What's an "Auto-Mini" folding bike? Can I use one for decades without having to replace the frame? I've been thinking of buying an internally-geared folding bike for commuting (5 km each way) and errands. I want to spend $100-$200, but I want a reasonable-quality frame; I don't want to ever have to replace the frame with a new one.

I see a bunch of "Auto-Mini" folding bikes for sale on Craigslist in my city.

How are the frames: are they well-made?

How's the bikes' ride quality?

[Edit: I've read that the frames are prone to cracking. Is the Auto-Mini still a reasonable choice, considering the criteria I mentioned above?]
Auto-Mini folding bikes


Auto-Mini folding bikes were made by the Austrian corporation Steyr-Daimler-Puch AG in the early 1970s; the bikes were usually sold in department stores. (Folding Cyclist, 2016.) In North America, vendors included J.C. Penney, Montgomery-Ward, and Simpsons-Sears. (thebikeguy, 2007; Martin, 1996; Thomas, 2011b;
cf. Bikeworks, c. 1998.) In my experience, the main-tube sticker always says "Auto-Mini" in huge type, with the word "Junior" in faint type inside the letter "T" of the word "Auto". The head badge may have "Executive", "Iverson", "Senator", or another "brand name" on it; this varies according to which store sold the bike. (Folding Cyclist, 2016.)


About the bikes:


They have 20" wheels. Like most small-wheeled folding mikes, an Auto-Mini can be adjusted to fit an adult or a child (cf. UsedOttawa, 2012). An Auto-Mini uses a Thompson-style bottom bracket. Keep it lubricated (Scott, 2008), as it's a hassle to replace it with a modern bottom bracket (Rehder, 2007, quoting Chen).
There were at least two distinct types of Auto-Mini. They differ slightly: for example, one has a slightly-larger frame; one has a slightly-smaller one (Thomas, 2011c). Thomas bought the slightly-larger type (Thomas, 2011c) and provided a detailed parts list in a blog entry (Thomas, 2011a).


About the frame and the ride quality:


"I have a few of them myself and find that they are a good sturdy riding bike." (Scott, 2008.)
"They are prone to cracking where the main tube intersects with the seat tube. There are fixes". (Rehder, 2007, quoting Chen).
"For some reason I find these ride nicer than the other old folders &mdash; maybe they got the wheelbase just right or the weight is a little less. I own a few (they're cheap) and they suffer from frame breakage in a couple of places; where the seat tube meets the bottom bracket shell (too much stress) and where the two thin seat stay tubes meet the seat tube (lousy welds). If you can weld, you can improve the frame by adding a piece of tubing between the bottom bracket shell and the main tube. Otherwise, ride gently." (Seal, 2011).


In sum, if you want a quality frame, spend more and buy something better than an Auto-Mini. "Spending $100 - $200 on a folding bike won't get you quality of any sort. Folding bikes with quality frames are significantly more expensive. You may want to save up for a bit before buying, or find a way to get a non-folding bike." (Fein, 2013).



One possible alternative to an Auto-Mini: a Raleigh Twenty

Among vintage folding bikes, the Raleigh Twenty is a better bike overall (cf. Rehder, 2007). The Twenty's main deficiency is its braking power &mdash; which is "barely adequate" in dry conditions, and non-existent in the rain. (Rehder, 2007). For safety reasons, if you buy a Twenty, you should probably upgrade it in order to correct this deficiency; there are various ways do so (Martin, 2012).



Postscript

Please feel free to edit this post and add more information or your own personal opinions.