Like most meditations, you can begin by being aware of your breath while on the bike. How does it feel to breathe in and out while you're moving along? You can spend some time here, feeling the breath going in, going out. You can picture all the good things flowing into your system on the in-breath, and then the out-breath is where everything you don't need flows out. You don't need to pull in forcefully the stuff you need, and you don't need to push out the stuff you don't. It just flows in and out, naturally. This feels very good.
The next place to go is your pedaling. Pay attention to how your feet feel at each stroke. If you need to shift here, do so. You don't want to feel like your feet are pressing hard -- shift until you are one gear away from pressing, and the feet are nicely spinning. You should now be into a good cadence. You can feel how the feet and then the legs are working well. When your feet and legs are moving along with little effort, you can then check out the other parts of the body while you're pedaling. Does your back feel relaxed? Hands? Face? Do you feel like they are all working together, smoothly?
If you can move along, comfortable with your breath, your body, and your pedaling, then you are in your bicycle home. Any time you have an experience on your bike that disturbs you, such as a motorist who came too close, or the recollection of something embarrassing you did the day before, you can return to your breath and your pedaling, and be in a place of calm and peace.