I write as one who has been there, done that, and torn the T shirt!
You may also have heard that swans can break a man’s arm, but it doesn’t put you off walking by the river.
What happens when you UPD from a Coker?
If you UPD forwards, the seat hits the ground hard. The angle of impact is much steeper than on a smaller uni, so the top of the seat may tear. However, it does act as a brake, and the Coker will usally stop within a few feet. The rider goes much further than the Coker!
This only happens if you are riding somewhere near your maximum speed. Otherwise, it’s just like a UPD on a normal uni, and you can usually catch the seat with your hand as you step off.
But the ‘There goes my Coker!’ dismount is very particular to Cokers, and is mainly a problem for new riders.
It ONLY happens when you try to slow down or stop the Coker, and you fail. So it COULD happen on a very steep down hill, or it COULD happen if you tried to stop too quickly.
What happens is you fail to allow enough time for the wheel to stop. You try to stop in 2 wheel turns instead of 3, or 3 instead of 4. You misjudge it, and the rising pedal ‘flicks’ past top dead centre, and as your foot was exerting maximum downward force on it, your foot kicks the Coker forwards. You UPD off the back, and the Coker sets off on a frolic of its own, dragging its seat behind it. This can also happen on a smaller uni with ultra short cranks, but the Coker definitely goes further.
This has happened to me approximately 3 times. Two of those were when I was very new to riding it; one was when I had a particular reason for dismounting from high speed - it was the end of a timed distance ride.
In normal use, once you have learned to gauge the stopping distance, the situation will never arise. Do NOT let it stop you buying a Coker.
How safe in traffic? Dismount for any junction where you have to give way. Don’t rely on idling. (It can be idled, but I think not reliably enough to be safe on the highway.) If you stick to fairly quiet roads, don’t go for silly speeds, and use common sense and dicretion, it’s safe on the roads. For pure road use, I prefer the greater safety and manoeuvreability of a 28.