Why not claim mileage for biking?
In our expense report system, it's specifically listed as car mileage.
My casual internet searching says it looks sketchy to use the car rate for biking, using search terms like "irs biking mileage deduction". You might be able to manually deduct biking expenses but not using the $0.5x/mile rate cars get.
We have managers with diesel sipping Jettas and managers with big @$$ pickups, all claiming the same mileage rate as they travel from facility to facility. Obviously some are making better net revenue than others from the flat rate per km reimbursement.
On the continuum from big @$$ pickups through TDI VWs, hybrids and Teslas, into motorcycles, Vespas, and electic scooters, and then into true electric assist bicycles and then pedal bikes, some creative tax lawyer must be figuring out the legitimacy of claiming mileage for a pedal bike.
I think the easiest way to flip it around would be to "normally bike" to work (is that...3x? 5x? per week?), then when I get sent somewhere that's too far for practical biking, I wouldn't have to deduct my standard commute. Until something else works. That and I suppose I could ask if the mileage deduction is standard for "just get there" versus mode, as far as reimbursement.
Kind of a weird system anyway - we have something like 3-4 of us in a more or less line near the start of our big weekly drive, but since you get reimbursed, no one's killing themselves to set up carpools. Seems like it'd be beneficial to have a "got there" rate maybe not the full charge to encourage carpooling. (in other words, I make money driving myself versus ride sharing unless it's my car).