I posted this up about 3 years ago over on the OC, thought it might be useful to someone over here.
I'm sure a few people have asked in the past for data on the aerodynamic properties of the GT-Four, however after several searches I haven't been able to turn up anything.
So I decided to get the calculator out, sit down and do some research / testing. The procedure is from Race Technology who specialise in dataloggers etc, you can find them with a quick google.
To calculate the aerodynamic properties the procedure is as follows: -
On a flat road with no wind accelerate the car to 65 mph put the car in neutral to allow the car to decelerate, record the length of time it takes for the car to slow from 60 mph to 55 mph
I did this 3 times and recorded times of 5.3, 5.3 and 5.2 seconds for the purposes of the calculation I will use 5.3.
The next test is similar: -
Again on a flat road accelerate the car to over 15mph and place the gearbox in neutral record the time taken for the vehicle to slow from 15mph to 10mph, I also did this test 3 times and recorded times of 9.6, 9.5, and 9.6 seconds. I will go with 9.6 for the calculation.
Calculation
CdA = Mass x (Time2 – Time1) / 169 x Time1 x Time2
Where – Mass = Weight of the car, I have assumed a weight of 1500 kilos
Time1 = 60-55mph time
Time2 = 15-10mph time
CdA = 1500 x (9.6 – 5.3) / 169 x 5.3 x 9.6
CdA = 6450 / 8599
CdA = 0.75
With this figure we can also derive other values, the website
http://www.bgsoflex.com/airdragchart.html gives details how to calculate the frontal area of a car, I took the dimensions from the UK sales brochure for the Celica:- Height – 1.305 metres
Width – 1.725 metres
Using the arbitary figure of 85% from the website you get a frontal area of 1.91 m2
Using the frontal area and the CdA the co-efficient of drag can easily be found:-
Cd = CdA / Frontal Area
Cd = 0.75 / 1.91
Co-efficient of drag = 0.39
The rolling resistance is calculated as: -
Rolling Resistance = 238 x Time1 – 11 x Time2 / 1000 x Time1 x Time2
Rolling Resistance = 238 x 5.3 – 11 x 9.6 / 1000 x 5.3 x 9.6
Rolling Resistance = 1155.8 / 50880
Rolling Resistance = 0.0227
So in summary:-
CdA = 0.75
Frontal Area = 1.91 m2
Co-efficient of Drag = 0.39
Rolling Resistance = 0.0227
If you can compare these with figures for other cars – most manufacturer websites quote these figures and
http://www.carfolio.com has figures for some cars.
The parameters for the road test were as follows: -
Facelift UK ST205 with low 3 point rear spoiler
Goodyear Eagle F1 GSD3’s inflated to 35psi (cold)
½ tank of fuel.
Apologies for the immensely long boring and totally geeky post but maybe someone will find it useful.
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