2010 GMC Terrain: Ratios, Not Cylinders
August 17, 2010
In the beginning the American car had a big engine with lots of cylinders. The wide, lazy powerband made it possible to drive around all day in one gear, which was a way better deal than shifting the agricultural-style transmissions of the day. Later the automatic transmission with its hydraulic torque convertor made it even more practical to drive round in one gear.
But then came the challenge of fuel economy. Now there were fewer cylinders and more gear ratios as the transmission was made to work harder to keep the engine working within a narrow band of peak fuel efficiency. And as the band of fuel efficiency became ever more narrow, the number of gear ratios ever increased.
This has not always been a good thing, especially with automatic transmissions.
Initially these automatics cycled so clumsily between their small number of ratios that the engine labored as if it were something adapted from a particularly bad washing machine. The continuously variable transmission promised to cut down on the cycling, but the racket from under the hood as the engine raced along hasn't made many friends for the CVT. Meanwhile the simple multiplication of ratios hasn't proved to be the magic answer, either, as the dynamic confusion caused within the six-speed automatic of the BMW 750i and the eight-speed automatic of the Lexus LS 460 has shown us.
So imagine my surprise to be reminded yet again on a trip to Northern California and back that the seemingly harmless six-speed Hydra-matic 6T70 in the GMC Terrain makes good on the promise of the automatic transmission.
You don't expect much from the Terrain's powertrain, just another too-small inline-4 matched with a six-speed automatic, a kind of default combination for every frugal crossover on the road. But thanks to the magic of direct fuel injection and variable valve timing, this engine pulls strongly across a wide range of rpm. And thanks to thoughtfully developed electronics, the Hydra-matic responds with extremely refined shift action.
Climb a grade with the GMC Terrain and the transmission drops a ratio (or two) without making you wince, and the engine picks up the slack without a struggle. It's not as if you feel as if you're at the wheel of something with 600 hp, and this vehicle still struggles if you stomp on the gas pedal at low speed since you still have a lot of weight and not so many horses to pull it with. Yet the Terrain's performance at cruising speed on the freeway is really refined for such an unpretentious vehicle.
Now that there are new federal fuel-efficiency mandates on the horizon, we'll be facing a lot more powertrains that try to make magic with gear ratios rather than cylinders. But the GMC Terrain and the Hydra-matic 6T70 make me think that there might not be a disaster of dynamic awfulness ahead.
Michael Jordan, Executive Editor, Edmunds.com @ 12,470 miles