radman1 said:
I am considering moving up to a hydrostat cab tractor. Does anyone know the amount of drawbar/rear wheel HP loss for a hydrostat compared to gear drive. I have a Kubota 3710 GST and dealer said expect to lose about 20% in pulling power with hydro. He recommended an increase from 37hp to 46hp (ie. 4630) to have the same pulling ability with hydro. This would suggest considerable power loss. Most bigger tractors talk about drawbar hp in specs but don't see this in the compacts. Is this because of so many hydro's in the compact class that companies don't want to show specs with lower drawbar hp for hydro tractors with the same engines?
Years back, International Harvester marketed a few bigger, higher horsepower farm tractors with HYDRO trannies. They didn't catch on like one would have thought. I recall reading in a farm magazine at the time of tests done, measuring the "in-efficiency" of a hydrostatic tractor. The "testing" was very informal, and as I recall, done in such a way as to get the results that the "tester" was looking for. In other words, they wanted the hydro to "fail". Where they found the biggest weakness was in heavy drawbar loads. (pulling primary tillage tools. i.e. plow, chisel plow, ect) The "failure" or highest levels of inefficiency was after a few hours of sustained work, after the hydro's fluid had time to really heat up.
Once any product or concept has a "bad name", that reputation may never go away. Now consider the fact that I own gear drive tractors with the exception of a John Deere 265 lawn tractor. (17HP/48" cut/hydrostat tranny) I don't feel that I'd gain any advantage with a hydro (full sized) tractor, but you can't beat the convenience of hydrostat when working in tight quarters that requires constant speed changes and direction changes. Also, with the rising popularity of hydro, the concept has seen constant improvement.
To attemt to answer the question posed in the original post, I doubt the measureable inefficiency is more than 1 or 2% initially. (as an average. certain brands and/or models may vary slightly) Maybe "if and when" the tractor in question has done a days work plowing the north 40, that may read higher. Go mow the pasture and it may well read the same as when you drive it off the dealers lot.
You have to gauge the inefficiency of power delivery against the efficiency of power used in a given time. In other words, in the hands of most compact, subcompact, or utility tractor buyers (in todays market) a hydro is a better choice. Easier to operate, less wear and tear (over a clutch), faster "cycling" when used in let's say, loader work, and every bit as long lasting as most any gear transmissions (when cared for and used properly).
Long and short.... It's just a numbers game. A 35 HP gear tractor and a 35 HP hydro tractor should be an even match for work accomplished when you consider all factors. The tiebreaker would be "which one is easiest to operate". Game/set/match to the hydro.
I honestly believe that most people "over-rate" the specifications on tractors. It's not so much "about the numbers" as some manufacturers would like you to believe. To me, it's "How much". How much does it cost? How much will it do? and how much time will it go before it wears out or breaks down?
Modern gear trannies are a world away from older designs. They aren't the balky old crash boxes they used to be either. It's all about what you're used to and what you feel most comfortable with.
Just like eating ice cream. You can have chocolate, strawberry, or vanilla. Your choice. No one can tell you which one YOU like.
