The "appraised value" of used bikes varies a lot by location... The location could impact your formula, and each location has different hot items. For example, in my area a mountain bike will retain more value than a road bike or hybrid.
Remember that with bikes, typically any warranties are not transferable, so this impacts the value of recent model years more than things like a car, where the warranty might follow to the new owner.
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Slow Ride Cyclists of NEPA
People do not seem to realize that their opinion of the world is also a confession of character.
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