Power to acceleration relationships

Original post by JDV10

This discussion is awful.

Implying different engines, cars, model, etc. Don't all have different power bands, gear ratios, grip, transmission losses, etc...

Also, measuring HP/Mass isn't the 'Correct' way of thinking about it, try Torque/Mass. It might be easier for you chaps to understand.

In fairness to the OP, your last line doesn't exactly show a lot of technical understanding - power is more important than torque. If you've got enough power but insufficient output torque, you just need to adjust your gearing. If you've got adequate (but not excess) torque and your rotational speed is too low, you're stuffed until you can get more power...

Reply 22

OP

Original post by JDV10

This discussion is awful.

Implying different engines, cars, model, etc. Don't all have different power bands, gear ratios, grip, transmission losses, etc...

Also, measuring HP/Mass isn't the 'Correct' way of thinking about it, try Torque/Mass. It might be easier for you chaps to understand.

Really don't see why torque is more important than bhp. If that was the case all the diesels would be fast and the petrols slow.

Reply 23

JDV10

6

Well, this thread is categorizing things into an automotive application in one post, the physics in the other.

Like saying, double the horsepower and you will half the 0 - 60 time?!

Horsepower isn't even a force. When have you ever seen
F=M*A with horsepower?

Never, because torque is a force, over a distance.

Torque is more appropriate because horsepower is related to torque at a specific RPM, high revving diesels generally have more 'power' than petrol cars, however, they're harder to make.

As much as I appreciate people applying STEM course material to Automotive discussion, they're are too many dynamic variables that you guys just haven't considered.

tl;dr

Horsepower is a man made thing, it's used in the modern day for mouth breathers to find out 'how wikked sik mi whip is doe'

Reply 24

OP

Original post by JDV10

Well, this thread is categorizing things into an automotive application in one post, the physics in the other.

Like saying, double the horsepower and you will half the 0 - 60 time?!

Horsepower isn't even a force. When have you ever seen
F=M*A with horsepower?

Never, because torque is a force, over a distance.

Torque is more appropriate because horsepower is related to torque at a specific RPM, high revving diesels generally have more 'power' than petrol cars, however, they're harder to make.

As much as I appreciate people applying STEM course material to Automotive discussion, they're are too many dynamic variables that you guys just haven't considered.

tl;dr

Horsepower is a man made thing, it's used in the modern day for mouth breathers to find out 'how wikked sik mi whip is doe'

Nah, you have to quadruple the horsepower to half the 0-60 time

Reply 25

While I realise the OP can be a little 'over enthusiastic' and his obsession with saloons is bordering on the comical, I don't think people are being very fair here. There's not many people on this forum with a technical interest in cars so it's a shame to see it being discouraged. That said of course, if you (OP) are going to create a thread like this, don't just tell people they're wrong!

Original post by JDV10

Never, because torque is a force, over a distance.

Force x distance is work, not torque. Torque is a force acting about an axis. Whilst I'll accept that might be what you were trying to say, your wording was closer to the definition of work than torque and was at best ambiguous.

Torque is more appropriate because horsepower is related to torque at a specific RPM, high revving diesels generally have more 'power' than petrol cars, however, they're harder to make.

Power is related to torque at all speeds, as power = torque x rotational speed. Nothing more, nothing less. Peak torque doesn't tell you much in all honesty. A BMW 335D has higher peak torque than a John Deere 6630, but there'll only ever be one winner in a tug of war. There's a limit to what power will tell you, but it does at least give you a reasonable idea of the capability of a piece of equipment.

If you're going to try and knock someone on a technical basis, at least make sure you know what you're talking about.

(edited 10 years ago)

Reply 26

JDV10

6

Original post by CurlyBen

Force x distance is work, not torque.

Torque is measured in Newton Meters or lb/ft

I'm pretty sure that's the definition of force/distance

for example:

420 Newtons over 1 Meter. Thus 420 NM

I understand where I may have confused people not mentioning that it's a rotational force however.

Reply 27

Original post by JDV10

Torque is measured in Newton Meters or lb/ft

I'm pretty sure that's the definition of force/distance

for example:

420 Newtons over 1 Meter. Thus 420 NM

I understand where I may have confused people not mentioning that it's a rotational force however.

Lb/ft is a unit of mass per length, or a way of expressing a distributed load. The unit you're looking for is lbf.ft (note that it is lbf. - a pound is a unit of mass, pound force is a unit of force, although this is often missed). / and over mean divided by. Force/distance doesn't feature in any common equation I know! 420Nm is equivalent to a force of 420 Newtons acting radially at a distance of 1 metre. 420 Newtons over a meter would be a force acting above a piece of measuring equipment.
If you can't get these basics right, you're on pretty shaky ground...

Reply 28

OP

Original post by CurlyBen

A BMW 335D has higher peak torque than a John Deere 6630, but there'll only ever be one winner in a tug of war..

That's only cause the tractor weighs more that it would win the tug of war lol

Reply 29

Original post by traintracks1995

That's only cause the tractor weighs more that it would win the tug of war lol

The Deere is less powerful and it generates less torque at the flywheel. The BMW just lacks the appropriate gearing... (and admittedly enough fatties in the boot to keep traction)

Reply 30

OP

Original post by CurlyBen

The Deere is less powerful and it generates less torque at the flywheel. The BMW just lacks the appropriate gearing... (and admittedly enough fatties in the boot to keep traction)

But if they both weighed the same and the beemer had a short enough first gear then the beemer will win?

Reply 31