Why does the Fisker Ocean have such a low top speed?

Question

The Fisker Ocean has 564 hp, a 3.9 sec 0-60 and does a 1/4 mile in 12.5 sec finishing at 110 mph. These performance figures compare well to for example the Range Rover Sport SV with 626 hp, 3.4–3.6 sec 0-60 and 11.8–12.0 sec 1/4 mile. However the Fisker Ocean's top speed is far lower, at 128 mph compared to the Range Rover's 180. Even the 334 hp diesel Range Rover SD V8 manages 135 mph, though it takes twice as long to 60.

What is the reason for this seeming discrepancy?

Manufacturers Specs

Car and Driver Ocean Fisker One

Car and Driver Range Rover Sport SV

Parkers Range Rover SD V8

Answer 1

Just guessing, but I believe the reason is gearing.

Electric motors have a speed range of around 0 - 10000 RPM to 0 - 20000 RPM. Unlike internal combustion engines that have to be rotating at least 1000 RPM to produce useful torque, electric motors produce very good torque already at 0 RPM.

So because of the speed range that extends to 0 RPM, it is very tempting to remove the gearbox and have only a single gear.

Let's assume that the particular motor has a speed range of 0 - 20000 RPM.

Now the big question is, at what vehicle speed should the motor be rotating at 20000 RPM.

You could make it rotate 20000 RPM at 128 mph. This is a speed that someone might actually drive at a German Autobahn.

Or you could make it rotate 20000 RPM at 180 mph.

If you make it rotate 20000 RPM at 180 mph, the vehicle can go faster.

If you make it rotate 20000 RPM at 128 mph, the vehicle has a lower single-speed gear, and as we know from gearbox cars, a lower gear means faster acceleration.

So it's your choice. Either make the top speed so high nobody actually utilizes that speed and reduce acceleration, or make the top speed something that can be actually utilized by a sane person and increase acceleration.

Theoretically there's also the possibility of adding a two-speed gearbox to the car, but it increases the price of the car, adds complexity and is a part that can fail.

Also three other considerations:

• Electric vehicle advertised horsepowers are momentary numbers. Fisker Ocean can't produce 564 hp continuously from a full battery until the battery is flat. 564 hp EV means it can produce 564 hp for the typical duration of an acceleration. Top speed requires continuous power. Internal combustion engines can produce max power continuously, if the cooling is adequate (and why wouldn't it be adequate).
• Driving at top speed drains the EV battery flat so fast, faster than it would drain a full gasoline/diesel tank empty, so it probably doesn't make sense to have a ridiculously high top speed.
• Fisker Ocean is a SUV, and SUVs have lots of air resistance. However, Range Rover is a SUV as well. A sports car would probably have a higher top speed.

Answer 2

Likely because it's not the market they're aiming at, the number of people who are interested in driving their SUV at speeds in excess of 130mph (or even just the bragging rights of owning one that can) is pretty small, so 128mph is "fast enough" for most. Making an SUV-type vehicle that can comfortably cope at speeds in that sort of 180mph range is no easy undertaking. It isn't just the power required to get there (which is no small amount) it's the aerodynamics to keep it stable (which would likely compromise the low-drag goals of an EV), it's the brakes to get it stopped in a reasonable manner, it's the battery capacity to maintain that speed for more than a mile or so without needing to stop and recharge.

Conversely achieving impressive acceleration figures up to the range of realistic speeds is comparatively easy, it's largely a function of higher power + traction to put that power down and low drag to reduce resistance. Electric motors are mechanically quite simple compared with their internal combustion counterparts, particularly as you ramp up the power levels, transmission and tires to get the power down are a well understood domain and you're aiming for low drag with an EV anyway for range reasons.

Fisker achieve their figures with what they call "boost mode" - they run the motor at higher output for short bursts (such as doing a 0-60 launch or quarter mile), this is where the 564hp comes from incidentally, normally it's only producing 468hp (a respectable figure to be sure - but about 160hp down on the SV), the "boost mode" is a short duration (not sure how short tbh) burst of full power and it's limited to 500 uses over the lifetime of the car, precisely because the car isn't built to be driven like a 568hp supercar day in day out, there's concerns about extra wear placed on drivetrain components and why go to the extra expense and hassle of building to accommodate that when, as Henrik Fisker put it:

"Is it something people really want? Because most likely, they'll try it 10 times and then they probably won't do it much more—except if they have a friend out and they want to show off."

So there you have it from the proverbial horse's mouth - Fisker didn't build an SUV-supercar because they aren't aiming at those customers, they're aiming at the people who want a quick-enough luxury SUV with the occasional "floor it!" moment for shits and giggles.

Answer 3

Stability, not straight-line performance

Sports cars have a low centre of gravity. The reason isn't really aerodynamics - track cars do make use of ground effect, but it's less of a thing for road cars which need some clearance to get over speed bumps, potholes and badly-rounded-off ramps. The primary reason is stability.

Even if you're not going round corners too much, a car will still roll somewhat on its suspension. Even in a straight line, imperfections in the road will make your car roll, and the faster you're going, the more energy goes into that. As soon as you add the real world, with corners, idiot other drivers, little Jimmy who's run out into the road, moose, and all the other features of the real world which you might not want to T-bone, the ability to turn is kind of a thing too.

All of which means that if you want to drive fast, the last thing you want to be in is an SUV. They're all, without exception, less stable than saloon cars when it comes to roll - and compared to genuine sports cars they aren't even playing the same game.

Having helped people out of a Toyota Land Cruiser which overturned on a country road at a fairly uneventful speed, I'd be deeply worried about anyone who wanted to drive any SUV over 100mph. If you're a good enough driver to handle it, you're also a good enough driver to know it's not a good idea. Pretty much by definition then, the only people doing this are automatically a danger to themselves and others. If they've limited to to 120mph, that's still some way faster than I'd be happy with me or mine being in or near.