Plug-In Hybrids Are a Lot Slower in EV Mode, Our Tests Show

• The Toyota Prius Prime and other plug-in hybrids are sluggish in EV mode in our acceleration testing.
• PHEVs are heavier than regular hybrids and have electric motors that aren’t as powerful as pure EVs, leading to slow 60-mph runs on electricity alone.
• In electric-only mode, the Prius Prime and other PHEVs took about twice as long to accelerate to 60 mph.

Welcome to Car and Driver’s Testing Hub, where we zoom in on the test numbers. We’ve been pushing vehicles to their limits since 1956 to provide objective data to bolster our subjective impressions (you can see how we test here).

Plug-in hybrids such as the Toyota Prius Prime, for example, occupy the space between hybrid and electric vehicles. PHEVs have an internal-combustion engine that works with one or more electric motors (just like regular hybrids that don’t have a plug), but they also have a larger battery pack than a traditional hybrid to provide more electric-only range and the ability to plug in to recharge like an EV.

While PHEVs might sound like the best of both worlds, it’s more complicated than that, especially since they’re usually heavier than hybrid equivalents yet their electric motors aren’t as mighty as EV alternatives. And for anyone who loves an electric car’s speedy acceleration, that sensation is lost in translation on plug-in hybrids when motivated by electricity alone. As our 60-mph acceleration testing reveals, PHEVs are downright slow in EV mode.

The sprint to 60 mph is a staple of Car and Driver’s comprehensive testing regime, but when it comes to testing plug-in hybrids in electric-only mode, we’ve only done a few. That’s largely because automakers use different operating strategies. Some such as Toyota allow drivers to “lock” the powertrain into EV mode, whereas others such as Volvo lack a dedicated EV mode, meaning the gas engine fires up after a certain amount of throttle input. The latter makes achieving a credible electric-only 60-mph time very tedious.

Still, to show how much more slowly PHEVs accelerate in EV mode, we collected test results from a Toyota Prius Prime, a BMW X5 xDrive50e, a Lexus RX450h+, and a Mercedes-Benz GLE450e. We tested all four in both hybrid and electric-only modes and found that when their gas engines were left offline, their 60-mph times roughly doubled.

Toyota Prius Prime

Thanks to its plug-in-hybrid powertrain, the Toyota Prius Prime is more powerful than the regular Toyota Prius, which is a traditional hybrid. Naturally, the Prime is quicker in hybrid mode, and its larger 10.3-kWh battery gives it an EPA-estimated electric driving range of up to 44 miles. However, the Prime’s plug-in system also makes it about 300 pounds porkier than its hybrid sibling. That added mass is motivated by an Atkinson-cycle 2.0-liter four-cylinder engine that produces 150 horsepower and 139 pound-feet of torque. Paired with two electric motors, the Prime’s total system output is 220 horsepower. In hybrid mode, the front-wheel-drive Prime used all that to hit 60 mph in 6.5 seconds. However, that time stretched to a sluggish 11.7 seconds in EV mode, as our 3536-pound test car was propelled solely by a 161-hp electric motor driving the front wheels.

Acceleration Times (Hybrid mode/EV mode)

• 60 mph: 6.5 seconds/11.7 seconds
• 1/4-mile: 15.1 seconds at 94 mph/18.7 seconds at 75 mph

Lexus RX450h+

Lexus subscribes to the same PHEV philosophy as its parent company, meaning its plug-in models have a dedicated EV mode just like Toyotas. The Lexus RX450h+ is, of course, a ritzier experience than the Prius—it’s quicker too. The mid-size luxury SUV has a 2.5-liter Atkinson-cycle four-cylinder with 180 horsepower and 168 pound-feet of torque. Helping juice those numbers to a combined 304 horses are three electric motors that draw from an 18.1-kWh battery. A pair of e-motors on the front axle generate 179 hp and 199 pound-feet, while a third motor with 53 hp and 89 pound-feet is attached to the rear axle and helps provide all-wheel drive. Flatten the RX450h’s throttle in hybrid mode and it hits 60 mph in 6.0 seconds. Switch to EV mode, and the electric motors need 10.6 seconds to move the 4866-pound plug-in-hybrid Lexus SUV to the same mark.

Acceleration Times (Hybrid mode/EV mode)

• 60 mph: 6.0 seconds/10.6 seconds
• 1/4-mile: 14.6 seconds at 95 mph/17.7 seconds at 74 mph

BMX X5 xDrive50e

The BMW X5 is a mid-size SUV with a plethora of powertrain options. These range from the standard 375-hp turbocharged inline-six to the 617-hp twin-turbo V-8 that motivates the hi-po X5 M. Somewhere in the middle is the plug-in-hybrid xDrive50e, which has a turbocharged 3.0-liter straight-six that makes 308 horsepower and 331 pound-feet of torque. The gas engine partners with an electric motor that’s integrated into the housing of the eight-speed automatic transmission. Fed by a 19.2-kWh battery, the e-motor packs 194 horses and 280 pound-feet. Altogether, the X5’s plug-in-hybrid powertrain produces 483 horsepower and 516 pound-feet of torque, which helps the all-wheel-drive SUV hit 60 mph in a hasty 3.9 seconds. Accelerating with electricity alone, the 5473-pound Bimmer reached 6o in 9.3 seconds, which is the quickest of the PHEV bunch we tested but slow, nonetheless. When in EV mode, the plug-in X5 can travel at speeds of up to 87 mph without the gas engine getting involved.

Acceleration Times (Hybrid mode/EV mode)

• 60 mph: 3.9 seconds/9.3 seconds
• 1/4-mile: 12.5 seconds at 110 mph/16.9 seconds at 80 mph

Mercedes-Benz GLE450e

The Mercedes-Benz GLE450e is the plug-in-hybrid member of Mercedes’s mid-size luxury SUV lineup, and it has a 2.0-liter turbo four producing 248 horsepower and 295 pound-feet of torque. The gas engine pairs with a 23.3-kWh battery that feeds an electric motor making 134 horses and 325 pound-feet of torque. The PHEV GLE’s total output is 381 horsepower and 479 pound-feet. The hybrid all-wheel-drive setup shoved the 5940-pound Merc to 60 mph in a tidy 5.3 seconds. However, taking the gas engine out of the equation meant the trip to 60 took almost three times as long, with the mark arriving in 14.4 seconds, by far the slowest EV-only time of all four PHEVs we tested. For comparison, the similarly sized Mercedes-Benz EQE500 SUV, with its 402-hp dual-motor electric powertrain, sped to 60 mph in 4.2 seconds.

Acceleration Times (Hybrid mode/EV mode)

• 60 mph: 5.3 seconds/14.4 seconds
• 1/4-mile: 13.9 seconds at 99 mph/19.7 seconds at 69 mph

Source: Motor - aranddriver.com