How Important is Torque for Off-Roading

[roaniecowpony]

Not sure as I have a Sport. I have experienced a couple times "running out of torque" when climbing a steep hill while fully loaded with overlanding gear.

You ran out of horsepower.

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[RockyMtnHigh]

You ran out of horsepower.

No, he ran out of torque.

When the Jeep is climbing a hill, there are two places torque is produced. 1) at the engine, and 2) by the weight of the Jeep rolling back down the hill, by the tires, at the axle. When the torque produced by the engine is greater than the torque produced at the tires, you go up. When the torque produced at the tires is greater than that produced by the engine, you stall.

 

[GtX]

Not sure as I have a Sport. I have experienced a couple times "running out of torque" when climbing a steep hill while fully loaded with overlanding gear.

What do you mean by "running out of torque" specifically?

 

[roaniecowpony]

No, he ran out of torque.

When the Jeep is climbing a hill, there are two places torque is produced. 1) at the engine, and 2) by the weight of the Jeep rolling back down the hill, by the tires, at the axle. When the torque produced by the engine is greater than the torque produced at the tires, you go up. When the torque produced at the tires is greater than that produced by the engine, you stall.

As you may know, there is no horsepower without torque, but there is no movement of a vehicle without motion of the engine. We can take a little 100 hp tractor engine and put lots of gear reduction on it and produce thousands of lbs/ft torque. That little tractor might be able to drag the same maximum weight as the max a big 400 hp pickup can. But the little tractor will take much longer to move the load the same distance as the truck. Another example is an electric motor, where the motor will produce maximum torque at motor stall. But there is no work getting done when the motor is stalled. Torque without motion does no work. The definition of horsepower is "work". The definition of torque is "force". Horsepower is a quantitative methodology that combines force, movement, and time.

So, "running out of horsepower" is "running out of torque and motion".

 

[RockyMtnHigh]

As you may know, there is no horsepower without torque, but there is no movement of a vehicle without motion of the engine. We can take a little 100 hp tractor engine and put lots of gear reduction on it and produce thousands of lbs/ft torque. That little tractor might be able to drag the same maximum weight as the max a big 400 hp pickup can. But the little tractor will take much longer to move the load the same distance as the truck. Another example is an electric motor, where the motor will produce maximum torque at motor stall. But there is no work getting done when the motor is stalled. Torque without motion does no work. The definition of horsepower is "work". The definition of torque is "force". Horsepower is a quantitative methodology that combines force, movement, and time.

So, "running out of horsepower" is "running out of torque and motion".

Yes, torque and horsepower are linked.

Torque is work done about a radius (Torque = Force x Radius). Horsepower is (linear) work done over time.

HP = (RPM x Torque)/5252. So when you're talking about a 100hp engine vs a 400hp engine, you're talking about more Torque (HP stats are given at the optimal RPM range, so we can't mess with that right now). Gear reduction multiplies the torque, not the HP. When you're struggling to climb a hill in 4hi, you can shift into 4low (increase your torque) and make it up the hill. So I'll stand firm, stalling is always due to lack of torque. But when the torque goes away, yes, the horsepower goes away too.

 

[RockyMtnHigh]

What do you mean by "running out of torque" specifically?

When the torque needed to keep you moving up the hill is greater than what you are currently producing. Basically when you stall.

 

[roaniecowpony]

Torque is work done about a radius (Torque = Force x Radius).

I believe the definition if torque does not include "work", but rather static force.

 

[RockyMtnHigh]

I believe the definition if torque does not include "work", but rather static force.

When a force moves an object, work is done.

 

[txj2go]

When the torque needed to keep you moving up the hill is greater than what you are currently producing.

In theory there is no such thing, you just need to match the gearing to the task. Our garage's 2-post lift will raise a car straight up in the air with a relatively small electric motor because it has very high effective gearing. Your real world limitation is either traction or lowest combined gear ratio. When you stalled on the hill were you in 4LO with the transmission in first? I believe I've seen people run 2 transfer cases in series so they really multiplied their crawl ratio.

 

[txj2go]

I believe the definition if torque does not include "work", but rather static force.

Yes torque is a static measurement irrespective of speed. You can apply torque to the wheels but that doesn't mean that the vehicle moves, but the torque is still there.

 

[RockyMtnHigh]

In theory there is no such thing, you just need to match the gearing to the task. Our garage's 2-post lift will raise a car straight up in the air with a relatively small electric motor because it has very high effective gearing. Your real world limitation is either traction or lowest combined gear ratio. When you stalled on the hill were you in 4LO with the transmission in first? I believe I've seen people run 2 transfer cases in series so they really multiplied their crawl ratio.

Yes, we could make a Jeep with a 1hp engine that produces 1 lb-ft of torque and gear it to oblivion. But for the vast majority of us, that's not the case. We have 275hp with 265 lb-ft of torque. The only way we can capitalize on those two factors is to select different combinations of gears, which is the same as selecting a new torque value. If we strive to keep the engine running around 2000-2500 RPM, regardless of what gear combo we selected, we always have the same amount of horsepower.

Torque is the major player when it comes to off-roading. Momentum can push you up a hill for a while, but once gravity takes over again, you need torque.

 

[RockyMtnHigh]

Yes torque is a static measurement irrespective of speed. You can apply torque to the wheels but that doesn't mean that the vehicle moves, but the torque is still there.

Torque can be a static measurement, in which case we call it a moment, and no work is done. But if the object moves, its dynamic torque and work is done.

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