[travislambert]

Keeping the engine closest to redline puts the most power to the ground. I'm pretty sure it's as simple as that (for most cars).

[enzia35]

Originally Posted by Waiting46

Good to know the car will do nearly 300 at max gear/rpm

'Cept that physics is a complete bitch.

[I`m Batman]

Originally Posted by travislambert

Keeping the engine closest to redline puts the most power to the ground. I'm pretty sure it's as simple as that (for most cars).

NICE! Wheel torque, NOT engine torque. Stupid gears! lol Let me plug the gear ratio into the spreadsheet...

RPM Tq__ G1_ G2_ G3_ G4_ G5_ G6
1000 300 798 534 390 300 222 150
1500 340 904 605 442 340 252 170
2000 380 1011 676 494 380 281 190
2500 410 1091 730 533 410 303 205
3000 425 1131 757 553 425 315 213
3500 440 1170 783 572 440 326 220
4000 450 1197 801 585 450 333 225
4500 460 1224 819 598 460 340 230
5000 445 1184 792 579 445 329 223
5500 425 1131 757 553 425 315 213
6000 400 1064 712 520 400 296 200

[draph]

I got my mechanical engineering degree a long time ago and my career started in engineering project management (ie don't feel I've ever been a "real" engineer); but my gut tells me there isn't a post that got it right quite yet...

Posters so far are using engine torque, not the force of the tire contact patch with the ground to accelerate the car. Power is the measure of the speed of torque delivery to the ground - so you want maximum power to the ground for maximum acceleration.

Maximum acceleration in a car is at the power peak point in a given gear. So, what gear achieves maximum acceleration at a given speed is the gear that puts the rpm closest to the power peak- BUT, if the power curve falls off quickly after the power peak, or happens to be peak operational rpm, one might want to select a gear that puts rpm below the power peak. That might be a better trade-off than shifting to land right at the power peak, only to have to shift again a millesecond later, because the power falls off 40% or you hit fuel cutoff 200 rpm later. Arguably, cars with peaky power curves require more gear ratios to enable keeping the power delivery in the narrow sweet spot of the rpm range. No engine has a perfectly flat power curve, but big V8s and twin turbos have a flat enough power curve, you can probably be plus or minus 1000 rpm from the peak power point that you will be very close to optimum acceleration.

We can partially blame automotive press and marketing agencies for misrepresenting torque to a certain degree. On those puny 4 cylinder engines and diesels, turbos have helped add torque at low rpms, which flattens out the *power* curve (more torque delivered at lower rpms creates more power at those rpms); but focusing on torque is making people forget it's all about the *power* - speed of delivery of torque for accelerating a car.

If above doesn't help: One might notice torque ratings on some cars are now shown as "300 lb feet from 1100 to 5000 rpm". If max acceleration was all about torque, then that would suggest maximum acceleration in that particular car can be achieved using the top gear starting at 1100 rpm. That, obviously, is not true, because peak horsepower for that engine is NOT 1100 to 5000 rpm. Also, if that were the case, the car could have a 2 speed transmission, one for getting it off the line to 1100 rpm, the the other to achieve maximum acceleration and fuel economy at the same time from 1100 to 5000 rpm...

[draph]

Thanks, Batman... you beat me to it...Yes, wheel torque to the ground, not engine torque.

[travislambert]

Originally Posted by draph

Thanks, Batman... you beat me to it...Yes, wheel torque to the ground, not engine torque.

Right... Obviously, traction, turns, shift efficiency, etc. add complexity, but in general it's as simple as staying in the lowest gear you can. You need either a ton a variance in the engine torque curve or extremely close gear ratios for that not to be the case.

Batman's chart makes it pretty clear.

(Draph, I think you must have missed the video I posted as well which makes the same point you did.)

[RollaMo]

Originally Posted by Waiting46

Good to know the car will do nearly 300 at max gear/rpm

Yeah, good luck getting anywhere close.
You won't have enough "power" to get anywhere close to red line in 6th gear.
Without mods, you won't even get to red line in 5th gear.

Originally Posted by enzia35

'Cept that physics is a complete bitch.

[Donner]

Hello,

It may be helpful to explain what is meant by those words. Think of a triangle.

On the three corners are Torque, Power, and Endurance.

Power is how much you can lift.
Torque is how quickly you can lift it.
Endurance is how many times the cycle can be repeated.

This is a reasonable way to think about the differences in the terms...

Races say it this way. Power decides how fast your car is going when it hits the wall. Torque decides how quickly it smashes into it.

Kindest,

Donner

[Donner]

Originally Posted by travislambert

Keeping the engine closest to redline puts the most power to the ground. I'm pretty sure it's as simple as that (for most cars).

Yep yep...

Well said.