Originally Posted by
cycle_maven
The locknut and or the steering tube might be stripped. One bump and the headset loosens.
I've had threaded headsets stay tight on an unsuspended MTB for a year between services. This was hard riding by a clyde on singletrack, with jumps and drops. Maybe if the threads get damaged it will loosen up, but mine is/was fine. I think in terms of actual mass times acceleration, a road bike going over a half-inch obstacle on skinny tires puts more instantaneous force on the headset than a suspended MTB dropping a foot. The reason threadless headsets evolved is because keeping 5 different lengths of suspension forks of each type in stock was economically unfeasible.
Not
all of my headset
always loosened. But it was common enough. And, if it happened in the field further than a few hundred yards from a trailhead, there is no way to fix it. When it happened, the headset was quickly ruined.
Although a headset loosening can happen with suspension, it's less common for obvious reasons. I am talking about mountain bikes with rigid forks before the advent of suspension forks when comparing it to road bikes.
Finally, although threadless does offers benefits to manufacturers, they offer equal, if not greater, benefit to riders. They reduced the number of loosening headsets on mountain bikes to near zero and, even if the headset does loosen, they are simple to fix in the field.