Random resistance spikes while in ERG mode? (kickr snap/iphone/windows)

Did a couple of searches in the Kbase and community and didn’t see anything like this…

Today I was doing a 2x20 FTP workout. at random times, I was getting consistent resistance spikes from the trainer. I was trying to hold 195W and once every few minutes the resistance would crank up and zwift would tell me I was doing 149W. just for one second. The timing of these spikes was seemingly random. Same thing happened when doing an FTP test a couple of days ago.

It’s getting to be super annoying.

Anyone else experienced this or have thoughts on the cause/a fix? 

An update on this in case anyone else experiences the problem…

The Wahoo folks had me update to a beta firmware and it fixed the issue. 

I had the same problem. I’ve been using ERG mode for about 9 weeks and it has been getting worse. I was at the point where I was going to have to give up on ERG mode altogether.

Today I think that I have finally found the solution so I wanted to pass it on.

The problem seems to be that the optical sensor is too far from the flywheel to reliably register the reflector on the flywheel as it passes by. It measures the rpm of the flywheel by sensing the reflector as it passes so failing to register causes the rpm and hence the power to appear too low.

As a quick test I used some tape to pull the shroud which houses the sensor closer to the flywheel and that seems to have done the trick. I was getting 5 - 10 resistance spikes per 5-minute block yesterday. Today I rode 85 minutes without a single spike.

The sensor is located at approximately the 1:00 position as viewed from the bike’s drive side. Try to get the shroud here as close to the flywheel as possible without it rubbing if you are having the resistance spike issue.

I hope this helps!



Latest firmware ans it is still happening for me. i have also experienced it on a tacx neo. Its a Zwift software issue. Like usual. Poor quality control on Zwift’s part.

I have also random power spike in ERG mode with my gen1 Kickr.

Most of workouts work as should but in some there is at a random point a power spike (Kickr locks up). As far I remember it only happens once in the workout.