Instant Torque (Electric Cars vs. Gas/Diesel Cars)

[Ryuk1990]

So I hear a lot about how electric cars are great because electric motors get instant max torque at 0 RPM.

However, can't the same be done with an internal combustion engine if you have a clutch?

 

[Kozy]

No. Run an ICE to slow and it will stall. Even below about 2000rpm in most engines, there is very little torque.

 

[SteamKing]

That pesky transmission is there for a reason, and it's not to give you an extra hand rest.

 

[Ryuk1990]

I'm not familiar with stick shift cars at all (or car mechanics in general) so bare with me as I have no idea what I'm talking about. But can't you rev up the engine to its max torque almost instantly using a clutch without moving the car and THEN hit the pedal to get that same feeling of instant torque that you would get from an electric car?

 

[OmCheeto]

I'm not familiar with stick shift cars at all (or car mechanics in general) so bare with me as I have no idea what I'm talking about. But can't you rev up the engine to its max torque almost instantly using a clutch without moving the car and THEN hit the pedal to get that same feeling of instant torque that you would get from an electric car?

Yes, but this involves the clutch slipping. If you do that a lot, the clutch will wear out prematurely. Have you ever changed brake pads? Changing the clutch disk is about 100 times worse, as it involves removing the engine, transmission, or both.

Typical costs:
Having a clutch replaced can cost $400 -$3,000 or more, depending on the make, model and type of vehicle;

 

[SteamKing]

More likely, you'll stall the engine.

Hit what pedal?

With a manual transmission, the clutch is disengaged to allow the engine to run without load. Consequently, it takes very little throttle to rev the engine to its max. torque RPM. If you put the transmission into its highest (1:1) ratio and engage the clutch, the engine still must overcome the inertia of the car before movement can take place. More often than not, doing this will stall the engine rather than getting the car to move. Also, since the clutch is a friction device, engaging it repeatedly at high RPM will rapidly burn out the friction plates, requiring a costly clutch replacement.

Doing the same thing with an automatic transmission may not stall the car, but soon you will need a new transmission, which is even more costly to replace than a clutch.

 

[xxChrisxx]

I think the main point to take is that there is a difference between having torque being produced at a specific high RPM and slipping something to achieve pull away, and having produced at zero RPM.

 

[Highspeed]

Ryuk1990, Yes, what you're talking about is possible. You can just dump the clutch at peak torque. You will get the results above though...fast wear and broken parts. You could also use a slipper clutch that will only lock-up above a certain rpm. It's not instant, but will allow the engine to rev up before being loaded at peak torque (or whatever rpm you set it for). You could also use a high-stall torque converter. It doesn't hammer the drivetrain like a clutch, but creates a whole lot of very hot transmission fluid, so you'll need a good cooler. Driveablitlity would be poor with a slipper clutch or converter that stalled that high, so daily use wouldn't be possible. Is there a point beyond a theoretical question? It's going to be a loooooooong time before a Prius can pull a travel trailer, or before an electric truck can pull a semi-trailer for 500 miles a day. ICE vehicles overcome the lack of instant torque through gearing, so there is really no need to turn an ICE into an electric motor.

 

[Ryuk1990]

Is there a point beyond a theoretical question? It's going to be a loooooooong time before a Prius can pull a travel trailer, or before an electric truck can pull a semi-trailer for 500 miles a day. ICE vehicles overcome the lack of instant torque through gearing, so there is really no need to turn an ICE into an electric motor.

It was more about having that fast smooth acceleration that the Tesla Model S offers with an ICE car.

 

[SteamKing]

Most cars with automatic transmissions accelerate quite smoothly from stop to highway speeds. The shift points of the transmission provide a momentary change in the sound of the engine as the revs drop, but other than that, everything is quite smooth. Also, new transmissions have up to eight speeds, rather than the three or four or older transmissions, making the process even smoother, as the engine revs do not need to drop as much between shifts.

It might be you are thinking of the so-called Continuously Variable Transmission (CVT), which doesn't operate using conventional reduction gears.

http://en.wikipedia.org/wiki/Continuously_variable_transmission

These transmissions allow the engine to maintain a constant speed as the vehicle accelerates. Although such transmissions have been used in a variety of automotive applications, several factors have kept them from replacing conventional transmission designs (see the article above for more details).

 

[AlephZero]

It was more about having that fast smooth acceleration that the Tesla Model S offers with an ICE car.

Tesla S: 0-60 in 5.4 sec, top speed 125 mph, "handles like a sedan" (to quote the Tesla website)
Porsche 911S turbo: 0 - 62 mph in 3.1 sec, 0-124 mph in 10.3 sec, top speed 200 mph, handles like a car.

 

[AlephZero]

But can't you rev up the engine to its max torque almost instantly using a clutch without moving the car and THEN hit the pedal to get that same feeling of instant torque that you would get from an electric car?

Yes, but this involves the clutch slipping. If you do that a lot, the clutch will wear out prematurely.

That depends on the design of the clutch. Back in the 1970s I used to drive a british-designed sports car with a 6 speed gearbox. More accurately, it had a 4 speed conventional box and pedal-operated clutch, and a separate epicyclic gearbox and clutch that was operated electrically from a switch in the top of the gearstick, to switch between gears 3 and 4, or 5 and 6. (The manual box and clutch selected either 1,2,3,5 or 1,2,4,6).

The epicyclic gear change was designed to operate at any engine RPM and throttle position, and changed gear in less than a second. Floor the throttle, flip the switch, and get a kick in the back ... (or on a bad hair day, over-rev the engine when changing down without first engaging brain).

 

[xxChrisxx]

That depends on the design of the clutch. Back in the 1970s I used to drive a british-designed sports car with a 6 speed gearbox. More accurately, it had a 4 speed conventional box and pedal-operated clutch, and a separate epicyclic gearbox and clutch that was operated electrically from a switch in the top of the gearstick, to switch between gears 3 and 4, or 5 and 6. (The manual box and clutch selected either 1,2,3,5 or 1,2,4,6).

The epicyclic gear change was designed to operate at any engine RPM and throttle position, and changed gear in less than a second. Floor the throttle, flip the switch, and get a kick in the back ... (or on a bad hair day, over-rev the engine when changing down without first engaging brain).

It doesn't make any difference on design, a slipping friction clutch transmissting lots of torque will wear prematurely.

And a British 70's sports car in the US... an MGB?
What you are describing is an overdrive in 3rd and 4th.

The solenoid should automatically disengage the overdrive in 2nd and 1st. If/when it fails, and you can engage the overdrive in the lower gears, it slips and wears the cone clutch out. Also the overdrive is not designed to give you 'a kick in the back'. It's designed for cruising.

The reason for the lurch when you engage the overdrive whilst still having the throttle open is that wheels suddenly wanted to be traveling much faster than the road speed (as overdrive is effectively a longer gear). Two things can happen in this case, the wheels slip or the overdrive clutch slips to synchronise the road and engine speed. As it's rather dangerous for the wheels to start slipping at high speed, the clutch was designed to slip first.

This abuse of the overdrive clutch is what caused MG to stop the overdrive from engaging in 3rd on later cars

 

[sgb27]

More likely, you'll stall the engine.

Hit what pedal?

With a manual transmission, the clutch is disengaged to allow the engine to run without load. Consequently, it takes very little throttle to rev the engine to its max. torque RPM. If you put the transmission into its highest (1:1) ratio and engage the clutch, the engine still must overcome the inertia of the car before movement can take place. More often than not, doing this will stall the engine rather than getting the car to move.

The technique asked about by the OP involves flooring the throttle and then controlling the clutch pedal to ensure RPMs stay around max torque (gradually engaging it as car speed builds) - if you're stalling the engine you're engaging the clutch too quickly.

 

[SteamKing]

The technique asked about by the OP involves flooring the throttle and then controlling the clutch pedal to ensure RPMs stay around max torque (gradually engaging it as car speed builds) - if you're stalling the engine you're engaging the clutch too quickly.

Perhaps so, but it is a maneuver which I think could only be accomplished with not a little skill and a fairly robust clutch. All in all, even with the best technique, I still see a much shorter clutch life, perhaps shorter engine life to boot.

 

[cjl]

Tesla S: 0-60 in 5.4 sec, top speed 125 mph, "handles like a sedan" (to quote the Tesla website)
Porsche 911S turbo: 0 - 62 mph in 3.1 sec, 0-124 mph in 10.3 sec, top speed 200 mph, handles like a car.

That's not really a fair comparison though, since the Tesla is a much different car in a completely different category of size and performance (and is half the price of a 911 Turbo S). A BMW M5 or Audi RS6 would be a much better comparison (and should still win in all performance metrics).

 

[Averagesupernova]

No. Run an ICE to slow and it will stall. Even below about 2000rpm in most engines, there is very little torque.

Interesting. I just drove a Volvo semi-tractor with a Detroit diesel in it and it governs out when it approaches 2000 RPM. ALL the torque is below 2000. Yes, the thread is about diesels too.

 

[xxChrisxx]

That's not really a fair comparison though, since the Tesla is a much different car in a completely different category of size and performance (and is half the price of a 911 Turbo S). A BMW M5 or Audi RS6 would be a much better comparison (and should still win in all performance metrics).

It's ironic that you picked two cars with pretty much the same power as the 911 turbo s. New Golf R. 300bhp and 0-60 in 4.8 with the DCT.

Hot hatch progress... its mind bending.

 

[NigelTufnel]

Generally with ICE the larger the displacement the lower the rpm at which it makes max torque. If you want more torque without having to rev the engine just get a bigger engine.

Here's a 14 cylinder diesel that makes over five million foot pounds of torque at only 102 rpm
http://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C

 

[sgb27]

Perhaps so, but it is a maneuver which I think could only be accomplished with not a little skill and a fairly robust clutch. All in all, even with the best technique, I still see a much shorter clutch life, perhaps shorter engine life to boot.

Isn't this what everyone does when they try to pull away "quickly" in a manual transmission (eg pulling out onto a busy road)? You rev the engine up a bit (to around max torque), then release the clutch in a controlled manner whilst pressing the accelerator harder to keep the rpms more or less constant. In most cars the clutch will only slip for a fraction of a second until the car is moving fast enough to match the 2000-3000rpm. Yes it does wear the clutch more than a slower pull-away, but it's not going to destroy anything. Try the same technique in 2nd or 3rd gear, then you'll smell the clutch burning away :-)

 

[SteamKing]

Isn't this what everyone does when they try to pull away "quickly" in a manual transmission (eg pulling out onto a busy road)? You rev the engine up a bit (to around max torque), then release the clutch in a controlled manner whilst pressing the accelerator harder to keep the rpms more or less constant. In most cars the clutch will only slip for a fraction of a second until the car is moving fast enough to match the 2000-3000rpm. Yes it does wear the clutch more than a slower pull-away, but it's not going to destroy anything. Try the same technique in 2nd or 3rd gear, then you'll smell the clutch burning away :-)

Maybe you can do this all day in a little four-banger car, but you take a big torquey V8 and drop the clutch at 3000 rpm, you will wear out your tires. You don't always have to smell the clutch plate burning to bring the day for a new clutch closer to today.

 

[SteamKing]

Generally with ICE the larger the displacement the lower the rpm at which it makes max torque. If you want more torque without having to rev the engine just get a bigger engine.

Here's a 14 cylinder diesel that makes over five million foot pounds of torque at only 102 rpm
http://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C

The Sulzer engine is specially designed to operate at low RPM because it is directly connected to the propeller of a ship. A propeller of the size used to drive the ship operates most efficiently at this low speed. For smaller craft, higher speed diesels are used with reduction gears so that the engine can operate at its most efficient speed while the propeller operates at its most efficient but slower speed.

 

[sgb27]

Maybe you can do this all day in a little four-banger car, but you take a big torquey V8 and drop the clutch at 3000 rpm, you will wear out your tires.

The question was whether you can make an ICE generate peak torque at 0mph (as electric motors can), what happens at the tyres is exactly the same for electric and ICE. If you had a powerful enough electric motor and commanded it to generate peak torque from 0mph all day you would also wear out your tyres.

 

[mheslep]

so there is really no need to turn an ICE into an electric motor..

Besides the 0 rpm torque question there is the advantage of efficiency. The electric motor is far more efficient tank to wheels than the ICE, and always will be.

 

[rcgldr]

So I hear a lot about how electric cars are great because electric motors get instant max torque at 0 RPM.

Peak torque for an electric motor occurs at 0 rpm and decreases linearly until it become zero torque at max rpm. Internal combustion engines produce peak torque at some rpm, but with an ideal CVT (continously variable transmission), peak torque delivered to the rear wheels occurs at the rpm corresponding to peak power.

However, can't the same be done with an internal combustion engine if you have a clutch?

Yes, or with a CVT.

Note that the limiting factor for peak torque at the driven tires is limited to the amount of traction available. Dropping the clutch at high rpms or attempting to apply peak torque from an electic motor onto the driven wheels could result in the wheels spinning, assuming sufficient torque at low speeds is enough to spin the driven wheels.

Diesel electric locomotives use diesel engines to drive generators which in turn deliver electricity to electric motors directly attached to the driven wheels of the locomotive. It's a heavy equivalent to a CVT, but heavy is a good thing for locomotives (to get enough traction to pull the remainder of a train).

 

[SteamKing]

Besides the 0 rpm torque question there is the advantage of efficiency. The electric motor is far more efficient tank to wheels than the ICE, and always will be.

I don't know what you mean by the statement that "The electric motor is far more efficient tank to wheels than the ICE, ..."

The electric motor is not a prime mover; it depends on an external source of energy, be it a battery, a fuel cell, Fred Flintstone running on a treadmill, whatever.

If you want to measure the efficiency of the electric motor compared to an ICE, you must compare like with like, i.e., for the electric motor, you've got to throw in the efficiency of the generating plant as well.

 

[OmCheeto]

I ...
The electric motor is not a prime mover; it depends on an external source of energy

And that would be...

If you want to measure the efficiency of the electric motor compared to an ICE, you must compare like with like, i.e., for the electric motor, you've got to throw in the efficiency of the generating plant as well.

Feynman's dad!

------------------------
It's ok to ban me. Really. I've things to do.

 

[mheslep]

I don't know what you mean by the statement that "The electric motor is far more efficient tank to wheels than the ICE, ..."

The electric motor is not a prime mover; it depends on an external source of energy, be it a battery, a fuel cell, Fred Flintstone running on a treadmill, whatever.

If you want to measure the efficiency of the electric motor compared to an ICE, you must compare like with like, i.e., for the electric motor, you've got to throw in the efficiency of the generating plant as well.

"tank to wheels" is a common standard of efficiency found all throughout the literature. Its importance lies is due to the finite amount of energy is carried on board the platform. The efficiency of conversion of the on board energy source to motion is the critical measure of efficiency in determining both maximum range per energy carried and cost per unit distance traveled. Note this is the case regardless of the efficiency of the process used to make the carried energy.

So as I say, the typical electric motor as found in the currently available EVs has an efficiency of over 90%. The batteries are likewise about 90% efficient on discharge. The typical combustion engine and drive train currently on the road is around 15% efficient, moving to around 20% for the fleet of all new vehicles. The gap between the two, tank to wheels EV and ICE efficiency, will always be large due to thermodynamics.

Finally, we don't commonly see demands that ICE mpg calculations include the large energy overhead in refining oil to gasoline or the energy consumed in oil extraction.

 

[SteamKing]

That's what a prime mover is. You add fuel to the engine and get the work out. An electric motor has no tank, and you can't consider the charge in the battery to be the equivalent.

 

[mheslep]

An electric motor has no tank, you can't consider the charge in the battery to be the equivalent.

Why not? It is commonly done.

 

[SteamKing]

A lot of things are commonly done, but that does not mean it is necessarily the correct way of doing things.

Look, a prime mover takes the potential energy stored in a quantity of fuel and turns that potential energy into useful work. We look at the work obtained versus the amount of energy contained in the fuel. The ratio of work obtained to energy input is the definition of thermal efficiency of a prime mover.

On the other hand, the electricity which charges a battery in an electric car doesn't come straight out of the ground. It has to be generated somewhere. In the US, with certain exceptions, electricity is generated by burning coal or natural gas. The potential energy contained in that coal or natural gas is the basis for ultimately generating the electricity which goes into the battery of an electric car. That must be the basis for realistically assessing the relative efficiency of two vehicles which use different means of propulsion.

 

[OmCheeto]

A lot of things are commonly done, but that does not mean it is necessarily the correct way of doing things.

Look, a prime mover takes the potential energy stored in a quantity of fuel and turns that potential energy into useful work. We look at the work obtained versus the amount of energy contained in the fuel. The ratio of work obtained to energy input is the definition of thermal efficiency of a prime mover.

On the other hand, the electricity which charges a battery in an electric car doesn't come straight out of the ground. It has to be generated somewhere. In the US, with certain exceptions...

You mean like solar panels on your roof?

[Oeva-list] my first solar year with Leaf EV, solar PV, and TOU
...
I spent only $406 for over 11000 miles of travel and all the electrical needs of my house, including winter hot water.
...

I think my favorite comment that he made was:

The grid is a nice battery I can rent for $10.12 a month

Gary drives a Nissan Leaf, and has recently upgraded to a Tesla S. His garage mounted solar array is rated at 4900 watts.

I don't think he's into spinning tires though. We leave that, to Mr. Wayland.

...1250 foot pounds of torque, at zero [rpm]*

Only about 150 more than the $2,500,000.00 http://www.motortrend.com/roadtests/exotic/1206_2013_bugatti_veyron_grand_sport_vitesse_first_drive/.

*Trying to bring us back on topic.

 

[OmCheeto]

Interesting article:

Jens Schulenburg claims that at full throttle the Super Sport/Vitesse engine will consume more air in one hour than a human does in a month, though that statistic is purely academic, because at full throttle the Vitesse's W-16 will gulp through an entire tank of gas -- 26.4 gallons -- in just eight minutes.

Good god. That's 3.3 gallons per minute.

Thank god it reaches 60 mph in only 2.5 seconds. Slightly less than a second slower than Mr. Wayland's '72 Datsun.

(Ha ha!)

 

[Ryuk1990]

Tesla S: 0-60 in 5.4 sec, top speed 125 mph, "handles like a sedan" (to quote the Tesla website)
Porsche 911S turbo: 0 - 62 mph in 3.1 sec, 0-124 mph in 10.3 sec, top speed 200 mph, handles like a car.

I just wanted to add that the Tesla Model S Performance goes 0-60 in 4.2 seconds.

Is the heaviness of lithium ion batteries what's slowing down electric cars? I mean, electric motors are superior to IC engines, right?

 

[OmCheeto]

I just wanted to add that the Tesla Model S Performance goes 0-60 in 4.2 seconds.

Is the heaviness of lithium ion batteries what's slowing down electric cars? I mean, electric motors are superior to IC engines, right?

"superior" is a subjective term.

f=ma

which yields: a=f/m

therefore, with two vehicles with similar motive forces, the one with the smaller mass will have a higher acceleration value.

Tesla S:

Curb weight: 4,647.3 lbs
torque 430 Nm​

Porsche 911 S Turbo:

Curb weight: 3680 lb.
torque 710 Nm​

Given that the Porsche has both higher torque and weighs less, it's a no brainer that it's faster.

I don't believe the Tesla S was designed as an adrenalin pumper.

Tesla S mpge: 95
Porsche mpg: 19

You can try and power a car with a 99.99% efficient electric sewing machine motor.
That's much superior to the 25% efficiency of a 530 hp gasoline engine.

Yes?

 

[xxChrisxx]

A lot of things are commonly done, but that does not mean it is necessarily the correct way of doing things.

Look, a prime mover takes the potential energy stored in a quantity of fuel and turns that potential energy into useful work. We look at the work obtained versus the amount of energy contained in the fuel. The ratio of work obtained to energy input is the definition of thermal efficiency of a prime mover.

On the other hand, the electricity which charges a battery in an electric car doesn't come straight out of the ground. It has to be generated somewhere. In the US, with certain exceptions, electricity is generated by burning coal or natural gas. The potential energy contained in that coal or natural gas is the basis for ultimately generating the electricity which goes into the battery of an electric car. That must be the basis for realistically assessing the relative efficiency of two vehicles which use different means of propulsion.

There is a pretty good reason people use tank to wheels. Any why it's the more useful metric for cars.

1. Noone who is diving round in their car gives a toss where the energy comes from. Mr. D. River wants to know how far he can travel without having to fill up with juice.

2. Well to wheel is an utter nightmare to work out, both for petrol and for electric. Electric because you have different methods of generation. Does your argument for efficiency fall down when you consider renewably generated electricity? This is not dismissive, it's a very real question for the 'greeness' of EV. It's fairly obvious that an EV powered by a windmill and sunshine is far better on CO2/km than one powered by black coal.

Also, what about CHP plants? How do we take our value for efficiency then, do we dismiss the heat as only the electricity is useful to us? If so, when distilling fuels, do we dismiss the energy that isn't in the form we want?

One can become infinitely pedantic about well to wheel calculations. Especially for comparison of two different fuel types. It's why they are generally avoided, or treated separately.

You people really know how to kill a good car thread with boring stuff.

Good god. That's 3.3 gallons per minute.

Thank god it reaches 60 mph in only 2.5 seconds. Slightly less than a second slower than Mr. Wayland's '72 Datsun.
(Ha ha!)

Only about 150 more than the $2,500,000.00 Bugatti Veyron Super Sport.
*Trying to bring us back on topic.

Glad someone is. Even if you completely miss the point of the Veyron. :P

The reason that the Veyron is so impressive is not that it's fast. It's because it's a luxury barge that goes like a speedboat.

If you just wanted to build a fast car, you wouldn't do draw the Veyron. It was conceived by the marketing men first, given it's vital stats, then given to the engineers to say 'make it work boys'.

 

[Ryuk1990]

"superior" is a subjective term.

f=ma

which yields: a=f/m

therefore, with two vehicles with similar motive forces, the one with the smaller mass will have a higher acceleration value.

Tesla S:

Curb weight: 4,647.3 lbs
torque 430 Nm​

Porsche 911 S Turbo:

Curb weight: 3680 lb.
torque 710 Nm​

Given that the Porsche has both higher torque and weighs less, it's a no brainer that it's faster.

I don't believe the Tesla S was designed as an adrenalin pumper.

Tesla S mpge: 95
Porsche mpg: 19

You can try and power a car with a 99.99% efficient electric sewing machine motor.
That's much superior to the 25% efficiency of a 530 hp gasoline engine.

Yes?

Yeah, but batteries are the culprit for why electric cars are heavy and thus aren't quite as fast as the high performance gas cars of today, right?

I always thought that electric motors can give more power than a typical IC engine for the same mass.

Oh and the Model S has 600 N*m of torque. Or were you talking about torque at the wheel?

 

[rcgldr]

Therefore, with two vehicles with similar motive forces, the one with the smaller mass will have a higher acceleration value.

Tesla S:

Curb weight: 4,647.3 lbs
torque 430 Nm​

Porsche 911 S Turbo:

Curb weight: 3680 lb.
torque 710 Nm​

Given that the Porsche has both higher torque and weighs less, it's a no brainer that it's faster.

One issue here is that engine torque is multiplied by the overall gearing, and assuming a car is reasonably geared, the car with a higher power to weight ratio (as opposed to a higher torque to weight ratio) will accelerate faster.

For example, two ICE that produce the same torque, but the second engine produces it's torque at twice the rpm of the first engine, and makes twice the power as the first engine throughout the range of operating rpm. Assuming the gear ratio for the second engine is double that of the first engine, then the driven wheel torque of the second car is double that of the first car.

 

[mheslep]

the electricity which charges a battery in an electric car doesn't come straight out of the ground.

Nor does gasoline or diesel.

...In the US, with certain exceptions, electricity is generated by burning coal or natural gas. ...

Coal 32%, natural gas 32%, other non-fossil sources (nuclear, hydro, wind, other) ~33%. And, in areas where the automobiles densities are highest in the US (California, Atlantic seaboard), the ratio of non-fossil sourced electricity is higher still.

 

[zanick]

One issue here is that engine torque is multiplied by the overall gearing, and assuming a car is reasonably geared, the car with a higher power to weight ratio (as opposed to a higher torque to weight ratio) will accelerate faster.

For example, two ICE that produce the same torque, but the second engine produces it's torque at twice the rpm of the first engine, and makes twice the power as the first engine throughout the range of operating rpm. Assuming the gear ratio for the second engine is double that of the first engine, then the driven wheel torque of the second car is double that of the first car.

One of the problems of comparing performance of the electric Tesla and gas cars , is that the tesla only uses one gear ratio and a very broad HP curve. (forget about the flat torque and all the marketing hupla) its HP curve dies out at 130mph and past 80mph is pretty anemic . However, if it had just one more gear, (and here were versions in the past that did have 2 gears), it would be a high speed monster too, being able to take its 420hp engine , to near 180mph
I like this look at an actual tesla dyno run... It clearly shows its advantages and disadvantages over a comparable powered V8 gas engine.
what it shows it that the penciled HP curves vs the tesla dyno run, can actually make the same rear wheel torque initially (due to gearing) as the tesla... and it has power to use at much higher vehicle speeds.

 

[rcgldr]

One of the problems of comparing performance of the electric Tesla and gas cars , is that the tesla only uses one gear ratio and a very broad HP curve.

Not sure why this old thread was brought up again, but assuming that the Tesla motor is similar to typical DC motors, then the torque is greatest at zero rpm and linearly decreases to zero at maximum rpm. Peak horsepower occurs at 1/2 of peak rpm. To prevent wheel spin, the torque is limited to some maximum value, so you get a flat torque versus rpm curve until the maximum motor torque versus rpm decreases below that of the limited torque.

 

[zanick]

Not sure why this old thread was brought up again, but assuming that the Tesla motor is similar to typical DC motors, then the torque is greatest at zero rpm and linearly decreases to zero at maximum rpm. Peak horsepower occurs at 1/2 of peak rpm. To prevent wheel spin, the torque is limited to some maximum value, so you get a flat torque versus rpm curve until the maximum motor torque versus rpm decreases below that of the limited torque.

actually, most AC servo motors, as what is powering the Tesla has a flat torque curve, until the inductive losses start effecting current rise in the motor windings where the torque will fall off linearly.
as far as comparisons to a gas engine.. starting torque in most V8 cars can be as high or higher.. most of the time, its tire grip limiting for both car's power plants.

 

[cjl]

One of the problems of comparing performance of the electric Tesla and gas cars , is that the tesla only uses one gear ratio and a very broad HP curve. (forget about the flat torque and all the marketing hupla) its HP curve dies out at 130mph and past 80mph is pretty anemic . However, if it had just one more gear, (and here were versions in the past that did have 2 gears), it would be a high speed monster too, being able to take its 420hp engine , to near 180mph
I like this look at an actual tesla dyno run... It clearly shows its advantages and disadvantages over a comparable powered V8 gas engine.
what it shows it that the penciled HP curves vs the tesla dyno run, can actually make the same rear wheel torque initially (due to gearing) as the tesla... and it has power to use at much higher vehicle speeds.

The penciled in curve for an engine/transmission combo is incredibly closely geared, and doesn't really look right to me. 4th gear runs out at 85mph, and 5th at 110, which is pretty unreasonable for any high performance vehicle.

 

[zanick]

The penciled in curve for an engine/transmission combo is incredibly closely geared, and doesn't really look right to me. 4th gear runs out at 85mph, and 5th at 110, which is pretty unreasonable for any high performance vehicle.

Actually, its a 6 speed based on another dyno run. its safe to use a post shift RPM level to be about 75% of redline. with 1st gear redlining at 40mph or so, the rest is just simple math... yes, this would be a little close in gear ratio, but widening it up, to say 70% (pure street car ratios), wouldn't change things all that much.
The point seems to be clear, the gas engine has quite a bit of advantage passed 80mph and the same starting forces. the advantage the electric car has, is that it can be a closer performer, with similar max HP output, without a gear box. (only a single reduction)

 

[cjl]

What car is that based on that has 300+hp, but runs out of gears with a 6 speed at 140mph? Even in a racecar, there are several tracks where that 6th would be a bit too short. I'd expect the gearing for a sleekish 300hp car to be more along the lines of (gear: speed at redline):

1: 40
2: 70
3: 95
4:115
5: 145
6: 170

 

[zanick]

What car is that based on that has 300+hp, but runs out of gears with a 6 speed at 140mph? Even in a racecar, there are several tracks where that 6th would be a bit too short. I'd expect the gearing for a sleekish 300hp car to be more along the lines of (gear: speed at redline):

1: 40
2: 70
3: 95
4:115
5: 145
6: 170

you are too focused on the micro details of the graph. sure, its not a realistic spread as I worked backward with a close ratio gear box , more like a 7 speed.
the point is, your gear ratios are not too viable either.
most 6 speeds look like this:
8:1 1st
7:1 2nd
6.:1 3rd
5.:1 4th
4:1 5th
3:1 6th
this is a 80-75% drop (apprx) per gear.

regardless, you can see the average HP that is kept pretty consistent out to redline. that's the point. the tesla has a flat HP curve, which is ideal for wide spacing in gears , or in its case, NO GEARS. :)

 

[cjl]

the point is, your gear ratios are not too viable either.

You should let Porsche know - those are very close to the ratios in my 6 speed box in my Cayman S...

 

[zanick]

You should let Porsche know - those are very close to the ratios in my 6 speed box in my Cayman S...

I thought those were gear ratios, not speeds in gears as they are. yes, they are normal.
regardless of the actual rations, its the space you need to look at and if you do, you can see that the ratios I posted are very close to your ratios as well.
So, the point is, with 6 speeds its easy to keep the car in the HP range to have max acceleration potential at any speed. (proportional to the power, as acceleration is)
again, the Tesla has a broad HP curve, which eliminates the need many gears. 2 gears would keep it on par with most cars... 1 gear as it has now however, loses a lot of acceleration perforamance after 80mph.

 

[SteamKing]

most 6 speeds look like this:
8:1 1st
7:1 2nd
6.:1 3rd
5.:1 4th
4:1 5th
3:1 6th
this is a 80-75% drop (apprx) per gear.

It's not clear for what sort of gearbox these ratios are intended. For automotive use, the fourth or fifth gear is typically a 1:1 ratio, with the higher gears (5th or 6th) typically being overdrives (that is, the gear ratio is less than 1). Of course, the final drive ratio in the differential also must be factored into give the true ratio between engine speed and wheel speed.

 

[zanick]

It's not clear for what sort of gearbox these ratios are intended. For automotive use, the fourth or fifth gear is typically a 1:1 ratio, with the higher gears (5th or 6th) typically being overdrives (that is, the gear ratio is less than 1). Of course, the final drive ratio in the differential also must be factored into give the true ratio between engine speed and wheel speed.

Its very clear... I've given you the overall ratios. you can make up any combination of rear end to transmission as you would like and it doesn't matter if 4th gear is 1:1 or 2:1, or .5 :1.
actually, Porsche has a lot of cars with 1:1 happening in 4th... as in my race car. :) you might want to talk to porsche about that. :)

so, fine, let's use your ratios.. it doesn't matter . I just picked some general close ratio numbers. your very nice Porsche street ratios are pretty close, at .57, .73, .and the rest are over .8 (post shift) RPM values vs redline

again, ratios do not matter.. the point is the gears keep the engine in the max HP range which is essential for maximzing acceleration at any speed.
the tesla falls on its face after 80mph after a gallant effort up to 80mph to have on par acceleration to any like 420hp car (actually, more like 475hp as folks are measuring 420hp at the driven wheels) after that speed, the car is anemic vs any car 300hp and even less!