A cyclist appears at the end of the path. Your dog's head snaps around, the body drops forward, and you are holding 60 pounds of dog going the other way. Joggers do the same thing at half the speed.
Why bikes and joggers are the worst case
They move fast, they move past rather than toward, and they keep going. To a dog that reads as something leaving, which is the pattern that triggers chasing most reliably.
Chasing also pays for itself. The bike does go away every time, so the behaviour works from your dog's point of view, whether or not you say anything.
The one number that decides everything
Working below the threshold at which your dog reacts is the condition for learning in the presence of a trigger. The practical test is food: if your dog cannot take a treat from your hand, you are too close.
Find that distance once and use it as your working number. For most adolescent dogs on a shared path it is 30 to 60 feet, which is further back than it feels reasonable to stand.
What to do on the walk tomorrow
Walk on the far side of the path, with your body between your dog and the traffic. Keep 4 feet of slack in a leash held with both hands.
Scan ahead, not at your dog. You want to see the bike 10 seconds early, which is the difference between moving away and being run past.
The moment you see one, say your dog's name once and walk briskly 20 feet off the path. Feed 5 treats one at a time while the bike passes.
Feed until it is gone, then stop feeding. The food starts when the bike appears and stops when it does not.
Do that same sequence every time for 3 weeks, including the times it feels unnecessary. Consistency at a workable distance is what changes the association.
Where to practise on purpose
Sit on a bench 60 feet back from a cycle path with a bag of chicken. Feed 3 pieces per bike, do 10 bikes, and go home. That is the session.
Move 10 feet closer only when your dog can watch a bike, take food, and look back at you without any pull. That means 8 bikes in a row.
Go back 20 feet whenever a bike surprises you both at close range. That is not a setback, it is the plan working.
Equipment, honestly
A well-fitted harness with a front and back attachment, and a 6 foot leash. No extending leash on a shared path, because you cannot shorten one in the second you need it.
You will be told a correction on a prong or remote collar stops chasing quickly. A review of aversive training methods found them associated with worse welfare outcomes and no training advantage. Dogs trained with aversive methods showed more stress-related behaviour than dogs trained with rewards.
Safety note
Get help now if your dog has made contact with a person or a cyclist, or if there has been any bite. The same applies if the lunging comes with the kind of hard, silent stillness that is not excitement. That needs a veterinary examination and a qualified behaviour professional. Book the veterinary appointment too if this started suddenly, because pain often presents as a change in behaviour.
Today's version, in one line: find the distance where your dog can still eat, and walk tomorrow from there.