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High speed acceleration - revisited

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A lot of us (including me) bemoan the highway-speed acceleration of our cars since it feels nowhere near as brutal as the off-the-line launch - mainly due to the fact that we have a fixed gear. I came across a video I'd missed from carwow that made me question whether it's really as "slow" as we think...


Starts at 6:10 if it doesn't take you there.

An RS6 is about as savage of a car as any of us could expect to encounter... Even if the M3P lost, just hanging in the same vicinity as a car like this @ highway speeds is pretty damn formidable.
 
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It's certainly not slow at high speed, it just feels slow in comparison, and you continue "slowing" down the faster you go.

100mph = 400hp
110mph = 385hp
120mph = 369hp
130mph = 351hp
140mph = 330hp

That's current draw out of the battery, so of course there is some losses to the wheels.
That's why my strategy is to declare victory @ 110 and go home
 
It's also just physics. Since E=MV^2, it takes 4X as much energy to get from 75-150 as it does 0-75. So even if you have the exact same HP, your acceleration is falling off the faster you go.

The car is basically traction limited to 45 MPH, so you get a nice clean 1G up to there, which really scrambles your brain compared to an ICE, with the gear change interruptions and torque curves, but then that 1G fading off is that much more noticable.
 
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It's also just physics. Since E=MV^2, it takes 4X as much energy to get from 75-150 as it does 0-75. So even if you have the exact same HP, your acceleration is falling off the faster you go.

The car is basically traction limited to 45 MPH, so you get a nice clean 1G up to there, which really scrambles your brain compared to an ICE, with the gear change interruptions and torque curves, but then that 1G fading off is that much more noticable.
The reason that perceived power is lower is mostly about air resistance and in case of EV with back current, although Plaid motors clearly mostly fixed that issue.

Acceleration=power/velocity/mass
 
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I find this thread hilarious because this is by far the fastest car, even on the highway, that I've ever owned. It's amazing to be able to blow by people that are driving stupid.

it's pretty decent for sure, but when you start looking at the 60-130 times, it's not even remotely close to most cars that would be considered performance in nature. From a roll, the Tesla is out of its peak powerband, whereas gas cars are just coming into theirs. Throw in the fact that 'most' cars don't weigh over 2 tons, that's a second disadvantage.

From what I watched on the MSPlaid release the other day, it looks like that car runs roughly 400hp on the launch up to 35-40mph, then the real power comes in and it ramps up to 1000hp. Really wish they would do something like that for the M3P, obviously it wouldn't be to that level, but an extra 200hp at 45 instead of pulling power, would make this a mid-10 second car and much more fun.
 
ICE cars lose a significant amount of acceleration at higher speeds too. They lose torque to the wheels (and hence acceleration) every time they upshift. Whether you lose thrust to gear changes in an ICE vehicle or back EMF in an EV, you still can't get as much acceleration the faster you go. From 60-110, the M3 can easily compete with most performance oriented cars. Above about 120 MPH, back EMF becomes more of a disadvantage than gear changes and the ICE competitors will start to catch up.

Mike
 
ICE cars lose a significant amount of acceleration at higher speeds too. They lose torque to the wheels (and hence acceleration) every time they upshift. Whether you lose thrust to gear changes in an ICE vehicle or back EMF in an EV, you still can't get as much acceleration the faster you go. From 60-110, the M3 can easily compete with most performance oriented cars. Above about 120 MPH, back EMF becomes more of a disadvantage than gear changes and the ICE competitors will start to catch up.

Mike
Not the case. My car shifts in 90 milliseconds, while holding boost, so at the end of the shift, the car is still under full power. This is not really a debate that can be argued, when you simply review the dragy charts for 60-130 times.

But of course, as with most things that involve mentioning a Tesla not being the best at something, people will try to use any technicality they can to try and justify in some way that a Tesla is better, or the test just isn't fair.
 
Not the case. My car shifts in 90 milliseconds, while holding boost, so at the end of the shift, the car is still under full power. This is not really a debate that can be argued, when you simply review the dragy charts for 60-130 times.

But of course, as with most things that involve mentioning a Tesla not being the best at something, people will try to use any technicality they can to try and justify in some way that a Tesla is better, or the test just isn't fair.

It makes no difference how long it takes your car to shift. When you shift, you change the gear ratio and you lose torque to the wheels. It's simple math. For example, a Challenger with an A8 transmission has a 1st gear ratio of 4.71 and 2nd gear is 3.14. When the transmission shifts from 1st to 2nd, you lose 33% of the torque to the wheels and your acceleration will drop accordingly.

Mike
 
Edit: This is in response to Sam1's post about the plaid s. I apprently didn't quote it correctly

Ramping up is an understatement. It hits peak power and pretty much just stays there. I thought for sure Tesla would solve acceleration drop off with the trimotors by just running the third one as an additional gear ratio. Nope, they just spin them all all the way to 200mph (20k rpm apparently). Insane.

tesla-model-s-plaid-delivery-day-perfect-power-curve.webp


It's it bit frustrating the 3's power curve is like the p85's (just a bit higher and extended out to 165mph) when they're now capable of this. I suppose it's for the best. I'd hate to have to buy another one when mine is so new.

Hopefully there's some gains in the existing motors they've purposely left on the table till now. Even without the carbon sleeving, the s performance has managed to hold near peek power for a bit instead of dropping off immediately like the 3s. Guess we'll see.
 
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Edit: This is in response to Sam1's post about the plaid s. I apprently didn't quote it correctly

Ramping up is an understatement. It hits peak power and pretty much just stays there. I thought for sure Tesla would solve acceleration drop off with the trimotors by just running the third one as an additional gear ratio. Nope, they just spin them all all the way to 200mph (20k rpm apparently). Insane.

tesla-model-s-plaid-delivery-day-perfect-power-curve.webp


It's it bit frustrating the 3's power curve is like the p85's (just a bit higher and extended out to 165mph) when they're now capable of this. I suppose it's for the best. I'd hate to have to buy another one when mine is so new.

Hopefully there's some gains in the existing motors they've purposely left on the table till now. Even without the carbon sleeving, the s performance has managed to hold near peek power for a bit instead of dropping off immediately like the 3s. Guess we'll see.
Watch the actual video of the run, my quote is correct. The on screen data shows around 400hp output on launch, then it almost instantly jumps up to 1000hp once the car is going a bit down the road.

There would be absolutely no way that car can launch with 1000hp on street tires. Simply impossible. It would completely blow the tires off.
 
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It makes no difference how long it takes your car to shift. When you shift, you change the gear ratio and you lose torque to the wheels. It's simple math. For example, a Challenger with an A8 transmission has a 1st gear ratio of 4.71 and 2nd gear is 3.14. When the transmission shifts from 1st to 2nd, you lose 33% of the torque to the wheels and your acceleration will drop accordingly.

Mike

Again you are incorrect. but there's no reason to belabor the point. I'll just say that you are correct, the M3P is faster from a moving start than any gas car that exists, just because arguing with a Tesla Stan is not productive.
 
Again you are incorrect. but there's no reason to belabor the point. I'll just say that you are correct, the M3P is faster from a moving start than any gas car that exists, just because arguing with a Tesla Stan is not productive.

I'll agree to disagree as well. Arguing with a Tesla Stan is about as productive as arguing with someone who lives in a world where gear ratio has no effect on wheel torque.

Mike
 
I'll agree to disagree as well. Arguing with a Tesla Stan is about as productive as arguing with someone who lives in a world where gear ratio has no effect on wheel torque.

Mike
Gear ratio matters only because ice has very narrow powerband. With variator you can stay on peak power at any speed.

ICE is torque and power limited all the time - cylinder pressure and airflow. Electric motor mostly limited by power since the main limitation is temperature.

Torque on wheels is irrelevant, only power and speed defines acceleration.
 
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You are confusing torque which is a unit of force and power which is work (force and distance). Torque at the wheels directly dictates your acceleration. If your engine/motor has 400 lb/ft of torque and you have a 3.23 axle ratio and a 4.71 first gear, you'll have 400*3.23*4.71 or 6085 lb/ft of torque at the wheels assuming once you get off the line, you can keep the engine in its power band where it is making close to 400 lb/ft. If your second gear is 3.14, you'll have 400*3.23*3.14 or 4057 lb/ft of torque in second gear. If you account for some (maybe 10%) drivetrain loss and factor in your wheel/tire radius, you can calculate exactly how many pounds of force are being applied to the car to accelerate it: f=ma.

If you don't understand, check:

Take a look at the graphs at the bottom that show wheel torque in each gear. Your acceleration will decrease by the amounts shown in the chart for each gear, plus a significant amount due to air friction when you start going fast.

So as I said, you will lose acceleration simply due to the loss of torque multiplication each time you shift. And an EV will lose torque at the motor due to back EMF. Both ICE and EV will start to accelerate slower and slower as they approach higher speeds, even without air friction. 6 in one hand, half a dozen in the other.

Mike
 
you will lose acceleration simply due to the loss of torque multiplication each time you shift
Optimal shift points for ICE exist for a reason. If you shift past optimal, you're actually improving acceleration despite the loss of torque multiplication.

In general, it makes no sense to argue these torque vs power concepts. Both are intimately interconnected.
 
Optimal shift points for ICE exist for a reason. If you shift past optimal, you're actually improving acceleration despite the loss of torque multiplication.

In general, it makes no sense to argue these torque vs power concepts. Both are intimately interconnected.

Optimal shift points occur when you either run out of RPM or the torque curve on the high end drops more than the equivalent ratio change of the next gear. If your torque curve is relatively flat and your gear changes can keep you in that power band, you WILL lose acceleration the moment you change to the next gear. Period.

Exactly, HP and RPM. That's why Formula 1 cars have (roughly) 1000hp and only 400 ft/lbs of torque. Since the M3P has more wheel torque, it should accelerate faster than a formula 1 car now too, Using Mikey's logic.

And by your logic, you can get the same amount of acceleration by starting in second gear. Or third gear. Or any gear. The fact is, even if you had an ICE engine that had a perfectly flat power curve from 0 to redline, as soon as you change gears, your acceleration will drop by the same ratio as the gear change.

Mike
 
If your torque curve is relatively flat and your gear changes can keep you in that power band, you WILL lose acceleration the moment you change to the next gear. Period.
Thanks for admitting you were wrong in your previous blanket statement. Real-life torque curves are often not flat at all, especially high in the rev range.

A transmission is just a mechanical device to help ICE engine to stay in the power band, and a crude one at that. Imagine an efficient CVT and make your argument with that assumption. If it doesn't work, you're doing something wrong.
 
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