Why do electric cars accelerate faster than most gas-powered cars, even though they have less horsepower?
In: Technology
Combustion engines produce zero torque at zero rpm. You have to rev the engine into the powerband to get peak power. You then need a transmission in order to make sure that you don’t have to continue turning the engine faster and faster to get more power. When you shift gears, there’s a loss of power to the wheels.
Electric motors can produce torque as soon as power is applied. They provide that power continuously.
A gas car cannot bring its full horsepower to bear from a stop. It can only do that when its engine rpm is in a specific range.
Now, you can keep the rpm in that range better by using more gears, but then you spend more time switching gears, and during that time the engine isn’t doing anything useful.
Electric motors have access to their full power output across a wide range of speeds, requiring no gearshifts, and giving them almost as much torque as they could want from a stop.
I think the assumption in the question is wrong. Most very fast electric cars have gobs and gobs of horsepower. Tesla’s line up starts at nearly 300 horsepower and they have options up to 500 or more. 500 HP is A LOT.
But as other point out, excellent low end torque (and fancy traction control) can do a lot for vehicles when weight and power output are similar.
Imagine you are spinning a really heavy wheel but you can only push it once every full rotation.
At low speeds you can push it once a minute. As it gets up to speed you have the opportunity to push it more and more often. So 2 times a minute, then 3 times then higher and higher until you physically can’t push any harder past, say, 10 rotations a minute because your arms are weak.
An engine works the same way. At low speeds you’re not able to use full power because the piston needs to return to its original position before it can push again.
An EV can use full power from the very beginning because electric motors use magnets which can exert power at every point in the rotation.
While comments regarding ICE engine power bands are valid, acceleration is more based on torque – NOT horsepower. Horsepower is more an indicator of top speed.
Most cars are engineered for what we know is the “car” feel, but imagine these two extremes.
A high torque engine but lower horsepower – such as a diesel engine that can push a large amount of freight but can’t go fast.
A high horsepower engine but low torque – a small car that can go fast but can only accelerate slowly, taking forever to get up to speed.
Yes, im general, electric engines have access to immediate torque, but not all EVs are performance oriented with quick response.
Electric motors can build a magnetic field and force instantaneously. Combustion engines take time to inject air, ignite it, and get a ton of rotating parts moving. And even if you do all that, you lose a bunch of that energy to heat. There’s just loads of inefficient and physical speed bumps in the way of generating power.
Eli5: it’s the difference between turning on a light switch and lighting a candle. You get light at the end of them both, but one is quicker to get there.
Power is force times speed, so if you can push harder and are going faster you are pushing with more power. Pushing at low speed requires little power, and pushing super fast against little resistance requires little power.
In a gas car the engine spins the wheels with tiny explosions, like if you imagine an old sail boat steering wheel with all the handles and you can slap the handles. Imagine you can only slap the wheel with one kind of slap, no strong and weak slap. The max power is when you are slapping as fast as you can, each slap is the same strength and you are fishing them out as fast as you can, any faster and the slaps become weaker. So overall a gas car has zero power at zero speed, power increases as speed increases until you reach the max power speed, and then as you go faster it drops off. Changing gears is like making the wheel bigger or smaller and you have the same handle spacing, so bigger wheels turn slower and take more slaps to go all the way around.
An electric car is generally current limited, the battery could source a lot more but the switches that connect the battery to the motor can only handle so much before they melt. Current times voltage is power, and the batter has a roughly constant voltage. Also current is proportional to torque. The voltage needed to spin a motor slowly increases with speed. So an electric car has full torque at zero speed, and at every speed up to the point where the motor voltage needed is close to the battery voltage minus losses, or you hit the power limit of the switches. This is a bit like having a water hose to push up a kite, you have a lot of pressure when the hose is close to the kite, and within a certain distance it is basically full power, and the you get to a point where the water stream spreads out and pushes less hard, and eventually there is some maximum height where you can just barely keep the kite aloft
In a gas-powered engine, the pulling force comes from fuel going boom. Each time the engine goes round, you get a fixed number of booms. To make the calculation easier, let’s say you get one boom each time the engine goes round. So if the engine goes round once per second, you get one boom per second. If the car speeds up so the engine goes round 50 times per second, you get 50 booms per second, so 50 times more force. This is why gas-powered engines stall at very low speeds and why they need an electric starter motor: if the engine is not going round fast enough, there are no booms and not enough force to keep it going.
Electric engines do not work like this. Instead, electric engines work by electricity going through a wire, which turns the wire into a magnet, which creates the pulling force. All of this is happening continuously, and is (more or less) unaffected by how fast the engine is going round.
Now, the horsepower rating of an engine does not measure how hard the engine can pull. It is a measure of the maximum power output of the engine. This means that if an electric engine and a gas-powered engine have the same horsepower, and if they are somehow in cars with the same gear ratios, then they can pull identical loads at the same maximum speed. However, the electric engine will be able to pull just as hard from 0 speed until it reaches this maximum, whereas the gas-powered engine will not reach its maximum pulling power until the engine is spinning at its optimum speed.
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