208 LOGGING 
2-ton tractors 20 rated brake H. P. 12 rated draw-bar H. P. 
5-ton " 30-40 " 18-25 
10-ton " 60 " 40 
The motors have four four-cycle vertical cylinders, which have 
a normal speed ranging from 700 to 900 R. P. M. Many tractors 
have three speeds, low from 1 to 2 miles, medium from 2| to 
3|, and high speed from 4 to 6 miles per hour. Speed is 
varied in much the same way that it is on motor-trucks. Full 
crawler tractors have no differential. Two steering clutches of 
multiple disc, dry-plate type, provide independent and positive 
control of each traction member. 
The consumption of gasoline in logging operations, per working 
day of 10 hours, averages from 8 to 11 gallons for a 2-ton, from 
15 to 25 gallons for a 5-ton, and from 25 to 35 gallons for a 10- 
ton tractor. Gasoline is used as a fuel in most cases, since 
it is often impractical to burn cheaper liquid fuel, even in tractors 
which could use it, because the life of the motor is decreased and 
cylinder oil costs are greater. 
The lubricant expense usually does not exceed from $1.50 to 
$2 daily for a 5- or 10-ton tractor. Anti-friction bearings 
are extensively used in these machines. Crawler members are 
well adapted for work in mud, and their flexible track requires 
no lubrication. 
The useful life of a tractor on a logging operation is from 3 to 5 
years when it is used contiijiuously. The depreciation and 
maintenance charges vary widely with the conditions and 
character of work, the care received and the make of the trac- 
tor. Repair bills may be from $2 to $4 a day, especially when a 
crawler tractor on a logging job is operated by a man who is 
not sufficiently skilled to handle intricate machinery. The care 
of tractors at the camp and minor repairs often are made by the 
drivers, but when there are three or more machines at one camp, 
an expert should be employed to do this work. 
Skidding in open forests may be done with crawler tractors 
without any preparation of the roads. In dense forests the roads 
are of the same type as those required for animal logging. Timber 
is skidded by tractors often in long logs or in tree lengths and are 
cross-cut at the landing because the efficiency of skidding as well 
as of cross-cutting is increased. Skidding in tree lengths may 
be facilitated also, to some extent, by felling trees with the tops 
