OP
marrt
Platinum Member
I was able to dig the tractor out yesterday and do some tests. Placing the tractor on a dirt pad I had leveled with another machine, I was able to get it to spin the tires in low range at 2000 RPMs (I didn't test any RPMs lower than 2000). Placing the tractor in midrange, it would not spin the wheels at any RPM setting. If I feathered the tram carefully, about half the time the engine would idle down and I would let off the tram. At other times, I could move the tram slowly through its range without the engine idling down (the reliefs popped I guess).
In the past when thinking the tractor was underpowered, I would be digging and simultaneously lifting with the bucket. This obviously applies a lot of pressure to the front tires which may help them maintain traction. I didn't perform this exact experiment because I don't know if it would change the outcome and I didn't want to continuously strain the tractor just to confirm a theory. Overall, I think the tractor is probably performing as designed. The reliefs may be set a little low since I could not get the tractor to spin in midrange. However, this is sort of a moot point because one can always switch to low range when needing additional torque.
The (infamous) video I posted earlier where geared and hydrostatic 3901’s were compared is still a bit informative. When placed in high range, first gear, the geared tractor would spin the wheels at a high rate of speed. Since my hydrostatic tractor would not spin the wheels in midrange, there's no way I could get will spin anywhere near this speed (I realize the conditions are different). This suggests to me a geared tractor is able to put more torque to the ground over a wider range of travel speeds. When using ground engaging equipment, this could make a significant difference. Of course, we knew this already as a hydrostatic transmission is not nearly as efficient as a geared transmission in terms of applying torque to the ground at a given load and speed. But I would bet a geared 3901 would “feel” significantly stronger if compared side by side over a range on duties. My neighbor has an old Ford (Japanese built) tractor with less horsepower than my Kubota. And I know for a fact he can run circles around me when pushing snow. That tractor has an amazing amount of low end grunt.
Like so much in the tractor world, everything is a tradeoff.
In the past when thinking the tractor was underpowered, I would be digging and simultaneously lifting with the bucket. This obviously applies a lot of pressure to the front tires which may help them maintain traction. I didn't perform this exact experiment because I don't know if it would change the outcome and I didn't want to continuously strain the tractor just to confirm a theory. Overall, I think the tractor is probably performing as designed. The reliefs may be set a little low since I could not get the tractor to spin in midrange. However, this is sort of a moot point because one can always switch to low range when needing additional torque.
The (infamous) video I posted earlier where geared and hydrostatic 3901’s were compared is still a bit informative. When placed in high range, first gear, the geared tractor would spin the wheels at a high rate of speed. Since my hydrostatic tractor would not spin the wheels in midrange, there's no way I could get will spin anywhere near this speed (I realize the conditions are different). This suggests to me a geared tractor is able to put more torque to the ground over a wider range of travel speeds. When using ground engaging equipment, this could make a significant difference. Of course, we knew this already as a hydrostatic transmission is not nearly as efficient as a geared transmission in terms of applying torque to the ground at a given load and speed. But I would bet a geared 3901 would “feel” significantly stronger if compared side by side over a range on duties. My neighbor has an old Ford (Japanese built) tractor with less horsepower than my Kubota. And I know for a fact he can run circles around me when pushing snow. That tractor has an amazing amount of low end grunt.
Like so much in the tractor world, everything is a tradeoff.
