convert tractive effort to torque

[itbmils]

OK boys and girls - I have a math quiz for you all

I have just had a power run done on my R32 GTR and have a reading for tractive effort, and I want to convert that to an approximate torque figure (Nm)

from the following web site

http://www.webster-inst.com/techinfo/equat...eqnfr/eqn17.htm

we see that the tractive effort is obtained by multiplying the torque by the total ratio of power the train and dividing this sum by the rolling radius of the driving tyres. (easy)

TE = (T * R * 1000) / r

where

T= Motor torque in kg/millimetres (the number I wish to calculate)

R = Overall gear reduction including both axle and transmission (NFI)

r = Rolling radius of loaded driving tyre in millimetres (measure)

So in my example, I have a measured TE of 6300 newtons – based on the output of the power run on a 4 wheel dyno.

BUT

I do not know R or r

Any idea what the overall gear reduction is in an R32 GTR in 4th gear.

Any idea how a can obtain an accurate measure of the rolling radius of my wheel. I have 235/45/17s (with a tape measure I get 2070mm ?)

come on guys – I'm sure this must have been covered before

[Oosh]

4th gear is 1:1, and the diff is 4.11:1 (i believe) so R = 4.11?

But using that formula and your figures ends up with 3173Nm! :headspin:

[itbmils]

Hmm

I don't think she's that strong

any other input - have we missed something ?

what's a std GTR deliver in terms of torque anyway ?

[itbmils]

OK

according to http://www.jbskyline.net/R32/GTR/Specs/

final drive is 4.111 and std torque is 360Nm @ 4400rpm

If I run the numbers I still get 3172Nm (way too much) - is this a bogus formula or what ?

[itbmils]

found another formula

T = (9.545 * Power in watts) / RPM

so I get

T = ( 9.545 * (291.7awkw * 1000) / 6500RPM = 428Nm

A more realistic result - but I still have ZERO idea is this is even in the ball park.

A std GenIII V8 reports 475Nm with 255kw and the New Gen4 GTO reports 530Nm with 297kw (these will be @ the engine numbers tho )

[Scooby]

I think r = the way you have measured it ie half the diameter. that would make sense.

As for gear reduction, as far as I know it's not just final drive ie 4.11 as you have to take the effect of the gearbox ratio into account. What I'm not sure of is the way you combine these - presumably by dividing or multiplying - although a google search might help. Or just ring a uni engineering faculty and ask, that sometimes works.

I think the second formula looks like it might be OK, they're torquey little suckers.

Good luck

Regards

[itbmils]

oops RADIUS not Diameter (bugger)

the RADIUS of my wheel is only 315mm

so I now get

6300 = ( T * 4.111 * 1000) / 315 ) = 482.72Nm

that seems reasonable to me - based on seat of the pants experiance

[Oosh]

Actually that 3000 odd figure is Newton Millimetres so thats even stonger! :confused:

We have taken in to account the gearbox, he said 4th gear, and that's 1:1, 1 engine revolution = 1 tail shaft revolution. So we can ignore it.

The problems in the radius bit i think too.

[Oosh]

oops RADIUS not Diameter (bugger)

the RADIUS of my wheel is only 315mm

so I now get

6300 = ( T * 4.111 * 1000) / 315 ) = 482.72Nm

that seems reasonable to me - based on seat of the pants experiance

There we go!

[xRHETTx]

Torque (Newton-metres) = Force (metres) x radius (metres)

So that should be correct...

[neil_se]

Wouldn't it be easier to convert your horsepower to torque using the rpm? :confused:

[xRHETTx]

Wouldn't it be easier to convert your horsepower to torque using the rpm?  :confused:

You can do it this way, but i wouldn't use horsepower, i'd stay in metric units to make it easier.

Torque is also a power multiplied by an angular velocity, so if you look on a dyno graph the power should be simply the torque multiplied by the rpm times some conversion factor based on the gear the car is in and the radius of the cars wheels.

[rob82]

TE=6300 R=4.11 r=(((17/2)*25.4)+45)/1000 - radius of a 17inch tyre plus with 45mm profile.

Thererfor r = 0.2609 meters. So T = TE*r/R, T = 399N.m. QED

[blind_elk]

... the rolling radius of my wheel. I have 235/45/17s (with a tape measure I get 2070mm ?)

That's the rolling CIRCUMFERENCE! Rolling radius will be:

(17* 25.4 + 235 * .45 * 2) /2

(approx 321 mm)

[pnblight]

ok what the conversion for ftlb to newtons

as mine made 410ft/lb on 275/35/18 at about 6500rpm is high torque point and hold around 400 for about 2000rpm. And made 529.4rwhp

R=324.85mm

6500 = ( T * 4.111 * 1000) / 324.85 ) = 513.6Nm

does this sound right

pete

[Oosh]

Go to http://www.joshmadison.com/software/ and download "Convert" great tool for that and MANY other unit conversions, more than you'll ever need / use.