Horsepower rating vs pulling power - 3039R vs 3046R

[4570Man]

I can't agree. If your theory is true there would be no need for the larger HP engine.

My Brother had a L3240 Kubota HST. All it did was aggravate me. Gutless wonder. Same tractor in the higher HP versions works great.

Let's not complicate the issue by comparing gear drive to HST. That wasn't the original question.

The L3240 could have definitely used more HP but it’s really a nice tractor. It’s way better than the higher HP to weigh economy tractors. I know my L3240 would move more dirt than the L3800. And referring to a different post the engine size has zero to do with loader strength. That’s entirely to do with the cylinder size and pressure. Which is using a pretty small percentage of the engine HP. A wood splitter can generate 20-30 tons or really an unlimited amount if you can build a frame to hold it with a single digit hp engine.

 

[arlen4720]

It boils down to weight and traction. More HP is going to pull faster but has little to do pulling force. I’ll hook my 6 liter gas burner dump truck to a diesel pickup with double or 3 times the hp anytime. I can’t come close to pulling a load up hill as fast but they don’t stand a chance in a tug a war. If they’re not satisfied with loosing once we can try again with my 95 HP backhoe.

If you had a geared transmission of two identical tractors except for the HP, the larger horsepower tractor would indeed produce more drawbar force (assuming 100% traction to keep the debate simple). This is not the case with a HST transmission.
I love my HST tractor, but the typical HST tranny employed in tractors does have some shortcomings compared to geared transmissions. Without going down the road of which one is better, I hope we can at least agree that Geared and HST trannies are wildly different animals.

 

[4570Man]

If you had a geared transmission of two identical tractors except for the HP, the larger horsepower tractor would indeed produce more drawbar force (assuming 100% traction to keep the debate simple). This is not the case with a HST transmission.
I love my HST tractor, but the typical HST tranny employed in tractors does have some shortcomings compared to geared transmissions. Without going down the road of which one is better, I hope we can at least agree that Geared and HST trannies are wildly different animals.

Unlike trucks pulling a grade tractors are geared deep enough to spin and loose traction when trying to pull something that they can’t pull. If you’re successfully putting the power to the ground like a truck pulling a grade or a tractor pulling a disk more HP is going to pull faster but when you hit the lowest gear for maximum pull pretty much anything especially tractors are going to spin makings traction the limiting factor. My gutless as described by another member L3240 could spin out in low low in the best traction conditions while wearing a loader, loaded tires, and a backhoe in 4x4. If I had a higher hp model maybe I wouldn’t have to use low low but how is it going to pull any harder? Really I didn’t use low low very often. Having a 6 speed HST vs most tractors 3 speed was the redeeming feature of that under powered tractor.

Would having more HP have been nice, yes.
Could it have done more work with more HP, yes
Could it have pulled any harder with more HP, no.
Could a lighter but equal hp tractor like a L3200 do more work or pull harder, definitely not.

 

[arlen4720]

Unlike trucks pulling a grade tractors are geared deep enough to spin and loose traction when trying to pull something that they can’t pull. If you’re successfully putting the power to the ground like a truck pulling a grade or a tractor pulling a disk more HP is going to pull faster but when you hit the lowest gear for maximum pull pretty much anything especially tractors are going to spin makings traction the limiting factor. My gutless as described by another member L3240 could spin out in low low in the best traction conditions while wearing a loader, loaded tires, and a backhoe in 4x4. If I had a higher hp model maybe I wouldn’t have to use low low but how is it going to pull any harder? Really I didn’t use low low very often. Having a 6 speed HST vs most tractors 3 speed was the redeeming feature of that under powered tractor.

Would having more HP have been nice, yes.
Could it have done more work with more HP, yes
Could it have pulled any harder with more HP, no.
Could a lighter but equal hp tractor like a L3200 do more work or pull harder, definitely not.

Ha! You’re skillfully dodging my point. You are parking on traction. Let me put it this way...
If you have 2 gear transmission tractors identical except HP, the the higher HP tractor will exert more torque as measured at the wheel hub.
If you have 2 HST tractors identical except HP they will both exert the same maximum torque as measured at the wheel hub.
Let’s see you dodge that!:drink:

 

[4570Man]

Ha! You’re skillfully dodging my point. You are parking on traction. Let me put it this way...
If you have 2 gear transmission tractors identical except HP, the the higher HP tractor will exert more torque as measured at the wheel hub.
If you have 2 HST tractors identical except HP they will both exert the same maximum torque as measured at the wheel hub.
Let’s see you dodge that!:drink:

That’s irrelevant because it’ll never happen. You’re skillful dodging the most important part. Unless maybe you plan on parking the tractor in pond and waiting for it to freeze. I’ve acknowledged your point. Wouldn’t more toque be the same thing as pulling the same load up a hill faster? Have you ever seen a tractor or vehicle fail at pulling something because it just couldn’t power through it. Probably not because they all spun out first. On the unlikely event that did happen wouldn’t a deeper gear solve the problem?

 

[sd455dan]

Thanks for the responses. I think that loader lift capacity is determined by the amount of pressure to the cylinders, which is limited by the pump and unaffected by engine hp. I'm wondering if maybe pressure to the drive is also pump limited, and therefore drive/pushing/pulling power is also unaffected by engine hp?

Here's a few examples of required power for some chinese tractors hydraulic pumps - as volume increases so does kw to spin them

an example of different volume pumps


Model




(KW) (last figure)

CBN-E304 4 2.63
CBN-E306 6 3.95
CBN-E308 8 5.27
CBN-E310 10 6.58
CBN-E312 12 7.9
CBN-E314 14 9.22
CBN-E316 16 10.53
CBN-E320 20 13.17
CBN-E325 25 16.46


so a 25ml per revolution pump takes 16.46 KW @ rated speed and pressure
where a 4ml per revolution pump only requires 2.63 kw @ rated speed and pressure

 

[arlen4720]

That’s irrelevant because it’ll never happen. You’re skillful dodging the most important part. Unless maybe you plan on parking the tractor in pond and waiting for it to freeze. I’ve acknowledged your point. Wouldn’t more toque be the same thing as pulling the same load up a hill faster? Have you ever seen a tractor or vehicle fail at pulling something because it just couldn’t power through it. Probably not because they all spun out first. On the unlikely event that did happen wouldn’t a deeper gear solve the problem?

I just think it’s good to understand the physics involved before the discussion can advance to actual practical limitations.
As far as a “deeper” gear solving the problem? Our rules are that we have 2 identical tractors except HP.
Drawbar pull rating at 100% traction aren’t useless, they are measured all the time by the Nebraska testing labs and give you an idea of what the maximum work that can be done with a machine compared to another machine.

 

[Dave81]

Ha! You’re skillfully dodging my point. You are parking on traction. Let me put it this way...
If you have 2 gear transmission tractors identical except HP, the the higher HP tractor will exert more torque as measured at the wheel hub.
If you have 2 HST tractors identical except HP they will both exert the same maximum torque as measured at the wheel hub.
Let’s see you dodge that!:drink:

Thank you for the detailed explanation. I was suspecting this but didn't have the hydro mechanical knowledge to know for sure. :drink:

 

[ovrszd]

Ha! You’re skillfully dodging my point. You are parking on traction. Let me put it this way...
If you have 2 gear transmission tractors identical except HP, the the higher HP tractor will exert more torque as measured at the wheel hub.
If you have 2 HST tractors identical except HP they will both exert the same maximum torque as measured at the wheel hub.
Let’s see you dodge that!:drink:

You were doing so good until the last paragraph. It's simply not true.

Don't think the HST is the limiting factor. It is not. The input HP/Torque is.

 

[arlen4720]

You were doing so good until the last paragraph. It's simply not true.

Don't think the HST is the limiting factor. It is not. The input HP/Torque is.

They will both have the same relief pressure setting in the HST.