Speed, rpm, gear ratios and tire relationships – Mr. Gasket 8703 Hot Rod Calculator 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 dragstrip 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.
speed — Based on gear Ratio, RPM and Tire Diameter
In this example, calculate your top speed in 2nd gear, assuming
you are shifting at 5,500 RPM. 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.
KeysTroKe
disPlay
1. Clear all stored values:
(Clear All)
all Cleared
2. Multiply the final-drive ratio and 2nd gear ratio, and enter that
as your Gear Ratio:
Gear
raTio
6.1292
3. Enter your shifting RPM and tire diameter:
rPM 5500.
(New Tire Dia)
Tiren
siZe
26.
in
4. Calculate the speed:
*
sPeed 69.409
MPH
* Repeated presses of
will toggle through the inputs and outputs,
starting with the entered Gear Ratio.
(cont'd)
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