# Conversions and Formulas

### Formulas

The horsepower needed to overcome aerodynamic drag at a given speed is: HP = k*A*Cd*v^3

` Where HP is horsepower, k is the density of air, A the frontal (cross-sectional) area, Cd the  coefficient of drag, and v the velocity. The density of air depends on  conditions but is nominally .08 lb/ft^3.`

Aerodynamic drag is calculated as: F = 1/2 CDAV^2

` Where: F - Aerodynamic drag force, C - Coefficient of drag, D - Density of air (nominally  about 0.08 pounds per cubic foot.. yes I know that's not a technically accurate mass but  it saves converting to and then back from metric), A - Frontal area, V - Velocity of  object`

To estimate engine HP from 1/4 mile run: HP = ((trapspeed/234)^3) * weight

Tire Diameter in inches = ( ( Tire Width * Aspect Ratio ) / 25.4 ) * 2 + Wheel Diameter

` Example: 245/40-17 would be ( ( 245 * .40 ) / 25.4 ) * 2 ) + 17 =  24.71653543307`
` `
` MPH = ( RPM * Tire Diameter ) / ( ( gear ratio * final drive ) * 336 )`
` Example: ( 8000 * 24.71653543307 ) / ( ( .771 * 4.062 ) * 336 ) =  187.9074535627 MPH`
` Of course the tires expand at high speeds so this isn't totally accurate.`

### VERY Rough Rules Of Thumb

Each 10 degree F drop in temperature = 1 % gain in HP

` Each 10 lbs. removed from the vehicle = 1 HP for acceleration (top speed is not noticably  affected)`
` Each 10 HP added = 0.1 second in the 1/4 mile`

### Volume

1 Imperial Gallon = 4.5461 liters (l)
1 liter (l) = 0.2200 Imperial Gallons
1 US Gallon = 3.7854 liters (l)
1 liter (l) = 0.2642 US gallons
1 Imperial Gallon = 1.2009 US Gallons
1 US Gallon = 0.8327 Imperial Gallons
1 liter = 61 Cubic Inches (ci) [approximate]

### Distance

1 mile (mi) = 1.6093 kilometers (km)
1 kilometer (km) = 0.6214 miles (mi)

### Fuel Consumption

1 Mile/Imp. Gallon = 0.354 kilometers/liter (km/l)
1 kilometer/liter (km/l) = 2.825 miles/Imp. Gallon
1 mile/US gallon (mpg) = 0.425 kilometers/liter (km/l)
1 kilometer/liter (km/l) = 2.352 miles/US gallon (mpg)

### Mass

1 kilogram (kg) = 2.2046  pounds (lbs)
1 pound (lb) = 0.4536 kilograms (kg)
1 gram (g) = 0.0353 ounces (oz)
1 ounce (oz) = 28.35 grams (g)

### Pressure

1 pound/square inch (PSI) = 0.0689476 bars
1 bar = 14.5037681 pounds/square inch (PSI)

### Power

1 PS = 0.98632 HP
1 HP = 1.01387 PS
1 kgm = 7.23 lb. ft.
1 lb. ft. = 0.14 kgm

Reference