4570Man
Super Star Member
- Joined
- Apr 7, 2015
- Messages
- 17,829
- Location
- Crossville, TN
- Tractor
- Kubota M59, Kubota L3800, Grasshopper 428D, Topkick dump truck, 3500 dump truck, 10 ton trailer, more lighter trailers.
Absolutely. Weight is traction. Case closed? Well-l-l no when the development does not cover a common exception that is a norm for most of us. We have tractors equipped with loaders. We ballast and counterweight by necessity to improve the force application platform. This weight is more traction and more potential force ... if you can get requisite torque to the axles.
The feature of HST allowing infinite speed control from 0 to top speed of each range presents the possibility of "infinite"/huge wheel torque at creep speed in any range. Creeping speed requires so little of the engines power that the operator has no indication of the tremendous forces that may be being applied. Wisely, the HST designers include a relief valve between the output of the variable displacement pump and the hydraulic motor that drives the wheels through the range gears. So when the relief operates and the wheels wont turn you shift to a lower range. When the wheels wont turn in the lowest range that is the limit of motive force that the tractor will apply.
With a gear tractor the link between engine and wheels is fully mechanically defined. Engine speed and wheel speed are always directly proportional. There is no variable between engine and final drive that the operator can control. The engine feels wheel torque and the operator can gauge it by sound and gear down where needed. The hidden "infinite" torque possibility of a zero to xspeed is removed, so the automatic resetting "fuse" in the HST isnt needed. The wheel torque is limited by the gearbox amplification of clutch slip torque. Presumably the designers choose components with accommodating safety factors. Apparently so, at least in above creeper gearset reduction transmissions.
So, Which transmission on a comparably powered tractor will provide greater motive force (wheel torque/r) ? Absent a specially contrived test you can only find out by equipping the tractors with loaders and requisite counterweight and ballast for safety and prudence. Then use them on the high side of their loader capability. I think you will find as I have, that you will occasionally find the wheel torque limit of the HST tractor but never the one of the gear tractor. Indeed, the manual trans seems to spin wheels nonchalantly in 1st gear on loads it wont move.
If you chained the tractor wheels to the ground so they can’t just spin and chained to front end down so it can’t flip the gear tractor would absolutely make more torque. Probably so much so that it would self destruct. But if you did a more realistic test and chained both tractors to an unmovable object and tried to pull it both tractors will break traction and spin out making the drawbar pull very similar.