2014 BMW i3 REx vs Chevrolet Volt comparison [photos: David Noland, Tom Moloughney]Enlarge Photo
But at higher speeds, or on hills, the battery may be called upon to help out. After a few minutes of helping out, the battery state of charge may fall to near zero.
When that happens, the car goes into a "limp-home" mode that limits speed to about 40 mph. At that point, the driver must either limp home or pull over for a while to allow the REx engine to charge the battery back up above the limp-home threshold--or better yet, above the 6percent REx kick-in threshold.
Can the i3 REx engine really hack it?
In three years and 35,000 miles, I've never encountered a situation that came close to overpowering the Volt's engine. (The mountains in my neck of the woods are measured in hundreds of feet, not thousands.) The only time I ever used Mountain Mode was just to see how it worked.
But I was eager to try out the i3 in range-extended mode, with that little two-cylinder scooter engine humming away back there. Did it have the guts to maintain a safe, comfortable speed on the New York State Thruway?
2014 BMW i3Enlarge Photo
To my surprise, the answer was yes. Tom and I drove about 25 miles on the Garden State Parkway, New York State Thruway, and New Jersey Route 17, maintaining speeds of 60 to 65 mph as traffic allowed.
We weren't the fastest drivers on the road, but we weren't the slowest, either. At this quite reasonable speed, with a few brief uphill stretches here and there, the little i3 REx engine did a fine job of maintaining normal driving performance at the 6-percent battery charge level.
All the while a modest hum emanated from the back, at a steady cadence--unlike the Volt REx, which throttles constantly according to demand.
Ride and handling
Both Volt and i3 handle very well in normal day-to-day driving. But once again, there's a clear philosophical difference between the two cars.
The Volt has a smooth, solid, luxury-car ride. The steering is low-effort and vibration-free. It's a heavier car, and feels like it.
2014 BMW i3 hits the race trackEnlarge Photo
The i3, on the other hand, is a BMW. The design philosophy is to keep the driver in intimate touch with the road. As a result, there's more feedback from the steering wheel, more vibration. It takes more effort to turn it.
If you're a BMW-type driver, you call this "sporty and responsive." If not, you might call it "jittery and a bit harsh."
I happen to fall, just barely, into the latter camp. I appreciated the i3's sporty, responsive feel. But I prefer the Volt's solid, smooth ride, especially at high speeds on the Interstate.
In terms of high-performance handling, I'm not qualified to evaluate either car. The only four-wheel drift I've ever done was in an icy parking lot at 20 mph. Heel-and-toe? I read about it once.