Fender troubles in city
 

I have to take my bike in a small elevator, so sometimes I need to hold the bike up on just the rear wheel (front tire is in the air at about head height).

I'd like to cut my fender down a bit to allow this function - where can I find a diagram that will show me how much I can cut off safely and still avoid a trail on my back. I don't ride in a group, so keeping people behind me dry is not a priority. Thanks!

Use a meter stick, or something similar, to make a tangent using the wheel as the circle. The part of the tangent that points up is the path of the water spray from that part of the wheel the stick is touching. So draw that line just short of vertical and where the stick intersects the fender is where you cut. Should work in theory, though I've never tried it myself.

Take a look at photos of Handsome Cycles Mud Butler fenders as a reference for length. I use them on my bike, which I have to stand up in the elevator everyday. Unless I go completely vertical, the bike doesn't hit the fenders. Total coverage during riding and people don't mind riding behind me.

Sounds like the wrong bike for the purpose. However, trimming a fender by eyeball should be a piece of cake.

I commute on a Bianchi Bergamo and the rear fender works great for keeping the spray under control and I can walk the bike around nearly vertically as needed. There's a photo at this site:
https://www.bicyclebluebook.com/sear....aspx?id=96043

HTFU and ride the stairs, weenie.

Water leaves the tire on a tangent (although it looks radial). So, if you cut the fender to where it jut barely allows the rear tire to touch the ground when vertical, the spray leaving at that point would be vertical and not wet you unless there were a strong tailwind.

You could buy more forgiveness to put the bike vertical by attaching a stiff but flexible, rubber or plastic extension 4 or 5 inches long. That would allow the combined fender to extend beyond 3 o'clock (when the bike is on the road) and yet allow standing on the flap without damage.

BITD when I had a fendered bike and rode elevators with it, used a stiff rear brace that could handle the weight of the bike then stood the bike up on my foot and "walked" it into the elevator, and out again at my floor.