The four-cylinder was increased to 1.8 liters for 2010, and horsepower went to 98. Combined with the electric motors, there's a total of 134 hp. The larger engine provides more torque, allowing the Prius to maintain freeway speeds at lower rpm, boosting fuel mileage. It's an Atkinson Cycle engine (different valve timing and breathing). CO2 emissions have been reduced from a score that already tops the charts.
The Hybrid Synergy Drive system, with two compact motor generators within the transaxle, delivers operating voltage of 650V. It uses gear drive, allowing the motor to turn 13,500 rpm. The Power Control Unit (inverter) is compact. The Nickel-Metal Hydride battery pack is compact and powerful. The accessory drive belts have been eliminated, with such things as the AC compressor and water pump now driven electrically. This means the air conditioner works, though not full blast, even with the engine turned off.
There are three driving modes: EV, or all-electric, with a very limited distance at 25 mph or less (if there's enough juice in the battery), most useful for underground parking garages; ECO, which minimizes fuel consumption by reducing the throttle opening and restricting the air conditioning; and Power for full acceleration.
The difference between Power and ECO is 4.1 seconds from 50 to 70 mph, versus 5.8 seconds. If you're in ECO and floor it, it will kick itself into Power, which is also the default mode when you start it up. So you have to set ECO mode at every stop, to get the best mileage. But we wonder why anyone would drive around town in Power mode, because ECO feels no slower. The Prius accelerates from 0 to 60 mph in 9.8 seconds, usually fast enough though slow by modern standards.
When you accelerate hard and it kicks into Power mode, it can be abrupt, like a transmission kick-down. But like all hybrids it uses a CVT, continuously variable transmission, which is technically not an automatic because it doesn't have gears. Most of the time you're not aware the Prius CVT is there, which is how they're supposed to work.
The Prius is EPA-rated at 51 city and 48 highway, for a combined 50 miles per gallon. We got 54 mpg driving gently but still sometimes using Power mode, over 23 miles of city-highway driving; and later 70.5 mpg over a 34-mile street course in a competition with other automotive journalists. We averaged 28 mph, about average for the group.
The winner, a specialist hypermiler, got 94.6 mpg driving by all the tricks. He averaged 19 mph, moving at about 30 mph in the far right emergency lane of the 50-mph highway, showing that it takes travel in an unreal world to achieve those big numbers. An opposite leadfoot extremist managed to get 26.8 mpg. The other 26 of 28 drivers got between 63.3 and 75.3 mpg.
Later, during our one-week drive of the prototype PHV, we got 41.8 mpg for about 180 miles, 26 of them on full electric, and most of the rest at 65-70 mpg in Power mode.
One flaw in the Prius is its bumpy ride: pretty rough over patchy stuff, we noted during our test drive. The suspension was given a slightly wider track and increased roll rigidity for 2010. The pre-2010 Prius didn't feel as harsh. The 15-inch wheels are fitted with low-rolling-resistance tires (195/65R15), and maybe that explains it.
We also drove a Prius with the optional 17-inch wheels and 215/45R17 tires, which felt slightly smoother although theoretically they should be firmer; we got better mileage with them, 57.4 mpg, although the Prius chief engineer said the 17s deliver about 5-percent less mileage.
We thought road noise was high.
The four-wheel disc brakes are sensitive, and we could hear rubbing at low speeds with ours, partly because there was no engine noise when backing off, and possibly because of the regenerative braking component: the more you use the brakes, the more battery juice you build up, enabling you to use EV mode more. On our 70.5-mpg run, we gently used the brakes a lot in city traffic, so we would get as many blocks as possible out of EV mode.
The handling is light enough around town, but out on the road, if you try to drive it aggressively in corners, it turns heavy and slow. The slower you drive it, the better it is. That said, cornering is much improved over pre-2010 models with the redesigned chassis and suspension.
We tested the optional Intelligent Parking Assist, part of the Advanced Technology Package available for Prius V, which parallel parks the car for you, if the space is big enough. It needs a margin of 7 feet 9 inches, more than half the length of the car; most drivers can handle a space that big with no worries, so it's fair to ask what's the point, unless you're not at all competent at parallel parking (and we know skilled race drivers who fit that description). Like many high-tech innovations, it does it because it can. You can set the distance you desire to the curb. Pull up, line up, press the button, it tells you when to go; then release the brake pedal and take your hands off the steering wheel and let it do its thing.