374 AGRICULTURAL ENGINEERING 



axle is pivoted at the center, and steering is accomplished by 

 revolving the axle about this pivot or king bolt. The main 

 advantage of this system is that the steering wheels may be 

 turned while the tractor stands still. 



In the other style the axle is pivoted just inside of each 

 steering wheel and each wheel is turned about its own pivot. 

 This style of steering mechanism is easy to handle while in 

 motion. It is quite positive, that is, there is no slack to take 

 up in the chains, and it is of more rapid action than the other 

 style. 



The Traction Wheels. The traction wheels should be 

 carefully considered in making a selection of a tractor, because 

 certain wheels are adapted to certain conditions. If the 

 ground over which the tractor must pass be soft, it is highly 

 desirable that both the drive and the steering wheels be as 

 high as practical. Wheels of large diameter present a larger 

 section of their periphery to the surface of the ground, and 

 so cut in but slightly. Extensions are provided by all manu- 

 facturers for making the drive wheels wider for work in 

 soft ground. Where the soil is exceedingly soft, the cater- 

 pillar tread or creeping grip should be used. It is possible to 

 use this type of tractor in marsh or swamp soils or over sand 

 where it is impractical to use horses. 



The Equipment. Too much emphasis cannot be laid upon 

 the importance of securing a tractor which is well equipped. 

 Often there is a serious loss of time resulting from the poor 

 quality of parts that cost but a few cents. A purchaser 

 should see that the tractor has modern high-class ignition, 

 carburation, and lubrication systems. 



QUESTIONS 



1. What are some of the conditions under which the gas tractor 

 can be used with economy? 



