I find having a secondary bike as a good backup investment, especially on those pre-morning commutes when one discovers a flat tire, broken spoke, or when one bike needs to be taken offline for a longer than expected duration due to repair work.
Instead of a radical difference between the two bikes, I try to make my bikes to being a close copy of each other, that way the riding styles and carrying capacities are similar.
Alternating my rides regularly between the two bikes also helps in spreading the wear among the bikes, plus it lets me have more flexibility when it comes to my maintenance schedule, giving me more time to make necessary repairs or maintenance.
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Prisoner No. 979