I made the spreadsheet initially because someone was telling me how much money they saved and they counted the miles they rode on the bike. No... We then chatted about what was spent in support of the bike to include increased wear and tear and so on. I love spreadsheets so I made one to capture all that. The costs of normal bike things were pro-rated on commute vs non-commute. Forty percent of miles due to commuting? Then forty percent of new tires cost gets attributed to that column. The fun thing is that as I improved the spreadsheet I just had to mark a line "C" for it to get included and it all calculated out.

If the commuting would put me significantly ahead I could easily say "It's an investment" but as I'm not a large mileage commuter I can't trick myself into it. So I just buy things anyway.