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What is wheel torque?

  • WHEEL TORQUE = ENGINE TORQUE * TOTAL GEAR RATIO - DRIVETRAIN LOSSES

    Votes: 8 61.5%
  • Gears don't matter. Wheel torque is whatever the dyno plot says it is.

    Votes: 1 7.7%
  • I don't know much about this issue to give a definite opinion.

    Votes: 4 30.8%

  • Total voters
    13
1 - 6 of 6 Posts

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The reason that this poll will not be answered by many people is that the first two selections are virtually the same.


It is the (engine torque * ratio) minus all the losses to the wheels (theoretical)

or

which means gearing does matter and that it equals what the dyno says. (actual)

and if you don't know what the first two are saying then you will probably not select the last one.
 

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Discussion Starter #3 (Edited)
e-squared said:
The reason that this poll will not be answered by many people is that the first two selections are virtually the same.


It is the (engine torque * ratio) minus all the losses to the wheels (theoretical)

or

which means gearing does matter and that it equals what the dyno says. (actual)

and if you don't know what the first two are saying then you will probably not select the last one.
Errr, no.

Wheel torque = engine torque * gear ratio - drivetrain losses.

That's A LOT MORE than what the dyno tells you, especially in low gears.

For example, 3.5 Altima SE puts more than 2000lb-ft of torque (yes, two thousand) to the wheels in first gear.

Dyno measures your rpms and the rpms of the dyno roller, and divides those two to get the total gear ratio from the engine to the roller. The computer then takes the measured torque at the roller and divides it with the total gear ratio.

Dyno shows you what your wheel torque WOULD BE if you were using 1:1 total gear ratios. Most modern cars use much shorter gears than that.
 

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Discussion Starter #4
Maybe my question should have been:

How much torque does the 3.5 Altima SE put to the wheel in 1st gear:

1. Close to 2500lb-ft (210*3.4 first gear *3.823 final gear)
2. Close to 210lb-ft (or whatever the dyno says)



Please correct me if I'm wrong on gear ratios. These were the only ones I could find on the net, and were for 2000 Altima SE.
 

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YellowBullet said:
How much torque does the 3.5 Altima SE put to the wheel in 1st gear:

1. Close to 2500lb-ft (210*3.4 first gear *3.823 final gear)
2. Close to 210lb-ft (or whatever the dyno says)

Yes you are correct that the number is around 2500lb-ft(theoretical). Of course this is the number around 4400 rpm (246lb-ft engine)

The tires cannot handle this much torque so they do a neat little thing, they break loose from the ground. After which the torque drops off dramatically, drop in coefficient of friction, nothing to push against. Thus this is considered a loss due to the tires.

Once you exceed the torque that the tires can handle in any gear or engine speed, they break loose and torque falls off dramatically.

This is why the dyno gives more of an actual number, pushing against a load to create torque and get a reading.

This is basically like calculating the max speed that your car will go from the gear ratios of the car and not including the fact that there is air out there.
 
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