200 LOGGING 
Trailers are now in extensive use with motor trucks since they add 
greatly to the average load capacity, because all trucks have a 
hauling ability greater than the volume of round timber which 
they can carry. Rubber-tired trailers, with two 40- to 44-inch 
wheels are recognized as the best type, and when operating on 
grades exceeding 9 per cent they should be equipped with brakes. 
They often have double bunks, from 7 to 9 feet long, usually 
8 feet, one being plain and the other having adjustable chock 
blocks. The rated capacity of trailers varies from 5 to 10 tons, 
and usually they carry about 60 per cent of the total load. They 
are connected to the truck by a wooden extension reach which is 
considered more satisfactory than one made from iron pipe 
because the latter bends and breaks more readily and is more 
expensive to repair or replace. 
Success in truck logging is largely dependent on good roads, 
which should be so constructed that they will stand up under 
weights of 20 to 25 tons during all kinds of weather. Trucks 
cannot be operated successfully on dirt or gravel roads during 
wet weather, and dirt roads soon develop chuck holes during 
dry weather unless they are watered.^ 
Various types of plank and pole roads have been developed by 
loggers who have endeavored to improve the traction surface 
in the forest over which they are hauling, especially if the bottom 
is soft or liable to severe wearing. 
Plank roads on tangents have two traction surfaces from 20 
to 30 inches wide which comprise the base on which the truck 
travels. The traction surface should be at least 24 inches wide 
on curves since the trailer has a tendency to cut across the curve 
and to displace the guard rail unless there is ample clearance. 
The stringers comprising the traction surface should not be less 
than 6 inches in thickness, and from 10 to 16 inches in width. 
Two or more pieces form a single stringer, and they are drift 
bolted to crossties spaced about 2^ feet center to center. 
These planks are bedded in the ground surface so that they rest 
on a solid foundation. On grades that exceed 8 per cent, the 
planks forming the traction surface are laid crosswise on a sub- 
stantial base of timbers, the spacing between planks being about 
1 inch. This form of track is more expensive to construct than 
1 During dry weather, a dirt road usually can be kept in condition by the 
application, daily, of 1000 gallons of water per mile. 
