Calculating Speeds in Gears

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

[Wayne Presley]

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.