8 and 9-speed transmissions and gas mileage vs cost

Does it matter? Gas mileage vs costs

Savings from Adding 1 mpg
Savings from Adding 3 mpg

Do differences in gas mileage really matter? It depends.

The average car is driven around 12,000 miles per year. Gaining just one mile per gallon (1 mpg) on a heavy duty truck can, at $3.75 per gallon, save around $180 per year (see chart for “15 mpg”). That same one-mpg gain on a compact car is good for just $27 per year.

Gaining 3 mpg on that 15 mpg truck saves $500 a year. On a highly efficient small car, it would save just $77.

The real savings will depend on how much distance is covered, gas prices, and how much driving is done in the city vs the highway (highway mileage is aided mostly by tall overall top gear ratios and aerodynamic tricks, city mileage by weight reduction.)

These calculations go a good way towards explaining why the first Chrysler vehicles to get a serious, systemic gas-mileage workover in recent years were the Ram series. Those are the vehicles with the biggest impact. Adding two or three miles per gallon to the Dart would not save owners much; but the same gain in a Ram 2500 can result in serious savings.

Eight and nine speed automatics

While most automakers are using gasoline-electric hybrids, electric vehicles, and direct injection, Chrysler leaned on transmissions to stay in compliance through 2015. Chrysler has spent $1.3 billion since 2007 to gain efficiency from its gas engines, and makes its own 8-speed and 9-speed transmissions (from a ZF design).

Chrysler started using eight-speed transmissions with the 2011 Chrysler 300 and Dodge Charger; highway mileage shot up from 27 mpg to 31 mpg (highway) and at least two seconds dropped from the 0-60 time. These transmissions don’t just add gears; their range (bottom to top gear) is wider, so cars can be more responsive from launch, yet less thirsty at highway speeds. The transmissions have lower parasitic losses and shift more quickly than conventional automatics, and have speedy lockup torque converters to reduce slippage. Having a large number of gears allows the transmission to keep engine rpm relatively stable and in its “sweet spot.”

Front-wheel-drive cars, such as the minivans, will get 9-speed transmissions. Rear-wheel-drive cars, including Ram 1500, Challenger, Grand Cherokee, and Dart, will get 8-speed transmissions. Both are expected to increase acceleration.

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