Why do EV have low max speeds?
Discussion
TheBinarySheep said:
Pistonheadsdicoverer said:
PS: Should have said: Why do SOME EVs have low max speeds?
The max speed on the Nissan Ariya is 99MPH and I've noticed that mainstream EVs (except for Tesla) seem to have similarly low max speeds.
Is it because efficiency nosedives beyond a certain speed?
I think it's more an efficiency thing.The max speed on the Nissan Ariya is 99MPH and I've noticed that mainstream EVs (except for Tesla) seem to have similarly low max speeds.
Is it because efficiency nosedives beyond a certain speed?
Some EV's have decent top speeds. Model 3 Performance is 162 mph I think.
The Nissans must be limited. My old 60kw Leafs top speed was 99 too. And that’s all the speedo went to !
Bobley said:
Rolling resistance increases with speed but as a proportion its pretty small once you're at high speed. Aero drag power is proportional to speed cubed so no matter how good your CdA is, once you're above 80mph its getting considerable.
Those relationships are to calculate the power required, but because your speed is obviously distance/time, the relationships between energy and distance, which is what is draining the battery over a given journey length, are the important ones to consider.Rolling resistance measured as energy/mile remains quasi-constant regardless of speed and the energy consumed per mile by drag increases with the square of speed.
JonnyVTEC said:
Peak power is quite different to continuous power rating in an EV.
Unlike an ICE.
The end.
Cruise power for both EVs and ICEs isn't very high, unless we are talking 100 mph ++.Unlike an ICE.
The end.
At 70 mph on a flat road, a model 3 only requires about 17.5 kW or 23 bhp to maintain speed.
This curve shows the energy consumption per mile.
Cruise power (in Watts) can be calculated by multiplying the speed by the Wh/mile value from the solid red curve.
Data is for 15C ambient temperature.
And for the 'weight is absolutely everything' folks, the car, all 1.8 tons of it, is achieving 160 mpg at 70 mph.
The dashed red line is the theoretical consumption without the mass of the battery, about 8% better at 175 mpg.
GT9 said:
Cruise power for both EVs and ICEs isn't very high, unless we are talking 100 mph ++.
At 70 mph on a flat road, a model 3 only requires about 17.5 kW or 23 bhp to maintain speed.
This curve shows the energy consumption per mile.
Cruise power (in Watts) can be calculated by multiplying the speed by the Wh/mile value from the solid red curve.
Data is for 15C ambient temperature.
And for the 'weight is absolutely everything' folks, the car, all 1.8 tons of it, is achieving 160 mpg at 70 mph.
The dashed red line is the theoretical consumption without the mass of the battery, about 8% better at 175 mpg.
That's interesting, I would have assumed that an EV would have been fairly efficient between the 0 and 20mph range?!At 70 mph on a flat road, a model 3 only requires about 17.5 kW or 23 bhp to maintain speed.
This curve shows the energy consumption per mile.
Cruise power (in Watts) can be calculated by multiplying the speed by the Wh/mile value from the solid red curve.
Data is for 15C ambient temperature.
And for the 'weight is absolutely everything' folks, the car, all 1.8 tons of it, is achieving 160 mpg at 70 mph.
The dashed red line is the theoretical consumption without the mass of the battery, about 8% better at 175 mpg.
_Hoppers said:
That's interesting, I would have assumed that an EV would have been fairly efficient between the 0 and 20mph range?!
I suppose it's all relative!200 Wh/mile = 200 mpg equivalent.
1000 Wh/mile = 40 mpg equivalent.
This chart blow compares the Tesla with a modern Golf ICE.
The EV is 3 to 4 times more efficient than the ICE at any speed.
0-20 mph suffers for all powertrain types because the 'other' consumption forms a higher proportion of overall consumption.
Other being heating/cooling, ancillary devices, etc.
Edited by GT9 on Wednesday 17th April 09:23
GT9 said:
Cruise power for both EVs and ICEs isn't very high, unless we are talking 100 mph ++.
At 70 mph on a flat road, a model 3 only requires about 17.5 kW or 23 bhp to maintain speed.
This curve shows the energy consumption per mile.
Cruise power (in Watts) can be calculated by multiplying the speed by the Wh/mile value from the solid red curve
I see what you did there. But the top speed of a model 3 isn’t 70mph…At 70 mph on a flat road, a model 3 only requires about 17.5 kW or 23 bhp to maintain speed.
This curve shows the energy consumption per mile.
Cruise power (in Watts) can be calculated by multiplying the speed by the Wh/mile value from the solid red curve
autumnsum said:
It's going to be cost, right? Much cheaper to make parts which have a lower max speed.
Tesla said that was the reason the cheap M3 has a low top speed.
This is false,Tesla said that was the reason the cheap M3 has a low top speed.
Tesla said the reason for the 124mph VMax on the new Model 3 is its tires, which were designed for optimized low rolling resistance, with the tradeoff being a lower tire maximum speed rating.
Answering the original question:
Not all EVs have low max speeds:
- Rimac Nevera: 258 mph
- Lucid Sapphire: 205 mph
- Tesla Model S Plaid with Track Pack: 200 mph
- Tesla Model 3 Performance: 162 mph
- Tesla Model S Raven Performance: 155 mph
(n.b. that none of the above have multi-speed transmissions)
Multi-speed transmission EVs:
- Porsche Taycan Turbo GT: 190 mph
- Porsche Taycan Turbo/Turbo S: 162 mph
That said, the 2 main speed-limiting factors for all EVs are:
- maximum electric motor RPM
- tire maximum speed rating
Not all EVs have low max speeds:
- Rimac Nevera: 258 mph
- Lucid Sapphire: 205 mph
- Tesla Model S Plaid with Track Pack: 200 mph
- Tesla Model 3 Performance: 162 mph
- Tesla Model S Raven Performance: 155 mph
(n.b. that none of the above have multi-speed transmissions)
Multi-speed transmission EVs:
- Porsche Taycan Turbo GT: 190 mph
- Porsche Taycan Turbo/Turbo S: 162 mph
That said, the 2 main speed-limiting factors for all EVs are:
- maximum electric motor RPM
- tire maximum speed rating
CheesecakeRunner said:
Whilst there are engineering reasons, the main one is that a bog standard family car doesn't need to go more than 100mph, so manufacturers don't bother dealing with those engineering reasons to make them go faster.
Outright speed is simply not a selling point in those car segments.
Where it is a selling point, such as Porsche with the Taycan, they have much higher top speeds.
This basically, higher top speeds on most ICE cars are a by-product of achieving half decent acceleration without screaming it’s knackers off at typical cruising speedsOutright speed is simply not a selling point in those car segments.
Where it is a selling point, such as Porsche with the Taycan, they have much higher top speeds.
On EV it doesn’t matter so why not have shorter gearing with smaller, cheaper, lower torque motor
Less torque means less current so less pricey copper in the motor and wiring, lower spec power electronics, also smaller, lighter, cheaper friction brakes/suspension.
Virtuous circle and 99.9% of customers WGAF, particularly as if it’s a cheaper car it’ll probably have a smaller batter so likely won’t go very far at top speed anyway
With electric drive trains current follows torque and voltage speed. The system needs to designed so the car can get away on the worst gradient and have adequate top speed. Both the electrical and mechanical compromises are easier the lower the top speed. Mechanical stresses follow the square of speed so designing for 150mph more than twice as exacting than 100. And the motor needs to turn as fast as possible to make it small and light and make the power. Presumably the simpler rotors of induction motors makes it easier than with buried magnets in synchronous types.
After all the analysis and modelling Porsche concluded a gear box was still easier than a wider range motor/electronics, on the world's best performance electric car, the Taycan.
The high top speeds of modern cars are a buy product of having good aerodynamics for efficiency and high power for good acceleration in ever heaver vehicles. No body needs it and a tiny fraction must explore it.
After all the analysis and modelling Porsche concluded a gear box was still easier than a wider range motor/electronics, on the world's best performance electric car, the Taycan.
The high top speeds of modern cars are a buy product of having good aerodynamics for efficiency and high power for good acceleration in ever heaver vehicles. No body needs it and a tiny fraction must explore it.
granada203028 said:
After all the analysis and modelling Porsche concluded a gear box was still easier than a wider range motor/electronics, on the world's best performance electric car, the Taycan.
Not necessarily easier, more that they were able to extract ultimate performance with 2 speeds, and important to their brand, an ability to deliver that performance repeatedly without de-rating as well as having supreme acceleration at de-restricted autobahn speeds.The point is that 2-speeds just isn't necessary for more mainstream EVs.
GT9 said:
granada203028 said:
After all the analysis and modelling Porsche concluded a gear box was still easier than a wider range motor/electronics, on the world's best performance electric car, the Taycan.
Not necessarily easier, more that they were able to extract ultimate performance with 2 speeds, and important to their brand, an ability to deliver that performance repeatedly without de-rating as well as having supreme acceleration at de-restricted autobahn speeds.The point is that 2-speeds just isn't necessary for more mainstream EVs.
jinba-ittai said:
The Taycan 2 speed gearbox was more a marketing exercise in the end - from what I hear the 1st gear is only used when in launch mode - so for 99% of drivers 99% of the time it's totally pointless, just extra weight to carry around and more R&D + manufacturing cost to be recovered
Whenever you switch the car to Sport or Sport Plus mode it will use both gears. I imagine quite a few owners use those modes very regularly.I agree though, pretty pointless as the vast majority will never see the other side of 100mph so a single gear would have more than sufficed.
jinba-ittai said:
The Taycan 2 speed gearbox was more a marketing exercise in the end - from what I hear the 1st gear is only used when in launch mode - so for 99% of drivers 99% of the time it's totally pointless, just extra weight to carry around and more R&D + manufacturing cost to be recovered
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