Hi medion,
Hard to say, especially without knowing what you're eating, how much insulin you're using, and what type of insulin it is.
I'm a cyclist too though (7 miles per day each way to the office and back, and a long run out at the weekend if I'm lucky).
The exercise definitely makes the insulin work much more effectively. At a guess, you're cycling after breakfast and the food is balancing the insulin you use first thing. On the way home, you probably haven't eaten for a few hours and the insulin still in your bloodstream is made more effective without the food to counterbalance it.
I find if I cycle really hard (race those couriers!) it will actually raise my blood sugars as a result of the stress hormones (adrenaline, cortisol). Options might be to reduce your basal dose to have less insulin circulating, or eat something small before the ride home.
Let us know how you get on.
All the best,
fergusc