Created basic calculations related to gears.

cyclinglib/gain_ratio.py

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+from cyclinglib.gear_ratio import GearRatio
+from math import pi
+
+from cyclinglib.speed import Speed
+
+
+class GainRatio:
+
+    def __init__(self, gear_ratio: GearRatio, wheel_circumference_mm: float,
+                 crank_length_mm: float):
+        self._revolution_length_mm: float = crank_length_mm * 2 * pi
+        circumference_ratio: float = wheel_circumference_mm / self._revolution_length_mm
+        self._gain_ratio: float = circumference_ratio * gear_ratio._gear_ratio
+
+    def speed_at_cadence(self, cadence: int) -> Speed:
+        """
+        Cadence is specified in revolutions per minute.
+        """
+        revolutions_per_second = cadence / 60
+        meters_per_second_crank = revolutions_per_second * (
+            self._revolution_length_mm / 1_000)
+        return Speed(meters_per_second_crank * self._gain_ratio)
+
+    def __str__(self) -> str:
+        return f"Gain ratio: {self._gain_ratio}"
+
+
+def calculate_gain_ratio(front_teeth: int, rear_teeth: int,
+                         wheel_circumference_mm: float,
+                         crank_length_mm: float) -> GainRatio:
+    return GainRatio(GearRatio(front_teeth, rear_teeth),
+                     wheel_circumference_mm, crank_length_mm)

cyclinglib/gear_ratio.py

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+class GearRatio:
+
+    def __init__(self, front_teeth: int, rear_teeth: int):
+        self._gear_ratio: float = front_teeth / rear_teeth
+
+    def __str__(self) -> str:
+        return f"Gear ratio: {self._gear_ratio}"

cyclinglib/speed.py

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+class Speed:
+
+    def __init__(self, meters_per_second: float):
+        self._meters_per_second: float = meters_per_second
+
+    def meters_per_second(self):
+        return self._meters_per_second
+
+    def kilometers_per_hour(self):
+        return self._meters_per_second * 3.6
+
+    def miles_per_hour(self):
+        return self._meters_per_second * 2.23693629
+
+    def __str__(self) -> str:
+        mps = self.meters_per_second()
+        kph = self.kilometers_per_hour()
+        mph = self.miles_per_hour()
+        return f"m/s: {mps} km/h: {kph} mi/h: {mph}"