range as function of speed - Jaguar I-Pace EV400 Forum
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post #1 of 6 (permalink) Old 09-11-2018, 01:00 AM Thread Starter
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range as function of speed

I have noticed in my A3 etron that the range decreases dramatically as my freeway speed increases.
It has been my sense that the drop in efficiency is larger than with a gas engine.
Excuse me, I mean 'petrol' engine.

It has now occurred to me that this is because when you coast with a petrol engine it's neutral.
Whereas if you coast with an electric motor that's doing regen you have the same loss of efficiency as when the motor is powering the car.

Soooo .. the difference between, for example, 65 and 75mph in fuel economy for a gas engine is smaller than that for an e-motor. By my calculations, on the iPace, going 75 vs 65 will reduce your range by just under a third! (That's a lot.)

I would be very interested to hear about robust empirical data from Tesla owners: if you really know your average speed and consumption, and you do the 65 vs 75 mph comparison, what's your range difference?
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post #2 of 6 (permalink) Old 09-11-2018, 01:14 AM
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It has now occurred to me that this is because when you coast with a petrol engine it's neutral.
Whereas if you coast with an electric motor that's doing regen you have the same loss of efficiency as when the motor is powering the car.
Your sense is right - EV efficiency is more sensitive to speed - but I believe you're mistaken as to the reason. I'm no expert myself, but as I understand it, the issue is that gasoline engines have lots of mechanical inefficiency, so things like speed and wind resistance have a relatively minor impact on overall efficiency. You can coast in neutral in an EV, but you would still have relatively greater loss of efficiency (than a gas car) at high speed, because there is so little inefficiency in the electric motors.
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post #3 of 6 (permalink) Old 09-11-2018, 01:17 AM
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There's nothing magical about EVs that makes them use up energy more quickly than ICE as the speed rises. I can get ~23mpg at 65mph in my truck, or I can drive it as I normally do, fast as I want, and get 15-16. Driven hard on a race track, the lowest I've gotten is 6mpg in a 550i. The FRS didn't fare much better. I think I got like 10 at the track.
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post #4 of 6 (permalink) Old 09-11-2018, 01:14 PM
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EVs suffer more than modern ICE cars do at higher speeds.
Cylinder deactivation, VVT, tall gearing, 8-10 speed digital automatics, lighter weight, all help ICE cars over their EV brethren to enhance efficiency at high speeds.

And there is a basic physics issue with electric drive. The more amps you need, the warmer the components get. The warmer the components get, the higher the electrical resistance. ICE engines run more efficiently as their temperature climbs.

Good news? EVs are far more efficient at higher altitude than ICE engines are. If anything, an EV gets better economy at 10,000' DA than sea level at 75mph. The opposite is true for piston engines.
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post #5 of 6 (permalink) Old 09-13-2018, 01:32 AM
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I think it's more that ICE have come up with ways to reduce their horrible inefficiencies when at a steady state speed. It's not that EVs are taking more of a hit at speed than ICE. It's that ICE vehicles are taking less of a hit than ICE vehicles normally do while accelerating.
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post #6 of 6 (permalink) Old 09-13-2018, 11:10 AM
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On the Tesla website, there is a tool where you can play with the speed, the temperature, whether you are usin AC or net etc and you can see the estimated range. Scroll down to the bottom of the link below. The I-Pace will perform similarly.

The S75D loose about 100km of range going from 100 to 120 kph. Should be similar on the I-Pace.

https://www.tesla.com/fr_CA/models
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