I've had pretty bad asthma since ~age 8 or 10 (>30 yrs). Mostly allergy and temp/humidity shock related, not exercise at all per se. So I wrap a scarf around my lower face, very loosely, when biking in the 20s, for instance, to give the air a little time to warm up and moisten up before it gets inside me.
I think it's all about knowing yourself and your asthma, and I've definitely had time to ponder it, work around every permutation of treatment, avoidance, etc...