Doc_Wui

I have two folders with the Downtube Nova threadless stems, and a Downtube FS8 with their 1 1/8" threaded stem. All seem pretty sturdy to me although the last one always had some play in the hinge bearing, but it's not going to break. With almost 6000 miles on two of these ebikes, I'm wondering about the alloy fatigue at the bases, and wondering if people replace them. And what would you use?

Duragrouch

The long stems on folding bikes are pretty stout, as it's a safety issue. In fact, one stem was recalled, I don't know exactly what was the defect, but it was. In general, aluminum can be more susceptible to fatigue stress, but that is why the aluminum stems are extra stout, usually thick one-piece forged at the base with no weld. I prefer the earlier chrome-moly steel stems (welded, but a fantastic weld) because they are a bit stiffer, not because of the steel, because if you put enough aluminum on it, it can be just as stiff, but because the aluminum stems often telescope to adjust for height, and that's where you can get a bit more flex plus squeaking, not terrible, but noticeable when the bike is loaded with cargo, more inertia to swing left and right. My steel stem is fixed in height, no telescoping joint, equal in height to the telescoping ones at max height, and I like the handlebars up that high, so zero penalty for me to use the fixed stem. On one other thread here, someone did have an aluminum Dahon stem that did develop fatigue cracks at the stem telescoping joint, and they drilled holes at the end of the cracks to try to stop that, and it lasted another year before they replaced it.

On all parts of a bike, periodically inspect for cracks, because fatigue failure starts with cracks, and you can often see an impending failure before it fails "catastrophically", an actual engineering term that means complete failure without warning.