I'm thinking along the line of a cycling shirt with a zipped pocket and keeping it in there inside of a holster. I'm concern about it printing.
Id be more concerned about sweat. My bike shirts are soaked, and in short order. You would need a good, water proof holster to keep what ever you were carrying separated from it.
The other issue I have with the pockets on the bike shirts is, anything with even a little weight, tends to rub me badly. A gun would be a killer.
What strikes me first is that if you have a situation to draw your weapon, you'll have enough trouble staying on your bike.
I think in most cases, its best to use your bike to just get out of there (like a car), rather than to try and draw and fight, especially while still on a moving bike.
Things generally happen so fast, you dont have time to react. I once got hit broadside by a German Shorthaired Pointer while riding in a group. I saw the dog coming, charging actually, but I was in the middle of the pack, and had nowhere to go. The dog hit the macadam, thought better of it, panicked, tried to put on the brakes, and started to slide, and slid right into me, and pretty hard. I dont know how I stayed upright, but I did. If I had gone down, it wouldnt have been fun, and the thought of a gun in my shirt, or even a holster, against my body, rolling around on the macadam, isnt a pleasant one. At least in my CamelBak, Ive got padding between me an the gun, and the gun has padding, between it and the ground.
This is one of those cases where you need to adjust your carry mentality, and have a slightly different strategy on what you might do. For me, critters (for the most part), are less of a threat, as I can usually power out of them, if Im paying attention. Even if they are close, a little messing with their timing/ooda loop (dogs have them too, if you didnt know
), and you can usually get by them before they can recover enough to get to you. If not, put the bike between them and me and we have a talk. So far, the only one that got teeth on me, was some little lap terrier, who I thought was "all bark", and he got a hold of my shoe, and was going around with it as I pedaled. I was laughiung harder than I was worried.
People are really not much different, unless youre somehow pinned in, oor knocked down. In either case, my basic plan is to "run away", and create distance, while unlimbering my shooter from my CamelBak, which is really a lot asier and more natural than it might sound. A little practice, and I think you;ll understand what I mean.