Calculated Industries Hot Rod Calc 8703, User Manual

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36 — H
OT
R
OD
C
ALC
™
outputs, starting with the current final-drive ratio input.
The effect to the final-drive (D-EFF) of going from a tire diameter
of 28.9 to 33 inches is an estimated ratio of 2.697, which will
create a fairly noticeable loss in your four-wheeler’s pickup from
a stop or while rolling down the highway. To get back to a similar
responsiveness on the new 33 inch diameter tires, you would want
to install a set of final-drive gears closer to a 3.5 ratio (D-EQV).
Next, calculate the effect of the tire change to your speedometer.
You made the switch to the 33 inch tires, and you want to know
what your actual speed will be with an indicated (gauge) speed of
65 MPH.
Don’t clear the memory on your calculator, we can use your inputs
from the previous example which are currently in memory.
4. Enter a target indicated (gauge) speed of 65 MPH:

SPEED S 65. MPH
5. Calculate the effect to speedometer:

TIRE 1.142 RATIO

(Final drive ratio)
D-EFF 2.697 RATIO

(Equivalent drive ratio)
D-EQV 3.517 RATIO

(Actual speed)
SPD ► A 74.221 MPH

(Gauge speed)
G ► SPD 56.924 MPH

SPEED S 65. MPH
Repeated presses of [Tire Ratio] will toggle through the inputs and
outputs, starting with the current final-drive ratio input.
For the entered indicated (gauge) speed on your speedometer of
65 mph, the actual speed is 74.221 mph (SPD
►
A) after switching
from 28.9 to 33 inch diameter tires. So, if you want to be going the
legal 65 mph, you want your speedometer to read about 57 mph.