Tractor Drawbar Pull from Power
The drawbar pull a tractor develops at a working speed for a given power.
Example
You enter
- Power (hp) 75
- Power basis pto
- Ground speed (mph) 4.5
- Surface firm_soil
You get
- Drawbar pull 4,500 lb
Checked against published worked examples from: Kansas State University Cooperative Extension (Taylor, Schrock, Wertz).
Details, formula, and sources
Scopepull = 375 x drawbar_hp / speed (a PTO rating converts first with drawbar_hp = pto_hp x tractive efficiency). A 75 PTO-hp tractor at 4.5 mph on firm soil (efficiency 0.72) pulls about 4,500 lb; on soft or sandy soil (0.55) only about 3,440 lb, because slip wastes power. Answers 'how much can it pull' instead of the power from a measured pull. Traction can limit the usable pull below this; ballast and tires govern.
Formula or tablepull_lb = 375 × drawbar_hp / speed_mph; a PTO rating converts first with drawbar_hp = pto_hp × tractive_efficiency. The inverse of drawbar_hp = (pull × speed) / 375.
Source and editionASABE D497 (Agricultural Machinery Management Data) by name; Nebraska Tractor Test Lab publications.
Free accessNebraska Tractor Test data free at tractortestlab.unl.edu.
What governsEstimate. AHJ and licensed professional govern.
API field namespower_hp, power_basis, speed_mph, surface, pull_lb
- Tractive efficiency 2WD: concrete 0.87 / firm soil 0.72 / tilled 0.67 / soft or sandy 0.55; MFWD, 4WD and track are higher; a soft surface wastes power as slipASABE D497
- Traction may limit the power-based pull can exceed the traction limit (weight x soil coefficient); ballast and tires govern the usable pulltraction mechanics