Is a 6 foot rotary cutter maximum size with only 43 PTO horsepower?

[RickB]

A big factor is how heavy the brush is and how fast you go. You could get a 10 footer if you go slower or have a light load.

another thing to think about is weight. an 8' dual spindle is easier to pull than a 7' single.. which is very heavy and just over 7' long and wide.. whereas a 8' dual spindle is just over 8' wide, but only just over 4' long.

We have something called June grass here that would want 7 hp per foot - wiry, 18" tall, dense - really takes a lot to cut. 5' weeds are dead easy in comparison. So it depends what you're cutting.
Jim

Rules of thumb have varying applicability.

 

[mapper]

Keep in mind that the hp rating is what the gear box is rated for, if the rating is 30-60 hp then a 50 hp tractor is unlikely to break the gearbox a 70 hp tractor could break it if the going gets heavy.
Like the previous posters pointed out, how wide you can go depends on the the weight you can lift on the hitch, what you are trying to cut and how fast you want to go.
I have a 5' rotary cutter, when I bought it I had an 8N Ford, it was all that the Ford could handle, when the grass was tall and thick it could stall the tractor if I was not careful. With my current tractor I can pretty much wade through most anything I run into on my property. I could go up to a 6' cutter with no problem now but the one I have is paid for

 

[IndyIan]

Unless your mowing a smooth field you can't go fast anyways and a rotary cutter doesn't have a minimum speed that it works well at, so I'd recommend going wider and then you can always slow down for the really heavy stuff if you ever cut that. I kick myself for getting a 5'er, as the only time it makes my tractor work is cutting gopher mounds...

 

[MF283]

Unless your mowing a smooth field you can't go fast anyways and a rotary cutter doesn't have a minimum speed that it works well at, so I'd recommend going wider and then you can always slow down for the really heavy stuff if you ever cut that.

Yep, done that with 5'-20' mowers.

 

[brown40]

Usually that 5 hp per foot figure is what gets recommended for implements--get over 1/3 of your weight behind your rear fulcrum (tires), and you can get a very lively ride over bumps or grades, if not impossible for your machine to do safely. You can have the tail wag the dog.
The other risk is putting a gearbox with 2, 3x the rating of your PTO driveline behind it. If you are running an overpowered implement you must have working shear protection and overrun protection inside or out of the tractor or the 3/4" drive can get twisted by the 1 1/4" gearbox input and mass its connected to--then huge repairs.
Nothing different from what others have said
What your use is makes a difference, and if maintenance of a level, lightly grown field is all you're doing you can probably do with a big light duty cutter, but you'll destroy it trying to reclaim areas. A narrow heavy duty will be more durable for reclamation, but leave you a long time for open field.
The weight hanging, swinging, shuddering, banging, and bouncing on the pins of the three point, and the cost of repairs to that part of the tractor dictates what I'm willing to risk. I went medium 5' on a 30hp PTO (~900# on a ~3900# unit). I should have gone six, but would have had to operate differently a number of occasions. How much does your tractor weigh?

 

[plowhog]

Its a Massey Ferguson cab model 1758. Basic weight is about 4,600 lbs, and I am having rears loaded with rimguard. Not sure how to estimate total weight since I have not yet taken delivery, but ballparking 5,000 lbs would probably be good?

 

[Soundguy]

If your rear tires are 17.5L-24, they will hold 55g rimguard at about 75% fill, with a ADDED weight each of 589#. 1178#

So 5778# minimum, if your 4600# is accurate, no front fill, and those are the correct rears.

If fronts are filled, those could be 10-16.5 and an additional 12g per side with an added weight of 128.4# per side... Or a min of 6034#