power and torque curve, and maximum acceleration

[Stan Weiss]

This was done about 8 years ago for a thread on another forum.

It has was done using an evenly spaced 7 speed trans and shows wheel torque in each gear against both MPH and RPM. Yellow lines are are at peak wheel torque in each gear. Red line is where the wheel torque drops to the point it is equal to the wheel torque in the next gear.

Stan

[Murci.sv]

the maximum torque point in a given gearbox ratio corresponds to the maximum G-force. All right. What is the importance of “jerk” in the perception of acceleration? I have read here several times that "constant" acceleration is less well felt than acceleration
less linear (high jerk rate). is it true?

[GreenV8S]

Murci.sv said:

less well felt

Since feeling is obviously subjective, there isn't any right or wrong answer. It will vary from person to person, car to car, perhaps run to run.

My own perspective is that I tend to get the most sense of acceleration in vehicles where the acceleration is relentless, not the ones where I get thrown around. But YMMV.

[Murci.sv]

not wrong, it depends on each person. However this jerk thing seems to be scientifically true, turbo cars generally feel faster with that push in the back as torque increases at boost. It still feels less strong despite similar or better acceleration figures. the torque curve seems to play a role here

[GreenV8S]

Murci.sv said:

However this jerk thing seems to be scientifically true, turbo cars generally feel faster with that push in the back as torque increases at boost. It still feels less strong despite similar or better acceleration figures. the torque curve seems to play a role here

Given that you acknowledge it's entirely subjective, and you have obviously made up your own mind, why are you asking? It's not as if you're going to convince anyone to change their subjective opinion, nor should you care about their opinion either way.

[Inline__engine]

i think someone noted above the acceleration is a result of the net force acting on the vehicle and its mass and rotational mass moment of inertia

This simplifies down to in a given gear the acceleration will be exacly proportional to the engine torque with the following assumptions

Traction is 100% maintained
No slipping of clutches or converter etc
Neglect losses and retarding forces that are/could be a function of vehicle speed, engine speed, time e.g drag, drivetrain losses, gradient etc

Edited by Inline__engine on Wednesday 6th March 03:05

[The Wookie]

GreenV8S said:

Given that you acknowledge it's entirely subjective, and you have obviously made up your own mind, why are you asking? It's not as if you're going to convince anyone to change their subjective opinion, nor should you care about their opinion either way.

To be fair it’s mostly subjective but it’s not entirely subjective, from what I understand it’s physiologically related to the body’s ability to react to an acceleration.

Easiest way to think about it is standing on a tube train. If the acceleration builds up slowly enough for you to change your stance and balance against it, you’d be able to stay on your feet without bracing yourself to 0.5G before you started sliding down the train, still on your feet.

But if it snapped straight to 0.1G from a standstill you’d be on your arse in a split second because you wouldn’t have time to move your muscles to reorient and rebalance yourself.

That rate of change is what’s relevant to the body’s ability to react to it, so it’s what dominates our perception, hence the shock factor of jerk.

Probably the evolutionary difference between getting shoved by an enemy vs standing on a steep slope.

[Inline__engine]

the body does not sense simply acceleration it is more complicated than that we sense jerk as well and perhaps snap and others in different ways using different senses

similarly the body does not simple sense temperature alone

this appears to be beyond what the OP intended getting clarification though

[Crudeoink]

I think I have a design for the fastest car ever. Each wheel is powered by a Milwaukee impact wrench, 1000nm of torque to each wheel, 4000nm total, each wrench only weighs 1.5kg so we've got 4000nm of torque with a powertrain that has a mass of only 6kg! Tesla Plaid only makes 1400nm so we're easily double that torque output

[LennyM1984]

Crudeoink said:

I think I have a design for the fastest car ever. Each wheel is powered by a Milwaukee impact wrench, 1000nm of torque to each wheel, 4000nm total, each wrench only weighs 1.5kg so we've got 4000nm of torque with a powertrain that has a mass of only 6kg! Tesla Plaid only makes 1400nm so we're easily double that torque output

Ha ha I have also had the same thought. I tried to explain to a friend with a 335d that my dewalt impact gun made more torque than the engine in his car but he simply wouldn't believe me (in large because he did not appear to understand the difference between torque and power).