Vehicle lead control

1. A vehicle comprising:

rear ground traction members;

front ground traction members;

a rear drive system to drive the rear ground traction members;

a continuously variable speed front drive system to drive the front ground traction members;

a rear speed sensor to output rear speeds of the rear ground traction members;

a front speed sensor to output front speeds of the front ground traction members; and

a controller to:

select a chosen lead for a rear speed of the rear ground traction members based on evaluations of different tractive efficiencies for different leads for the rear speed; and

output control signals to the continuously variable speed front drive system to drive the front ground traction members at the chosen lead.

2. The vehicle of claim 1 further comprising an operator interface to receive a ground speed input from an operator, wherein the rear speed is based upon the ground speed input.

3. The vehicle of claim 1 , wherein the controller is configured to select the rear speed based upon different tractive efficiencies for different leads for each of multiple different rear speeds.

4. The vehicle of claim 1 further comprising a database comprising the evaluations of different tractive efficiencies for different leads for each of multiple different rear speeds.

5. The vehicle of claim 1 , wherein the controller is configured to select the chosen lead additionally based upon a geographic location of the vehicle.

6. The vehicle of claim 5 further comprising a lead map identifying different recommended leads for the rear speed at different geographic locations, wherein the controller is configured to consult the lead map based upon the geographic location of the vehicle.

7. The vehicle of claim 1 , wherein the controller is configured to select the chosen lead additionally based upon a current condition and/or type of terrain underlying the vehicle.

8. The vehicle of claim 7 further comprising a terrain map identifying different conditions and/or types of terrain at different geographic locations, wherein the controller is configured to consult the terrain map based upon a geographic location of the vehicle.

9. The vehicle of claim 1 , wherein the controller is to output a recommendation for the chosen lead to an operator, wherein the control signals are output in response to further operator interface.

10. The vehicle of claim 1 , wherein the controller is configured to automatically output the control signals in response to the selection of the chosen lead.

11. The vehicle of claim 1 , wherein the controller is configured to select the chosen lead additionally based upon a current draft of the vehicle.

12. The vehicle of claim 11 further comprising a draft sensor to output signals to the controller indicating the current draft of the vehicle.

13. The vehicle of claim 11 further comprising an implement identification sensor to output implement identification signals to the controller, wherein the controller is configured to identify an implement currently attached to the vehicle and to determine the current draft of the vehicle based upon the implement currently attached to the vehicle.

14. The vehicle of claim 1 , wherein the controller is configured to select the chosen lead based upon an implement attached to the vehicle.

15. The vehicle of claim 1 , wherein the controller is configured to determine and record the evaluations of different tractive efficiencies for different leads for each of multiple different rear speeds.

16. The vehicle of claim 15 further comprising:

a ground speed sensor to output signals indicating a ground speed of the vehicle; and

a torque sensor to output signals indicating torque applied to the rear ground traction members and the front ground traction members,

wherein the controller is configured to determine the evaluations of different tractive efficiencies for different leads for each of multiple different rear speeds based upon different ground speeds of the vehicle, different torques applied to the rear ground traction members and the front ground traction members, different draft values for each of the different leads for each of the multiple different rear speeds.

17. The vehicle of claim 15 further comprising a draft sensor for outputting signals indicating the different draft values.

18. The vehicle of claim 15 further comprising an implement sensor for outputting signals indicating an identification of an implement attached to the vehicle and/or a state of the implement, the implement and/or a state of the implement corresponding to a particular draft value.

19. The vehicle of claim 1 , wherein the controller is configured to determine and record the evaluations of different tractive efficiencies for different leads for each of multiple different rear speeds.

20. The vehicle of claim 1 , wherein the continuously variable speed front drive system comprises:

an electric motor;

a hydraulic pump driven by the electric motor; and

a hydraulic motor driven by the hydraulic pump and operably coupled to the front ground traction members by a planetary gear assembly, the planetary gear assembly comprising:

a sun gear coupled to and driven by the hydraulic motor;

a ring gear coupled to and driven by the electric motor; and

a planet carrier carrying planet gears intermeshing between the ring gear and the sun gear, the planet carrier having an output shaft operably coupled to the front ground traction members to drive the front ground traction members.