Because they spend the vast majority of their operating time stopping, idling, and accelerating at low speeds, . They are pretty much a worst case scenario for ICE efficiency.
But then the cars do not need to be electric! A hybrid with a small battery will suite this as well and, given the current price of batteries, will be cheaper.
... because the test driving cycle is based on 8 miles city, 6 miles freeway, and then 11 miles stop/go with 700 stops; and if I remember correctly is based on all accessories (i.e. air conditioning) running for the entire time.
This is not your EPA passenger vehicle test cycle.
> Cars are most fuel efficient when they're rolling about 50MPH.
They're even more efficient rolling at 40 MPH or 30 MPH or even 20 MPH, as long as it's consistent (not stop-start). Air resistance scales with something like the cube of velocity and begins to be noticeable around 20 MPH.
Efficiency is easy to ball park, but if you want to get precise then every vehicle is going to have it's own moving target. I would argue that no vehicle is especially efficient at 20mph for long durations. Sure you have no air resistance, but you also are spinning a 6 speed transmission when you really only need one. 90% of the car is being wasted. You might as well just drive a self propelled lawn mower.
Even two vehicles of the same make will be different due to differences in operating conditions.
An ICE engine, especially gasoline powered ones, operate with widely varying levels of efficiency. Lets think of a car in 4th gear at 50mph with 15% throttle applied. Now imagine climbing a steep hill. The car can stay in 4th gear and climb the hill with 65% throttle, or downshift to 3rd and climb the hill with 45% throttle. Speed alone doesn't determine fuel efficiency. Intake vacuum (or boost in certain applications) determines fuel efficiency. The trick is to try to go as fast as you can while consuming the least amount of fuel. There is nothing "efficient" about driving a 250hp, 3.0L V6 at 20mph.
It's the reason why vehicles have a separate "city" and a "highway" fuel economy rating, since the former takes into account the expected stopping and starting you do in city traffic which you would not on an uncongested highway. It also makes intuitive sense if you understand physics: in a non-hybrid ICE vehicle, you impart energy from the engine into the wheels to accelerate the vehicle and you impart energy from the wheels into the brakes to decelerate, effectively wasting the original energy from the engine as heat. In hybrids and EVs some of that energy can be recovered by using the motor as a generator to recapture it in a useful form.
Wouldn't it be more-so that with ICE vehicles you loose 100% of the kinetic energy as heat when stopping. With an EV you convert a portion back to the battery packs with regenerative breaking.
Correct, though many times costs are not just fuel - total ROI includes service cost, availability of replacement parts, insurance costs, etc - a NG car could cost more in fuel and still be cheaper for effectively forever depending on how the books land.
Not trying to be rude, but it's because it's intro Physics (F=m*a, with F coming from fuel, battery, or brakes), with an understanding that the process that generated that force has an efficiency that's less than 100%, mixed with a dash of intro Calculus (integral of force).
