Might be easier to go by a schedule than mileage...
I'm new to drive chains, so I'm still finding my rhythm for lube. (Wow... so hard to avoid the double entendres... hard... dammit.)
I've decided to set a schedule rather than a mileage.
My normal riding consists of
28 miles to work
3 miles to lunch
3 miles back
28 miles home
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62 miles per workday
x 5 days per week
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310 miles per week
I figure that since I occasionally need to take the cage (eggs are too delicate for a backpack, don't want to try putting a 40lb bag of dog food in there), and there are weekend runs for fun, then 300 miles a week is a good long-term estimate.
So...
600 miles per cleaning
/ 300 miles per week
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2 weeks between cleanings
Every other Friday I check, clean, and lube the chain. Far easier than being a slave to my odometer. =)