I have only encountered one aggressive dog whilst cycling who lunged off the footpath as I cycled by on the road. Apparently this dog (who lives in my road) hates anything & everything.
My Flatcoated retriever Teasel has only ever growled once at 1 person & that was a cyclist, it was 5.30am we were walking to the fields got to the end of the narrow pavement there was a male cyclist tucked into the hedge waiting for us to clear the pavement so he could cycle along it (the road is perfectly clear, safe & well lit). She was either being protective for me or telling him it's illegal to cycle on the pavement. If they are on the road she doesn't even acknowledge them.
Whilst walking my 5 I will always put them on the lead when I spot runners, horse riders, other dog walkers etc not too many cyclists across the fields, a problem is when they sneak up behind you giving you no time to act. Mostly it's better just to let mine carry on snuffling in the hedgerows than call them in so drawing attention to people passing.
They have all been running with me, know what bikes are & are most definitely called in when horses are around if only held by their collars because the horse has come along so fast there's been no time to clip leads on. It's only the afghanX who thinks they are big dogs she can trot alongside, no barks, growls or nipping just a haughty prance at the side, she is the one who spends most time on a lead even in the fields because of her independent nature.
What is a problem is a family with husky crosses who have a large scooter to which they attach the dogs to pull them around the fields, these dogs hate most other dogs & have had a go at most of the dogs so the feeling is mutual. the owner bombs around the field & by the time you've seen him and started to call the dogs in he's behind you - nightmare.