Tractor Sizing What effect does HP have on residential lawn tractors?

[ForumJunkie]

Stupid question.

Let's say 2 tractors.
Identical except 17hp vs. 22hp.

How does that affect things?

Speed of blade? Better cut?
Or max MPH speed of the tractor?
Or does it mainly matter when there is tall grass that is slowing the blades?

 

[LS Tractor Owner]

I can't say for sure, but I think HP is going to come into play depending on the load...high, thick, or wet grass will put more load for sure. The speed (mph) would probably be a little faster, but probably not noticeable.

 

[Diggin It]

Maybe the last one. Does better on hills as long as the trans can handle them. Helps with pulling loaded trailers/carts. Blade and ground speed are probably more a function of belts and pulleys.

Main thing I saw was that 20HP and higher are usually two cylinders which tend to run smoother and quieter. Though I think my X300 is a 17HP VTwin.

 

[kthompson]

The higher hp will handle heavier load. Using mower as in your example yes the larger HP will handle heavier grass with same size mower at higher ground speed. Blade speed without load should be the same. Same as in an vehicle. Take two cars or suv or pickups. Just alike but different HP engines. The lower HP engine will strain or even stall with a load the larger hp engine takes in stride.

 

[jaxs]

That's a simple question that has no simple answer. It easily require's a thick book just to begin understanding horsepower vs work. To get you started,look at hp ratings of big box lawn & garden tractors and those in Kunota's 12 to 25 hp line up. It will require several hours of reading and research before it start's to become clear the numbers on hood aren't something you should hang your hat on. Pay close attention to torque #s alongside hp #s.
My first lesson over 60 years ago was being told "you can move a locomotive with a motor scooter engine if you have the right gears".
The principle still come's to mind today as I continue learning.

 

[DK35vince]

My first lesson over 60 years ago was being told "you can move a locomotive with a motor scooter engine if you have the right gears".

Possibly, but you would likely measure its speed by inches per hour vs MPH.

 

[jaxs]

Possibly, but you would likely measure its speed by inches per hour vs MPH.

Thank you for letting me know that. All these years I was thinking inches per month or even years but now I know and don't have to go to the trouble of testing it. On second thought,are you calculating uphill or downhill?

 

[zzvyb6]

Essentially deck width capability and ground speed. So, its grass volume per second. I have the 17 hp gas F-525 48" mower deck and an F-935 diesel with a 72" deck. Ground speeds are about the same. This implies that it takes about 10 hp just to move the machinery along at speed and with enough reserve to climb a decent hill.

 

[kenmac]

"you can move a locomotive with a motor scooter engine if you have the right gears".

Possibly, You would have to have the means of transferring that power to the ground.
Doesn't matter how much torque you have, if you can't transfer it to the ground (traction) you have wasted power

 

[MossRoad]

Stupid question.

Let's say 2 tractors.
Identical except 17hp vs. 22hp.

How does that affect things?

Speed of blade?
Speed of the blade is gonna be the same on both.
Better cut?
The cut is based on first, sharp blades, second, keeping the blades spinning at the same RPMs throughout the job.
Or max MPH speed of the tractor?
If the tractors are geared the same, then both will make the same speed in a given gear. However, with more HP, you may be able to keep your blade speed up and use a higher gear to cover more ground in the same amount of time
Or does it mainly matter when there is tall grass that is slowing the blades?
That matters, too. So do hills. Not only does the tractor have to spin the blades, and keep them spinning, it has to pull itself up hills. More available HP will do both better.

At least that's the way I understand it.