Speed, rpm, gear ratios, and tire relationships – Calculated Industries 8703 User Manual
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Speed, RPM, Gear Ratios, and Tire Relationships
Speed, RPM, gear ratios, and tire sizes are interrelated, and with
any three values, the fourth value can be solved on your calculator.
Getting these four areas set up properly on your road or drag strip
vehicle can have very positive performance effects.
For the following examples, we will use a 1990 Ford Mustang
5.0 LX with a 5.0 liter V8 engine and the T-5, 5-speed manual
overdrive transmission. The manual transmission ratios are 3.35
for 1st gear, 1.99 for 2nd, 1.32 for 3rd, direct drive 1.00 in 4th, and
an overdrive 0.68 in 5th. The final-drive ratio is 3.08. Lastly, the
tires have a diameter of 26 inches.
In this example, calculate your top speed in 2nd gear, assuming
you are shifting at 5,500 RPM.
First, clear the memory on your calculator, including temporary and
semi-permanent entries.
KEYSTROKES DISPLAY
ALL CLEArEd
You will need to find the correct multiplier for 2nd gear. Recall that
the final-drive ratio is 3.08 and 2nd gear is 1.99.
1. Multiply the final-drive ratio and 2nd gear ratio, and enter that as
your Gear Ratio:
GEAR S 6.1292 RATIO
2. Enter your shifting RPM and tire diameter:
RPM S 5500.
TIREn S 26. SIZE IN
3. Calculate the speed:
SPEED 69.409 MPH