It’s been a saga, but I’m pretty sure I understand something that has helped me figure out how to use the Renpho with Zwift with at least course-grained reliability. I have the bike, and I connect to the app on an iPhone 12. No other additional stuff.
Erg mode works, but it’s dead easy. This bothered me (feels like I’m riding with no resistance). So I turned it off and use the gears - way better for just working out. BUT gear 20 felt too easy compared to riding the bike without Zwift at its highest resistance level (40 N*m - not sure what those units are, but that’s the readout). It made me wonder whether I could calibrate this.
Based on this article (www . zwift . com/ca/video/how-to-cycling/calibrate-smart-trainer), no, you can’t calibrate the Renpho - no little “gear” appears beside the unpair screen, at least not on a phone.
But: the resistance for each Zwift “gear” changes depending on what N*m resistance you’ve set the bike at when it connects. And it’s unreliable 
Here’s how I’ve come to this conclusion: Normally I turn on the bike, pedal, connect through the Zwift app and I’m ready to go. I’ve found that gear 20 in Zwift is something I can sprint at. I’m not an athlete, but I used to be, so maybe being able to sprint at gear 20 makes sense? Looking at my body in the mirror these days… no, no that does not make sense.
So I wondered if the resistance in the gears auto-calibrated depending on what the bike’s resistance was set at when it first connects to Zwift?
I think it does. I don’t think this is by design. But if I connect to Zwift with the Renpho set at 10 N.m while pedalling, go into Ride mode, jack my gear to 20, sprint and then disconnect from Zwift while I’m pedalling, then once the app actually disconnects, the bike is left at 32.5 N.m resistance.
But if I turn the Renpho up to 14 N.m, pedal and connect to Zwift, then if I do the same thing (go on a ride, jack the gear to 20th gear and pedal and disconnect), the bike’s resistance is at 40 N.m (max) after the app is disconnected. And you can definitely feel the difference in 20th gear in the two scenarios.
What I haven’t tried: trying these setups for timed sprints at a fixed cadence to see if Zwift’s stated power output differs. If the resistance is truly different in these scenarios, then pedalling at gear 20 at the same cadence should yield different power outputs for each (I think).
Why unreliable?: Clearly this isn’t “planned” behaviour – when Zwift initially connects, the Renpho will immediately display a 10 N.m power on the resistance knob (in both scenarios), the felt resistance will change and then I get bumped into Gear 4, which is the starting gear for Zwift. For me, that gear is too easy to know whether or not the different starting resistance of the Renpho has made any difference. But if I pedal hard in 20th gear and do all the steps above, in all cases but one, the bike has disconnected from Zwift and remained at 40 N.m if I initially connected at 14 N.m. But for the three times I initially connected at 10 N.m and tried this out, twice it ended at 32.5, but once it ended at 37.5.
So… MAYBE if you want 20th gear in Zwift to correspond to the max resistance of the Renpho bike, try turning the initial resistance on the bike up to 14 N.m and pedal while you connect to Zwift.
This could be complete smoke and mirrors on my part, but whatever the actual case and whether you do actually have predictable control, something changes – gear 20 can be made to feel very different depending on the bike’s initial resistance when you connect.
If you try this and figure it out better than I have (or you figure out that this is all in my head), please reply - I would love to know more!
