I need a new car


Reading: My daughter is a starving medical student and I promised her she could have my twelve year old car in March of 2015.    So now I am in the market for a new car and I would like the class to help me evaluate my options based on performance, carbon footprint, and cost of ownership.   A wrinkle in the purchasing decision is that I won’t really get to drive the new car.   I am getting our three year old Toyota Highlander that I use for towing boats, hauling gear, and driving on Maine dirt roads.   It is a wonderful vehicle, but a real fuel hog.   My wife is going to get the new car and she wants a reasonably sporty four door wagon with room in the back for a seventy pound black Labrador Retriever.  We are considering several models:

1) VW Golf Sport Wagon (with gasoline or diesel engine)  – expected out in early 2015.


Drivetrain: 170-horsepower, 1.8-liter turbocharged gasoline four-cylinder with five-speed manual and six-speed automatic transmission; 150-hp, 2.0-liter turbocharged diesel four-cylinder with six-speed manual or dual-clutch automatic transmissions

Hits dealerships: Early 2015

Say goodbye to Volkswagen’s Jetta SportWagen and hello to the 2015 Golf SportWagen taking the Jetta’s place as one of the few dedicated station wagons competing against an entire segment of compact SUVs. The new wagon will make its North American debut at the 2014 New York International Auto Show.

More 2014 New York Auto Show News

Volkswagen’s replacement sits on the new 2015 Golf platform to offer increased interior and cargo volume compared to the outgoing Jetta wagon. The Golf wagon is longer, wider and also lighter, more fuel efficient and still available in a diesel TDI version — with a new, more powerful engine — while a new turbocharged four-cylinder gasoline engine improves fuel economy up to 17 percent.

This wagon is definitely firing on all cylinders. Icing on the cake for the New York Auto Show is that Volkswagen is showing off a TDI wagon concept with all-wheel drive, a configuration that readers have been asking about for some time.


Bumper to bumper, the Golf SportWagen is 1.1 inches longer than the outgoing Jetta wagon and more than a half-inch wider. It also sits almost an inch lower for improved aerodynamics that combine with the longer hood and more chiseled front styling to give the wagon a more carlike look compared to the previous frumpy wagon. The Golf uses high-strength steel to reduce weight; it also optimizes components such as seats, air conditioning and electrical architecture to further reduce weight. Available features include bi-xenon headlights with LED daytime running lights and 18-inch aluminum-alloy wheels.


The additional exterior size helps on the inside with 10 percent more cargo room with the rear seats folded that Volkswagen says matches compact SUVs’ size and versatility. The Golf wagon also gains nearly a half-inch more front and rear headroom as well as more rear leg and shoulder room than the Jetta wagon. Available interior features include a panoramic sunroof, automatic climate control and parking assist.

Under the Hood

A 170-hp, turbocharged four-cylinder engine replaces the 2.5-liter five-cylinder as the base engine offering. Volkswagen claims fuel economy is boosted as much as 17 percent in highway ratings compared to the outgoing engine, which was rated up to 33 mpg on the highway with manual transmission and 30 mpg with automatic. Base engines are paired with either a five-speed manual transmission or six-speed automatic.

The TDI diesel engine in the 2015 Golf SportWagen is a new 2.0-liter making 150 hp, up 10 hp over the existing TDI Jetta wagon with highway ratings up to 42 mpg. No torque numbers were available at this time. A six-speed manual transmission or dual-clutch automatic are the diesel’s transmission choices.

Front-wheel drive is the only option at the car’s launch. However, Volkswagen is bringing an all-wheel-drive concept version of the TDI-powered wagon to the New York Auto Show. If it’s something you want, be sure to let VW know.      Details from Cars.com.

2. 2014/2015 Prius V, model five


Crafted from the proverbial rib of the iconic Toyota Prius hatchback is the slightly larger Prius V wagon. Meant for people who want a hybrid car but find the standard Prius too small, the 2014 Toyota Prius V features considerably more cargo room and a bigger rear seat.

Measuring an inch wider, 6 inches longer and 3 inches taller than the hatchback, the Prius V offers 60 percent more cargo space, with a full 34 cubic feet of space behind the rear seats. It also features 60/40-split rear seats that slide and recline, as well as a front passenger seat that folds forward to accommodate longer items.

Of course, the Toyota Prius V wouldn’t be a Prius if it didn’t achieve stellar fuel economy. While its EPA rating of 42 mpg combined (44 mpg city/40 mpg highway) falls well short of the hatchback Prius’ 50 mpg combined rating, this wagon is still in the fuel economy stratosphere and one of the most fuel-efficient family cars you can buy. Apart from its extreme mpg, the Prius V wagon is a fairly unremarkable but easy car to drive, and its smooth, quiet ride makes it a viable choice for road trips.

Of course, there are other highly fuel-efficient wagons out there. One of our favorites is the 2014 Ford C-Max Hybrid, which offers more style, a nicer interior, better driving dynamics and even higher EPA fuel economy ratings. The Ford doesn’t have as much cargo space, though. The diesel-powered 2014 Volkswagen Jetta Sportwagen TDI is another good alternative, particularly if you’re interested in a wagon with a more premium-feeling interior. Still, the competent 2014 Toyota Prius V remains a top selection in this group, distinguishing itself with versatility, frugality and an abundance of Prius-style green cred.

Powertrains and Performance

The 2014 Toyota Prius V is powered by a 1.8-liter four-cylinder engine teamed with two electric motors and a battery pack. Combined output is 134 horsepower and 153 pound-feet of torque. Power is sent to the front wheels via a continuously variable transmission (CVT). The Prius V features three selectable driving modes: Eco (which slows response to accelerator-pedal inputs to promote fuel-efficient driving), Normal (the default mode) and Power (which makes the throttle more responsive).

In our track testing, the Prius V accelerated from zero to 60 mph in 10.3 seconds: considerably slower than the VW Jetta wagon (8.8 seconds) and the Ford C-Max (8.1 seconds). The EPA rates this hybrid wagon at 42 mpg combined (44 mpg city/40 mpg highway), and we’ve found it easy to achieve these numbers in real-world driving.  www.edmonds. com.

3. Chevy Volt



Whether you want a diesel sedan that will take you more than 800 miles between fill-ups or an electric-only vehicle that has just enough power for your morning commute, there’s something out there that meets your needs. Somewhere between those two extremes is the 2015 Chevrolet Volt, a plug-in electric hybrid that offers electric-vehicle benefits like gasoline-free commutes, without the restriction of being tethered to a plug for long journeys.

One distinctive trait about the 2015 Chevrolet Volt is that it offers a longer electric-only range than most plug-in hybrids (think 40-ish miles). Ostensibly, what makes this plug-in Chevrolet appealing to shoppers is its ability to tackle the short daily commute on electric power while also offering the range necessary to facilitate weekend road trips. You plug it in at home for a charge, but if your travels take you farther than expected, a gasoline-powered engine that serves as a generator kicks in to extend the Volt’s range. At this point it’s similar to a standard hybrid, using gasoline along the way. However, when you exceed the electric-only range and run on gasoline, the Volt gets an EPA rating of a mere 37 mpg combined, while the Toyota Prius and some of its ilk get upward of 50 mpg combined. Some owners may be thrilled to go weeks or months without ever visiting the pump, while others may be looking for a vehicle with better overall fuel economy.

If the 2015 Chevrolet Volt’s specifications meet your driving needs, quality should be your next consideration. In an Edmunds.com “B” rating, the Volt was easy to drive with a comfortable and silent ride, but its interior design had some glaring flaws. The layout and design earn points for their futuristic aesthetic, but the touchscreen is poorly organized and endlessly frustrating. The sloping rear roof impinges on rear headroom, and the T-shaped battery interferes with hip space in the backseat. This hybrid isn’t big on storage space, either, offering a paltry 10.6 cubic feet of cargo space in the trunk.

Thanks to its range, the 2015 Chevy Volt doesn’t have direct competitors, but there are a few other plug-in hybrids worth considering. The 2015 Ford C-Max EnergiHonda Accord Plug-In and Toyota Prius Plug-In are all strong choices, but keep in mind that each has a much shorter electric-only range than the Volt. If you’re considering all-electric cars, we recommend checking out the 2015 Nissan Leaf for its proven reliability and respectable electric range. Still, of the bunch, the 2015 Chevrolet Volt stands out as a rewarding car to drive. If it fits your lifestyle, we’d definitely recommend taking it out for a spin.

The front-wheel-drive 2015 Chevrolet Volt is powered primarily by an electric motor that puts out 149 horsepower (111 kilowatts) and 273 pound-feet of torque. The electric motor is fed by a 16 kilowatt-hour (kWh) lithium-ion battery pack until the battery charge is 70 percent depleted, at which point the Volt’s 83-hp, 1.4-liter four-cylinder, gasoline-fueled engine springs to life to power the electric motor. The engine is used primarily as an electricity generator to power the electric drive motor, though in some situations it can also kick in to boost the car’s performance. There are Normal, Hold, Sport and Mountain modes designed to maximize the powertrain’s performance and efficiency in different situations.

Recharging the battery pack completely requires you to plug the car in to a 120- or 240-volt outlet, though regenerative braking and the engine generator can help recharge it to a certain extent. Using a 240-volt power source takes about three hours to recharge a depleted battery.

In Edmunds performance testing, the Volt took 9.2 seconds to accelerate from zero to 60 mph in electric mode and 9 seconds flat with the engine generator. Both are reasonably quick times for the traditional hybrid segment.

In long-term Edmunds testing, our Volt had an average all-electric range of 37 miles (against an EPA estimate of 38 miles), with certain charges ranging from 25-50 miles. Once the battery was depleted, the Volt averaged 35 mpg in our yearlong test, a few mpg under the EPA’s combined estimate of 37 mpg. The Volt’s “Hold” mode allows the driver to optimize the car’s efficiency by locking out all-electric propulsion until it’s deemed necessary, and this can be useful on commutes that involve both city and highway travel.  www.edmonds.com

As I was investigating car options I visited the local car dealerships and test drove a number of cars.   Being an unrepentant techno geek I asked why the Prius gets better fuel efficiency in the city rather than the highway.    I also wanted to know why the diesel VW Golf had better fuel economy than the gasoline version.   The car sales folks were clueless.   Clearly not a product of a liberal arts education.   I started to do some digging to get the answers to my questions.

Cars move when we apply power to the wheels (Read about horsepower).  Traditionally, the power came from an internal gasoline engine.  Today we have cars powered with gasoline, diesel, and electric engines.   This is what I learned starting with a conventional gasoline engine:


If we assume the transmission is close to 100% efficient we can calculate the maximum efficiency of an internal combustion engine driven car based on the Carnot equation and the maximum temperature stability of steel.   An ideal internal combustion engine would have an efficiency of 37%, but in practice it is often half this value (Read more about gasoline engines). Diesel Engines are more efficient than gasoline engines (Read about Diesel Engines).  Electric motors have efficiencies of over 85% (reference).

The three videos below illustrate the engineering behind the superior fuel economy of hybrid electric cars.

Read more about Toyota hybrid drive train.  It is important to note that the Toyota V uses a combined electric/gasoline engine with 100% of the energy from the car coming from gasoline!

Finally, the value of a car depends on purchase price, depreciation, reliability, and the less tangible quality of performance.   Consumer Reports has done a nice job of combining these factors into a car value score (internal access only).


Before class prepare answers to the following questions assuming that I drive 15,000 miles per year and that I will own the car for ten years:

1) How many gallons of fuel and mass of carbon dioxide will be produced over the ten year lifetime of the gasoline Golf Sportwagon, TDI Golf Sportwagon, and Prius V wagon based on the published fuel efficiencies?

2) How much will this fuel cost over ten years?  Be specific about your economic assumptions.

3) Based on the data below, and assuming that I am going to finance 100% of the car at 2.99% per year for five years, what is the lifetime cost of running the car (ignore taxes and insurance)?

Volkswagon   Toyota
Golf Sportwagon SE w/ sunroof Golf TDI with sunroof Prius V five
Truecar price $24,437 $26,050 $26,354
Actual Mileage (MPG) 23 36 41

4) What is the actual energy efficiency of each car?  As a good assumption, we can assume that the energy from the engine needs to do two things,

A) Accelerate the car to a highway cruising speed:   KE = 1/2 mass * V2
B) Overcome the drag of moving through the air:
Drag Energy = 1/2 * air density * drag area* V2 * distance

See attached Excel sheet. for the calculations.  Why did I multiply step A by ten?  What takes more energy, acceleration or drag?

5) How much electrical energy in kJ is required to recharge a Chevy Volt’s battery assuming it has a 70% charge.   If  you were using a 120 volt charger with a maximum charging current of 10 amps, how long would it take to fully charge the battery?

Remember that V*I = Power (watts J/s).    Energy (J) = Power (watts) * time.

6) Come to class prepared to work through calculations 1-4 for the Chevy Volt.   Why is this calculation more difficult?   What additional data would you need to compare the Volt to the other vehicles?

7) Be prepared to make a recommendation on my new car!




Details on a planetary gear system.

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