What was the maximum survivable speed any human reached before the modern era (of parachutes, airplanes, rockets, etc.)? Would a medieval peasant ever see anything approaching the peak speed of a humble soccer-mom minivan (~100MPH)?

Horses: <44–55MPH. Human sprinters reach a world record speed of 26MPH. But thoroughbred horses have a world record of 44MPH, and quarter horses can hit 55MPH. (One might wonder if there were historical horses which were faster, but we can be certain there were not: contemporary horse-racing records are an upper bound. Peak horse speed has improved markedly over the past few centuries; Gardner 2006’s win time-series starting in the 1846 Epsom Derby suggests horses have become roughly a quarter faster if we compare then versus now, so medieval horses would be at least a quarter slower, suggesting they were more like 33–42MPH.)

No premodern boat, not even oar-powered vessels (10MPH?) or the clipper ships (20MPH?), approaches 44MPH. Planes and gliders did not exist, so those are out.

A medieval trebuchet or a large-bore gun could accelerate a human to much higher speeds, but they would not survive it, so that doesn’t count (likewise for ‘standing on a couple barrels of gunpowder or a volcanic explosion or a meteorite impact site’). Is 44MPH the best we can do?

Skis/Skates: <87MPH. Can we do better? What about more gentle forms of gravity power, like skiing? Modern speed skiing has set shocking speed records as high as 158MPH in 2016; it’s unclear how much this relies on special slopes & hyper-modern technology to speed up over more medieval-esque “a stick of wood with beeswax rubbed on one side used on the nearest hill” skiing, but WP notes that in 1898_128ya an American reached 87MPH, which is fairly old and already 10MPH beyond high diving. Ski history is vague before the 1800s, so it’s hard to be any surer. Maybe. But skiing brings us to another possibility which pushes the speedometer both up and back: what about skiing on ice? Ice-skaters can hit 34MPH, but are limited by the need to power themselves, rather than use gravity or the wind. So what about a ship on ice?

Diving: <120MPH. The trebuchet and parachute examples suggests the main problem is not reaching a high peak speed (plenty of methods work, gravity-based or otherwise), it’s surviving the speed, and particularly the landing. That immediately suggests water as the landing method. Where would we have a large pool of water to land in? At a cliff, one can, with no equipment, do cliff high diving; there are many tall cliffs, so one can likely reach a high speed, with an upper bound at terminal velocity, which for a human is ~120MPH.

Diving: 75MPH. What’s the actual record for cliff diving? Apparently it is ~75MPH: that’s the final velocity I see quoted for Laso Schaller’s 2015_11ya cliff dive record from 193ft. Since this is <120MPH, that suggests that the limit is more the diver’s durability than cliff heights, and indeed, Schaller was injured in his dive, and many other high divers have been injured or died. Inasmuch as things like rubber bands and aerogel were unavailable, it’s hard to see how anyone could arrange better landing than open water. So that sets a new peak human speed: any young idiot could for all human history go jump off a tall cliff and hit ~75MPH, far faster than any ship or horse or sprinter.

Ice boats: 107MPH. Ice is inherently flat and extremely smooth, self-lubricating, and exposed to winter winds. Serious large-scale iceboats date back to at least the 1600s, with the Icicle setting a record of 107MPH in 1885_141ya! An iceboat is mechanically simple, and the rigging & sails don’t look much different from the European ships that were sailing the globe, so while the Icicle may have set that record in 1885_141ya, I see no reason similarly fast iceboats could not have been built centuries earlier even than the commercial iceboats in the 1600s, and the speed of iceboats would have been clear to anyone who used them. I think a medieval speed demon could have surpassed 75MPH using an iceboat, but would not have reached 107MPH as they couldn’t’ve afforded such a grandiose iceboat as the Icicle benefiting from recent materials like steel (or we would likely have records of such an aristocratic folly).

Still < minivans. So I conclude that a medieval peasant would likely never experience going faster than 75–107MPH (and towards the lower end). Remarkable—a single minivan contains more concentrated speed than a medieval peasant would see in a lifetime!