I actually have a 11-34 mega range on a trigger shifter already installed using the original derailer. Going back to my original question does the 8-10 speed wheel not work if I'm using a 7 speed cassette?
As
@PedalUma said: No. Even if you convert to a cassette the spacing will be wrong, although you can use a spacer to sort of fix that. I wouldn't. I'll let you in on something that the lifers around here know already. I am an admin on the Sondors Facebook user group and I saw the prototypes of these mid drive bikes well before they hit production, as well as earlier versions that led up to the production models. I know the arguments that were made to use 7 spd freewheels (the manufacturer building to Sondors specs argued chain strength and shift simplicity for noob riders) and I argued strenuously against them (we were not a part of the design process we just got an inside look and I made my concerns known as an experienced high-powered mid drive builder). The Rockstar was eventually changed to a SRAM 11s drivetrain which was a very good thing, but the other two models remained as-is.
My point behind mentioning this at all is to justify my telling you that you will be well-served to remove that drivetrain entirely, since now you pretty much have to replace its core - the hub. At this point Uber Boost is going to be helpful as you want the space to convert to ... 9 speed. That means throw out the cluster (cassette), chain, derailleur and shifter. 9 speed is the de facto standard for hi power mid drive builds for a reason, although there is a great case to be made for 11s (which I will skip because its too much money and overkill for you).
@PedalUma 's Box 3 suggestion is excellent, but you can spend less and do at least as well for yourself. The Box 3 cluster is actually a Sunrace steel cluster whose model designation escapes me at the moment (I own one of each), and its construction is strong but not best for a mid drive. You can see why when looking at the little bare alloy spacer in the pic above. That is needed because the bigger cogs are bolted onto the next smallest cogs. They don't attach to a spider that is full-width. So the spacer makes up the difference. In phone conversations with Box I asked one of their tech guys if that construction is going to hold up under a strong mid drive ... and they didn't know. It is meant to be strong and live in an mtb world. Not an emtb world. But it is a strong product. Whats better?
The Microshift Advent all steel 11-46T cluster. These cogs are single-piece hardened steel and they go all the way to the center. Not even a spider. AND they are pinned together. AND the Microshift Advent derailleur and single gear (best for ebike) shifter that go with it are cheaper than the Box. I have Box components on two bikes. One is a Box Two derailleur and Box Two shifter, with Box 3 cluster. The other one is a Box Two Derailleur, Box One e-shifter and Microshift cluster. And then I have a third bike that is Microshift Advent everything. The Advent parts are less flashy but cheaper than the already budget Box stuff and work great. I like the high quality fit/finish and glass smooth shift of the Box stuff, but the Microshift is so good for so much less its the way for the rider to go who is trying to justify a drivetrain change. The shifter, derailleur AND rear cluster ran me about $125 total. This and the fixed hub will transform your bike. Add in a SRAM EX1 ebike chain ($25 on Amazon) and you won't have to screw with anything in your drivetrain until you actually wear it out.
