During my week with the Toyota Prius c (reviewed previously by Alex) I averaged about 62 miles-per-gallon. On my standard suburban run to the kids’ school, the trip computer once reported 82 mpg, and topped 70 mpg a number of times. But drive the Prius c “normally” with the A/C on, and the gas engine gets a little noisy and fuel economy “plummets” into the low 50s, as attested by the trip computer for my wife’s stints in the car and by the EPA (53 city, 46 highway, 50 combined). If a car achieves much better numbers only when driven in a special way, does it count? Or, if the engine somewhat noisily struggles under moderately heavy acceleration, should the car not be recommended at all?
The special method for getting the most out of a full hybrid is fairly simple in theory, but not always so simple in practice. A feathery foot on the go pedal is only part of it, and the easiest part at that (if one can ignore the faces in the rearview mirror). A light foot on the brake is even more important, as the entire point of a hybrid is to recoup kinetic energy rather than burn it off through brake friction. The heavier your foot on the brake, the more the pads and rotors must be used to slow the car. The hard part: if a light suddenly turns red or someone slows dramatically in front of you, you might not have a choice. Unless you manage to anticipate these events well in advance, you’re going to waste energy. Skilled hypermilers learn to constantly scan far down the road.
One unexpected byproduct of this driving style: safety benefits even more than fuel economy. Driver training performed as part of the Japanese ReCoo program to reduce CO2 emissions ended up improving fuel economy by 4.4 to 8.7 percent and reducing traffic accidents by 45 to 51 percent.
The largest problem I found with the Toyota Prius c wasn’t among those noted by other reviewers, some of whom have panned the car. The way I was driving the Prius c, the 73-horsepower Atkinson-cylce 1.5-liter four-cylinder engine didn’t often make much noise. When I had to accelerate con brio, the 99-horse (combined gas and electric) powertrain delivered well enough (though if you want oomph remotely worthy of a “power” mode in a Prius you’ll have to scrape together another $4,065–$2,935 after adjusting for feature differences—for the original “liftback”). Road and wind noise were no more pronounced than in the average small hatchback. I wouldn’t have felt the need to remark on them at all if others hadn’t. And the hard interior plastics were dramatically textured in at least eight different ways (I lost count) by Toyota’s ADHD-afflicted designers, so they’re at least interesting. They don’t seem notably cheap compared to those in other sub-$20,000 cars. The 2012 Honda Civic’s interior bits are considerably nastier.
Instead, the most significant problem I encountered with the Prius c involved its ability to decelerate. A critical variable when hypermiling a hybrid: how quickly can the powertrain’s generator slow the car? In the case of the Prius c, the answer is all too often “not quickly enough.” If you’re moving along at 50+ miles-per-hour, then depress the brake to the extent suggested by the driving efficiency display (the most helpful I’ve yet experienced), the car hardly slows at all. You need over a quarter mile to bring the car to complete stop from a moderately high speed without relying to a significant extent on the friction brakes. When decelerating from 40 or less this isn’t nearly as much of a factor, but it remains a factor at all but the lowest speeds.
You’ll know if you’re braking too aggressively. The information display grades you, not only overall, but each time you accelerate and each time you brake to a stop. This might sound like a PITA, but it actually can make efficient driving into a video game. Not interested? There are other screens to choose from (one of which reports the dollars you’re saving).
The Prius c suffers more from this deceleration problem than other hybrids I’ve driven because of tradeoffs made by Toyota. The Prius c weighs over 600 pounds less than the regular Prius, and only about 185 pounds more than the slightly smaller, non-hybrid Yaris. This is partly because, compared to the regular Prius, it’s nearly 20 inches shorter, a couple inches narrower, and a couple inches lower. But Toyota also reduced the size of the hybrid components and the battery pack. The smaller battery pack doesn’t only have a lower capacity. It also cannot charge and discharge as much electricity per second. (Toyota told Alex that the difference was about a third.)
The upshot: to go more than 70 miles on a gallon I had to anticipate any need to stop well in advance. This required a fair amount of luck. I couldn’t have any light go yellow when I was too far away to go through it but not far away enough to slow through regen alone. I couldn’t have cars ahead of me slow unexpectedly. I had to pay strict attention to what was going on well ahead of me at all times.
Unwilling or unable to make this happen? Then efficiency suffers even more in the Prius c than in other hybrids. Drive both the Prius and the Prius c like you would a regular car and they end up just a couple mpg apart in the high 40s to low 50s. In the interest of providing apples-to-apples comparisons, the EPA does just this, and ends up with similar numbers for both. As have other reviewers. The highest mpg logged by previous drivers: a mere 57.1.
But the Prius c does have a significant fuel economy advantage when hypermiling. The best I ever observed in the regular Prius was 66.4, and this with fewer complete stops than when I achieved 82.0 in the Prius c. Both figures were obtained on A/C-free trips where I never had to make heavy use of the brake. But even in typical suburban conditions the Prius c ends up with about a ten mile-per-gallon advantage when both are driven as efficiently as is practically possible.
So, should special performance dependent upon a modified driving style count? Or, in the interest of fairness and prevailing social norms, should a car only be evaluated when driven “normally”?
For what it’s worth, this question doesn’t apply only to the Prius c, or even only to economy cars. Back in 1985, I drove a car with a high-revving DOHC engine for the first time. The 112-horsepower 1.6-liter engine in the now legendary AE86 Corolla GT-S peaked at 6,600 rpm and redlined at 7,600. I went there. Repeatedly. This decidedly unnatural behavior (back when many engines peaked in the fours and the now-enshrined square-bodied Panthers peaked at 3,200) opened my eyes and radically transformed what I expected from a driver’s car. Enthralled, I took a friend to test drive the GT-S. He drove it, never taking the engine over 3,500 rpm, and couldn’t see what I thought was so special. As far as he could tell the GT-S drove just like a garden variety 70-horsepower Corolla!
Toyota provided the Prius c with insurance and a tank of gas (which still registered 20 percent full after 450 miles of driving).
Michael Karesh operates TrueDelta.com, an online provider of car reliability and real-world fuel economy information.