25mph is 36.7 ft per sec.

At 5 ft behind him, you have 0.14secs to react if he has to do an emergency stop - which he can probably do in a shorter distance than you.

And by react, I mean slam on your brakes while simultaneously deciding what your best course of action is and where you should steer in order to avoid becoming an exhaust - sorry - muffler ornament. People who react that fast are generally known as benjohnsons

In cycling language, riders who do as you claim you were doing are known technically as "the late..." Donations in lieu of flowers...