I live in the USA and if I want to get rid of my car I would need to be able to cover 70 miles round trip with moderate exercise in a reasonable amount of time. I think if I could cruise at 35MPH (56 KMH) that would be enough to make the switch.
It may be stupid, but I'd like to try to avoid an electric motorcycle - those need insurance, registration fees, real parking spaces, and a special license. Also, I enjoy getting some activity while riding. FWIW I'm not worried about legality, but I do plan to stay off bike paths/sidewalks to avoid endangering pedestrians and other cyclists.
My idea so far is to start with a gravel bike frame for aerodynamics, efficiency, and sturdiness in case of a pothole or rogue curb. From there I'm thinking about a 1500w hub motor, dual batteries, higher gears, bigger brakes, and permanent lights for visibility. Also a good helmet of course, crashing at that speed can be pretty bad.
Has anyone done something like this and had it go well/poorly? Anything I'm clearly missing in my plan? Also feel free to tell me if I'm an idiot, but I already know that bit.
That's fair, but what is the limiting factor? Frame geometry? Power? I downhill mountain bike and regularly hit 45 on open sections. I think if the motor could keep up the bike would be fine.
I think if the motor could keep up the bike would be fine.
You are not quite correct. The more powerful a bike's motor is, the beefier the frame and wheels have to be, or it will literally bend or break when you apply too much torque. You also need a strong suspension, thicker tires, and (most important) solid disc brakes. So most bikes that are very fast and powerful end up looking more like small motorcycles.
There are some relatively "stealthy" ebikes that go as fast as you want, however:
The biggest is probably just efficiency, both with aerodynamics and how motors work (from a quick search, rolling resistance seems to go up with speed, too). Faster is more work thus less range. That and battery (or just total) weight.
Personally I went with the cheapest, smallest, and lightest ebike I could find that still has gears. Aside from trails, it's easier to lift/store and transport for 1-way trips. I definitely couldn't go 70 miles, 35 miles is a maybe (I have gone ~22 miles before as someone relatively not in shape, also battery indicator on my bike seems to be unhelpfully cautious/lacking resolution).
I feel like paying 2x+ what I paid isn't worth it either (especially when they have worse aspects) but cheap is probably not for everybody, at very least because it's a 250w motor so it doesn't go very fast (particularly on its own, but gears help). Haven't ridden it in months because my local trail won't be finished with maintenance until next year (I have no navigation and I don't want to deal with pulling into ditches).