Torque

[M3Kevin]

Great explanation of something I have wondered about for a long time.
Kevin

Originally Posted by bruce.augenstein@comcast.

Behind the wheel, the 335i does indeed feel a bit livelier than the M3 in everyday driving, and in fact it probably really is livelier. This point has been debated at great length in these pages, both with and without rancor, but the primary point is, as footie has said, "you get all the thrill without the speed" in the turbo car. To the driver, the 335i feels effortless, since you can give it gas at low rpm in a higher gear and the car will pull very hard without the sturm and drang associated with high revs. By contrast, the M3 will actually be quicker from pretty much any speed to any other speed, but because of its gearing, you will always be looking at greater revs, and the associated feel to the driver of greater effort.

In regard to horsepower vs torque, quite simply horsepower rules. Take any two cars that weigh the same, and in a side-by-side acceleration contest, the car with more horsepower at any given point will be accelerating harder than the car with less horsepower. Torque and gearing simply don't matter at all. In fact, horsepower is kind of a simple shorthand in that context. You can do all that computing of torque at the drive wheels if you like, but you'll find that more power equals more torque at the drive wheels, pure and simple.

I've used an example of a waterwheel generating some 2600 pound feet of torque - at 12 rpm. If you hooked that waterwheel to the drive wheels of a car, that car would jump from zero to 12 rpm of the drive wheels very quickly. But since 12 rpm of the drive wheels is equivalent to about one mph, what if you wanted to go faster?

Well, you'd have to gear it up. If you wanted to go 60 mph you'd need to gear the waterwheel up by 60 times - thus netting you about 43 pound feet of torque at the drive wheels. 43 foot pounds of forward thrust in a car weighing thousands of pounds just isn't enough to get the job done. In fact, it almost certainly isn't enough to overcome wind and rolling resistance at that speed. If you do the math (horsepower equals torque times rpm over 5252), you'll find that the waterwheel is only making about 6 horsepower.

The solution would be to speed the waterwheel up. Using a convenient flood (and assuming the waterwheel wouldn't fly apart), what if we could speed the water wheel up to, say, 120 rpm, while making the same amount of torque?

Well, the car would then be going 12 mph. Gearing it up to go 60 mph would now reduce the drive wheel torque to about 520 pound feet. That's still not a lot, but it's plenty to keep the car rolling at 60, and you could probably still accelerate at that speed. Doing the math shows, TA DA!, about 60 horsepower - so you can see that raising the rpm by a factor of ten gives you an increase in power by a factor of ten.

In fact, that's the horsepower story. It's torque at rpm. Raising the rpm at which torque is delivered gives you more power by a like amount - and more power gives you a greater ability to accelerate, period.

Bruce

Edit: PS - For a more complete explanation of power vs torque, go here, in note 31.

[J08M3]

Originally Posted by BMW-videos.com

I can bet your GTO weighs a decent amount more then your M3. I'd probably agree that your m3 is a bit faster. Lighten that GTO a bit, probably stiffen the suspension and it could turn pretty well. Either way i'd probably also prefer the m3.

Actually the GTO was supposed to be 3,700 lbs so I guess it was about the same weight. Definitely fast in a straight line. Would be tough to tell which is faster in the 1/4 mile, both felt pretty equal without having either on a track. The torque in the GTO got me used to not having to downshift so much for acceleration. Just push the gas and the thing would put you in the seat and take off. But the suspension setup fails horribly compared to the M3. Forget about turning and stopping the GTO. At least the OEM setup. Definitely interesting to compare the cars back to back though. One with a 6.0L 400 ft. lb. engine and the other with a 4.0L 300 ft. lb. engine. Two totally different feels from behind the wheel. I remember three years ago when the GTO came out it got reviewed as the poor mans M3, and I got a kick out of that because I only bought it after finding out I couldn't afford an E46. Not much touched the GTO in the $30K price range though.

[lucid]

Originally Posted by bruce.augenstein@comcast.

Not in this case.

I guess I set myself up for that one though...

Originally Posted by bruce.augenstein@comcast.

"If a tree falls in the forest, and there's no living thing present to hear it, is it still the husband's fault?"

I wouldn't know as I have the great fortune (or misfortune) of not being married.

[96OCTNE]

When will people stop with the M3 vs 335i comparison, it's getting old. really old.

[mattwhite]

Originally Posted by BMW-videos.com

I don't get it. Are some of us trying to say torque isn't too important? How about when you're coming out of a sharp turn? If I recall correctly, the AUDI R10 is destroying the competition in lemans because of all the torque its twin turbo diesels produce. if you can hook, low rpm torque will catapult you out of corners. IMO, f1 cars have so little torque because there engine displacement is so highly limited. To make the horsepower and torque they have to rev to 19,000rpm plus period or else they wouldn't make the power. I'm sure if they weren't so liter limited you could have F1 cars that could run endurance races (since current engines will not withstand extremely long durations). What would an f1 car with a 7 liter engine and almost seamlessly fast shifting be like? I think if useable that torque will fling them out of corners at dangerous speeds. I think torque is underestimated.

Go do a track day in your C6 Vette with 400 ft/lbs of torque (or more?). When you get passed by a Lotus Elise with 138 ft/lbs of torque, ask yourself if torque is so important.

Torque is great for the street if you don't feel like downshifting. It also can mask lots of mistakes on a racetrack. In the way it is being discussed here, it does not inherently make a car faster.

[jm1234]

Originally Posted by mixja

The problem with the above comparison is that although it takes into account the gearing of the car in terms of torque to the wheels, it doesn't take into account the effect of the gearing in terms of vehicle speed.

Because the 335 has a taller ratio in 1st gear, it travels further in a single engine revolution - the best way to take this into account is to plot vehicle speed (rather than engine RPM) vs torque to the wheels - this gives a more accurate picture of what will actually happen in terms of the relative acceleration of the two vehicles.

In effect, the taller gearing will stretch the torque curve of the 335 to roughly the same width of the M3 curve, when you apply vehicle speed on the X axis rather than engine speed...

Here's rear wheel torque vs. speed if that's what you are looking for. Obviously, rear wheel torque depends on gear so I show that as well. Again, the engine can't stay in the same gear over the entire speed range so I just select the gear with the most rear wheel torque and show the rear wheel torque for that gear. The spreadsheet doesn't use engine speeds above redline. This spreadsheet takes into account gearing (transmission and diff) and stock wheel size.

It does seem that both a stock MT 335 and MT M3 have near the same optimal shift point.

[lucid]

Originally Posted by jm1234

Here's rear wheel torque vs. speed if that's what you are looking for. Obviously, rear wheel torque depends on gear so I show that as well. Again, the engine can't stay in the same gear over the entire speed range so I just select the gear with the most rear wheel torque and show the rear wheel torque for that gear. The spreadsheet doesn't use engine speeds above redline. This spreadsheet takes into account gearing (transmission and diff) and stock wheel size.

It does seem that both a stock MT 335 and MT M3 have near the same optimal shift point.

I can't see your spreadsheet. You forgot to attach it?

I dug up my spreadsheet and realized I was actually calculating speed at max hp in 1st gear (which was relevant to another discussion) and not the optimum shift speeds, which are at redline for both cars. The 1st to 2nd gear shift speeds with stock wheel and tire sizes for the two cars are indeed almost identical according to my calculations:

335: 42.7 mph @ 7000 rpms
M3: 42.1 mph @ 8400 rpms

Is this what you get as well?

[jm1234]

Originally Posted by lucid

I can't see your spreadsheet. You forgot to attach it?

I dug up my spreadsheet and realized I was actually calculating speed at max hp in 1st gear (which was relevant to another discussion) and not the optimum shift speeds, which are at redline for both cars. The 1st to 2nd gear shift speeds with stock wheel and tire sizes for the two cars are indeed almost identical according to my calculations:

335: 42.7 mph @ 7000 rpms
M3: 42.1 mph @ 8400 rpms

Is this what you get as well?

That's because I'm an idiot. I got the same shift points from 1 to 2 with the 335 shifting a tiny bit sooner. It does appear that each car shifts at redline to get max rear wheel torque.

[lucid]

Originally Posted by jm1234

That's because I'm an idiot. I got the same shift points from 1 to 2 with the 335 shifting a tiny bit sooner. It does appear that each car shifts at redline to get max rear wheel torque.

Wow, your plots are cool.

Where did you get the torque data from?

You might want to add the RS4.

Another suggestion is to normalize by weight although that can be tricky as published numbers don't seem to be obtained by using the same methodology...

[ArtPE]

again, talking about T & P as if they are seperate qtys, is not accurate

HP = T x w
w = 2 Pi rev/sec or 2 Pi rev/min / (60 sec/min x 550 lb-ft/min)= rpm/5252

HP = T x rpm/5252

so yes, for 2 cars at the same speed (axle speed) the one with the higher HP will accelerate faster at that instant...
but that is a consequence of more TORQUE...
T is the instantaneous force...lb-ft, notice no time component, instantaneous...

100 HP = 55,000 ft-lb/sec (force x distance/time) ...it's the RATE of work per unit time, or the derivative of work, and work done = energy expended...how much energy is release over time...the more energy, or the shorter the time, the more power...

torque is useful, it can be converted to linear force, or thrust...
if a car has say 3000 lb-ft at the wheels, and the wheel is 1.1' radius, thrust = 3000/1.1 ~ 2727 lbs (force F)
now, for a constant force, which will accel faster? a car with mass m1 or 1.2 x m1???

obviously m1...because F = ma, rearranging, a = F/m...so for a constant F, a smaller mass accels faster...

let's say the car weighs 2800 lbs, it's mass is 2800/g...
a = 2727/(2800/g) so a = 2727/2800 g ~ 0.97 g or 31.4 ft/sec-sec...assuming no slip, good traction

if the car weighed say 4000 lbs...a = 2727/4000 g ~ 0.68 g, much slower ~ 22 ft/sec-sec...

[lucid]

Originally Posted by ArtPE

again, talking about T & P as if they are seperate qtys, is not accurate

HP = T x w
w = 2 Pi rev/sec or 2 Pi rev/min / (60 sec/min x 550 lb-ft/min)= rpm/5252

HP = T x rpm/5252

so yes, for 2 cars at the same speed (axle speed) the one with the higher HP will accelerate faster at that instant...
but that is a consequence of more TORQUE...
T is the instantaneous force...lb-ft, notice no time component, instantaneous...

100 HP = 55,000 ft-lb/sec (force x distance/time) ...it's the RATE of work per unit time, or the derivative of work, and work done = energy expended...how much energy is release over time...the more energy, or the shorter the time, the more power...

I think what confuses most people are dyno charts, which attempt to plot torque and power on the same chart, which, of course, is technically inaccurate since they are two different concepts as you state above, and there exists two seperate charts overlaid on top of each other, rather than a single chart. But that gives the impression that there is a one vs. the other scenario, whereas they are simply related but different constructs.

[swamp2]

Originally Posted by mattwhite

Go do a track day in your C6 Vette with 400 ft/lbs of torque (or more?). When you get passed by a Lotus Elise with 138 ft/lbs of torque, ask yourself if torque is so important.

Torque is great for the street if you don't feel like downshifting. It also can mask lots of mistakes on a racetrack. In the way it is being discussed here, it does not inherently make a car faster.

Not a valid point at all. The reason an Elise (or any car X) can overtake a Vette (or any other car Y) on the track does in fact have very little to do with the peak torque of the engine (nor peak hp). Power to weight is in fact the critical parameter. In this specific case, driver skill, suspension and suspension set up and tire choice likely have something to do with it as well.

[mixja]

Originally Posted by jm1234

Here's rear wheel torque vs. speed if that's what you are looking for. Obviously, rear wheel torque depends on gear so I show that as well. Again, the engine can't stay in the same gear over the entire speed range so I just select the gear with the most rear wheel torque and show the rear wheel torque for that gear. The spreadsheet doesn't use engine speeds above redline. This spreadsheet takes into account gearing (transmission and diff) and stock wheel size.

It does seem that both a stock MT 335 and MT M3 have near the same optimal shift point.

Nice graph - that's exactly what I was referring to...

It would be interesting to see the M3 DCT on there, the shorter ratios will bring in more in line with the C63 in terms of shift points but the torque to the wheels will be higher...

This really illustrates that the wide power band of the M3 makes it such a truly remarkable car that can make it perform almost as fast (if not as fast with the DCT) as something like a C63...

[hellrotm]

Originally Posted by J08M3

Remember you only get horsepower because of Torque. Horsepower is just a mathematical number based on torque and time. Torque is an actual measurement.

Oh that is so so so WRONG.

Horsepower is derived from torque and rpm. More horsepower can come about in two ways, make more torque, or make torque at a higher rpm. The M3 V8 uses high revs or rpms to create its horsepower.

Your statement, "you only get horsepower because of Torque." NOT CORRECT.

[J08M3]

Originally Posted by BlackJetE90

Oh that is so so so WRONG.

Horsepower is derived from torque and rpm. More horsepower can come about in two ways, make more torque, or make torque at a higher rpm. The M3 V8 uses high revs or rpms to create its horsepower.

Your statement, "you only get horsepower because of Torque." NOT CORRECT.

Actually it is correct and you just said the same thing I said. Horsepower is derived from torque. more horsepower comes from more torque, or higher RPM. The thing with the RPM part is that will only make more HP if the torque is still there. At a certain point any engine starts to lose torque over a certain RPM. When it loses enough torque because it's not running efficiently anymore the horsepower will start to come down again no matter how high the RPM goes. That is why this M3 makes peak HP before it redlines at 8,400 RPM. If you simply needed just RPM peak HP would be at the redline.

[footie]

Originally Posted by mattwhite

Go do a track day in your C6 Vette with 400 ft/lbs of torque (or more?). When you get passed by a Lotus Elise with 138 ft/lbs of torque, ask yourself if torque is so important.

I don't see how your comparison has anything to do with torque. This is purely driver ability and the handling/braking of the car, the only time torque will have any bearing on the race is when you enter a straight where that extra torque can used.

Originally Posted by mattwhite

Torque is great for the street if you don't feel like downshifting. It also can mask lots of mistakes on a racetrack. In the way it is being discussed here, it does not inherently make a car faster.

Disagree completely with that opinion, torque (low end grunt) is as important as HP (high end grunt) but neither are anymore important than chassis balance, grip or braking ability. Torque helps coming out of mid to slow corners where as HP helps as you approach the end of a long straight, what happens in the corners and the braking points are IMO far more important.

[mattwhite]

Originally Posted by footie

I don't see how your comparison has anything to do with torque. This is purely driver ability and the handling/braking of the car, the only time torque will have any bearing on the race is when you enter a straight where that extra torque can used.



Disagree completely with that opinion, torque (low end grunt) is as important as HP (high end grunt) but neither are anymore important than chassis balance, grip or braking ability. Torque helps coming out of mid to slow corners where as HP helps as you approach the end of a long straight, what happens in the corners and the braking points are IMO far more important.

Of course it has something to do with torque. The Vette can be in any number of gears when exiting a corner and still pull out fine due to its large amount of torque. The Lotus needs to be in the right gear so that the revs are high enough that it will be able to exit quickly. With equal drivers, a Vette and an Elise are pretty well matched on most tracks. If torque meant so much, the Vette would absolutely destroy the Elise. But it doesn't. Why? In part because by keeping the Elise in its optimal power band, the benefits of the Vette's torque are greatly reduced.

Ask anyone who has a reasonable amount of racing and track experience and they will tell you that torque as a separate measure is nowhere near as important as horsepower.

[footie]

I won't get into a pissing contest about experience because it serves no purpose other than inflate someones ego. If you believe that HP is the most important thing with regards to racing then who am I to argue.

[J08M3]

I don't understand all the arguing here... You can't have horsepower if you don't have any torque. Really quite simple. We all agree that torque is work, and horsepower is work done in an amount of time how can anyone possibly argue that one is not important? If it wasn't for torque HP simply wouldn't exist.

[rzm3]

ok i have been thinking about this problem more and here is my answer:

Let's assume two identical M3's are side by side doing a drag race. Car A starts out in 1st gear, and Car B starts out in 2nd gear.

Obviously, Car A will accelerate faster than B, because it is in 1st gear, which means more torque at the wheels.

Now think about HP, it is the same at the wheels for both cars (because gearing does not change power (assuming 100% efficiency); it only changes torque).

Hence, this simple scenario shows that wheel torque is what matters in acceleration.

Of course, the M3 does benefit greatly from being a high-rev engine, since you do not need to shift as much because of the wider torque/power band.

[lucid]

Originally Posted by J08M3

I don't understand all the arguing here... You can't have horsepower if you don't have any torque. Really quite simple. We all agree that torque is work, and horsepower is work done in an amount of time how can anyone possibly argue that one is not important? If it wasn't for torque HP simply wouldn't exist.

Yeah, that will always be the case. There will always be people arguing one is more important than the other whereas they are related concepts via a rather simple formula really...

[mkoesel]

I always LOL at the torque vs. horsepower discussions. People talk about them as if they are at odds with each other - like one has to win or something. I mean what the fuck? Of course people only argue it like that precisely because of the car they drive anyway.

Its like asking - So, on a racetrack, which one is better: speed or acceleration? Um hello?