hydrostat vs gear hp loss

[Soundguy]

I think he's stating that if you take a gear and HST tractor.. and both are otherwise identical, and the hst is rated for slightly less drawbar hp, and then you ballast each unit till it is at a stall point on a pull, with no tire slippage.. then the unit with more drawbar hp will be doing more work...

Soundguy

 

[dieselsmoke1]

I think he's stating that if you take a gear and HST tractor.. and both are otherwise identical, and the hst is rated for slightly less drawbar hp, and then you ballast each unit till it is at a stall point on a pull, with no tire slippage.. then the unit with more drawbar hp will be doing more work...

Soundguy

Agreed. Don't know quite how to figure the amount of ballast weight required to reach this point as mine has no qualms spinning all 4 on demand as it sits now. I would guess most other CUT's could do the same. But if you could weight to that point, it's no contest, the gear driven wins on a dead pull.

 

[_RaT_]

Agreed. Don't know quite how to figure the amount of ballast weight required to reach this point as mine has no qualms spinning all 4 on demand as it sits now. I would guess most other CUT's could do the same. But if you could weight to that point, it's no contest, the gear driven wins on a dead pull.

I suppose it would also come down to just how strong the drivetrain, the clutch system, the axles, basically everything involved. If you get to the point where you have ballasted a tractor so much that your tires no longer slip, you probably need a different tractor. I know with my L3830 HST with a 1000lb box scraper and a bucket heaped with about 20 cu ft of dirt that I am still able to spin the tires. My tires are ballasted as well which adds about 1200lbs as I recall. I have no desire to ballast more as I would think doing so also increases my chance of breaking something. I'm good, I'm good...

 

[radman1]

Holy cow batman! I opened a can of worms with this thread. I too thought the 20% loss of drawbar hp was probably an overestimate but the dealer who told me is usually correct or close in most things. For over 95% of us drawbar hp loss is nearly a non-issue unless using a blade, disc, subsoiler etc. Lets say with a gear drive I can pull my loaded box blade at 5 mph. The same hydro can only pull it at 4 mph. (20% loss) Most of us would never know the difference or care. Most of us are more concerned with overall engine and PTO hp, loader specifications and 3 pt lift capacity which are more directly needed for the tasks we plan to use the tractor for.

 

[JerryG]

Not trying to be obstinate here, but I just can't get my arms around what you're saying. How can a gear drive develop more traction than an identical HST? More work to the ground, yes I can see that, in terms of speed. Is that what you mean?

Man, we are having a communication problem.
No, a gear can't develop more traction than a hydro. But, if two identical tractors except one with a hydro and the other with gears both having the correct ballast, the gear tractor will put out more power to the ground. (drawbar power for pushing or pulling)

 

[_RaT_]

Man, we are having a communication problem.
No, a gear can't develop more traction than a hydro. But, if two identical tractors except one with a hydro and the other with gears both having the correct ballast, the gear tractor will put out more power to the ground. (drawbar power for pushing or pulling)

Which would probably mean it will pull it faster. That is for sure the biggest difference I have seen between my manual and hydrostat drive. I can pull my boxscraper with rippers down more easliy with my manual then with my hydrostat. Even though the two tractors are different, there is no doubt in my mind that a tractor identical to mine except with a manual transmission would do the job more easily and quicker. There are trade offs

 

[BillyP]

Holy cow batman! I opened a can of worms with this thread. I too thought the 20% loss of drawbar hp was probably an overestimate but the dealer who told me is usually correct or close in most things. For over 95% of us drawbar hp loss is nearly a non-issue unless using a blade, disc, subsoiler etc. Lets say with a gear drive I can pull my loaded box blade at 5 mph. The same hydro can only pull it at 4 mph. (20% loss) Most of us would never know the difference or care. Most of us are more concerned with overall engine and PTO hp, loader specifications and 3 pt lift capacity which are more directly needed for the tasks we plan to use the tractor for.

Yes, Robin, you did open a can of worms. Don't worry though, this ain't the first and won't be the last. It's just one of the hottest debated subjects on TBN.

 

[Keith_B]

Holy cow batman! I opened a can of worms with this thread. I too thought the 20% loss of drawbar hp was probably an overestimate but the dealer who told me is usually correct or close in most things. For over 95% of us drawbar hp loss is nearly a non-issue unless using a blade, disc, subsoiler etc. Lets say with a gear drive I can pull my loaded box blade at 5 mph. The same hydro can only pull it at 4 mph. (20% loss) Most of us would never know the difference or care. Most of us are more concerned with overall engine and PTO hp, loader specifications and 3 pt lift capacity which are more directly needed for the tasks we plan to use the tractor for.

That's not the 20% loss at all. The HP formula has speed as a factor, but it is not the only factor. One horsepower is 33,000 foot-pounds per minute, going slower isn't going to compensate for the difference in horsepower, as the slower you go the less the HP.

The compensation will not come with decreased speed, but with smaller ground engaging impliments. Smaller plows, disks, boxblades, etc.

 

[dieselsmoke1]

Man, we are having a communication problem.

That's what the Bride said a few days ago

Yes, I agree that a gear driven unit will put more power on the ground than a hydro, no denying this, it's a fact. When you get down to the blood and guts, it's traction that critical. No doubt your geared CUT will spin the tires if demanded, so will my hydro.

In my opinion (which i am told occasionally has a limited value) a hydro should accomplish the same work as a geared, as ultimately it will come down to traction. A hydro will give up some speed compared to a geared when the drawbar hp max's out. However again, IMO and situation, I believe I can ultimately do more work faster because I change directions at will and accelerate the ground speed when the load on the engine allows. Maybe with the new powershifts and reversers on geared trannys this is not as big a deal as it once was. I'm an old throwback to when gears were just that, gears. And I gotta admit, I love push and go, lift and stop.

 

[LBrown59]

If a hydro has more than enough power to do the task you want to do with it then why do you need a gear with more power?

 

[dieselsmoke1]

going slower isn't going to compensate for the difference in horsepower

I can't quite follow you Keith.

Take 2 identical 40 hp tractors, geared if you like, and hook an identical 6' disk to both. Turn the fuel down to 35 hp on one tractor. Will they both pull the disk? I'm betting yes. The 40 may pull it in a faster gear than the 35, but they will both pull it. I'm thinking the same principle applies to a hydro with a 10%, 20% whatever drivetrain loss.

 

[Soundguy]

If a hydro has more than enough power to do the task you want to do with it then why do you need a gear with more power?

You may not need it... but you may be able to get it for the same price. The hydro tranny adds a small premium to the tractor price, and/or there may be a deluxe model line and an economy model line. especially in brands that have many different tractors of 'overlapping' hp regions.

Could be very easy to do away with a few bells and whistles and deluxe options.. and get more hp in a gear unit.. vs a more chromed hst model.. etc.

Either choice is valid.. depending on the buyer.

Soundguy

 

[Soundguy]

That's deffinately not an apples to apples comparison. For a valid comparison.. I would think you would need identical power units.. and have the difference int he drivetrain.. not 'detuning' one engine and then saying one does more work... etc.. ( That's like pointing at a hamburger and saying.. 'that's food'. .. etc.. )

In any case.. hp has a time variable inthe calc... Saying one unit pulls faster than another.. given same engine, and different drivetrrains. then.. I'd have to say the faster unit has more drawbar hp... which.. I think is what we all are agreeing on.. right?

Soundguy

I can't quite follow you Keith.

Take 2 identical 40 hp tractors, geared if you like, and hook an identical 6' disk to both. Turn the fuel down to 35 hp on one tractor. Will they both pull the disk? I'm betting yes. The 40 may pull it in a faster gear than the 35, but they will both pull it. I'm thinking the same principle applies to a hydro with a 10%, 20% whatever drivetrain loss.

 

[dieselsmoke1]

The example was to illustrate a point, albeit was a little far fetched.

Yes, I agree. Enough on this one. Thanks for the discussion, guys.

 

[yellowandbeige]

I'm sorry I have to add my two cents,

I don't think It's about being able to do the same work ( like moving a load ) faster or slower with gears vs hydro.
If you have two identicle tractors except tranny and are moving loads near or at thier limit the gear tractor will do the work abeit barely and the hydro's pop off setting will keep the tractor from moving the load. Thats the frustration with hydros. With a gear you either spin tires move the load or stall the engine.
With a hydro you might be working at the upper limits of traction and transmition and reach the point where the tranny won't move the load , won't spin tires and won't stall engine. Ask me how I know.
Y&B

 

[fish_wisperer]

I have a Mahindra 2810HST and if I remember correctly there was about 1.5hp lost to the pto vs gear. As far as drawbar hp, mines heavier than some others in it's hp class and with loaded rears it'll still spin the tires in 4wd if it meets an immovable object. What more could it do? I think soundguy might be onto something regarding relief settings, we've read about it before on TBN.

i think that sais it all, with loaded tires spinning anymore power is a waste.

 

[Soundguy]

Now that says it best.

Soundguy

I'm sorry I have to add my two cents,

I don't think It's about being able to do the same work ( like moving a load ) faster or slower with gears vs hydro.
If you have two identicle tractors except tranny and are moving loads near or at thier limit the gear tractor will do the work abeit barely and the hydro's pop off setting will keep the tractor from moving the load. Thats the frustration with hydros. With a gear you either spin tires move the load or stall the engine.
With a hydro you might be working at the upper limits of traction and transmition and reach the point where the tranny won't move the load , won't spin tires and won't stall engine. Ask me how I know.
Y&B

 

[art]

I've not seen a hydro that on a dead pull won't start a load that a gear drive will! That is when in the right range for the load! I've pulled 15,000lb tractors whith hydro shaft drive cadets like 129's 12 horse and I was able to spin the tires as well as not spin them. If a hydro won't spin in low range then it is to heavy and you will be burning a lot of extra fuel.

 

[Soundguy]

We have seen posts here, in the past few years where a tractor has crawled into an area that it would not crawl out of.. no tires spinning... I'm petty sure it was the relief valve opening.

Soundguy

 

[NewToy]

OK, I gotcha now but there's still not a 20% difference. Below is a link to some interesting reading. Although it doesn't go into HP loses, it's interesting. Look on page 4

http://www.eurageng.net/files/nl.pdf

I have a hard time believing that a hydro unit will give you a 74% efficiency increase in tilling applications and almost 50% mowing. Must be a magic tractor or the person operating the gear unit was completely inept.

John