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Maybe you can test it for us?
What is the most fuel efficient way to accelerate?
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Driving Instructions:
A ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal.
How do we get those approx instructions? Below:
Basic physics always applies: Isquared x R is always the power (energy rate) lost in the motor, batteries, and wires. (The other types of losses in the motor also increase a little due to the higher torque needed for brisk acceleration, but we can neglect that extra bearing friction usually.)
"I" is the electric current flowing, which is very high when flooring it. THAT is the main power loss, which creates extra heat in the battery, wires, windings, compared to taking it a bit easy on acceleration.
The main physics consideration above is a good starting place.
There are secondary effects (motor windage, bearing friction, iron losses,etc.), which translate into a motor efficiency map:
![34247]()
... that basically tells us to ramp up torque as our fixed-gear ratio vehicle gains speed into the redest region of the graph where we get the highest motor efficiency.
IOTW, make a bee-line to the middle of the red region until you are at the traffic-limited speed target.
Granted, air drag builds as you increase speed too, so best not to accelerate too rapidly into that energy-wasting situation too soon either. And keep currrent (amps) down to avoid the blue region on the left side of the graph during low-speed operation. ......So a ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal for that particular motor, and we assume our motors are at least similar to that efficiency map.
Deeper (Tech Warning: The following article could cause headaches unless you're into physics-engineering.):
x-engineer.org
A ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal.
How do we get those approx instructions? Below:
Basic physics always applies: Isquared x R is always the power (energy rate) lost in the motor, batteries, and wires. (The other types of losses in the motor also increase a little due to the higher torque needed for brisk acceleration, but we can neglect that extra bearing friction usually.)
"I" is the electric current flowing, which is very high when flooring it. THAT is the main power loss, which creates extra heat in the battery, wires, windings, compared to taking it a bit easy on acceleration.
The main physics consideration above is a good starting place.
There are secondary effects (motor windage, bearing friction, iron losses,etc.), which translate into a motor efficiency map:
... that basically tells us to ramp up torque as our fixed-gear ratio vehicle gains speed into the redest region of the graph where we get the highest motor efficiency.
IOTW, make a bee-line to the middle of the red region until you are at the traffic-limited speed target.
Granted, air drag builds as you increase speed too, so best not to accelerate too rapidly into that energy-wasting situation too soon either. And keep currrent (amps) down to avoid the blue region on the left side of the graph during low-speed operation. ......So a ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal for that particular motor, and we assume our motors are at least similar to that efficiency map.
Deeper (Tech Warning: The following article could cause headaches unless you're into physics-engineering.):
EV design – electric motors – x-engineer.org
Tutorial on how to calculate and simulate an electric motor for an electric vehicle (EV) design using Scilab and Xcos block diagrams
x-engineer.org
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More control and easier on the machinery the more gentle you are. Works for all, repeat all, things mechanical or electric.
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Wow! Very useful. I read the map to show the motor should be most efficient between 25 and about 50 mph (assuming the Bolt's gearing is roughly 10 mph per 1,000 rpm).Driving Instructions:
A ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal.
How do we get those approx instructions? Below:
Basic physics always applies: Isquared x R is always the power (energy rate) lost in the motor, batteries, and wires. (The other types of losses in the motor also increase a little due to the higher torque needed for brisk acceleration, but we can neglect that extra bearing friction usually.)
"I" is the electric current flowing, which is very high when flooring it. THAT is the main power loss, which creates extra heat in the battery, wires, windings, compared to taking it a bit easy on acceleration.
The main physics consideration above is a good starting place.
There are secondary effects (motor windage, bearing friction, iron losses,etc.), which translate into a motor efficiency map:
View attachment 34247
... that basically tells us to ramp up torque as our fixed-gear ratio vehicle gains speed into the redest region of the graph where we get the highest motor efficiency.
IOTW, make a bee-line to the middle of the red region until you are at the traffic-limited speed target.
Granted, air drag builds as you increase speed too, so best not to accelerate too rapidly into that energy-wasting situation too soon either. And keep currrent (amps) down to avoid the blue region on the left side of the graph during low-speed operation. ......So a ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal for that particular motor, and we assume our motors are at least similar to that efficiency map.
Deeper (Tech Warning: The following article could cause headaches unless you're into physics-engineering.):
EV design – electric motors – x-engineer.org
Tutorial on how to calculate and simulate an electric motor for an electric vehicle (EV) design using Scilab and Xcos block diagrams
One question: 1/4 of max pedal... am I right to understand you mean 3/4 pedal?
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For sure! I am generally easy on my vehicles at my age.
I have a basic understanding of getting good efficiency in gas engines but not electric motors hence I posted the question I did.
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I am surprised no one has yet suggested just watching the ring color around the speedometer. If you keep it green that is most efficient, if it turns yellow less efficient, the GM engineers know and provided the info to the driver. Keep the ring green for highest efficiency, or yellow for most fun ;-)
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Good point! But it is helpful for me to know the "why."
In theory. Maybe within 7% due to some small heat losses, as stated above.
Is that the basis of this question? To save a quarter?
Disagree.
When at the front of the line, show them the EV logos on the back of the car!
It's good clean fun!
A few still say they're big Golf Carts.
For me, the main message is simply that an EV is much better than an ICE at accelerating and decelerating. The EV performs at near-theoretical levels, while an ICE is quite inefficient during hard acceleration/deceleration. So if you drive hard in an ICE, you will see significant loss in efficiency. Drive hard in an EV and you won't see much difference.
You're right the Bolt runs 1,000 RPM for every 10 mph (7:1 gearing). Electric motors spin faster than gasoline engines, true.
If you look back at the efficiency map graph above, that motor maxes out at around 300 torque, and the center of the red region is around 1/4 to 1/3 of that, approx.
I think pedal position could be more of a power command, not strictly torque or speed, at least apart from 1-pedal driving, I'm not sure what GM is doing exactly.
Acceleration is proportional to excess torque, meaning maybe the better rule of thumb is stated as:
1. Accelerate lightly from a standstill to keep the amps down, within reason, so maybe that's about 1/4 pedal travel gradually eased in over 4 seconds.
2. Once at 20 mph, accelerate a bit harder to reach your target speed, up to 1/3 or 1/2 the max capability.
Main thing is to avoid the blue region of the graph, which says don't floor it right away when going from a full stop, since the current (amps) flow is too high (IsquaredR losses).
To do that, you want to ease into the pedal at first, to keep the initial blast of amps down, but notice the 80 torque line (1/4 of max capability) cuts right down the center of the red high-efficiency region.
The Bolt already limits current some automatically to avoid wheelspin off the line, but they left a lot of low-rpm current flow "peppiness" for customer satisfaction, a selling point in sales test drives and Car and Driver reviews.
The engineers sized the motor & hence the efficiency map to maximize range in the standard EPA range test, which is representative of mixed city & hiway anyway.
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For best efficiency you want to avoid tire slippage on launch and avoid braking so heavily that you exceed the capacity of the car to recapture your energy through regen.
To minimize cost, though, it pays to accelerate and brake moderately and to take corners at moderate speeds - because driving aggressively will shorten the life of your tires and of some of the suspension and drivetrain components.
My Plymouth Voyager goes through constant velocity joints every 100,000 km like clockwork, and that's despite me being quite a gentle driver. It's something I think about with regard to my Bolt because it has way more torque, it's so easy to apply that torque, and unlike the Voyager those forces are used to both the accelerate and decelerate the vehicle.
To minimize cost, though, it pays to accelerate and brake moderately and to take corners at moderate speeds - because driving aggressively will shorten the life of your tires and of some of the suspension and drivetrain components.
My Plymouth Voyager goes through constant velocity joints every 100,000 km like clockwork, and that's despite me being quite a gentle driver. It's something I think about with regard to my Bolt because it has way more torque, it's so easy to apply that torque, and unlike the Voyager those forces are used to both the accelerate and decelerate the vehicle.
This approach is dependent on the accel pedal "capability" (angle? distance?) being linear with the motor torque. Is this true? We already know that GM limits torque at lower speeds, but is it linear after than?
In my last reply to @Brad I said "I think pedal position could be more of a power command, not strictly torque or speed, at least apart from 1-pedal driving, I'm not sure what GM is doing exactly. "
Doesn't matter since acceleration, what the driver feels, is proportional to excess torque anyway. Make your foot do what it takes to get the accel you want.
It all boils down to not flooring the pedal too much starting out from a stop.
And you can increase acceleration a bit as you build speed without penalty really. You've got more freedom to accelerate once the motor is moving beyond around 20 mph speed. That's when you're no longer in danger of falling into the blue part of the torque vs. rpm efficiency map graph above.
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Great! Thanks for answering!
Fun calculation: How much thrust (force, Pounds, lb) does a Chevy Bolt produce at maximum? Usually we think of an F-15 having 'thrust' not a car, but it does, just the same.
266 ft-lbs x 7.05 gearing = 1875 ft lbs at the half shaft. Acting over a 1.06 ft tire radius = 1,769 lbf at the front wheels = 7869 Newtons
7869 Newtons force / 1616 kg mass = 4.87 meters/s2 = almost exactly 0.5 g's acceleration.
Since current & torque is limited at low speeds, you may only get 0.5 g's accel at around 20 mph or so (?). And it's limited by tire grip too, so not sure if you can actually get there. Add a driver and mass goes up, so 0.5 g's is for a hamster driver only....
266 ft-lbs x 7.05 gearing = 1875 ft lbs at the half shaft. Acting over a 1.06 ft tire radius = 1,769 lbf at the front wheels = 7869 Newtons
7869 Newtons force / 1616 kg mass = 4.87 meters/s2 = almost exactly 0.5 g's acceleration.
Since current & torque is limited at low speeds, you may only get 0.5 g's accel at around 20 mph or so (?). And it's limited by tire grip too, so not sure if you can actually get there. Add a driver and mass goes up, so 0.5 g's is for a hamster driver only....
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I wonder how much quicker the Bolt would be with better tires and a re-map of the controller?
I'd like to get 120 mph from my Bolt.
Adding in the weight of a driver to my last calculation, the Bolt pulls 0.47 g's if all 266 ft-lbs of motor torque is available from a standstill to some speed, say around 60 mph, and assuming no air drag. ......
The Bolt is said to do 0-60 mph in 6.5 seconds, so (26.8 / 6.5)/9.81 = 0.42 g's, lower due to all the current (torque) limiting near zero mph and air drag to 60 mph. Not lower by much. Therefore, only 10% is lost to avoid spinning the wheels & air drag to 60 mph. Not bad !! This shows it delivers almost all it's 266 ft-lbs right away & it's torque curve is extremely flat.
The Bolt is said to do 0-60 mph in 6.5 seconds, so (26.8 / 6.5)/9.81 = 0.42 g's, lower due to all the current (torque) limiting near zero mph and air drag to 60 mph. Not lower by much. Therefore, only 10% is lost to avoid spinning the wheels & air drag to 60 mph. Not bad !! This shows it delivers almost all it's 266 ft-lbs right away & it's torque curve is extremely flat.
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Look at that motor efficiency map. It ranges from 74%-94%. It's got such a broad and highly efficient band that I wouldn't bother trying to conserve every last electron even though efficiency is practically the only thing I think about. It's nothing like an ICE, which can perform at less than half of its max efficiency in normal operation.
So the key point is to drive 'cheaply in the Bolt?
Why?
It was already stated that full acceleration v. really slow acceleration is a 7% difference.
Do you really want to save a nickel to arrive minutes later at your destination?
Have fun! Explore the envelope of the Bolt's capabilities! You'll be a better driver for it.
Tires are cheap and the only other expense. (Come on, suspension components? Anyone??)
I tell people it's a hybrid. It burns electrons and rubber!
In Summary:
There is no inefficient way to drive a Bolt. Enjoy!
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