this currently exist? What item transmits speed data this way currently? I’m actually curious because that would be kinda cool.


(Marc-Andre Savage) #3

To my knowledge, the wheel speed is calculated by the head-unit (software in your case) using a given wheel circumference and signal interval from the speed sensor.  

Placing a second wheel magnet at the opposite end of the wheel and dividing the wheel circumference by 2 would give you speed, sampled twice per wheel rotation.  

All the end user would need to make this work is an additional $3 spoke magnet and an option in your software enable the 2X speed data rate. 


(Christian Wiedmann [X] 50) #4

I’m guessing this will be supported automatically when Zwift supports entering in your wheel size (which they’ll presumably eventually do to support bikes with different wheel sizes). Simply use two magnets and enter in half of the real circumference of your wheel.


(Graham Lang) #5

Why does wheel circumference matter on Zwift Island? We’re all, in effect, riding the same bikes. In the interest of fairness, wheel circumference is standard. As is bike weight. Entering your own wheel circumference would introduce another possibility for error/cheating.


(Christian Wiedmann [X] 50) #6

It matters when using zPower because Zwift needs to know the wheel

circumference to know how fast the trainer is spinning and hence how much power is being produced. You’re right that it doesn’t matter with other setups.


(Graham Lang) #7

Thanks. I don’t recall having to enter it when I first started using Zwift (I have since bought a Kickr so have true (ish) power values).