Hydrostatic trasnsmission vs. gear drive

[CobyRupert]

Other scenarios:
Not being able to hear a potential danger (a person or object) because either hydro engine rpms must be higher or tranny whine.
Close proximity of hydro fwd/reverse pedals (some models): Increased chance of accidental wrong direction versus manually moving a shifting lever (IMO).
There's many scenarios where there is a safety advantages of being able to quickly apply 1 independent rear break while maintaining power to the other wheel. Something not easily done on (some) hydro models.

Ok, ok I'm playing devils advocate here :devil:, and have an obvious bias. As been said before, there's pluses and minuses to both, and it comes down to personal preference. :2cents:

 

[Hermio]

Other scenarios:
Not being able to hear a potential danger (a person or object) because either hydro engine rpms must be higher or tranny whine.
Close proximity of hydro fwd/reverse pedals (some models): Increased chance of accidental wrong direction versus manually moving a shifting lever (IMO).
There's many scenarios where there is a safety advantages of being able to quickly apply 1 independent rear break while maintaining power to the other wheel. Something not easily done on (some) hydro models.

Ok, ok I'm playing devils advocate here :devil:, and have an obvious bias. As been said before, there's pluses and minuses to both, and it comes down to personal preference. :2cents:

Well, at least I don't have to worry about not hearing trees and stumps! I get you on the noise, though. It is my one complaint about HST drives. But my old Ford is actually louder, due to engine noise. The Mahindra 5035 HST is much quieter. As for engine rpm, that has nothing to do with the HST. Today's tractor engines tend to run at higher rpm because it allows the manufacturer to increase Hp more cheaply than to increase engine displacement. Today's gear drive tractors also have higher rpm than that of the older gear drive tractors. In fact, the Mahindra HST models have exactly the same engine as the gear drive models.

On a somber note, I once did run over a young faun with my Ford while bush hogging very tall grass. I simply did not see it until it was too late. The faun hid there quietly thinking it was safe. It made me feel very ill.

 

[ruffdog]

While it is true that most accidents are caused by operator stupidity, what we are talking about here is intrinsic machine safety. I maintain that in the woods, an HST transmission is intrinsically safer than gear drive. That does not mean that accidents will never happen with one. It just decreases the odds.

I have a HST and I sure wish my Dad had a HST. He has a Case 1390 4x4 with Ag tires and that thing will crawl through the hilly woods (no trails) with only a big tree to stop it. At his age, a HST would allow him to do work at a more controlled manor.

 

[s219]

Not really a valid analogy. To stop a car, you must use the brakes whether you have a manual or automatic transmission, so there is no difference in safety. To stop a rollover that might be caused by hitting an unseen object, you just have to stop delivering power to the axle. As a bonus, when you stop pressing the hydrostat pedal, you also get braking action.

In my case, I am alive today because of the hydrostat transmission on my Kubota, as I described previously.

Another aside: a hydrostatic transmission is NOT an automatic transmission. There is nothing automatic about it. It is fully manually controlled. It is just an infinitely variable transmission.

You must think I am stupid, but I was making analogies which seemed to cruise right over your head.

You have made some valid points in this thread, but I think you should stop short of pushing them as fact. Having operated and owned gear and HST tractors, I just don't think anyone with experience should limit themselves to an "opinion". Tractors are dangerous in many ways, and as soon as you think you know something it means you can become complacent. I think HST and gear tractors are equally dangerous, and I think the each have pluses and minuses when it comes to safety.

As for fuel efficiency, HST models lose quite a bit right off the bat, in the conversion of mechanical energy to hydrodynamic energy and back to mechanical. You can compare the PTO horsepower of HST and gear variations of a common model to get a general idea of the power loss, which tends to run in the 5-6% range. Integrated over time, that adds up to a lot, and is a far bigger effect than gear changes/etc. You can spin the 5-6% number a bunch of ways, but the easiest way to think about is that for the same amount of power put to the ground, an HST tractor will have to run at higher RPM and burn more fuel. There is no way around that.

I do think HST is superior for loader work and for the things most compact tractor owners do, which is why my new tractor is HST. But I am not under any illusion about safety, and I am well aware of the power/efficiency loss when there's an HST pump between the engine and the ground. The gear model of my tractor was unquestionably more effective at putting power to the ground.

 

[kco]

As others said safety is mainly due to the operator with a small portion due to mechanical failure.

I am only a hobby operator and have just had three tractors, a 9N, then a gear drive Kubota L275DT and now the DK35 HST. The L275 was a huge improvement over the 9N due to the 4WD and effective brakes. Like the OP, I find the DK35's HST much easier to operate and safer in exacting conditions that the L275 gear.

My work is often on rough hilly trails and close conditions near the house. For example, when reversing with a blade to pull snow away from a building I can go as slowly as I want just by easing up on the HST pedal and stop just by releasing the pedal. The HST acts as a brake. Once I have started forward I can increase to the maximum desired speed with the HST pedal. There are no engine speed or gear changes required.

With the gear tractor I had to change gears, lower the engine speed or slip the clutch while backing to the building. The other concern I always had, but it never happened, was the damage that could be done if my foot slipped off the clutch. If your foot slips off the HST pedal you just stop(at least on moderate slopes). So I think in that situation the HST is more forgiving if someone makes a mistake.

The HST lets me do more exacting work on rough ground where I did not go with the gear tractor. I have never come close to rolling either tractor but am able to do more with the HST because I can more precisely approach touchy spots.

As others said, accidents are over 99% up to the operator. We need to recognize the hazards, know our skill level, and know when to back off. An HST requires less operator skill but nothing will save us from poor judgement.

I think for small acreage owners, hobbyists and others in non-production situations an HST is the better choice.

Another HST advantage over gear for some of us as we age(I'm 71) is, not operating a clutch is much easier on the old back.

 

[flatpik6]

Mildly amusing to see the "veteran" posters with 2000 + posts get their hackles up when someone articulates thoughts and positions they don't agree with. So far I have not seen the OP make any move whatsoever toward personalizing the conversation. Hey "veteran" TBN'ers..... no need to get defensive and personal. Could be an interesting thread to read if you'll keep the egos in check.

 

[Hermio]

You must think I am stupid, but I was making analogies which seemed to cruise right over your head.

You have made some valid points in this thread, but I think you should stop short of pushing them as fact. Having operated and owned gear and HST tractors, I just don't think anyone with experience should limit themselves to an "opinion". Tractors are dangerous in many ways, and as soon as you think you know something it means you can become complacent. I think HST and gear tractors are equally dangerous, and I think the each have pluses and minuses when it comes to safety.

As for fuel efficiency, HST models lose quite a bit right off the bat, in the conversion of mechanical energy to hydrodynamic energy and back to mechanical. You can compare the PTO horsepower of HST and gear variations of a common model to get a general idea of the power loss, which tends to run in the 5-6% range. Integrated over time, that adds up to a lot, and is a far bigger effect than gear changes/etc. You can spin the 5-6% number a bunch of ways, but the easiest way to think about is that for the same amount of power put to the ground, an HST tractor will have to run at higher RPM and burn more fuel. There is no way around that.

I do think HST is superior for loader work and for the things most compact tractor owners do, which is why my new tractor is HST. But I am not under any illusion about safety, and I am well aware of the power/efficiency loss when there's an HST pump between the engine and the ground. The gear model of my tractor was unquestionably more effective at putting power to the ground.

Is it not a fact that HST tractors will stop when you release the pedal, whereas gear tractors require you to depress the pedal AND the brake in most cases? I am not dealing in opinion here. I am dealing in physics. I am not saying you can't get hurt on an HST tractor. Far from it. But since it takes an actual output of organized energy to prevent certain kinds of accidents with gear drives, whereas it takes less with HST, the odds of said accident decrease. This is a simple case of the application of the Second Law of Thermodynamics. (Yes, I am an engineer.)

Now, as regards efficiency, no doubt a gear drive tractor is more efficient in terms of power transmission efficiency. But what I am talking about is total system efficiency, including the engine. It is well known that an engine is less efficient when it is not working at its peak power output. In fact, it is still using fuel at idle, when it is connected to no PTO implement and the tractor is stopped, resulting in an efficiency of zero. Now, consider how each system performs under real world conditions, which usually involve variable load. With a gear drive tractor, most people will choose a gear so that the tractor will not stall during the most difficult work, allowing the engine to loaf along most of the time during the easy work. With an HST, the speed can be varied to make sure the engine is working harder most of the time. (Believe me, with only 16 Hp on my Kubota, I use the variable speed a low when operating a 4" brush cutter. By contrast, I do not change gears when cutting brush on my Ford 4110). This way of operating is more efficient when the engine efficiency is taken into account. It is somewhat similar to why variable frequency drives often save energy in industrial applications even though such a drive introduces some inefficiency.

 

[Hermio]

"Mildly amusing to see the "veteran" posters with 2000 + posts get their hackles up when someone articulates thoughts and positions they don't agree with. So far I have not seen the OP make any move whatsoever toward personalizing the conversation. Hey "veteran" TBN'ers..... no need to get defensive and personal. Could be an interesting thread to read if you'll keep the egos in check. "

Indeed. My intent was not to attack anyone who prefers gear drive. It was to bring up an issue that I have not seen discussed before. Maybe it will save someone's life. My own opinion is that it is not much of a safety issue in farming operations in open fields, but I do a lot of work in the woods, and I am absolutely convinced there is a higher degree of safety there using an HST.

 

[Buckgnarly]

OP, do you drive a manual transmission daily in your car? How often and how much do/have you driven manuals? Makes a huge difference in how you view the ability to quickly stop a stick.

 

[murphy1244]

Gear models are great for spreading fertilizer and sprays as you have a constant speed you can dial in.