First post here…
I’m experiencing something strange when pedaling at high cadence (90-100) on erg mode at relatively low wattage (85-110). As I ramp up toward a cadence of 90, it’s as if there is slop in the drive train that is causing the cranks to knock as they reengage. It’s not a continuous, fluid motion as I’d expect, which results in an awkward ride experience. Because of this, Zwift is showing constant power drops throughout the training session (FTP builder).
Does this sound like an issue with my bike, with my Kickr 2018 trainer, or with Zwift? I searched the forum and also Google, but couldn’t find anything directly related to this. I also realize it’s a bit difficult to explain exactly what’s going on.
Thanks!
Yo do realize you did not mention in your whole post which trainer it is? 
Haha, sorry!
I’m using a Kickr 2018…edited original post.
And u’re using a PC/MAC/Apple TV… ?
Ant+ or BT?
Tried switching it from ant to bt or bt to ant?
Tried ERG mode with the Wahoo app? Same result?
I’m using Apple TV with BT. I don’t have an option for Ant+ at the moment and would prefer to avoid that additional expense if possible.
I’ve not tried ERG mode with the Wahoo app, but will give it a go. For what it’s worth, the dropouts seem directly related to the slack in the crank. Again, it’s hard to describe, but it’s as if there is an intermittent knocking from the cranks as the drive train becomes “tight” again.
I’ve seen this in the past with my Kickr 1. Trying to recall how I solved it.
Tried changing trainer resistance in Zwift settings? Shooting ideas.
What gear are you in?
In ERG at low watts it may be that the trainer is struggling to limit you. If you are in a big gear, try shifting to an easier gear which will result in a slower flywheel spin speed.
This morning I was in the biggest gear on both cogs and the flywheel was spinning like mad. I’ll ease up tomorrow and see how that goes. If that doesn’t work, then I’ll play a bit with the resistance settings.
Yea, i suspect that the flywheel was spinning so fast that the Kickr couldn’t back off the resistance anymore.
The slop you are feeling is because the flywheel is spinning faster than the required power level it can support and in effect you are temporarily freewheeling for a short period of time. As your relatively lumpy pedaling catches up the freehub will engage again and you will hear and feel this through the drivetrain. Think of it like pedaling down a steep hill when the rear wheel is going way faster than you can generate power to drive the bike forward.
This will only happen in ERG mode as Zwift has told the trainer to hold you at a wattage level and it will do this based on your cadence. The resistance/trainer difficulty setting in Zwift will only effect the realism of the gradients that you will feel when in normal SIM mode (or just ridding along/non-workout mode). There are loads of topics here about what that does including this official one.
Shift to an easier gear to slow the flywheel spin speed.
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Thanks, David.
You’ve described the situation perfectly in terms of what I’m experiencing. I’ll shift into an easier gear and see how it goes. I’ll respond back tomorrow sometime.
Following up on this…
I tried shifting into an easier gear this morning and found some benefit. Still, I’m getting some of the same freewheeling and lack of resistance at low watts and high cadence. I’ll try messing with my seat height, as I think it might be a tad low. I’m out of ideas after this.