Torque? WRC cars

[kpt4321]

Torque is what gets the car moving. I is a rotational force.

Yes and no. Torque avaliable AT THE WHEELS is what gets the car moving. Horespower is basically a number that represents potential wheel torque, once gear ratio is factored in.

Torque may be the force, but when you move a car from one place to another, or you accelerate it to a certain speed, work must be done. Horsepower is work done over time, or the rate at which the motor can do work. More power means it takes a shorter amount of time to do the same work.

Dyno's cannot measure HP. They record torque and convert that to HP.

This is definately not true. Different kinds of dynos have different measurement methods, but for example a dynojet is perfectly capable of measuring power. By measuring the time differential between rotational velocities, the dyno can calculate how much energy was expended in a given time period, which is horsepower. Of course, that's also measuring acceleration, which is force, which is torque (but AT THE WHEELS).

The torque number you see on a dyno chart is the torque at the crank, which is the same thing as the torque at the wheels with a 1.00:1 gear ratio. The torque number on a dyno chart is NOT NOT NOT the torque that is avaliable at the wheels, which is by far the only thing that matters.

A Dyno Dynamics dyno measures the "tractive force" avaliable at the tire, which can be translated to wheel torque when a few other factors are known. From there you can solve for horsepower, and from there you can get the crank torque number shown on the dyno chart.

 

[greyforestgst]

tons of correct information

couldnt have put it any better

i wish i could explain the torque/hp relationship to non gearheads, but ive given up trying.

 

[BGRIPTP]

Does anyone know what kind of compression ratios rally cars run? I know they sure as hell don't run pump gas, so they can get away with higher compression/boost, which can only help torque.

I always thought Rally cars where ran on pump gas or something like that?

Ben

 

[CanadianTalon]

Dyno's cannot measure HP.

Sorry man, but that's incorrect. I know for a fact dynojets measure HP, and then calculate torque. If you ever make a pull on a dynojet where you don't have the RPM hook up connected, the dyno measures horsepower produced, but cannot show or measure torque because it does not have the engine RPM's to cross reference it to.

 

[ItsStockOfficer]

The torque number you see on a dyno chart is the torque at the crank, which is the same thing as the torque at the wheels with a 1.00:1 gear ratio. The torque number on a dyno chart is NOT NOT NOT the torque that is avaliable at the wheels, which is by far the only thing that matters.

It's definitely torque at the crank minus drivtrain loss, or it wouldn't cross the HP curve at 5252....

 

[ItsStockOfficer]

I was going by the GM rule, that torque is useful under 45mph. I figured that 45mph is the majority of mph a 100-130hp car would trap at, so with that said the car with the most torque would get down the begining of the track faster and run out of steam. If Im wrong Im wrong I was just going on pure numbers, I really dont care....
Andrew

The 45 MPH rule is comeplete BS. HP/Tq curves have nothing to do with road speed. So is your "If Im wrong Im wrong" attitude because your preching mis-information. DSM'ers are dumb enough on average as it is.

 

[sweet97]

Man I could very well be mistaken about how a dyno does it's measurements. I have thought for at least a couple years that they measure torque and convert that to HP. Well I may have learned something today but now there is a disagreement and someone who knows without a doubt needs to help out. Don't get me wrong as I am the last that wants to argue about something. It's just that there is doubt and.....Mark

 

[kpt4321]

It's definitely torque at the crank minus drivtrain loss, or it wouldn't cross the HP curve at 5252....

As long as the car is connected to the drivetrain and in gear, power at the crank and power at the wheels is the same thing. I am sure someone is going to argue about how you lose power through the drivetrain, but think about it. Yes, the drivetrain requires power and therefore is a source of loss, but since there is no point of slippage in the system the power is the same everywhere.

That is not the same for torque, because torque can be multiplied by gearing.

As such, it's exactly what I said. The number on a dyno is the torque at the wheels with a 1.00:1 gear ratio (which our cars do not have), or the torque at the crank, which is the same thing.

 

[kpt4321]

Man I could very well be mistaken about how a dyno does it's measurements. I have thought for at least a couple years that they measure torque and convert that to HP. Well I may have learned something today but now there is a disagreement and someone who knows without a doubt needs to help out. Don't get me wrong as I am the last that wants to argue about something. It's just that there is doubt and...

This can be a very difficult discussion, and a very difficult concept to grasp.

Also, keep in mind that horsepower and torque are not as far unique as people sometimes make them out to be. Horsepower is just torque, with reference to engine speed and some constants. Because of this close relationship, anything that measures horsepower is essentially measuring *A* torque, or the effect of a torque, and therefore is able to measure that torque.

However, you'll notice that I said A torque; what I mean by that is, while it is measuring a force, it's not the same force that you see on a dyno chart on the torque line.

Let's talk about why you can't measure torque on the dyno. Torque is effected by gear ratios, and the force it creates at the edge of the tire is dependant on the overall distance from the center of the axle to the tire's contact patch. Now, in order to calculate horsepower from torque alone (using the engine speed ratio of 5252), we need to know torque at the crank, or as I have said torque with a 1.00:1 gear ratio. The reason for this is that without any other references (such as velocity), if we use a torque value that is ot at the crank / through a 1.00:1 reduction, the horsepower numbers will rise or fall, which is incorrect. Horsepower everywhere in the system is the same, regardless of gear ratio. The same is not true for torque.

Ok, so in order to use torque, we need to solve for the torque at the crank. In basic terms, no dyno does this, and I highly doubt many of them can. The dyno doesn't know your car's gear ratios, nor does it know what gear you are dynoing in. In addition, the dyno does not know what the radius of the axle to the contact patch is, because you would have to measure it, and it's also going to change as you change the load on the tire.

Yeah, so measuring torque is almost useless, by itself.

So, what a dynojet does, is measure horsepower through measuring the work done in tiny time increments. This is directly related to force avaliable at the wheel, or at the tire contact patch to be more specific, and velocity.

Other dynos, like the Dyno Dynamics dyno, have more complex ways of measurement that are harder to understand. A DD dyno measures "tractive force," through a strain gauge that is mounted on the dyno which flexes when the rollers and brakes move due to the brake pushing back against the force exerted by the car. Then you get all kinds of funky math, some of which I do not fully understand, to get horsepower.

 

[ItsStockOfficer]

As long as the car is connected to the drivetrain and in gear, power at the crank and power at the wheels is the same thing. I am sure someone is going to argue about how you lose power through the drivetrain, but think about it. Yes, the drivetrain requires power and therefore is a source of loss, but since there is no point of slippage in the system the power is the same everywhere.

That is not the same for torque, because torque can be multiplied by gearing.

As such, it's exactly what I said. The number on a dyno is the torque at the wheels with a 1.00:1 gear ratio (which our cars do not have), or the torque at the crank, which is the same thing.

Sure, thats obviously true, but when most people, myself included, refer to crank torque or crank HP, we are refering to them as mesaured on an engine dyno, not a chassis dyno, and both will be higher. You're just playing with the nomenclature. I was never refering to measuring crank HP at the crank while doing a chassis dyno, which is ####ing silly.

 

[igs]

Torque is measured by force across distance.

That's work. Torque is rotational force.

 

[igs]

Sorry man, but that's incorrect. I know for a fact dynojets measure HP, and then calculate torque.

You cannot measure HP, PERIOD! HP can only be CALCULATED. HP IS a calculation.

 

[kpt4321]

You cannot measure HP, PERIOD! HP can only be CALCULATED. HP IS a calculation.

This is a very good, and true, point.

What I mean when I say they "measure" horsepower is that the torque is calculated after the horsepower, and not vice-versa.

Excellent point though!