Newton Units Vs Newton Meters

[Street Tuner]

It comes back to the education of the operators, and how they then pass this information on to the end users. All you need to do is read some threads here to glean that some folks think their 300rwkw @ 5500rpm T is making over 1000Nm at the crank when as we both know nothing could be further from the truth.

[Guest]

Try a tuner that bothers to set your car up on the dyno properly by entering either the kmh/rpm relationship in the gear the car is dynoed in, or (even better) uses the Dyno Dynamics inductive rpm pickup. Proper graphing of Nm with a Dyno Dynamics is quite easy, and wont give the bogus 1000Nm+ at the wheels figures that other dynos do

<{POST_SNAPBACK}>

The conversion from Newtons to Newton Metres is such:

Multiply the Newtons by 0.1085 and that will give you the Torque in NM.

The figure of 0.1085 is the roller radius in metres, and this is what is used

to calculate the Tractive Effort on DD Dyno's that have 217mm diameter rollers (99% of them).

So for example, if you have 5500 newtons, this will be 596.75 Newton Metres at the rollers.

If the dyno operator chooses to insert the correct kmh/rpm realationship, this 596.75nm figure would be reduced by the ratio of Engine Rpm to Roller Rpm to make the figure more user friendly, ie. you expect a torque loss at the wheels just like there is power loss, whereas in most cases there is a torque multiplication due

to gearing.

So if you had a vehicle that was making 256rwkw @ 100kph, this would be making 1000nm at the rollers (9216 newtons), is this bogus?

If you were still making 1000nm @ 180kph, you would be then making 460rwkw, is this still bogus, a soft tune on a GenT1000 easily does that.

If the correct kph/rpm was applied to the example of 1000nm at the rollers, it would be displayed as 769nm on a vehicle with 3.9 diff gears, done in a 1:1 gear ratio in the trans.

<{POST_SNAPBACK}>

take what todd has to say as gospel he builds some of the best dyno's in aust.

[Mustang D]

It comes back to the education of the operators, and how they then pass this information on to the end users. All you need to do is read some threads here to glean that some folks think their 300rwkw @ 5500rpm T is making over 1000Nm at the crank when as we both know nothing could be further from the truth.

<{POST_SNAPBACK}>

Totally agree Tuna, there is a huge amount of "assumed" crap relating to

dyno readings. If the guy using the dyno doesn't understand how it works, how is he supposed to rely that to the customer.

that's why Tractive Effort is displayed as most people don't know what it is so normally it is just accepted. (It's also a big number which people tend to like, and it takes no operator education)

The main thing to look for on a graph that shows either Torque, Tractive Effort, Motive Force or Derived Torque is to gauge the minimum and maximum point and see how much difference there is between them, this shows how much torque you have across the entire rev range.

[gogo]

Try a tuner that bothers to set your car up on the dyno properly by entering either the kmh/rpm relationship in the gear the car is dynoed in, or (even better) uses the Dyno Dynamics inductive rpm pickup. Proper graphing of Nm with a Dyno Dynamics is quite easy, and wont give the bogus 1000Nm+ at the wheels figures that other dynos do

<{POST_SNAPBACK}>

The conversion from Newtons to Newton Metres is such:

Multiply the Newtons by 0.1085 and that will give you the Torque in NM.

The figure of 0.1085 is the roller radius in metres, and this is what is used

to calculate the Tractive Effort on DD Dyno's that have 217mm diameter rollers (99% of them).

So for example, if you have 5500 newtons, this will be 596.75 Newton Metres at the rollers.

If the dyno operator chooses to insert the correct kmh/rpm realationship, this 596.75nm figure would be reduced by the ratio of Engine Rpm to Roller Rpm to make the figure more user friendly, ie. you expect a torque loss at the wheels just like there is power loss, whereas in most cases there is a torque multiplication due

to gearing.

So if you had a vehicle that was making 256rwkw @ 100kph, this would be making 1000nm at the rollers (9216 newtons), is this bogus?

If you were still making 1000nm @ 180kph, you would be then making 460rwkw, is this still bogus, a soft tune on a GenT1000 easily does that.

If the correct kph/rpm was applied to the example of 1000nm at the rollers, it would be displayed as 769nm on a vehicle with 3.9 diff gears, done in a 1:1 gear ratio in the trans.

<{POST_SNAPBACK}>

take what todd has to say as gospel he builds some of the best dyno's in aust.

<{POST_SNAPBACK}>

Hate to have to disagree a little bit...

What you are saying is absolutely correct, for torque in the dyno - this is different to torque produced by the car... As you have said, torque and force, unlike power are impacted by gearing and wheel diameters.

Surely since your CAR is producing the work, conversion of Newtons force at the wheels should be based on the CAR information, not the dyno. Since the gearing and wheel diameters are different on the car relative to the dyno, the calculation of car 'engine' torque using rolling diameters of the dyno will be erroneous (although as it happens it is close... ).

Similar process though and you should get the right anwser.

Take motive force in N, and multiply by the wheel rolling radius (in metres).

To calculate 'engine torque' at the wheels, divide the result by your diff ratio, and then divide again by gear ratio (usually the dyno result will be based on the 1:1 gear - if so then this make no difference). End result is what I call engine torque at the wheels.

e.g. Assuming a rolling diameter of 320mm or 0.32m for 18" wheels

A motive force of 7100N in 4th (1:1 gear ratio so ignore gears), and a mk 1 manual diff of 3.45

7100 * .32 = 2272Nm at wheels actual

2272 / 3.45 = 659Nm "engine torque at the wheels"

or approximately 659 * 1.22 = 803Nm at the crank!

Cheers,

Ben.

[Guest]

Try a tuner that bothers to set your car up on the dyno properly by entering either the kmh/rpm relationship in the gear the car is dynoed in, or (even better) uses the Dyno Dynamics inductive rpm pickup. Proper graphing of Nm with a Dyno Dynamics is quite easy, and wont give the bogus 1000Nm+ at the wheels figures that other dynos do

<{POST_SNAPBACK}>

The conversion from Newtons to Newton Metres is such:

Multiply the Newtons by 0.1085 and that will give you the Torque in NM.

The figure of 0.1085 is the roller radius in metres, and this is what is used

to calculate the Tractive Effort on DD Dyno's that have 217mm diameter rollers (99% of them).

So for example, if you have 5500 newtons, this will be 596.75 Newton Metres at the rollers.

If the dyno operator chooses to insert the correct kmh/rpm realationship, this 596.75nm figure would be reduced by the ratio of Engine Rpm to Roller Rpm to make the figure more user friendly, ie. you expect a torque loss at the wheels just like there is power loss, whereas in most cases there is a torque multiplication due

to gearing.

So if you had a vehicle that was making 256rwkw @ 100kph, this would be making 1000nm at the rollers (9216 newtons), is this bogus?

If you were still making 1000nm @ 180kph, you would be then making 460rwkw, is this still bogus, a soft tune on a GenT1000 easily does that.

If the correct kph/rpm was applied to the example of 1000nm at the rollers, it would be displayed as 769nm on a vehicle with 3.9 diff gears, done in a 1:1 gear ratio in the trans.

<{POST_SNAPBACK}>

take what todd has to say as gospel he builds some of the best dyno's in aust.

<{POST_SNAPBACK}>

Hate to have to disagree a little bit...

What you are saying is absolutely correct, for torque in the dyno - this is different to torque produced by the car... As you have said, torque and force, unlike power are impacted by gearing and wheel diameters.

Surely since your CAR is producing the work, conversion of Newtons force at the wheels should be based on the CAR information, not the dyno. Since the gearing and wheel diameters are different on the car relative to the dyno, the calculation of car 'engine' torque using rolling diameters of the dyno will be erroneous (although as it happens it is close... ).

Similar process though and you should get the right anwser.

Take motive force in N, and multiply by the wheel rolling radius (in metres).

To calculate 'engine torque' at the wheels, divide the result by your diff ratio, and then divide again by gear ratio (usually the dyno result will be based on the 1:1 gear - if so then this make no difference). End result is what I call engine torque at the wheels.

e.g. Assuming a rolling diameter of 320mm or 0.32m for 18" wheels

A motive force of 7100N in 4th (1:1 gear ratio so ignore gears), and a mk 1 manual diff of 3.45

7100 * .32 = 2272Nm at wheels actual

2272 / 3.45 = 659Nm "engine torque at the wheels"

or approximately 659 * 1.22 = 803Nm at the crank!

Cheers,

Ben.

<{POST_SNAPBACK}>

ben as an engineer you will apreciate the fact we were talking about chassis dyno's and what todd mentioned related to rwnm/rwkw

fact: you don't see rwkw calculators on engine dyno's because its not fact not acurate period!

fact: any operator that says fw power or torque can be measured acurately from the wheels does not know what he is doing or speeks with forked tongue!

fact: any dyno inc d/d, dts & etc that advertises engine power or torque from rear wheel calculations dont deal with facts!

hope this clears up why I agreed with todd on this ocation.

[gogo]

ben as an engineer you will apreciate the fact we were talking about chassis dyno's and what todd mentioned related to rwnm/rwkw

fact: you don't see rwkw calculators on engine dyno's because its not fact not acurate period!

fact: any operator that says fw power or torque can be measured acurately from the wheels does not know what he is doing or speeks with forked tongue!

fact: any dyno inc d/d, dts & etc that advertises engine power or torque from rear wheel calculations dont deal with facts!

hope this clears up why I agreed with todd on this ocation.

<{POST_SNAPBACK}>

Nick, I agree with all your points above - when measuring from wheels measurement is only as accurate as the instrument, the operator, and for the point being measured - ie the wheels.

Hence approximate fwkw...

However back to the original point and that is that the calculation set out for torque using dyno roller diameters is NOT correct for the car as I understand it - it is correct for the dyno. I do not beleive these are the same thing at all.

You can measure the speed and tractive effort/motive force or a derivitive in the Dyno, but any calculation of torque for the car must involve wheel radius etc. Since we generally talk about torque at the engine, it makes more sense to my mind to quote my "engine torque at the wheels" figure, which is real and measured, just with the diff ratio (and gear ratio) taken into account to 'normalise" it.

It is not reasonable to discuss measured torque at the wheels in the same way as power, because unlike power which should remain the same (instrument error and change in gear efficiencies asside) regardless of wheel size, diff, or gear, every one of these will change the torque measured from the wheels because it changes the gearing... Hence the 'normalising' to make it similarly comparable to discussion of rwkw.

Bottom line through is if you want to calculate torque and have an answer that is meanful in relation to the car, you need to use the details of the car to calculate it...

my 2c!

Cheers

Ben.

[R.E.Z.]

jsut my 2cents worth, fw torque will always be less than rw torque on the dyno.

[Draytox]

To convert newtons to newton metres simply multiply the newtons by 0.0833333333.

eg: 7100N * 0.0833333333 = 665.0598Nm