25 replies to this topic

[4ren]

Hi all!

Just thinking, I reached the following question mark: at the race start, obviously you look for maximum torque at the wheel, as that gives you maximum acceleration. BUT, the tires are not able to transmit all that power to the ground, as there is not enough adhesion.

Therefore, it wouldn't make sense to have the engine at its maximum torque, as you could damage the clutch and besides the traction control would reduce engine performance at the same time.

So, does anybody know at which RPM value is maximum torque obtained? And at which RPM & torque combination are the cars set up for starts? Everybody talks about max RPM and max power, but torque is not less important! How do they fine-tune the RPM for race starts?

Thanks for sharing your knowledge!;)

[Dmitriy_Guller]

Originally posted by 4ren
Everybody talks about max RPM and max power, but torque is not less important!

Max torque is less important than one of those two (max power). Anyone who claims otherwise either didn't analyze the relationship between torque, RPM, and power carefully, or lacks capacity to do so. In case you're unaware, though, this topic is very contentious, I suggest sticking to less contentious subjects like the abortion debate or Arab-Israeli conflict, and not provoke people with sentences like the one quoted.

[Ross Stonefeld]

Always use as much throttle as you can while keeping the tires under you *shrug*

Whatever rpm that is + a fudge factor to account for what you lose when you let the clutch out.

[McGuire]

Originally posted by 4ren
Hi all!

Just thinking, I reached the following question mark: at the race start, obviously you look for maximum torque at the wheel, as that gives you maximum acceleration. BUT, the tires are not able to transmit all that power to the ground, as there is not enough adhesion.

Therefore, it wouldn't make sense to have the engine at its maximum torque, as you could damage the clutch and besides the traction control would reduce engine performance at the same time.

So, does anybody know at which RPM value is maximum torque obtained? And at which RPM & torque combination are the cars set up for starts? Everybody talks about max RPM and max power, but torque is not less important! How do they fine-tune the RPM for race starts?

Thanks for sharing your knowledge!;)

Right, electronic traction & launch control systems (or a driver's educated right foot) are used to regulate the engine's torque relative to the available grip level. Some people will insist upon substituting the word "horsepower" there, but they are just talking themselves in circles. The property at work there is torque.

To answer your specific question, there is no specific answer. Depends on the grip available. However, generally the engine will be well beneath the hp and torque peaks under launch. A modern four-stroke engine in an F1 state o' tune will have its torque peak about three-quarters of the way up the operating range, roughly speaking.

[4ren]

Originally posted by Dmitriy_Guller

Max torque is less important than one of those two (max power). Anyone who claims otherwise either didn't analyze the relationship between torque, RPM, and power carefully, or lacks capacity to do so. In case you're unaware, though, this topic is very contentious, I suggest sticking to less contentious subjects like the abortion debate or Arab-Israeli conflict, and not provoke people with sentences like the one quoted.

Hi Dimitry,

I'm replying you with the only aim of clearing ideas, please take my message as a peaceful one. I expect the same from you. I am not provoking people, I just want to know a bit better the technics. I thought that was this forum about.

You know that maximum power is only obtained at high revs, and therefore, you may have lower torque at a given RPM than another engine whose maximum power is lower. The acceleration (assumed traction is not a problem, and aero effects left aside) is directly proportional to torque at wheel, which is translated into tractive effort at wheel/road contact. At this point, you may be using maximum torque, and maximum power is not relevant at all. Most important are the torque and its shape (torque vs. rpm graph). In fact, you want a constant torque value throughout all the rpm range.

[WPT]

4ren: Work out the case for a much less powerful engine first. This may give you the insight to solve your question. For instance, for a standing, slip the clutch start choose a gear ratio tall enough so the drive tires will not break traction . Now, with the engine at max torque peak rpm and the throttle wide open (one controls the engine rpm by clutch engagement, keeping it at max torque rpm). This results in a constant acceleration launch till the clutch is fully engaged. WPT

[Dmitriy_Guller]

Originally posted by 4ren

You know that maximum power is only obtained at high revs, and therefore, you may have lower torque at a given RPM than another engine whose maximum power is lower. The acceleration (assumed traction is not a problem, and aero effects left aside) is directly proportional to torque at wheel, which is translated into tractive effort at wheel/road contact. At this point, you may be using maximum torque, and maximum power is not relevant at all. Most important are the torque and its shape (torque vs. rpm graph). In fact, you want a constant torque value throughout all the rpm range.

The fallacy is that you assume the same gearing for both cars, and therefore the same RPM at a given speed in 1st gear. But why WOULD you want the more powerful car to be handicapped with the same gearing as less powerful car? That's like removing the whole advantage of having an engine with higher horsepower. In the same vein I can jump higher than Michael Jordan, if I make Michael Jordan wear lead boots. The moral of the story is that more power means more potential for torque multiplication.

For example, why is a car A with engine making 100 lb-ft of torque at 3,000 RPM accelerating worse than the car B with engine making 75-lb-ft of torque at 6,000 RPM, with both cars at the same speed? Because car B must necesserily have twice the gear reduction of car A to be at the same speed, and therefore the wheels of the second car actually experience 50% more torque, the torque that counts (and, amazingly enough, it also makes exactly 50% more horsepower at that speed than car A). Of course, if you gear both cars the same, then car B would probably be making even less than 75 lb-ft of torque at 3,000 RPM, and of course it will lose to car A making 100 lb-ft of torque at 3,000 RPM at the same speed. However, what you're doing is lugging the second car to make the first car look good, and that is the heart of the fallacy of the "torque wins races" herd.

[voice_of_reason]

The subject of getting an F1 car off the line is very different from the usual (tedious and depressing) circular argument about power vs torque.

The crucial difference is that at zero car speed there needs to be either or both of clutch slip or wheel slip to transmit the engine torque (if there was none of either, the engine would be at zero rpm too!).

Only once the phase of the start is passed during which there is slip across the clutch do the usual power/torque/gear ratio discussions become relevant.

max torque of a current F1 engine is at about 14500 RPM
max power of a current F1 engine is at about 18000 RPM

[WPT]

Start with the case of a much less powerful vehicle, so we are power limited in 1st gear. Assume we want a smokeless launch and have a really great clutch. Draw a graph of horsepower vs road speed for 1st gear. Now, a constant torque power curve (a slip the clutch while holding engine RPM constant type launch) on such a graph is a straight line running through the origin, with the greater the slope the greater the torque. Draw the steepest line running through the origin just tangent to the 1st gear power curve. It will be tangent at the engine's max torque RPM. Drop a vertical line from the tangent point to the road speed axis, draw a horizontal line from the tangent point to the HP axis, and now draw a straight line connecting these two axis intercept points. During the launch the straight line running through the origin is the power delivered to the drive wheels, the horizontal line is the power delivered to the clutch, and the line connecting the two axis intercepts is the power trying to melt the clutch. This is the best you can do with the given conditions.
Guller is right that you could do better in the above example by regearing the vehicle. But, for the case where you are right on the edge of breaking drive wheel traction, you might want to still gear for the engine's torque peak. Failure to control engine RPM should not result in smoking the tires, while if geared for the engine's power peak could result in a lot of smoke. WPT

[Dmitriy_Guller]

Originally posted by voice_of_reason
The subject of getting an F1 car off the line is very different from the usual (tedious and depressing) circular argument about power vs torque.

The crucial difference is that at zero car speed there needs to be either or both of clutch slip or wheel slip to transmit the engine torque (if there was none of either, the engine would be at zero rpm too!).

Only once the phase of the start is passed during which there is slip across the clutch do the usual power/torque/gear ratio discussions become relevant.

You're completely right, I myself was addressing the off-tangent comment by the original poster rather than the main question. Any torque/power discussion assumes lack of slip, which is not applicable at launch or low speeds. Also, there is nothing circular about arguments itself, it's the inability of the torque side to comprehend them that sends the discussion going round and round.

[NTSOS]

Just out of curiosity......the name: Dmitriy_Guller......is there a first or last name here and what might be the country of origin......I'm simply fascinated by your thought process.

John

[Paul Ranson]

There was a comment in Autosport this week about GP2 drivers stalling at the start because they're holding the engine on the rev limiter when they drop the clutch. I thought this thread was about that... (Which seemed quite interesting, as well as offering an insight into the young racing driver mentality.)

Paul

[NTSOS]

Hey Paul,

Check out my little adventure........one day when I finish my car and I'm going to terrorize your English countrysides, and hirer you as a competent race car driver.....pub to pub.

http://home.pacbell....lair/index.html

John

[McGuire]

Originally posted by NTSOS

I'm simply fascinated by your thought process.

John

[Ross Stonefeld]

Originally posted by Paul Ranson
(Which seemed quite interesting, as well as offering an insight into the young racing driver mentality.)

Quite depressing wasnt it. Its not enough that the drivers should be a bit more clever by what is effectively Formula 2 level, but you'd think someone on the team would say "10,000rpm isnt going to get you the start you're looking for..."

[J. Edlund]

For a F1 car the start is all about traction since the engine is powerful enough to overcome the grip at speeds below 150 km/h or so. Only above that speed the acceleration is determined by the output of the engine according to P = F*v where F is the force that pushes the car forward (F = F_acceleration+F_drag+F_rollresistance), v is the velocity of the car and P is the power output at the rear axle (in the case of a F1 that is about 95% of the engine output). Since the velocity will depend on engine speed and gearing, and that the force F will depend on gearing and power we can relate the acceleration to the torque output of the engine. It's important to understand this relation between torque and power if one wants to understand how the engine affects the acceleration of the car which can't depend on power or torque alone. In the case with low speed torque in a F1 it's mainly there to provide driveability, not performance of the car directly.

Most current F1 engines, and for the last few decades are designed so that there is 2500-3000 rpm between max torque and max power. Then, the engine should be capable of operating at speeds 500-1000 rpm above maximum power speed. If the engine can be used at speeds more than 1000 rpm over max power speed the max power speed and max torque speed should be increased for a even greater output. For the current F1 engines this means that if maximum power is at 18,000 rpm, the engine should be capable of 18,500-19,000 rpm and that max torque should be found at 15,000-15,500 rpm.

[McGuire]

Originally posted by J. Edlund
It's important to understand this relation between torque and power if one wants to understand how the engine affects the acceleration of the car which can't depend on power or torque alone. In the case with low speed torque in a F1 it's mainly there to provide driveability, not performance of the car directly.

I really couldn't disagree more. When you say torque relates to driveability but not to performance, I don't see how that can have any meaning. At any point, the vehicle's rate of acceleration will absolutely be determined by the applied torque at that point, period. Power is simply another way of doing the math...of stating the torque available at a particular rpm, or angular force times angular velocity if you prefer. The relationship between power and torque is absolutely set in stone: In the original Watt system, HP = torque x rpm/5252. Horsepower can only exist in the presence of torque in that measure, and vice versa. These are simply two different ways of measuring the force output of the same machine: one in force per instant or unit of shaft rotation; the other in force per unit of time.

In tightly regulated racing series, F1 being one, where the engines all have similar max horsepower, and where the cars all have approximately the same number of gears in the box, weigh about the same and have about the same frontal area, the advantage goes to the engine with the superior torque curve. This is really what racing engine development is all about. On most any road course, the engine spends only some fraction of the lap distance at max hp rpm. Everywhere else, the torque curve is crucial. All else being equal, it determines how long the engine will take to accelerate to max hp rpm.

[wegmann]

Not to be a party-pooper and no offense to anyone in particular, but is every thread that mentions either power or torque going to degenerate from now on?

[J. Edlund]

Originally posted by McGuire


I really couldn't disagree more. When you say torque relates to driveability but not to performance, I don't see how that can have any meaning. At any point, the vehicle's rate of acceleration will absolutely be determined by the applied torque at that point, period. Power is simply another way of doing the math...of stating the torque available at a particular rpm, or angular force times angular velocity if you prefer. The relationship between power and torque is absolutely set in stone: In the original Watt system, HP = torque x rpm/5252. Horsepower can only exist in the presence of torque in that measure, and vice versa. These are simply two different ways of measuring the force output of the same machine: one in force per instant or unit of shaft rotation; the other in force per unit of time.

In tightly regulated racing series, F1 being one, where the engines all have similar max horsepower, and where the cars all have approximately the same number of gears in the box, weigh about the same and have about the same frontal area, the advantage goes to the engine with the superior torque curve. This is really what racing engine development is all about. On most any road course, the engine spends only some fraction of the lap distance at max hp rpm. Everywhere else, the torque curve is crucial. All else being equal, it determines how long the engine will take to accelerate to max hp rpm.

What accelerates a car is the power of the engine, without power you won't go anywhere. To have power you must have torque but if you have twice the angular velocity or twice the torque isn't important.

The acceleration of the car will be defined by the power output of the engine according to

P = Fv

and if losses aren't included

F = ma
P = mav

Using torque applied to the rear wheels is just another way of calculating the force F.

As for the F1 engine it has been stated that

"F1-Engines must be developed for maximum power
output. Highest possible torque is essential, but is mainly
important for driveability reasons. High torque output at
100% throttle position allows a more accurate tuning and
controlling of the torque level at different opening angles
– the engine can be set up less sensitive on various
pedal positions. This helps for improved drivability of the
engine."

If one analyze how a F1 engine is used during a race one can come to the conclusion above. Basicly F1 cars are traction limited at speeds below about 150 km/h, and when you are going at speeds higher than 150 km/h the engine will operate at high speed, typically within the 2000-3000 rpm range where the engine is designed for maximum power output.

With a F1 engine, the most powerful engine doesn't have to be the one that produces the most torque, the Asiatech from the 2000 season did for example produce more torque than the winning Ferrari Tipo 049... the thing is that the Ferrari engine produced its somewhat less torque at a higher engine speed which gave it a 50-60 hp advantage.

[alpa]

Power (or torque) at low RPM is useful for driveability.
A lot of modern engines pretend to have a flat torque curve from a very low RPM, but in practice combustion instability at this RPM and insufficient crank inertia makes them undriveable below a higher limit.
Of course continious valve timing/lift of F1 engines avoids this problem, but other issues like low load injection precision, light flywheel (if any present) or injector placement (made for high power) remain.
To avoid tire burning the usual method is to lower the torque in some predefined risky conditions.

[voice_of_reason]

First a reminder:

The thread is supposed to be about standing starts, not the usual power / torque drivel-fest. See posts 8 and 9 for to explain why this is important.

Now some facts:

All current F1 engines have RPM max 18700 +/- 300 RPM
All current F1 engines have idle speed 4000 +/- 500 RPM
All current F1 cars have 6 or 7 speed gearboxes.
All the cars have the same startline mass within 5%, usually within 3%, even accounting for different refuelling strategies.

Now some observations:

F1 engine performance development is of course oriented towards finding power, but not maximum power at any cost - it is laptime that counts, or elapsed time to finish the race, or (hopefully not a surprise to anyone) race results! The corollary of this is that power curve shape (or torque curve if you are that way inclined) is important, and for equal max power, a broader power curve is faster than a narrow one etc etc...

There are at least 2 standing starts per race (one of the start and at least one pit stop) each of which represents a possibility of overtaking. The similarities between the cars (see above) are such that they all have very similar 1st gear ratios and performance differences at starts come from managing the effects described elegantly by WPT in his post.

After the clutch slip phase of the start, the traction control system is allowed (in the rules) to have authority over the engine torque. The car needs to be moving fast enough at the transition point from clutch slip to TC that if the wheels are spinning and the TC system reduces engine torque to reduce the wheelspin, the maximum available engine torque at the RPM corresponding to the car speed with optimum wheel slip is sufficient to accelerate the car. If not the RPM falls and the engine stalls. The moral of the story is that F1 engines need to drive cleanly from engine speed 10 000 RPM below the torque peak(!). It is not obvious that they are traction limited with no clutch slip at this RPM approx equal to their idle speed, so the power (or torque if you prefer) available at low RPM is truly important in the search for the best compromise of engine performance for best car performance!

[McGuire]

Originally posted by voice_of_reason
The moral of the story is that F1 engines need to drive cleanly from engine speed 10 000 RPM below the torque peak(!). It is not obvious that they are traction limited with no clutch slip at this RPM approx equal to their idle speed, so the power (or torque if you prefer) available at low RPM is truly important in the search for the best compromise of engine performance for best car performance!

Spot on, can't see how anyone could argue with that.

Of course I am probably being overly optimistic...

[J. Edlund]

Originally posted by voice_of_reason
After the clutch slip phase of the start, the traction control system is allowed (in the rules) to have authority over the engine torque. The car needs to be moving fast enough at the transition point from clutch slip to TC that if the wheels are spinning and the TC system reduces engine torque to reduce the wheelspin, the maximum available engine torque at the RPM corresponding to the car speed with optimum wheel slip is sufficient to accelerate the car. If not the RPM falls and the engine stalls. The moral of the story is that F1 engines need to drive cleanly from engine speed 10 000 RPM below the torque peak(!). It is not obvious that they are traction limited with no clutch slip at this RPM approx equal to their idle speed, so the power (or torque if you prefer) available at low RPM is truly important in the search for the best compromise of engine performance for best car performance!

When it comes to starts they are traction limited. Power output of the engine does therefore not affect the acceleration from standstill.

A F1 car have traction problems at the start due to allowed rear tire width have been reduced, which have moved the centre of gravity more forward. Add to that the low centre of gravity and the result is a low weight transfer at the start. Also, at standstill, and at low speeds there will be no or little downforce availible. The relative cold tires at the start also reduce the traction somewhat.

Even at idle speed (4000 rpm) the power availible from an F1 engine should be above 100 hp, and probably around 200 hp at 6000 rpm. But due to the clutch slipping higher engine speeds, where more power is availible can be used. In the start the clutch is infact heated to temperatures around 1000 degC due to slipping.
With the gearing used for first gear a car must probably use clutch slip up to at least speeds of 25 km/h or so (otherwise the engine speed would drop below 4000 rpm), at that speed the engine can create about 10000 N at the rear wheels which should be more than the tires can handle during these low downforce conditions.

[redline]

Hi All,

Don't really want to add fuel to the fire, but i remember an article a few years ago about traction control. It was called "32-bit Throttle Cable" and talked about maximizing acceleration off the line by modulating torque...

I will try and find it and post any relevant sections.

Cheers,

redline

[redline]

Found it.... Its rather long, so i'll only post some extracts...

~~~~~~~~~~~~~~~~~~~~~~~~

"In the "good old days", engine throttles were controlled via a cable and linkages, connected to the accelerator pedal under the driver's right foot. This mechanism modulated the air flowing into the engine, and hence the torque produced by the engine. The relationship between the driver's foot and the torque was complex and highly non-linear; in particular, it depended on the RPM of the engine. If the driver maintained a constant throttle opening while accelerating out of a corner, as the RPM rose the torque delivered to the rear wheels changed according to the torque curve of the engine. If the torque curve had peaks and troughs in it, and the driver was trying to balance the car with torque at the rear tires, the balance would change and upset the car's trajectory, unless he altered the throttle position. Engine designers tried to produce smooth torque curves, at a cost to maximum power, while the chassis designer tried to design a progressive throttle linkage such that the gain (ratio between pedal and throttles) was lower at small throttle openings, and higher when the driver wanted maximum power and pushed the pedal to the metal."

"It is the driver's use of the throttle that causes him to spin the wheels or power oversteer, but the engine control system does not use the throttles to control the torque, unless the driver persists in calling for too much for a significant length of time. Instead, fuel injection and ignition are used for instant modulation, being capable of controlling the torque even as the car rides bumps that may cause the wheels to break traction - hence the awful sound they make as traction control cuts cylinders in turn. Misfiring is pretty destructive to a racing engine, as one or two crankshafts left in the road have testified, and preventing too much slip in the first place is a priority. In control system terms, the driver makes an open-loop demand of torque, and the fuel injection/ignition system makes closed-loop adjustments to wheel slip. The driver may or may not make a change to his input, based on feedback of the sound the engine is making. If not, the throttles may be altered by the system to reduce misfiring. If the driver were able to make a better open-loop, initial input, the misfiring could be minimized.There are a number of options, the four main ones being: - throttle pedal as an engine torque demand; - throttle pedal as a rear wheel torque demand; - throttle pedal as a speed demand; - throttle pedal as a slip ratio command. As we have seen, modulating the airflow into the engine is not the ideal way of controlling torque. If the fully mapped characteristics of the engine are known, taking into account RPM, throttle opening, air density (including ram effects), engine temperature, fuel temperature etc., the throttles can be controlled by the engine computer to deliver torque proportional to accelerator pedal position. If the engine cannot deliver as much as the driver is demanding (due for instance to too low RPM) it just goes to maximum throttle. This is the most progressive engine, as it takes out all the dips and bumps in the torque curve, and means that the engine designer can tune for maximum power. The second option is a variation on this, with the gear ratio being used to modify the throttle setting so that the rear wheel torque is controlled directly. With the ratio selection now also under full computer control, the optimum ratio for acceleration can be selected instead of a higher than optimum ratio, which drivers often use to reduce the response of the engine to throttle changes and thus facilitate control of the car. The latter two approaches give the driver a smooth change in rear wheel torque as he moves the accelerator, greatly facilitating control of the car coming out of a corner. However the maximum torque that the rear wheels will accept without wheel spin or oversteer, changes as both the cornering load reduces and as the speed and aerodynamic load increases. Wheel spin or flick-oversteer will also be induced over bumps as constant torque is applied to the driven wheels. The third option gets round this problem by maintaining a constant wheel speed (and hence car speed) selected by the accelerator pedal position, with the car accelerating up to the selected speed at a rate proportional to the error between the actual speed and the demanded speed, the rate depending on the torque delivered. Full pedal gives full power, unless maximum speed is limited, as in the pit lane. In a corner, pushing on the accelerator pedal from a constant speed setting would increase power to increase speed, but would filter out engine characteristics and be reasonably benign over bumps. Drivers would have to adapt to this rather different approach. Better still would be the fourth option, which combines the best of the others."

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A bit off-topic, but its interesting that the author continuously refers to modulating torque.
Comments???

Redline

[desmo]

We had a thread here some time back reacting to the same article:

http://forums.atlasf...&threadid=30304

It's archived, so posts cannot be added to it. I'd try to merge this thread to it but I think the continuity would be weird.