gistfile1.rb

class Gear
        attr_reader :chainring, :cog, :wheel

        def initialize(chainring, cog, wheel=nil)
                @chainring = chainring
                @cog = cog
                @wheel = Wheel.new(rim, tire)
        end

        def ratio
                chainring / cog.to_f
        end

        def gear_inches
                ratio * wheel.diameter
        end
end

class Wheel
        attr_reader :rim, :tire

        def initialize(rim, tire)
                @rim = rim
                @tire = tire
        end

        def diameter
                rim + (tire * 2)
        end

        def circumference
                diameter * Math::PI
        end
end

@wheel = Wheel.new(26, 1.5)
puts @wheel.circumference

puts Gear.new(52, 11, @wheel).gear_inches

puts Gear.new(52,11).ratio