Whenever their is a movement, friction comes into action. The same is the case with earth moving equipments. We term this as rolling resistance and this has to be overcomed by vehicle engine so that it can move on that surface. This is the formula to calculate rolling resistance

R=R_fW + R_pPW

where

R = rolling resistance, lb (N)

p = tire penetration, in (mm)

R_f = rolling-resistance factor, lb/ton (N/tonne)

W = weight on wheels, ton (tonne)

R_p = tire-penetration factor, lb/ton in (N/tonne mm) penetration

R_f usually is taken as 40 lb/ton (or 2 percent lb/lb) (173 N/t) and R_p as 30 lb/ton in (1.5% lb/lb in) (3288 N/t mm).

So the above equation becomes

R=(2%+1.5 % p) W’=R’W’

where

W’ = weight on wheels, lb(N)

R’ = 2% + 1.5%p.

Case – When we have a slope

G = R_gsW

where

G = grade resistance, lb(N)

R_g­ = grade-resistance factor = 20 lb/ton (86.3 N/t) = 1%

s = percent grade which is positive for uphill motion and negative for downhill motion.

The total road resistance is calculated by adding the rolling and grade resistances and is given by:

T = (R’+R_g s )W’ =(2%b + 1.5%p + 1%s)W’

Loss due to Altitude

Generally we take 3 percent pull loss for each 1000 ft (305 m) above 2500 ft (762 m).

Measurement Units

Measurement units and standards are different in different countries but to maintain a standard, SI units are mostly used when dealing with projects involving different countries or even different states. Small projects can be done with the locally used unit system but when the project is big, one standard unit system is to be used.

Two most common system used in the United States are

United States Customary System (USCS)

System International (SI)

But the SI unit system is more widely used all over the world. Following is the table which shows how you can convert USCS measurements in SI measurements. ( Just multiply the USCS amount with the corresponding figure given in table below

Convert USCS into SI Units

USCS unit X Factor = SI unit	SI symbol
Square foot X 0.0929 = Square meter	M2
Cubic foot  X 0.2831 = Cubic meter	M3
Pound per square inch X 6.894 = Kilopascal	KPa
Pound force X 4.448 =  Newton	Nu
Foot pound torque X 1.356 = Newton meter	N-m
Kip foot X 1.355 = Kilonewton meter	LN-m
Gallon per minute X 0.06309 = Liter per second	L/s
Kip per square inch X 6.89 = Megapascal	MPa