Towing With Hybrid Trucks

Hybrid Towing

July 1, 2009
Filed under Towing Tips, Trailer How To

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Trailer enthusiasts who wish to drive a vehicle viewed as more eco-responsible than the average tow rig can now have their cake and eat it, too – as long as that slice of cake doesn’t weigh more than 6,100 pounds.

GM has graced its new hybrid Chevrolet Silverado and GMC Sierra pickups with a 6,100-pound tow rating, and based on our experiences with them, that figure is realistic. GM claims up to a 40-percent increase in city-driving fuel economy, and while our wheel time was too abbreviated to verify much along those lines, we did jot down some figures from the onboard trip computer’s instant and average fuel economy readout.

EPA estimates for the trucks include 21 mpg city and 22 mpg highway for 2WD models and 20 mpg for both city and highway for 4WD versions.

Both marques offer the hybrid in Crew Cab form alone, a move necessitated by the 300-volt nickle-metal-hydride Energy Storage System or ESS (aka a battery) dimensions and placement.

The Silverado and Sierra share virtually the same powertrain as the hybrid Tahoe and Yukon full-size SUVs. The engine is the 6.0-liter 332-hp V-8 with active fuel management, and the patented two-mode hybrid drive is integral with the 6-speed Electrically Variable Transmission (EVT). The EVT features tap up/tap down gear selection and grade braking, both of which help when towing in hilly terrain.

With the key in the ignition, nothing happens. Step on the pedal and the truck quietly starts rolling ahead. The in-dash readout screen which serves duty as the audio system monitor, GPS navigation screen and powertrain mode indicator, shows the driver what’s going on underneath. At first the indicator says the batteries are powering the electric drive with current indicators moving from battery to motor. As the accelerator is pressed farther, the gas-engine indicator comes on and the 6-liter first operates in four-cylinder mode under low demand.

When in gas-engine-operating mode the engine also recharges the batteries as indicated by the monitor-screen readout.

Although GM tech data claims the all-electric part of the drive will work up to about 30 mph before the gas engine kicks in, we were only able to coax it up to about 17 or 18 mph on electric alone running solo. Others in our group managed as much as about 23 mph on electric by feathering the throttle to an extreme degree. But that was at a speed that would have faster-moving city traffic piled up behind you and drivers leaning on their horns. Towing a 5,000-pound trailer we barely started rolling before the V-8 started up in fuel-saving four-cylinder mode and the transition to full V-8 power took place in short order.

Because the gas engine is so smooth in starting and running there’s very little input to the driver that anything else is happening under the hood as the electric-to-gas-and-back transitions are made.

If you choose more aggressive driving, the electric boost helps move the truck off the line in smart shape. Throttle response is as good or better than with the straight gas truck because the electric-motor torque comes into play at speeds when the gas engine is just getting spooled up.

While braking and coasting the system goes into regenerative braking mode and the electric drive motors act as generators and send charging current back to the battery pack. Four-wheel power discs with four-channel ABS, stability control and traction control are standard.

Stopping and starting represent the biggest changes to one’s perceptions. The gas engine shuts down when the truck comes to a stop. You sit a moment in silence, then you hit the throttle and the truck starts moving again under electric power. That’s when the electric-to-gas transition cycle starts again.

To keep important systems like power steering, power brakes and air conditioning running with the engine off, they’re all electrically powered. The power steering is 42-volt powered variable assist, the air-conditioning compressor operates on 300 volts and the brakes feature an electric-activated vacuum system.

If the system sounds familiar, it’s because the dual-mode hybrid was the result of a rare development cooperation between GM and Chrysler. Trailer Life covered the ill-fated Chrysler Aspen’s towing manners in the November 2008 issue. Functionally, both vehicles are nearly identical.

GM planned our test drive route in town, where the greatest fuel-economy gains stand to be realized. Solo, our truck recorded about 20 mpg at most, and other journalists on site reported numbers from 18 up to about 23 mpg. On the separate urban-driving towing loop, we were down in the familiar 12 mpg range. Not great figures, but solo driving for day-to-day family hauling is where this system, as with other hybrids, is designed to shine.

GM truck fans aren’t missing anything they love about the 1500 series trucks when they choose a hybrid model. Rather than produce an entirely new model to accommodate the hybrid powertrain, GM adapted its hybrid hardware to the existing trucks. All of the GM comfort and convenience features are there for your use and enjoyment.

GM admits its new hybrids won’t save the environment or the world as we know it. However, the new GM hybrid pickups are a step closer to that goal and are on the road that GM and the other car builders must travel. Pricing starts at $38,995.

General
Motors Corporation,
(800) 551-4123, www.gm.com/hybrid.

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