Torque, Horsepower, and speed, A technical discussion

[Lindenwood]

(moderator note)

Moved from the Model 3 Performance speculation thread
====================================


Just to be clear, ICE cars don’t at all maintain a constant motive force just because they can shift “back to peak HP.”

You’ll see in both scenarios the vehicles’ available wheel torque dramatically falls off with speed.

Almost all of the descriptions of M3Ps “falling on their face” or whatever, because they happen to trap a few MPH slower (which would equate to maybe 2-3 car lengths on a highway pull), are nothing but hyperbolic. In fact, it’s less about having disproportionally lower wheel torque at high speeds as it is about having disproportionally more wheel torque at low speeds.

 

[Izzyz28]

Well, yes, but here's the thing......the M3P's torque falls hard after 50-60 Mph, and it falls faster than the RPM required to make horsepower, so horsepower also falls off a cliff. This is exactly where the Plaid shines, because it maintains 90-95% of its horsepower all the way to top speed. The M3P puts down about 520 horsepower at the wheels peak, and that drops to about 350 horsepower at 110 Mph. I couldn't find a dyno graph at anything near top speed, but it's probably sub-250 WHP.

 

[terranx]

Just to be clear, ICE cars don’t at all maintain a constant motive force just because they can shift “back to peak HP.”

View attachment 1030404

You’ll see in both scenarios the vehicles’ available wheel torque dramatically falls off with speed.

Almost all of the descriptions of M3Ps “falling on their face” or whatever, because they happen to trap a few MPH slower (which would equate to maybe 2-3 car lengths on a highway pull), are nothing but hyperbolic. In fact, it’s less about having disproportionally lower wheel torque at high speeds as it is about having disproportionally more wheel torque at low speeds.

Your graphs don’t support your claims.

The model 3’s power falls off quickly, and torque therefore falls even quicker. As your second graph demonstrates, an ICE car uses multiple gears to keep the power relatively constant.

What the car needs is either a second gear or motors that can hold onto near peak power for longer. Tesla favors the latter strategy based on the Plaid. We’ll see how the new 4d2 motor performs

 

[FastLaneJB]

Well, yes, but here's the thing......the M3P's torque falls hard after 50-60 Mph, and it falls faster than the RPM required to make horsepower, so horsepower also falls off a cliff. This is exactly where the Plaid shines, because it maintains 90-95% of its horsepower all the way to top speed. The M3P puts down about 520 horsepower at the wheels peak, and that drops to about 350 horsepower at 110 Mph. I couldn't find a dyno graph at anything near top speed, but it's probably sub-250 WHP.

This surely doesn't really matter to most buyers. It's a daily driver and if obeying the speed limits in my country that's 70mph max. Even if you go a bit over, it's a very quick point to point car. When you have a lot of twisty roads, low down slow speed hard pull is what this car is great at.

I get on this forum it might matter more judging from the posts but Tesla makes the Plaid for those purposes. Otherwise as a fast legal speed road car at a sensible price, this has been hard to beat.

I'd like to see improvements but they also need to watch the price. As you creep up, expectations go up also.

 

[CKwik240]

Just to be clear, ICE cars don’t at all maintain a constant motive force just because they can shift “back to peak HP.”

View attachment 1030404

You’ll see in both scenarios the vehicles’ available wheel torque dramatically falls off with speed.

Almost all of the descriptions of M3Ps “falling on their face” or whatever, because they happen to trap a few MPH slower (which would equate to maybe 2-3 car lengths on a highway pull), are nothing but hyperbolic. In fact, it’s less about having disproportionally lower wheel torque at high speeds as it is about having disproportionally more wheel torque at low speeds.

In order to see the differences more clearly, you would need to overlay the torque graphs with the same account on both axes. Or graph both HP curves against vehicle speed. The ICE vehicle will kind of look like a saw blade but peaks would remain consistent. An ICE vehicle with a CVT would have a flat HP curve once it gets to peak HP and holds it...

 

[Lindenwood]

Your graphs don’t support your claims.

The model 3’s power falls off quickly, and torque therefore falls even quicker. As your second graph demonstrates, an ICE car uses multiple gears to keep the power relatively constant.

What the car needs is either a second gear or motors that can hold onto near peak power for longer. Tesla favors the latter strategy based on the Plaid. We’ll see how the new 4d2 motor performs

Both graphs literally show torque at the wheels. Wheel torque is exactly proportional to motive force on the vehicle. The graphs exactly support my claim.

If shifting gears allowed an ICE vehicle to maintain constant motive force as speed increased, then it would accelerate several times faster than an M3P at triple-digit speeds, which is not the case.

 

[Lindenwood]

In order to see the differences more clearly, you would need to overlay the torque graphs with the same account on both axes. Or graph both HP curves against vehicle speed. The ICE vehicle will kind of look like a saw blade but peaks would remain consistent. An ICE vehicle with a CVT would have a flat HP curve once it gets to peak HP and holds it...

Unfortunately, that’s incorrect. Horsepower is a great representation of total acceleration potential, but it does not represent instantaneous acceleration. At any given speed, the acceleration of the vehicle is exactly proportional to wheel torque minus various parasitic losses.

 

[Sellout]

…and here we go again.

So many of you just don’t seem to get it. It is a FACT that a Model 3 performance accelerates at 1g until about 40-50mph and then the acceleration rate is cut roughly in half. You’ve seen graphs displaying that in this very thread.

Whether that also happens with an ICE car is completely irrelevant. It happens in a model 3 performance, and it’s something that apparently some people don’t give a crap about but that doesn’t mean it isn’t happening.

Stop trying to convince us we’re crazy just because you don’t like the fact that we’re not so enamored with our Teslas that we can see something we want improved.

 

[Lets go Plaid]

I imagine all the journos who get invited to this pre launch driving swaray will be embargoed in posting anything until the official launch. It will be interesting to see who gets the gig, the usual YouTubers no doubt.

 

[Lindenwood]

…and here we go again.

So many of you just don’t seem to get it. It is a FACT that a Model 3 performance accelerates at 1g until about 40-50mph and then the acceleration rate is cut roughly in half. You’ve seen graphs displaying that in this very thread.

Whether that also happens with an ICE car is completely irrelevant. It happens in a model 3 performance, and it’s something that apparently some people don’t give a crap about but that doesn’t mean it isn’t happening.

Stop trying to convince us we’re crazy just because you don’t like the fact that we’re not so enamored with our Teslas that we can see something we want improved.

Given a 0-35 ratio (let’s call this “1st gear”) is mathematically 4 times larger than a 0-140 ratio (let’s call this 4th gear), such a vehicle will accelerate 1/4 as fast in 4th gear as in 1st gear. Therefore, it’s also a FACT that any vehicle with a multi-speed transmission will see also significant reductions in actual acceleration as gear ratios increase. More pointedly, if a vehicle can peak at 1g of acceleration in 1st gear, it will not see more than 0.25g in the above 4th gear.

Not saying you’re crazy. I’m just saying the differences in high-speed acceleration between an M3P and its competition are not nearly as significant as some perceive.

 

[CKwik240]

Unfortunately, that’s incorrect. Horsepower is a great representation of total acceleration potential, but it does not represent instantaneous acceleration. At any given speed, the acceleration of the vehicle is exactly proportional to wheel torque minus various parasitic losses.

If you analyze HP by vehicle speed, you can make a direct comparison.

But even if you just took a qualitative look and saw the overall HP is higher after a certain speed, you would easily know it's putting down more torque at those speeds. Look at the graph below. The HP output at Max acceleration will follow the uppermost path. This vehicle is still seeing between 400 and 450 HP while approaching 100 mph. By comparison, the M3P is not maintaining power. At any given speed in any car, a given HP will always equal a certain amount of force at the wheels. Looking at HP gives you a normalized comparison. You can actually calculate instantaneous wheel torque just by knowing HP (at a given speed) and vehicle speed (along with tire size so you can calculate wheel RPM) and plug it into the equation HP=(tq*RPM)/5252

 

[Lindenwood]

If you analyze HP by vehicle speed, you can make a direct comparison.

But even if you just took a qualitative look and saw the overall HP is higher after a certain speed, you would easily know it's putting down more torque at those speeds. Look at the graph below. The HP output at Max acceleration will follow the uppermost path. This vehicle is still seeing between 400 and 450 HP while approaching 100 mph. By comparison, the M3P is not maintaining power. At any given speed in any car, a given HP will always equal a certain amount of force at the wheels. Looking at HP gives you a normalized comparison. You can actually calculate instantaneous wheel torque just by knowing HP (at a given speed) and vehicle speed (along with tire size so you can calculate wheel RPM) and plug it into the equation HP=(tq*RPM)/5252
View attachment 1030469

Unfortunately, this isn’t how vehicle acceleration works. See my post before yours.

 

[mpgxsvcd]

If shifting gears allowed an ICE vehicle to maintain constant motive force as speed increased, then it would accelerate several times faster than an M3P at triple-digit speeds, which is not the case.

I only know of one ICE car that maintains near constant torque at the crank throughout the rev range that isn’t a diesel. That is the C8 Corvette Z06. Pretty much every other ICE vehicle has constant power after the peak HP at best.

Even the C8 Stingray has torque tapering off after the peak. Not as bad as the current Model 3 Performance but it still falls off.

It is extremely rare that a car can maintain constant crank torque throughout the entire rev range and that is why the C8 Corvette Z06 engine is so special.

 

[gearchruncher]

At any given speed in any car, a given HP will always equal a certain amount of force at the wheels. Looking at HP gives you a normalized comparison. You can actually calculate instantaneous wheel torque just by knowing HP (at a given speed) and vehicle speed (along with tire size so you can calculate wheel RPM) and plug it into the equation HP=(tq*RPM)/5252

First, your statement is only close to true if the car is not accelerating. It's absolutely possible to be at a given speed and have more or less force at the wheels if you are changing speed. So you cannot estimate force at a wheel from just RPM and speed unless you know acceleration.

Beyond that, here's a question that can be non-intuitive to a lot of people:

Say I have a Sedan and an SUV.
The Sedan has 1000lbs of aerodynamic and other drag at 100 MPH
The SUV has 1000lbs of aerodynamic and other drag at 50 MPH

Do they require the same horsepower to go 100 MPH and 50 MPH? I mean, the force at the wheels is the same, right?

Nope, the Sedan requires double the horsepower. Because work is force times distance, and the Sedan is going twice the distance in the same time, so it needs double the power even though the force is the same.

This is why it takes 8X the HP to go twice as fast in a given car. You get 4X the drag due to aerodynamics, but then you also go twice the distance in the same time.

 

[CKwik240]

Unfortunately, this isn’t how vehicle acceleration works. See my post before yours.

Actually, it's exactly how it works. Seriously. Try the math.

 

[Sweed269]

Actually, it's exactly how it works. Seriously. Try the math.

You are measuring engine output and not wheel torque on ice and wheel torque on the m3p. That is not how it works. You need to calculate wheel values to compare. If you do then they are very similar

 

[CKwik240]

First, your statement is only close to true if the car is not accelerating. It's absolutely possible to be at a given speed and have more or less force at the wheels if you are changing speed. So you cannot estimate force at a wheel from just RPM and speed unless you know acceleration.

Beyond that, here's a question that can be non-intuitive to a lot of people:

Say I have a Sedan and an SUV.
The Sedan has 1000lbs of aerodynamic and other drag at 100 MPH
The SUV has 1000lbs of aerodynamic and other drag at 50 MPH

Do they require the same horsepower to go 100 MPH and 50 MPH? I mean, the force at the wheels is the same, right?

Nope, the Sedan requires double the horsepower. Because work is force times distance, and the Sedan is going twice the distance in the same time, so it needs double the power even though the force is the same.

This is why it takes 8X the HP to go twice as fast in a given car. You get 4X the drag due to aerodynamics, but then you also go twice the distance in the same time.

My post was to explain power and torque. Outside factors like aero are ignored as it doesn't change the output of an engine or motor. You're generally a smart guy. I don't think you understood what I was trying to say...

 

[Knightshade]

So many of you just don’t seem to get it. It is a FACT that a Model 3 performance accelerates at 1g until about 40-50mph

That's not quite a fact...


G force calculator here:

G Force Calculator

Calculate the g force acting on an object in motion using the g force calculator.

www.omnicalculator.com

Actual 10 mph splits of a Model 3 Performance from 0-60 posted by myself multiple times in the thread.


0-10 is 0.948g so not quite 1 but you can see 1 from there
10-20 is also 0.948g so same


20-30 though is down to 0.893g
30-40 is also 0.893g


40-50 is all the way down to 0.813g

And of course by the time you're 50-60 is down to 0.68g

So it never quite hits 1g in the first place, and doesn't even stay above .9 past 20 mph- though it does drop off more quickly above 50.

Above #s are from a 2.99 (with rollout- 3.21 without) 0-60 run on a P.


From 0-10 mph BTW a LR AWD with boost is moderately close to a P- 0.91g... but by 10-20 drops to 0.746g and pretty much stays about there through 50 (dropping to 0.641 50-60)

 

[Sellout]

That's not quite a fact...


G force calculator here:

G Force Calculator

Calculate the g force acting on an object in motion using the g force calculator.

www.omnicalculator.com

Actual 10 mph splits of a Model 3 Performance from 0-60 posted by myself multiple times in the thread.


0-10 is 0.948g so not quite 1 but you can see 1 from there
10-20 is also 0.948g so same


20-30 though is down to 0.893g
30-40 is also 0.893g


40-50 is all the way down to 0.813g

And of course by the time you're 50-60 is down to 0.68g

So it never quite hits 1g in the first place, and doesn't even stay above .9 past 20 mph- though it does drop off more quickly above 50.

Above #s are from a 2.99 (with rollout- 3.21 without) 0-60 run on a P.


From 0-10 mph BTW a LR AWD with boost is moderately close to a P- 0.91g... but by 10-20 drops to 0.746g and pretty much stays about there through 50 (dropping to 0.641 50-60)

That’s a lot of detail. So it’s worse than I said it is. Almost make you not even want to drive it…

 

[Joshker]

Some serious discussion here. Pretty simple: If you've driven a Plaid S, the pull is absolutely bonkers from almost any speed, seriously feels the same from 0 as it does from 50... I think we can all agree we want that kind of consistent power band in the new 3. I think there a disconnect between who have and haven't driven the Plaid. If you have, it is absolutely obvious that the current Performance car lacks upper end power. Still a fun car, but will be much better if we can get the upper end pull...