3 Point lift capacity

[ByronBob]

How do you figure out how much weight the rear 3 point can lift? I went onto the Kubota web site for a BX2230 to see but I'm confused by the numbers listed there.

Anyone better at this than I am please feel free to chime in.

Thanks
Bob

[DiezNutz]

How do you figure out how much weight the rear 3 point can lift? I went onto the Kubota web site for a BX2230 to see but I'm confused by the numbers listed there.

You're typically given two numbers: (1) the capacity at the lift point (ball ends of the lift arms) and (2) the lift capacity 24" behind the LP, because this is a standardized representation of the location of the implement's CoG.

Why two numbers and why does it vary w/length? The 3PH hydraulics work by applying a torque to the lift arms - but the weight of the implement acts as a counteracting torque. Since Torque = Force (weight) x Distance, the further away the CoG of the implement is, the more torque it exerts on the lift arms, consequently the harder it is for the 3PH to lift. The max lift capacity is where the two torques cancel each other out.

Calculating the lift capacity of a given implement exactly is complicated by a few things:
(a) Actual CoG of the implement? 24" behind LP might be pretty close for a rear blade, but the CoG of a RFM for example is much further away.
(b) We don't know the exact distance between the LP and the point on the tractor about which the torque rotates
(c) Height of the implement. Lift capacity will actually vary a bit with the angle of the hitch due to the geometry involved.

Fortunately you can get a good approximation by making a few assumptions:
(a) make a best guess at the distance between CoG of the implement and LP
(b) extrapolate from the two figures given
(c) assume lift capacity is linear

The unknown distance (b) from pivot to LP is (I'll simplify the math; plug in values from any tractor):
b = (24")*(680) / (1210-680) = 30.8"

The lift capacity at any distance x from the LP is then approximated by:
1210*b / (x + b) = 37268 / (x + 30.8)

x = 24": 680 lbs
x = 48": 472 lbs
x = 72": 362 lbs

Final thing to remember is lifting (static) and carrying (dynamic) are two different things. Typically you can safely carry only about 1/3 to 2/3 of what you can lift, depending on the situation.

[ByronBob]

Wow thats a lot to chew on. I'm going to have to do some math.

Thank you so much for the help.

[RobJ]

It should be in you rmanual...here is mine... L2500

[DiezNutz]

It should be in you rmanual...here is mine... L2500

Rob, I think the point was he doesn't have the manual because he doesn't own the tractor (yet?). 'Cause as we all know Kubota is 100% STINGY about publishing their manuals online. Maybe a BX2230 owner out there could post this information from theirs?

[RobJ]

Oops, I think you are right. My Bad!

Right about Kubota, there should be a free download spot for past and present Kubotas. ALL!! A little CYA in this sue happy world.

But on the numbers and my L, I can't imagine lifting 1925# at the end of the lift arms...I think my tractor weighs 2000#!!

[ByronBob]

Rob, I think the point was he doesn't have the manual because he doesn't own the tractor (yet?). 'Cause as we all know Kubota is 100% STINGY about publishing their manuals online. Maybe a BX2230 owner out there could post this information from theirs?

I do own the 2230 but I'm looking for a rmsb and I don't know how much weight the lift arms can handle really. I can get a 48 inch blower I think but if I want a 60 inch I'm trying to figure out the weight and if it can handle that size.

Thanks guys...
Bob

[SPYDERLK]

Bob, Since, with a 3pt linkage - a parallelogram linkage [admittedly imperfect] - the implement does not pivot wrt the tractor as it is raised, you will be able to lift very near the full force available at the eyes regardless of how far back it sits. Thats assuming your front wheels stay down. There is no linear drop off as there would be if the implement were a rigid extension of the lift arms. The 24" behind the eyes must be more a safety thing, or maybe an issue of strain on the toplink. If the Center of Mass of the full weight rated implement is more than 24" behind the eyes it apparently exceeds the tractors margin for mobile safety. Weight in the FEL should allow you to handle a COM a little further back if you drive carefully.
larry

[jas67]

Bob, Since, with a 3pt linkage - a parallelogram linkage [admittedly imperfect] - the implement does not pivot wrt the tractor as it is raised, you will be able to lift very near the full force available at the eyes regardless of how far back it sits. Thats assuming your front wheels stay down. There is no linear drop off as there would be if the implement were a rigid extension of the lift arms. The 24" behind the eyes must be more a safety thing, or maybe an issue of strain on the toplink. If the Center of Mass of the full weight rated implement is more than 24" behind the eyes it apparently exceeds the tractors margin for mobile safety. Weight in the FEL should allow you to handle a COM a little further back if you drive carefully.
larry

Yes, but the further back the weight, not only does it need more weight on the front to keep the front down, but it puts more force on the top link, which could over stress the top link mount, which could result in a broken transaxel case. I remember seeing at least one thread, where someone broke the transaxle case by overloading the 3PH.

Just be careful!