What does horsepower actually mean?

[90cummins]

Torque gets the load moving down the road or field;
HP determines how fast you can go with it!

 

[J F]

What the heck...how did my above post end up with a link in it? Just darn.

 

[strum456]

Duplicate post dumb smart phone!

 

[strum456]

1st calculate work by multiplying force (pounds) by distance (feet) 2nd divide work by the time it took to do the work to get ft.lbs/sec 3rd divide ft.lbs/sec by 550 to get horsepower.

The above formula proves that a small force at a high speed or a large force at a low speed could produce the same amount of horsepower.

 

[bcp]

HP determines how fast you can go with it!

If one horse can run 30 mph, how fast can two horses run?



Bruce

 

[doall]

The gearing is also related to the tire sizes . The large back tires on a tractor is adding lower gears to already low gears. My toyota Tundra has 381 horse power, my new holland has 40. My tundra weighs more than the tractor, but I bet the tractor would pull the truck all over the place because of gearing and a larger foot print.

 

[scrappy isb67]

The gearing is also related to the tire sizes . The large back tires on a tractor is adding lower gears to already low gears. My toyota Tundra has 381 horse power, my new holland has 40. My tundra weighs more than the tractor, but I bet the tractor would pull the truck all over the place because of gearing and a larger foot print.

Larger tires REDUCE the mechanical advantage of the gearing. they will give better traction but hurt the power by raising(lower numerically) the final drive ratio. the only reason the taller tires on the tractor don't hurt it is because of the super low gearing that the tractor has to begin with. the tractor's gearing is 3-4X lower at least. if you put the same size tires on your truck it would have plenty of traction but no power due to the super high final drive ratio.
case in point I have a ~450hp 4wd diesel pickup, the stock tires are 32's. the axles have 3.73 gears. It had 37's put on it but the gears are still 3.73s.
the bigger tires effectively LOWERED my gear ratio to ~3.08. The truck would be more efficient and pull better with the stock tires as long as it could get traction. it has been proven on the dyno that larger tires hurt power if the gearing isn't adjusted to compensate for them.

 

[Monster5601]

Torque is power or twisting effort. Horse Power is more like speed.

Torque gets the load moving down the road or field;
HP determines how fast you can go with it!

Spot on but just to clarify, HP is how fast the torque can be applied.

 

[LD1]

Its actually a very simple measurement.

HP = (Torque x RPM)/5252


So your lawn tractor may only have 34lb-ft of torque since it's rated at 3600rpms.

A 21hp tractor rated at say, 2200 may have roughly 50lb-ft. As related to work ability, not only does the tractor have more torque but also more gearing and weight.

:thumbsup::thumbsup: I couldnt have said it better myself:thumbsup:

As to the mower vs tractor comparison......well to compare it depens on what you are doing. With the mower, its about HP. Because HP determins how well you can maintain a FAST blade speed and NOT bog down in heavier grass.

With a tractor, most of the time it is about torque being applied to the wheels to get traction. If you have the torque to spin the tires, more HP will only make them spin faster.

Also, back to the comparision, since some believe that these "small" engines are over rated on HP. Look at zero-turns. I have one that has a 25HP motor on it. You mention your tractor is ~21 or something. Put a 61" cutterdeck on it, and try to mow thick grass as heavy and fast as said zero-turn and see which engine bogs down quicker?? Because that is what HP does for you.


Another note, changing speeds (gearing) like PTO gearboxes or ground speeds does NOT change HP. Horsepower remains constant through out. Torque is the only thing that changes with a speed change.

IE: Slower =more torque
Faster = Less torque

Calculating it is easy with the formula I quoted from V...

 

[Baby Grand]

Fun fact: Torque multiplies; HP doesn't.

What this means is that you can change the Torque being delivered just by changing the speed (gear ratio). Regardless what gear ratio you are running, an engine producing 20 HP will deliver 20 HP to the final drive (minus frictional losses), even though the Torque has been increased or decreased by the transmission.

Heavy duty tractor engines can deliver high Torque over a broad range of engine RPMs. This allows flexible use of engine speed to the task.

Light duty lawnmower engines, as previously observed, only produce high torque at high engine RPM, so the HP drops off quickly below high engine RPM (HP is the product of both Torque and RPM). This results in an engine that must be "pegged" to get much done.