As mentioned the volt has the electric motor, gas motor and wheels all part of the same unit.
On the other hand, the bmw i3 is a serial hybrid. I think the two models are basically an EV and an EV+generator (range extender). One got more subsidies than the other.
What I wonder about is - what happens to the i3 when the electric battery is depleted and all you have is the generator? Can you maintain speed? Will you run out of battery first or run out of fuel?
I am on my second i3+rex. I love the things to pieces.
In the US the rex comes on when the main battery is down to 7% charge. (Europe or re-coding the car allows you to set when it comes on -- up to 75% I believe? I haven't coded either of mine) You can actually outrun the rex engine with the right combination of high speed, climbing grade, or cold weather. If it gets to 0% the car will literally shut down. A serious warning appears at 2% about this.
I've never had mine below 2.5% (there is a setting on the driver display that allows you to display this number). It takes uphill driving over 75mph in cold to really draw down those last few % and outrun the range extender.
The rex tank is 9L, so it adds about 70-100mi to the total range of the car depending on how you drive it. We add a few gallons a year to ours, as the EV itself is sufficient -- it's great for those surprises life throws you where you need another few miles.
On the other hand, the bmw i3 is a serial hybrid. I think the two models are basically an EV and an EV+generator (range extender). One got more subsidies than the other.
What I wonder about is - what happens to the i3 when the electric battery is depleted and all you have is the generator? Can you maintain speed? Will you run out of battery first or run out of fuel?