THE STEAM TRACTOR 59 



This effects a better distribution of weight for tractive effi- 

 ciency on level ground than the rear mounting, unless the 

 front wheels of the latter type tractor are set as far forward 

 as possible. However, the side-mounted construction is more 

 apt to lift the front wheels from the ground on a grade, and 

 the fire box may be dangerously weakened in the compar- 

 atively small area supporting the bracket. It is difficult to 

 keep the stub axles rigid, and the drive-wheels tend to become 

 closer together at the top, when, of course, the axle bearings 

 wear unevenly and the gears are thrown out of proper align- 

 ment. Truss axles extending underneath the fire box to each 

 stub axle relieve the strain on the fire box, but do not prevent 

 the unequal wear on the gears. On return-flue engines the 

 wheels are often mounted on a continuous axle ahead of the 

 fire box. On some very successful plowing engines a separate 

 steel frame is made to carry the engine and gearing, so as to 

 place no strain from these sources upon the boiler. This is 

 known as the under-mounted or frame-mounted type. It 

 accomplishes its purpose and makes the engine accessible at 

 the expense of greater exposure of the working parts to dust 

 and grit. 



Traction Wheels 



The patent expert of one of the great machinery companies 

 once said* that in building a tractor he would first build the 

 wheel and then the remainder. The traction wheel is a fun- 

 damental point, for no matter how much power the engine 

 may develop, or how efficient the traction gearing may be, the 

 tractor will not be successful if the wheel fails properly to grip 

 the ground. The effectiveness of the drive-wheel depends 

 not only on its character, but upon the distribution of the 

 tractor's weight. Nor will the same wheel with the same 

 weight upon it prove equally efficient in all conditions. It 

 has been claimed by advocates of special caterpillar and walk- 

 ing wheels that the slippage of the round-wheeled tractor is 



