Quote from colcob :

Sorry but I think you're wrong. Currently delivered torque absolutely dictates your acceleration.

Torque/effective wheel radius = delivered linear Force at contact patch.

Acceleration = Force/Mass

Therefore as weight = mass*g

torque/weight is directly analogous to force/mass which equals acceleration.

Therefore torque to weight is the most accurate way of defining a cars acceleration potential. The reason its never quoted is perhaps because people dont understand it.

That is at the wheels though. An engine could deliver a huge amount of torque at the fly wheel, but once geared to have any reasonable sort of top speed, deliver a relatively small amount of torque at the wheels.


Edit: Small example:

A lot of lotus 7 style kit cars are fitted with bike engines. These may produce a maximum torque of around 70lbft and typically weigh around 450kg, so a torque/weight of 155lbft/tonne.

A popular car engine fitted is a ford zetec, and cars with these fitted will normally weight about 650kg. A google for 'zetec dyno' has found one producing 150lbft maximum torque, so assuming that's a typical value, that is 230lbft/tonne.

The car engined car will still not beat the bike engined one (the bike engined one will batter the car engined one). This being because the bike engine produces useable torque up to 12000rpm, whereas the zetec only to about 7000. The gearing is altered to suite and the bike engine produces more torque/tonne at the wheels.

The bike engine produces ~150 bhp, so ~333 bhp/tonne. The car engine produces ~165 bhp so ~250bhp/tonne. Coincidence? I suppose it could well be and someone could most likely find an example to prove power not to be a good indicator either. For example I suppose if an engine gave a very narrow band of torque at high rpm? So that is maximum torque and maximum power values are both useless


Just my thoughts, might be a load of the brown stuff.

Quote from Gunn :

It may also be useful to find out out how quickly it takes the GTR to reach the FZ50's top speed. If the GTR car reaches the FZ50's top speed quicker than the FZ50 does, then the performance gap is widened even more than just a top speed rating would suggest.

OK. This is using GRC coz I'm too lazy to actually drive and time it, but the results should be reasonably accurate:
FZ50 top speed: 173mph
Time to get there: 90 seconds
Time for FZR to get there: 28 seconds

The difference will always be great though, since the last few mph take ages. For instance it still takes 60 seconds for the FZR to get flat out, so it took 32 seconds to get from 173 to 181mph. Likewise the FZ50 reaches 170mph in just 57 secs. So it took a whopping 33 seconds to gain 3mph.

Quote from dave_w11 :

That is at the wheels though. An engine could deliver a huge amount of torque at the fly wheel, but once geared to have any reasonable sort of top speed, deliver a relatively small amount of torque at the wheels.

You've got that the wrong way around. You gear down, not up. This goes back to skiingman's F1 comment, their torque isn't that impressive at the engine but with so many revs there gearing will be really short, so torque at the wheels will be monstrous. Add to that low weight and you've got something that flies.

Quote from dave_w11 :

A lot of lotus 7 style kit cars are fitted with bike engines. These may produce a maximum torque of around 70lbft and typically weigh around 450kg, so a torque/weight of 155lbft/tonne.

A popular car engine fitted is a ford zetec, and cars with these fitted will normally weight about 650kg. A google for 'zetec dyno' has found one producing 150lbft maximum torque, so assuming that's a typical value, that is 230lbft/tonne.

The car engined car will still not beat the bike engined one (the bike engined one will batter the car engined one). This being because the bike engine produces useable torque up to 12000rpm, whereas the zetec only to about 7000. The gearing is altered to suite and the bike engine produces more torque/tonne at the wheels.

The bike engine produces ~150 bhp, so ~333 bhp/tonne. The car engine produces ~165 bhp so ~250bhp/tonne. Coincidence? I suppose it could well be and someone could most likely find an example to prove power not to be a good indicator either. For example I suppose if an engine gave a very narrow band of torque at high rpm? So that is maximum torque and maximum power values are both useless

Hang on, you're not thinking about gearing reduction enough here. The bike engine revs twice as high, so to get the same speeds you need to double your gearing reduction, doubling your torque in the process. So now you've got the same torque (nearly) but less weight. See? So it accelerates quicker.

One big reason you can't give out torque-to-weight figures in reality is that it totally depends on the gearing. And then the difference between a peaky engine and a flat torque curve makes a big difference. So really you need a plot of the torque curve for each gear to analyse things. Just what GRC does.

Quote :

You've got that the wrong way around. You gear down, not up. This goes back to skiingman's F1 comment, their torque isn't that impressive at the engine but with so many revs there gearing will be really short, so torque at the wheels will be monstrous. Add to that low weight and you've got something that flies.

I meant a small amount of torque at the wheels compared to what an engine with less torque, but at higher revs could at the wheels after gearing. Not compared to the torque at the flywheel. I didn't put it very well though :sorry:

Quote :

Hang on, you're not thinking about gearing reduction enough here. The bike engine revs twice as high, so to get the same speeds you need to double your gearing reduction, doubling your torque in the process. So now you've got the same torque (nearly) but less weight. See? So it accelerates quicker.

I would say that amounts to the same thing I was trying to say: That although the torque/tonne is lower at the flywheel, after gearing (thanks to the higher revving bike engine), the torque at the wheels is higher than that of the car engine with higher flywheel torque.

Quote :

One big reason you can't give out torque-to-weight figures in reality is that it totally depends on the gearing. And then the difference between a peaky engine and a flat torque curve makes a big difference. So really you need a plot of the torque curve for each gear to analyse things. Just what GRC does.

That was the main point of my post aswell.


What is a GRC?

well i guess thay "souped" up the GTR's just like it was back in highschool..
Rims, bodykit, muffler and an intake, maybe a chip too. theres your 20 extra mph

Quote from noob4ever :

well i guess thay "souped" up the GTR's just like it was back in highschool..
Rims, bodykit, muffler and an intake, maybe a chip too. theres your 20 extra mph

hehe
BRILLIANT

Quote from noob4ever :

well i guess thay "souped" up the GTR's just like it was back in highschool..
Rims, bodykit, muffler and an intake, maybe a chip too. theres your 20 extra mph

Yeah they aren't much of a difference to their road-car counterpart.

To me they are really just the road cars made into some mid entry level race car... nothing like a GT1 or LeMans class car, but almost there.

Quote from colcob :

Therefore torque to weight is the most accurate way of defining a cars acceleration potential. The reason its never quoted is perhaps because people dont understand it.

It'd be nice if there were some big conspiracy to that effect....but thats just not the case.

A given acceleration over a given period of time requires a given amount of work to be done. This work cannot be done without power. All the torque in the world is nice, but means absolutely squat if the torque can't be produced far enough to the right of the graph.

I can give a very realistic and very obvious example which proves this point.

" torque/weight is directly analogous to force/mass which equals acceleration."

So I've got this electric motor that produces 2000lb-ft of torque at 1 rpm. It produces 300lb-ft at 1000 rpms. This is not an unrealistic torque curve for an electric motor.

Although it will smoke the tires even in fourth gear from a stop, no amount of gear swapping in the world will make it accelerate faster over any reasonable time period or distance than a 160hp gasoline engine making about 150lb-ft of torque.

By stating this:
Torque/effective wheel radius = delivered linear Force at contact patch.

you are implying that you don't understand the function of a gearbox. Bob did a good job of explaining its torque multiplication duties.

If torque to weight were a better indicator of performance than power to weight (obviously false with a basic look at physics) the izzy Celica would be faster/quicker than the duzzy Celica. Its not. Same goes for ZO6 vettes, which really don't make more torque than stock vettes. They move the torque curve further right, increasing the PRODUCT of torque and RPM......horsepower.

Quote from spoken like a phys prof :

But perhaps the rate at which the torque is being applied gives a better idea of how much energy is being put into the system, therefore HP: Weight should be more important....

Who cares if you've got all the force in the world if it takes a vast amount of time for it to be applied?

Right on, and thats exactly why the figure given is hp/weight, not torque/weight. Given non-silly gearing you can get pretty much the same result of calculation from hp/weight as you can by plotting torque available at a given engine speed/gear combo over time. Its a lot less labor intensive too, unless you have something cool like the tool Bob is using.

If you want to work out the top speed of a car, the rate of acceleration at any point, the force at the wheels, or pretty much any other performance related parameter, you use the torque curve and/or the gearing. You never ever need to use a power curve or power figure, as they don't actually tell you anything. Besides power is just a function of torque, and is so ridiculously easy to work out that if you REALLY want it you can have it...

Quote from dave_w11 :

What is a GRC?

The gearing tool I made for LFS, since you missed the link in my sig I'll put one here too: GRC

I think we're just misunderstanding eachother Skiingman. I'm talking about the actual torque delivered at the wheel (ie. post gearing) for a given moment. You seem to think I'm talking about the quoted torque peak figure, regardless of rpm.
Of course, higher power output effectively means being able to carry on producing high torque at higher revs, which means staying in a lower gear for longer, producing higher wheel torque for longer, hence acheving better acceleration.

Basically what I am saying is that the torque/power curve is all you need. Its the main defining characteristic of an engine.

Quote from colcob :

the torque/power curve is all you need. Its the main defining characteristic of an engine.

100% true. Anyone who tries to argue doesn't understand engines or physics enough to argue.

Hmm, and there was me trying to stay out of all internet torque/power wars. I thought I had seen enough of them but I can't resist.

First of all I think skiingman's posts are spot on. I am also quite suprised at some of the other posts I have been reading here. Examples:

Quote from Bob Smith :

Power to weight is irrelevant, I'd say it's the most useless statisitic you can have about a car IMO.

Quote from colcob :

Therefore torque to weight is the most accurate way of defining a cars acceleration potential. The reason its never quoted is perhaps because people dont understand it.

Quote from tristancliffe :

You never ever need to use a power curve or power figure, as they don't actually tell you anything.

Instead of posting long explanations I'll just make up a few questions to get people thinking: (multiple answers possible)

1) When is the best point to shift up?
a) when the next gear puts the engine at an rpm of higher power
b) when the next gear puts the engine at an rpm of higher torque
c) when the next gear will deliver more torque to the wheels

2) To get maximum accelleration out of an engine you can use a continuously variable transmission (CVT) that can keep the engine at a constant rpm. Which rpm should this be?
a) max engine torque rpm
b) max engine power rpm

3) You want to improve the accelleration of your car by getting a new engine. The dealer will only tell you either the max torque or max power value (no rpm value). Which one will give you more useful information?
a) max torque
b) max power
c) both the same

4) You want to improve the accelleration of your car by getting a new engine. The dealer will only tell you either the torque curve or the power curve. Which one will give you more information?
a)torque curve
b)power curve
c)both the same

5) With a given gear ratio you can go through the engine's rpm range by varying the speed of the car. At which rpm will you find the highest acceleration?
a) at max engine torque rpm
b) at max engine power rpm

6) At a given vehicle speed you can go through the engine's rpm range by varying the gear ratio between engine and wheels. At which rpm will you find the highest acceleration?
a) at max engine torque rpm
b) at max engine power rpm

7) Which question, 5) or 6) is irrelevant when you are a girl and are trying to determine the overall drag-strip performance of your car? (bash tristan not me )
a) 5)
b) 6)

Can you take my challenge?

I'll have a crack!

Quote from J.B. :

1) When is the best point to shift up?
a) when the next gear puts the engine at an rpm of higher power
b) when the next gear puts the engine at an rpm of higher torque
c) when the next gear will deliver more torque to the wheels

When the next gear will deliver more torque to the wheels than staying in the same gear. Tractive Effort

Quote :

2) To get maximum accelleration out of an engine you can use a continuously variable transmission (CVT) that can keep the engine at a constant rpm. Which rpm should this be?
a) max engine torque rpm
b) max engine power rpm

The rpm of most torque for most acceleration

Quote :

3) You want to improve the accelleration of your car by getting a new engine. The dealer will only tell you either the max torque or max power. Which one will give you more useful information?
a) max torque
b) max power

Technically both, as one can be derived from the other, but personally I would go for the torque curve so I didn't have to bother converting it.

Quote :

4) You want to improve the accelleration of your car by getting a new engine. The dealer will only tell you either the torque curve or the power curve. Which one will give you more information?
a)torque curve
b)power curve
c)both the same

Both the same, as the important one, Torque, can be derived from the power curve

Quote :

5) With a given gear ratio you can go through the engine's rpm band by varying the speed of the car. At which rpm will you find the highest acceleration?
a) at max engine torque rpm
b) at max engine power rpm

At max torque! Tractive Effort at wheels/Mass of car = Acceleration

Quote :

6) At a given vehicle speed you can go through the engine's rpm band by varying the gear ratio between engine and wheels. At which rpm will you find the highest acceleration?
a) at max engine torque rpm
b) at max engine power rpm

Max Torque rpm

Quote :

7) Which question, 5) or 6) is irrelevant when trying to determining the overall drag-strip performance of your car?
a) 5)
b) 6)

5 is irrelevant for drag racing, but drag racing is irrelevant cos only girls drag race. It's for people who can't do corners. Anyway, you can change your gear ratios, but in a flat out sprint you can't choose the best speed for acceleration

Quote :

Can you take my challenge?

I just did.

Personally, I think much of the confusion is do with difficulties in explaining/understanding, rather than us actually having it wrong in our heads.

Anyway, I'll have a crack at your test, I havent looked at tristans answers yet, and engines arent exactly my strong point, as you've noted.

1) When is the best point to shift up?

c) when the next gear will deliver more torque to the wheels

2) To get maximum accelleration out of an engine you can use a continuously variable transmission (CVT) that can keep the engine at a constant rpm. Which rpm should this be?

b) max engine power rpm
I cant quite work out why in my head, but it stands to reason that if you are going to run an engine at only one speed, it should be the speed which derives the greatest power from the engine. It think its because running at max power rpm would effectively allow the CVT to be running in a lower gear, thus delivering greater actual wheel torque throughout the speed range.

3) You want to improve the accelleration of your car by getting a new engine. The dealer will only tell you either the max torque or max power. Which one will give you more useful information?

b) Honestly not sure. Max power and max torque are both of questionable use and dont tell the whole story, so I'd probably plump for max power.

4) You want to improve the accelleration of your car by getting a new engine. The dealer will only tell you either the torque curve or the power curve. Which one will give you more information?

c)both the same, one derives directly from the other.

5) With a given gear ratio you can go through the engine's rpm band by varying the speed of the car. At which rpm will you find the highest acceleration?
a) at max engine torque rpm (aerodynamic effects notwithstanding)


6) At a given vehicle speed you can go through the engine's rpm band by varying the gear ratio between engine and wheels. At which rpm will you find the highest acceleration?

b) at max engine power rpm, because it will yield the shorter gearing thus greater delivered torque to the wheels.

7) Which question, 5) or 6) is irrelevant when trying to determining the overall drag-strip performance of your car?
a) 5)


I'd just like to point out that I didnt make it very clear that I was referring to actual wheel torque in most of my previous points, which is a quite different thing to engine torque alone, as the engine power capabilities will determine what gearing is used to turn engine torque into wheel torque.

Thank you for taking part Sirs. I won't tell my opinions yet, maybe some other people will give it a try. And I clarified questions 3) and 7).

Quote from colcob :

Basically what I am saying is that the torque/power curve is all you need. Its the main defining characteristic of an engine.

Yes, but you need the WHOLE thing, not just one figure from it. Thats the disadvantage of talking about torque. Uber torque at weaksauce rpms will not get the work done. Sure, if you have uber torque at macho rpms, you will get the work done in a hurry.

The best way to express a torque curve in a single figure is horsepower. This is why you see horsepower figures quoted versus weight, not torque versus weight.

500hp/ton ALWAYS results in a predictable acceleration over time, regardless of the actual torque curve...assuming we have decent gearing. So a 500hp electric motor with 5000lb-ft of peak torque will get from a>b in about the same amount of time as (opposite end of spectrum) a 500hp gas turbine making 80 or 90lb-ft of torque.

If you made the absurd statement that the 5000lb-ft/ton car is going to be faster than the 90lb-ft car, you better not be betting big money. You could very well be wrong.

Bob made these statements:
"Power to weight is irrelevant, I'd say it's the most useless statisitic you can have about a car IMO."

Obviously its not irrelevant. Fairly simple physics can show with the single hp/weight figure results nearly as accurate as his torque/gear model...which requires a LOT more knowledge of the way the system works. It would be very bad to assume the electric motor's torque curve would be similar to a gas motor and plug it into a torque and gear calculator.

"Power to weight tells you nothing really."

In fact, it tells you quite a bit. Knowing weight and something as seemingly unrelated as fuel consumption can give you fairly a fairly accurate representation of of the acceleration available at a given speed. What it doesn't give you a clue about is the gearing you'll need to achieve that. Thats a rather critical part of the setup, and thats why a gear calculator is indispensible.

Outside of the automotive world there are plenty of places where torque is as seemingly irrelevant as horsepower is here. Your typical airbus captain doesn't much care about the torques the turbines are producing, but the simple power to weight calculations are absolutely vital to getting off the ground at the appropriate speed and distance. If you think about it for half a second, the rate of acceleration that massive airliners achieve at a max performance takeoff is mind boggling given their mass.

LOL!!!

I like Q.7 now
And my answer to Q3 would now be Max Power. I would then use a bit of common sense, and look at the engine 'type'. A good, drivable, tractable, but not neccessarily highly tuned engine tends to produce similar hp and lbft figures (it doesn't work with Nm and kW). So a car with 500hp and 500lb-ft of torque will be much nicer to drive on the road that a 900hp 200lb-ft engine (pretty much regardless of gearing).

So if I was looking an engine that I knew produced 900hp, but didn't know the torque I'd ask myself a few questions? How long is the stroke, what capacity, what layout, which manufacturer. From that I'd be able to hazard a guess as to it's vague torque characteristics, and make the correct purchase.

Quote from skiingman :

Outside of the automotive world there are plenty of places where torque is as seemingly irrelevant as horsepower is here. Your typical airbus captain doesn't much care about the torques the turbines are producing, but the simple power to weight calculations are absolutely vital to getting off the ground at the appropriate speed and distance. If you think about it for half a second, the rate of acceleration that massive airliners achieve at a max performance takeoff is mind boggling given their mass.

The Airbus captain won't care one iota about torque on the turbines, as turbofan engines produce thrust, not torque (although torque on the driveshaft is obviously a factor in the production of thrust, but the internal workings of the turbofan are not of much interest to the Captain).

Quote from skiingman :

Yes, but you need the WHOLE thing, not just one figure from it.

Yeah, thats exactly what I was trying to say. Like I said, I was was talking about wheel torque, which is the car equivalent of thrust. How much of it you get at a given speed depends a lot on the engine power.
And I never said power to weight was irrelevant, it clearly isnt.

Interesting debate this though. Its certainly helped to clarify some of my slightly vaguer notions about torque/power.

As much as i like talking physics and stuff, i think this is a case of
of 'when it seems overly complicated, it MUST be simpler'. Personally
i think it is. There is one major problem in all the comparisions, we
don't REACH top speed in LFS, at least in most cars. There is no track
that is long enough (like when manufacturers test out their top speed...)
and to prove my point i made an experiment a while back. There was some
setup hacks for grip back then and you could literally take turns flat out,
accumulating speed lap after lap. NOT losing speed would be a better
word. There was nothing making the car accelerate faster, it simply didn't
lose much speed in turns turning any track into an endless stretch to
accelerate. Considering all the rest was stock, the XRGT Turbo could reach
260+km/h on Blackwood, it still had guts left for another 5-10kmh i'd say.
Try it now. If the XR GT Turbo can eventually reach 260km/h, i'm SURE the
GTR cars can reach close to 300 if given the room. The S2 oval has just
reinforced this by allowing cars to reach higher speeds than any other tracks.
If the oval hadn't been released, what 'top speed' figures would you use for
LFS ? 'Top Speed' and the fastest you've gone in 'x' car is not the same thing.

Comparing the Ferrari Maranello to a GTR is unfair for a few reasons.
Like i said above, the Maranello's top speed was surely tested on a track
providing it room to do so, a distance VS speed chart would be better for
comparing than a top speed figure imo as we have no actual data on top
speed of LFS cars. The Ferrari is a road car with little drag from aerodynamics
compared to it's equivalent race version, which could very well be compared
to the GTR, and in fact SHOULD be the car to compare it with, and not the
street car. What are the specs of the racing versions of the Ferrari ?

Quote from colcob :

2) To get maximum accelleration out of an engine you can use a continuously variable transmission (CVT) that can keep the engine at a constant rpm. Which rpm should this be?

b) max engine power rpm
I cant quite work out why in my head, but it stands to reason that if you are going to run an engine at only one speed, it should be the speed which derives the greatest power from the engine. It think its because running at max power rpm would effectively allow the CVT to be running in a lower gear, thus delivering greater actual wheel torque throughout the speed range.

You got it right. On CVT you have the most WHEEL torque at power rpm, it doesn't matter if engine torque is lower.

Quote from Bob Smith :

You got it right. On CVT you have the most WHEEL torque at power rpm, it doesn't matter if engine torque is lower.

are you sure ? looking at the graphs grc produces id say the most torque at the wheels is still at the torque peak of the engine (the optimum point for the transient behaviour though might be a little higher in the rpm band depending on how flat the torque curve is)

Yeah, but remember that torque at the wheels = engineTorque*gearRatio.

So for a given speed, if you run at a higher engine revs, you run a lower gear ratio. Which, if you are running at max power RPM, will result in greater wheel torque.

Quote from colcob :

Yeah, but remember that torque at the wheels = engineTorque*gearRatio.

So for a given speed, if you run at a higher engine revs, you run a lower gear ratio. Which, if you are running at max power RPM, will result in greater wheel torque.

Regardless of the technical benefits, I still hate driving CVT cars. The modern ones are getting good at sort of simulating gear-changes to comfort the ear, but I still get the feeling I'm driving a go-kart or a snowmobile. I suppose you likely get used to it.

Quote from tristancliffe :

The Airbus captain won't care one iota about torque on the turbines, as turbofan engines produce thrust, not torque (although torque on the driveshaft is obviously a factor in the production of thrust, but the internal workings of the turbofan are not of much interest to the Captain).

An interesting case where the captain cares all about torque and HP is only a figure of academic interest is the PT6 (or probably about any turboshaft/constant speed prop setup) captain pays attention only to torque. Since his prop turns (more or less) at a constant speed, torque is all he needs to know. Its also the only thing that can be easily directly measured, which is probably why they have a torque gauge and not a power gauge.

Quote from colcob :

Yeah, but remember that torque at the wheels = engineTorque*gearRatio.

which basically means that you scale the torque curve ... so the highest torque at the wheels for any gear ratio is always when the engine develops the most torque ...
so if your gearing always fits the current wheel speed perfectly youll get the most torque to the wheels at the engines torque peak