Yes, it's ok... sort of... I would probably say "Since I took up biking...", because if you've managed to lose 10 kilos by biking, it must have been over several weeks or a couple of months, I imagine. When you "have a crack" at something it's usually a short experimental attempt at an activity. Personally, I need to lose about 10 kilos, but I think "having a crack" at cycling might not be sufficient to achieve the desired result! 🙂 I'd probably give myself at least three months 😁