I've never felt the Spark EV was "tail-heavy."
The issue with the Spark EV is the dynamic effect of 600 lb. of battery on and behind the rear wheels. I find that the tail end really wants to swing out during hard cornering, and I'm pretty sure that's why Chevy put wider tires on the back.
I concur...it's caught me by surprise a few times up on Angeles Crest hauling up and down hill with my Spark EV. It hauls man out of the corners that thing is just quick.
But the traction control and poor front wheel traction just kills the performance of this car. I truly believe this thing could be a second quicker at least to 60 if it was RWD and had better grip...at least. And in gear acceleration would be just that much better too.
But yeah, this thing wants to seriously swing its rear out but the transition is predictable if not safe.
I am really really hoping the Bolt is quicker in both off the line and in gear acceleration than my Spark EV.