Do folders get sloppy over time?
 

Is it likely that hinges/joints in folders will develop some play after, say, 20 years of hard use by a heavy rider?

Big, hard-riding riders tend to break moving parts and even some static or semi-static parts---like bars, stems or crank-arms. Are they just as exhaustive on folders?

I would say after 4 years, my abused Dahon Piccolo was suffering from lose joints. Then again, that bike was attacked by bike crooks trying to steal it. A heavy rider who abuses any bike can break parts, stems etc.

The trick is to take care of your folding bike and treat it as gold. You'll get many years out of it.

By the way, even though my Piccolo was abused, it still had many years of service left.

Depends on the bike, I'd think....

I would not expect excessive wear for Bike Fridays, Swifts, Bromptons. I'd still check those bits every now and then.

Dahon, Giant Halfway, Downtube and others require a little more attention. For example, the hinges on my Dahon get a little loose on a regular basis, even without folding / unfolding the bike. But as far as I can tell, the mechanisms itself should last about as long as any other moving part on the bike.

Some on the Birdy forum are waaay beyond 10,000 miles with only the usual hub rebuilds, and things like that.

Tires wear out faster, so do hubs.

As far as hinges go, it depends on the bike. The Birdy, Swift, Go Bike, and Bike Friday have no hinges. Now, the range of hinge-free bikes is so large that you can get a true small space performance folder (e.g. Birdy), a fairly cheap closet/car bike (Swift)

The locking mechanisms that hold hinges closed, on Dahons for example, can develop play over time. They can be readjusted when this happens.

Miscellaneous parts can indeed break. It's hard to assess the general risk of this happening compared to non-folders, especially since we're talking about many different brands. Regular inspection to anticipate breakage before it happens is a good idea. Good brands can usually put up with quite a bit of hard usage. Bike Fridays seem to hold up well, among others.

Don't forget the Carryme. It also have an unsplit frame and is the perfect bus companion. Noticeably less flexy than my Downtube. In fact, since most of the flex on my Downtube seems to be in the handle bar stem, I imagine the Carryme is less flexy than the split stem Birdy too.