Calculating Speeds in Gears

G

Guest

Guest
Someone had requested info on this subject in the old forum and am passing this along.

The formula ts as follows:
AN=1000/(GR*DR)*(WD*PI/36)*60/1760 where:

AN=MPH per 1000 RPM
GR=Gear Ratio (1st, 2nd, 3rd, etc)
DR= Differential Ratio (e.g. 3:44)
WD=Wheel diameter in inches

Using the GT40, with a rear wheel diameter of 26 inches, a 3.44:1 differential ratio and a 5th gear ratio of 0.82, you can make the following predictions concerning its top speed in 5th gear at 6,000 rpm.

1000/(0.82 * 3.44 = 354.5 (Wheel revolutions per 1,000 RPM)
26 (Wheel diameter)/36 (convert diameter to yards) x 3.1426 (PI) = 2.27 (Yards per wheel revolution)
354.5 (Wheel revs per 1000 RPM) x 2.27 (Wheel diameter in yards) / 1,760 (Yards per mile) = 0.457 (Miles per minute per 1,000 RPM)
0.457 (Miles per minute per 1000 RPM) x 60 = 27.43 MPH at 1,000 RPM
At 6,000 RPM would give me a top speed of ≈165 MPH.

For those who are computer literate, the following BASIC program would expedite calculations.

10 CLS
20 INPUT “Enter wheel diameter in inches”; WD
30 INPUT ”Enter gear ratio”; GR
40 INPUT “Enter differential ratio”; DR
50 AN=1000/((GR*DR)*WD/36*PI)*60/1760
60 PRINT AN;” MPH PER 1000 RPM”
70 END
 
I have a Excel spreadsheet that has all the Audi box ratios and could be used for any by substituting the ratios in your box if you want it emailed to you.
 
Back
Top