How do you calculate torque/power at the wheels?
Discussion
As per the topic title, i am trying to figure out how to calculate the actual amount of torque a car produces at the wheels.
One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
You cant calculate it unless you know how much power is being lost through the transmittion etc. The estimates are around 15% for 2wd up to 20% for 4wd/awd. And then its the power produced at the flywheel minus the percentage, same for torque. The calculation you are talking about is the one that calculates HP from the torque.
Easyest way to find out is by going to a rolling road, who can tell you exactly what your car is making at the wheels (and offer a flywheel guestimate).
Easyest way to find out is by going to a rolling road, who can tell you exactly what your car is making at the wheels (and offer a flywheel guestimate).
Edited by RobCrezz on Monday 10th November 18:11
TomTom123 said:
The distance between the opposite forces multiplied by the strength of one of the forces.
(Or atleast that's what I need to know for these A-Level exams... heh)
That would be one hell of an equation for a car (rather than a twisting moment exerted on a pivot point in a bar and bolt fashion, which I assume is what that equation refers to)!(Or atleast that's what I need to know for these A-Level exams... heh)
While we're on the subject, I still don't understand the confusion over what hp and torque 'is'. It's harldy rocket science!
Oh yeah, and go to a dyno... way simpler, or buy one of those 'dataloggers' for an iPhone.
MrKipling43 said:
TomTom123 said:
The distance between the opposite forces multiplied by the strength of one of the forces.
(Or atleast that's what I need to know for these A-Level exams... heh)
That would be one hell of an equation for a car (rather than a twisting moment exerted on a pivot point in a bar and bolt fashion, which I assume is what that equation refers to)!(Or atleast that's what I need to know for these A-Level exams... heh)
transmission losses will be broadly the same for a dismal and a petrol(of the same car)
what your realy asking is how the higher torque of a dismal translates to the road.
the answer is that whilst the dismal has more torque at the engine, it's over a very limited rev range and at much lower RPM than the equivalent petrol engine, thus the gearbox of the dismal will have taller ratio's to make up for this.
net effect is that at the wheels, you will get (on average) the same torque for a given road speed (assuming the same power dismal/petrol engines).
what your realy asking is how the higher torque of a dismal translates to the road.
the answer is that whilst the dismal has more torque at the engine, it's over a very limited rev range and at much lower RPM than the equivalent petrol engine, thus the gearbox of the dismal will have taller ratio's to make up for this.
net effect is that at the wheels, you will get (on average) the same torque for a given road speed (assuming the same power dismal/petrol engines).
dizzy rebel said:
Fwd cars loose 30-50bhp through the drivetrain, rwd upto 60bhp and 4wd cars loose between 100-130bhp through the drivetrain
You what????!A given percentage, as stated by some other posts, is a good rough idea of transmissions losses.
Do you think a 100bhp bmw 316 has NO bhp at the wheels
Dracoro said:
dizzy rebel said:
Fwd cars loose 30-50bhp through the drivetrain, rwd upto 60bhp and 4wd cars loose between 100-130bhp through the drivetrain
You what????!A given percentage, as stated by some other posts, is a good rough idea of transmissions losses.
Do you think a 100bhp bmw 316 has NO bhp at the wheels
It actually works out pretty complex, with variable losses, much like a factor and an offset, so it's somewhere inbetween a percentage and static number, which is the main reason why there hasn't been anyone able to make an accurate formula to predict it.
Add to that the power output on an engine isn't the same as loads of different factors all add up, and also the correction calculations are a little rough, and there are different standards of correction!
Add to that the power output on an engine isn't the same as loads of different factors all add up, and also the correction calculations are a little rough, and there are different standards of correction!
Silverbullet767 said:
Dracoro said:
dizzy rebel said:
Fwd cars loose 30-50bhp through the drivetrain, rwd upto 60bhp and 4wd cars loose between 100-130bhp through the drivetrain
You what????!A given percentage, as stated by some other posts, is a good rough idea of transmissions losses.
Do you think a 100bhp bmw 316 has NO bhp at the wheels
So that Subaru Justy simply isn't going anwhere and the Impreza sport is gonna struggle racing 2cv's
dr.pepper said:
As per the topic title, i am trying to figure out how to calculate the actual amount of torque a car produces at the wheels.
One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
Torque a the wheels? What gear? This will have MASSIVE effect on your answer.One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
ridds said:
dr.pepper said:
As per the topic title, i am trying to figure out how to calculate the actual amount of torque a car produces at the wheels.
One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
Torque a the wheels? What gear? This will have MASSIVE effect on your answer.One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
dr.pepper said:
As per the topic title, i am trying to figure out how to calculate the actual amount of torque a car produces at the wheels.
One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
There was a very nice excel spreadie on SELOC iirc - you put in your power at wheels (the more plots the better), gear ratios, wheel size and it overlayed each gear on a graph with the actual torque - will dig it out One of the reasons i am interested in this is because of the endless Turbo diesel and Petrol comparisons. There's too much talk about power/torque at the engine, rather than the actual power at the wheels (after drivetrain losses).
I understand that it is something along the lines of the gear ratio's and the peak torque *5252?
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