Contact pressure/rolling drag is based on weight, not the number of wheels.
The Insight and the eVaro each carry two people and they are the best examples we have of parallel and series/serial hybrids, and this makes them the best concrete way to compare these types of hybrids.
Compare the Volt to what? Comparing it to itself is not a comparison.
Okay, I watched the
videos again, and it is used in *reduced* torque demand situations. Look at video #2, especially from 4:00 to the end. The engine does not always engage physically to drive the wheels above 70MPH. This is reiterated in video 3.
I think the biggest improvement in the efficiency is the change in the reduction gear ratio, by driving the the ring gear with the ICE (transmitted through the generator/2nd electric motor), which lowers the RPM of the primary traction motor.
So, they are using the second electric motor, or the ICE to spin the ring gear to reduce the reduction gear ratio, which lowers the RPM of the traction motor -- so they are expending energy to save some energy overall. I would think that a 2-speed transmission or a variable ratio transmission (over a fairly narrow range) would have been a better way to go?
Instead of just changing gears, or adjusting the ratio of the reduction gears, they spin the outer ring gear, which uses power all the time, rather than momentarily.... Sheesh, that doesn't make much sense to this layman!