beorn wrote
I was in fact wondering how could somebody descent on a road like that on
rollerskis!

I've heard some scary stories of people who did one of those big climbs in
the U.S. and did try to descend on their rollerskis, mentions of surprises
and scar tissue.

I've tried walking + running down, which for a big steep climb sometimes
leaves my legs sore for a couple of days from the repetitive impact. Or I
first use my car to leave my bicycle somewhere near the top, then drive back
down to the bottom to start my rollerski or inline-skate climbing. That's
how I skated up the upper half of Col de la Croix de Fer in France. But that
takes a lot of time, so it's better to find somebody else to drive the car.

Stelvio has a lot of bends and tight hairpins (48)

That's the east side of the pass (toward Prad Stilfserjoch in Sudtirol /
Alto Adige region). The rollerskier was climbing the west side (toward
Bormio in Lombardia region). The east side is more famous because of that
count of switchbacks, and that when you're about halfway up you can see all
the remaining switchbacks above you all at once. I think actually the west
side has similar steepness in its steep sections, but not as sustained --
and for it has more variety and interest as a climb, and much more fun as a
descent.

I did not enjoy descending those 48 switchbacks on the east side -- next
time if I climb up the east side again I would descend Umbrail (including
its 3km of gravel as noted by beorn) and make a loop back to Prad through
the Mustair valley in Switzerland.

Switchbacks -- When I have bicycled or skated up these big alpine climbs, my
experience has been that "switchbacks are my friend" -- the steepest
sections of these climbs are usually in between the switchback sections. I
suspect that once the engineers decide to put in switchbacks for some
section, they show off their design skill by limiting the steepness. So when
I made it up out of the trees on the east side climb and saw all those
remaining 22 switchbacks above me, instead of being intimidated, my reaction
was, "This one's in the bag".

Ken