NORTHEASTERN FOREST EXPERIMENT STATION 

Upper Darby , Pennsylvania 

t -- 

No. 71 

1957 

I -. 

Gentle-Grade Roads Mean Faster Skidding 

Skidding is often an expensive operation. This is 

especially true in mountainous country where the terrain is 

difficult and skidding distances are usually long. 

The customary logging practice in many parts of the 

Appalachian region is to run skid roads straight up and down 

hill. This is both inefficient and destructive. Roads wash 

out during heavy rains; watershed values are damaged; and 

shut-downs are necessary when the steep roads become slick 

and soft with rain or snow. 

Our experimental logging operations on the Fernow Experimental Forest have yielded considerable evidence to indicate that watershed values can be preserved and logging 

costs can be reduced by carefully laying out the skid roads 

at gentle grades up the s10~e.l With such a planned skidroad system, the total mileage of road required to log a 

given area may be much less. Also, we believe, the total 

skidding time may be less than by the old straight-up-anddown methods, 

In planning such a skid-road system, one of the practical questions that arise is: what is the ideal grade for 

skidding, considering both the incoming loaded and outgoing 

emptytrips? That is. onwhat percent ofgrade canthe 

skidder safely travel the fastest in terms of average roundtrip speed? 

To answer this question, at least for our particular 

skidding equipment and conditions, a time study was made on 

a commercial-sized logging operation on the Fernow lkperimental Forest. Skidding times were recorded over bulldozed 

roads of various grades. These ranged from uphill grades 

'Weitzman, Sidney. Mountain logging. South. Lumberman 185 (2321) : 199-202, illus. 1952. 
550 

500 

450 . I a 

g 0 

0 

0 

k I 

I 

s 400 

0 

0 t.- 

0 

4f 

I 

I 

0 

/ 

0 

0 

1 

dP 

P 

200 

nV 

rn 

LOADED TRIP 

0 

-10 -5 0 5 10 15 2 0 2 5 30 35 40 

SKID-ROAD GRADE, IN PERCENT 

Figure 1.--Average time for tractor and sulky to travel 

a 

1,000 feet on skid roads of various grades. 

(from cutting area to landing) of 7 percent to downhill 

grades of 39 percent. A TD-9 tractor equipped with winch 

and a rubber-tired sulky was used. The loads (the average 

run for the operation) ranged from 610 to 1,410 board feet. 

Times were kept separately for empty and loaded trips. A 

total of 78 observations on empty trips and 45 observations 

on loaded trips were taken. The average time required to 

cover a specified distance--1,000 feet--mas plotted against 

grade percent separately for empty and loaded trips (fig. 1). 

For the loaded downhill run, the most efficient grade 

was about 14 percent, but there was little difference in 

skidding time between grades of 6 and 27 percent. For grades 

of less than 6 percent the time increased rapidly because of 

increased friction. For grades of more than 27 percent, the 

time increased rapidly because greater care had to be taken 

to prevent the load from getting away. 

For the empty uphill run, the tractor was able to 

operate at top speed on grades up to about 12 percent. For 

steeper grades the rate of speed decre~sed rapidly. 

2 

1 

- 

EMPTY TRlP 

I 

0 

I 

0 

'qO' 
From the two curves derived from these data (fig. 1) , a table was prepared listing the time required to make a 

round trip for various grades (table 1). Skidding was fastest when the loaded trip was on a down-grade of about 10 

percent. However, there was little difference in round-trip 

times within the range of 5- to 15-percent grades. 

Table 1.--Average tine needed to skid a distance of 

1,000 feet on roads of various grades 

Jt Negative value is for grades running uphill from the 

cutting area to the landing. 

Grade of 

skid road 

(percent ) 

The data presented here are averages for a range of 

load sizes and road conditions. Although these factors 

doubtless affect skidding speed, not enough observations 

were obtained to provide reliable quantitative estimates of 

their effects. Despite these shortcomings, the data provide 

a good general picture of holm; skidding speed varies with 

grade. They also show rather conclusively that average 

skiddinp speed over a given distance is faster on gentle 

grades of 5 to 15 percent (downhill with the load) than 

either on the level or on steeper grades. 

--RUSSELL J. HUTNIK and SIDNEX WEITDIAN 

Minutes Minutes Minutes ?C 

-5 3.7 5 3 9 0 

O 3 7 4.2 7.9 

5 3.7 3 7 7.4 

10 3.7 3.5 7.2 

15 4.1 3.4 7.5 

20 5.0 3.6 8.6 

25 6.0 3.9 9.9 

30 6.9 4.6 11.5 

35 7-8 5.9 13.7 

bpty trip 

Mr. Hutnik is research forester, Mountain State Research Center, stationed at Parsons, iJ. Va. Mr. Weitman, 

formerly in charge of the research center in Elkins, is now 

chief of the Division of Watershed Management Research, Lake 

States Forest Experiment Staticn. 

Agriculture-Forest Service-Upper Darby 3 

Loaded trip Round trip