Kubota HP ratings, new vs. old

[jonness]

Do the newer Kubota tractors use a phony HP rating, or is the torque less per HP, or something else? My B1700D has far less HP and lifts far more weight. Why is this?

bx25:
23 engine HP; 17.7 pto
max lift fel: LA240 X 2.2 = 528 lbs
Rear lift (at ends): 991 lbs

b1700d:
17 engine HP; 14 pto
max lift fel: LA301 X 2.2 = 662 lbs
Rear lift (at ends): 1280 lbs

Thanks

 

[1970cs]

You are comparing a sub-compact tractor (BX) to a class 1 compact (B) physical size is the real difference.

Current production tractor is like comparing a L2501 class 2 to a B3350 class 1
24.8 hp 33 hp
Pat

 

[Billdog350]

HP and Torque don't drive lift capacity...the weight and physical size of the machine as well as loader configuration does.

You can set up a hydraulic pump with low volume and high pressure on a low hp motor (think log splitter) and have immense lifting capacity..but you'll flip your machine over pretty easily.

Manufacturers including Kubota will configure the hydraulic pump volume, loader cylinder diameter, and pressure relief to lift a load safely under most conditions. You can often "tweak" your relief pressure to lift a little more, but you'll never be able to lift more with a BX tractor than a B or L for instance. Regardless of HP.

Make sense?

 

[85Hokie]

Well said Bill and 70cs.....

and they both make excellent sense!

 

[Grouse Feathers]

You also have to be careful where you get the ratings. Places like TractorData.com may be not be perfect on all data for every model. Plus there appears to be several ways you can specify loader capacity. For example I think the newer BX25s are the same as the BX2370s which have a 3 point capacity at the lift points of 1210#.

 

[millsan1]

On of my big issues with HP being used to rate tractor motors is that HP is probably the least useful data when it comes to tractor work.

Torque is much more useful when it comes to tractors.

HP is a measure of torque vs RPM, specifically HP = Torque x RPM ÷ 5252

Let me explain.

Let's assume you have two motors, each make 25 HP.

Motor A makes 25 HP at 3,000 RPM and Motor B makes 25 HP at 2,500 RPM.

Motor A has 43.75 Lb Ft of Torque

Motor B has 52.5 Lb Ft of Torque

Both have the same HP, but Motor B is a lot stronger, by 20%.

 

[jonness]

On of my big issues with HP being used to rate tractor motors is that HP is probably the least useful data when it comes to tractor work.

Torque is much more useful when it comes to tractors.

HP is a measure of torque vs RPM, specifically HP = Torque x RPM ÷ 5252

Let me explain.

Let's assume you have two motors, each make 25 HP.

Motor A makes 25 HP at 3,000 RPM and Motor B makes 25 HP at 2,500 RPM.

Motor A has 43.75 Lb Ft of Torque

Motor B has 52.5 Lb Ft of Torque

Both have the same HP, but Motor B is a lot stronger, by 20%.

Interesting. So the physical stature of the B1700 allows it to handle more lifting power. Based on your formula, my calculation has the BX25 having about 35% more HP, 13% more torque, and 8% higher hydraulic flow rate than than the B1700. Despite having less flow rate, torque, and HP, the B1700 has 8% higher relief pressure at the PTO and 19% higher relief pressure at the FEL.

Thanks to everyone for your input!

 

[Billdog350]

Jonness, if you are taking into consideration the size of the hydraulic cylinders and leverage angles on the two machines, your calculations are likely correct...however I would bet that the lift cylinder size and location is different between the two machines, thus making the "relief pressure" calculation moot.

My point is that if Kubota puts a "large" cylinder in the 3 point or loader, they can lift more with lower pressure than a comparable "smaller" cylinder. Pressure factors into that. There are some old machines that can lift more with a 2000psi system than a newer machine with a 2500psi setup.

Make sense?

 

[millsan1]

Interesting. So the physical stature of the B1700 allows it to handle more lifting power. Based on your formula, my calculation has the BX25 having about 35% more HP, 13% more torque, and 8% higher hydraulic flow rate than than the B1700. Despite having less flow rate, torque, and HP, the B1700 has 8% higher relief pressure at the PTO and 19% higher relief pressure at the FEL.

Thanks to everyone for your input!

I used tractor data for this, so take it FWIW.

B1700 has 17 HP at 2600 RPM

BX25 has 25 HP, but at 3200 RPM

So the B1700 has 68% of the HP of a BX

BUT

B1700 has 34 lb ft of torque where the BX25 has 41 lb ft of torque

So the B1700 has 83% of the torque of the BX25

Again, torque is actual work, so the two machines, from a power point of view are actually pretty darn close.

 

[Grouse Feathers]

To tie this all together:
The engineers determine how much weight a given size tractor can safety lift. It has nothing to do with power, only with the weight of the tractor, height of the center of gravity and size of the base on the ground (all contribute to stability). The engineers then design the geometry of the loader and the size of the pistons to lift the safe load, this also has nothing to do with power.

The power determines how much work a tractor can do in a given period of time. If you compare two tractors each lifting 500# the the more powerful tractor will lift it faster.

 

[jonness]

I used tractor data for this, so take it FWIW.

B1700 has 17 HP at 2600 RPM

BX25 has 25 HP, but at 3200 RPM

So the B1700 has 68% of the HP of a BX

BUT

B1700 has 34 lb ft of torque where the BX25 has 41 lb ft of torque

So the B1700 has 83% of the torque of the BX25

Again, torque is actual work, so the two machines, from a power point of view are actually pretty darn close.

I'm thinking the B1700 torque is probably on par with the BX25 at the same RPM? So in order to take advantage of the higher torque of the BX25, you would have to have the engine revved at 3K or so. People tend to do most FEL and 3-point tasks at lower than 3K RPM, so perhaps the torque advantage goes to the BX when mowing lawns and going up hills but otherwise doesn't matter.

The B1700 and the B2100 have the same FEL and 3-point lifting specs despite having a 4hp difference at the same RPM and a similar physical stature. Based on what I'm learning here, the additional HP of the B2100 probably doesn't amount to a major difference in actual usability of the tractor. By the time the additional power of the B2100 is transferred to the wheels, they're probably losing traction anyways. It seems the B2100 would be a little faster tractor though.

 

[jonness]

Jonness, if you are taking into consideration the size of the hydraulic cylinders and leverage angles on the two machines, your calculations are likely correct...however I would bet that the lift cylinder size and location is different between the two machines, thus making the "relief pressure" calculation moot.

My point is that if Kubota puts a "large" cylinder in the 3 point or loader, they can lift more with lower pressure than a comparable "smaller" cylinder. Pressure factors into that. There are some old machines that can lift more with a 2000psi system than a newer machine with a 2500psi setup.

Make sense?

Interesting. Thanks