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?