portion to use. Tread can be replaced through recapping many times. A 

 maximum of three recappings is assumed in this study. Figure E-1 shows 

 the change in costs with tire use per day for four tread conditions. As 

 more recappings are applied the original tire cost is spaced over more 

 miles. 



Lubrication and oil change are carried out every 2,000 miles. This 

 sets a constant cost per mile for the two combined of 0.413 cents for the 

 190-crate truck and 0.461 cents for the 220-crate truck. 



Figure E-1. Tire Cost Per Day Relative to Daily Mileage of Truck. 



100 200 



Level of tire use — miles per day 



300 



Repair and Maintenance Cost 



Repair costs depend primarily on truck size, age, and mileage oper- 

 ated. As truck size increases these costs increase, but not in proportion 

 to capacity or price of truck. The larger the truck the higher the repair 

 bill for any particular job. 



For any particular truck size, repair and maintenance costs per mile 

 tend to increase with miles traveled at an increasing rate until it be- 

 comes necessary to carry out a major overhaul or replace the motor. 

 However, time depreciation affects repair and maintenance costs. A 

 truck traveling 50,000 miles in one year is likely to have a lower repair 

 bill per mile than one traveling 50,000 miles in five years. 



In this study it is specified that trucks will be traded just prior to 

 major overhaul or engine replacement. Based on data from assembly 

 firms, dollar costs of repairs for each successive 10,000 mile interval were 

 constructed for each truck size. The accumulation of these through each 

 10,000 mile interval until major overhaul or engine replacement occur- 

 red yielded the total repair cost. 



56 



