CALCS | BAS011 CAR PERFORMANCE ESTIMATE |

## NOTATION | |

A | frontal area A (ft^2) |

Ca | aerodynamic constant |

Cd | drag coefficient |

Cl | lift coefficient |

Ct | transmission constant |

Drive | FWD F, RWD R, 4WD 4 |

M | mass (t) |

mu | coefficient of friction |

P | power (bhp din) |

P1a/M | front wheels aerodynamic load fraction |

P1s/M | front wheels static load fraction |

Zcg/WB | (vertical centre of gravity)/(wheel base) |

* Verification that published test performance is realistic

* Performance estimation for cars not tested

* Estimation of power or Cd.A

* For cars with same Ca.A, estimation of performance or power.

Graph showing velocity-time & g-time plots

Ct Constant for power, gearing and weight correction. This is based on tested acceleration of a broad range of road cars and should typically be taken as 0.45 .

A frontal area (ft^2). In deriving the values of Ca and Ct, Cd.A values were taken from Autocar magazines dated 25/09/82 and 11/12/82. It can be difficult to obtain values of A for a particular car but if the max. speed and power of a variant are known, the program can be repeatedly RUN varying A until the known max speed is output, noting that it is only necessary to use a unit Cd of 1.0 during this process. Having obtained an effective Cd.A, the program can be used to estimate the effect of varying any of the input parameters for the car. It may be possible to obtain the value of A either from manufacturer's data or by measurement. A possible means of measurement is to photograph the car from the front, sum the area constituents by means of grid lines and scaling the result by means of a reference measure visible on the photo. Note that the visible parts of the tyres must be included in the area summation.

Cd drag coefficient. This may either be obtained from manufacturer's data or Cd.A may be estimated in the manner described for A above.

M mass (tonnes). This must be an operational mass, typically including two adults, 1/2 tank of petrol, water and oil.

P power (bhp din). DIN is recognised as being a strict measure of power and the uniformity this provides is the principal reason for using it.

Drive: F R or 4 (FWD RWD or 4WD). Drive configuration constitutes one of the parameters determining traction and therefore acceleration at low speeds.

mu road/tyre coefficient of friction (traction parameter). For road cars a value of 0.9 is probably reasonable.

P1z/M front wheels static load fraction (traction parameter). Equivalent to front/rear weight distribution.

Zcg/WB (Vertical Centre Of Gravity)/(Wheel Base) Traction parameter. For road cars a value of 0.25 is probably reasonable.

P1a/M front wheels aero. load fraction. Difficult to obtain. Will have negligible effect on road cars, use a value of 0.5

Cl lift coefficient. Difficult to obtain. Will have negligible effect on road cars, use a value of 0.0

The following sites have been found from a search on 'car manufacturers specifications':

www.carfolio.com

www.theinternetautoguide

These sites have weight distribution & aerodynamic data available but there are some omissions. Advice of other data sources would be welcomed.

## INPUT FORMAT | |||||||||

DAT011 | title | ||||||||

Ca | Ct | Cl | mu | Zcg/WB | P1a/M | ||||

enter | tab | de | limit | ed | data | ||||

Case | Cd | A | M | P | P1s/M | Drive | case title | ||

en | ter | tab | de | limit | ed | da | ta | ||

ENDDAT | |||||||||

## EXAMPLE | |||||||||

## Input | |||||||||

DAT011 | example | ||||||||

Ca | Ct | Cl | mu | Zcg/WB | P1a/M | ||||

.02177 | .45 | 0.0 | 0.9 | .25 | 0.5 | ||||

Case | Cd | A | M | P | P1s/M | Drive | |||

1 | .4 | 21.85 | 1.2 | 83 | .61 | F | Ambassador1.7 | ||

2 | .32 | 20 | 1.4 | 120 | .6 | F | Rover75 | ||

ENDDAT | |||||||||

## Output | |||||||||

OUTPUT | Ambassador1.7 | ||||||||

MaxSpeed: | 97.3 mph | ||||||||

Acceleration: | |||||||||

0toMPH | Time(s) | g | |||||||

10 | 1.02 | 0.447 | |||||||

20 | 2.13 | 0.348 | |||||||

30 | 3.86 | 0.227 | |||||||

40 | 6.33 | 0.163 | |||||||

50 | 9.69 | 0.121 | |||||||

60 | 14.2 | 0.0894 | |||||||

70 | 20.5 | 0.0628 | |||||||

80 | 30.1 | 0.0389 | |||||||

90 | 49.5 | 0.0162 | |||||||

OUTPUT | R75 | ||||||||

MaxSpeed: | 122 mph | ||||||||

Acceleration: | |||||||||

0toMPH | Time(s) | g | |||||||

10 | 1.04 | 0.44 | |||||||

20 | 2.08 | 0.433 | |||||||

30 | 3.46 | 0.285 | |||||||

40 | 5.4 | 0.21 | |||||||

50 | 7.95 | 0.162 | |||||||

60 | 11.2 | 0.128 | |||||||

70 | 15.3 | 0.101 | |||||||

80 | 20.6 | 0.078 | |||||||

90 | 27.6 | 0.0578 | |||||||

100 | 37.6 | 0.0391 | |||||||

END011 |