Brush cutter size for a given horsepower

[mcfarmall]

So is there a general rule of thumb for sizing a cutter to a tractor of a given horsepower? The old Farmall C can run a 5' cutter pretty well under most circumstances...loads the engine well in very tall grass but overall doesn't lug the tractor. When you consider that it is only rated at about 18 horsepower that's pretty good.

Or do you simply size the cutter based on the overall width of the tractor? If the outside of the rear tires measures 75" then go with a 7 foot (84") cutter. My father in law used to run a Frontier 7' finishing mower with ease using an antique John Deere 40.

To me, a 50 hp rated tractor should be able to turn a 7' cutter adequately.

Any thoughts? Please supply reasoning/facts with your replies.

 

[Jabonee]

All your PTO driven attachments will have a rated PTO HP spec. You just need to make sure your tractor and attachment match.:thumbsup:

 

[smstonypoint]

The rule of thumb is five PTO HP per foot of cutter. But it's just that -- a rule of thumb. Many manufacturers offer light-, medium-, and heavy-duty cutters with different recommended minimum HP requirements. For example, Woods offers 7' cutters with minimum HP requirements ranging from 35 to 65 HP (Rotary Cutters). IMO, most of the recommended HP requirements are conservative estimates.

I would want a cutter that is at least as wide as the tractor. A 50 HP tractor can handle a 7' cutter, but it may be challenged by a heavy-duty cutter.

Steve

 

[hinkle2121]

I run a rhino 284,(7') on my 5530. They recommend higher HP rating for it but the 5530 has no issue handling it even in thick brush. I have to leave my loader on while bush hogging on any slopes because of the weight of the cutter will cause front end to bounce when on rough terrain. Tires are also loaded. It is a very heavy duty cutter though

 

[CobyRupert]

I'd want one as wide as the tractor.
But as somebody here once said; the weight of the tractor determines what it can do, the horsepower determines how fast it can do it,

 

[RedNeckRacin]

5 PTO HP /Ft is a good rule of thumb.(Note:most tractors now advertise flywheel hp so make sure you look at the right number)


If you have light cutting needs you can stretch that some and get away with less. If you have steep hills you might not want to go less than that. I have a medium duty cutter MX 10 and right about 7hp/ft and I think its a good match size and weight wise. In light cutting its no problem, when I get into vegetation that's taller than the front tires (11.2-24) I could use some more HP but its not required. I generally get a better cut quality at that point by going slower unless I'm just trying to get it knocked down. I will say that if I hit a gopher hole mound or something I gotta be quick to either pick the cutter up or throw the pto out. The tractor takes a little longer than I would like getting back to rpms but I wouldn't want any smaller cutter for as many acres as I mow per year.

 

[LD1]

I am not a believer in the HP per ft rule on a bushhog.

IMO, get as big of a cutter as your tractor can physically handle, and still be able to pull in low gear.

Alot of people seem to think that if they start bogging down the tractor when mowing at 4-5MPH that the cutter is either too big, or the tractor not powerful enough. Nonsense. Just gear down. My tractor has a first gear of 0.9MPH, and even 3rd gear is still under 3MPH.

I have a 6' mower and 29 PTO HP. I have NEVER even came CLOSE to running out of power. Sure, I bog the engine down a bit, but thats what the transmission is for. I have NEVER used 1st or 2nd gear mowing. And only once-in-a-blue-moon do I have to slow to 3rd gear.

Honestly wish I had an 8' twin spindle.

I would rather mow with an 8' cutter at 3MPH than a 4' cutter at 6 MPH. Work done is gonna be the same in a given time frame. Larger cutter allows you to enjoy a smoother ride. Because I find myself having to slow down more because the ground is rough, than because of lack of power. And many times, I can mow in 5th and 6th gear and have power to spare. But cannot go any faster because I start over-running the cutter.

And what I mean by overrunning the cutter is....you have two blades with lets say a 8" cutting edge. So each revolution of the bushhog is cutting 16" of material. If I pick 7th gear at ~8.5MPH, I am physically travelling forward more than 16" each time the bushhog makes 1 revolution.

So I am limited to 6th gear ~6MPH.

And even if you get into some nasty conditions, and tractor isnt geared low enough, you dont have to take full passes. You can have an 8' cutter and take a 5' swath if conditions suck. But you cant take an 8' swath with a 5' cutter in the easy conditions

 

[oosik]

LD1,

Very insightful comments. Its not my intention to steal this thread but I do have a question. My M6040 is rated at 55 pto hp and max rotary cutter weight of 1200 pounds. The horns of my dilemma are - I want a heavy duty cutter but the weight limitations of the 3-point will not allow for anything much over 60". The pto hp would allow for a much larger cutter than the weight limitation of the 3-point recommends. My rear tread width is 80".

What are the thoughts on going over the recommended 3-point weight limitations? My apologies to the OP on this question.

 

[mcfarmall]

Good information.. Thanks LD1 for the explanation. I find that sometimes when the going is rough, I do like you do and simply take a narrower swath in heavy grass. Then I gear up and take a full pass where the growth is lighter.

 

[LD1]

I think thats either a typo or a VERY conservative recommendation of 1200#. You have a 5000# tractor with a 3PH rating of 4000#. (basically double what I have on both specs). I carry a 1100# cutter no issues at all.

If I had a 6040 or similar spec'd tractor, I'd have no issues hanging a 10 or 12' cutter back there. or even consider a batwing tow-behind. Like I said, if you aint in your slowest gear, you aint out of power. And I'd rather cut a larger swath at a slower speed vs a narrow swath at high speed. Smoother ride and easier on equipment.

Others can probably chime in as to what a 5000# tractor with a 4000# lift capacity can handle as far as physical size and weight are concerned. Thats outside the realm of my experiences.