A little sun on your face is hardly any exposure at all to increase levels. Summer riding though helps with leg exposure.
The best thing you can do is to lay out in your swim suit if you can and get full body rays. I’ll lay out 10-15 minutes per day when I can (even in the spring, summer, or winter when possible). It’s just enough for a vitamin D boost with no risk of burning. It’s also good for mood.
I also think that D supplementation is not the same as getting it made from UV exposure. Research is showing that UV may be good for the heart. It’s good for T levels.
Google, “boost testosterone levels naturally” and you’ll come up with things like weight lifting, sleep, sunshine, and eating adequate protein. Athletes need a lot of protein to support training.