I enjoy riding bicycles and have done so since very young. Perhaps ten years ago, I got into anal play with masturbation and found that massaging my prostate would produce some orgasms to remember.
Just out of curiosity, I tried a butt plug instead of the slim vibrator I usually used. It was pretty good as it too vibrated but didn't allow me to actually pump in in and out. That's when I got the idea.
Riding very early and sometimes very late in the evening on a nearby bike trail which is not used all that much. I find I can leave the house with the butt plug in me, tight spandex type bathing suit on but with the front cut out for my cock, which I leave out. Over this, baggy shorts. Hit the trail and boy, I'll tell you, that butt plug with the very wide base is really grinding on my prostate with each rotation of the pedals.
At first I had a problem cumming too fast but learned to lift my weight off the seat for a while until things start really feeling so good. Then more pressure down on the seat and with my right hand, just rest it on my cock outside my shorts and very soon, my cock goes from hard to super sensitive and super hard and I'm cumming like, well, it's almost impossible to describe. I have on a few occasions run off the bike trail which only makes the feelings more intense, the bumps and all. After the first time, I learned to put a condom on before I head out too. What a mess to clean up if you don't.
I was never really caught doing this but had a couple close calls. I moved a while ago and at first would load up the bike but it got to be a hassle driving home after and all so just quit. Tried a stationary bike but not nearly the same. Those brave and want to try something different, go for it. Just be careful.