Wildlife Loop Road through Custer State Park is paved end to end; any street-legal car handles it without a second thought. Tincup Pass in Colorado needs low-range gearing, off-road tires, and skid plates, and it's rated for experienced drivers only even with that gear. Neither route calls itself "high-clearance recommended." But plenty of routes in between do, and the phrase alone doesn't tell you which end of that range you're actually looking at.
"High-clearance recommended" is one of the most common lines in a trail or route description, and it's doing almost no work by itself. It shows up on gravel byways any stock 4WD SUV clears in dry weather and on 4x4 trails that will high-center a crossover in the first mile. The difference isn't in the phrase. It's in the rest of the sentence.
Guadalupe Rim Road in Texas shows the split hiding inside "high-clearance" itself: the guide calls for "AWD or 4WD recommended," then narrows that immediately to "high-clearance 2WD manages most of the road in dry conditions." Figueroa Mountain Road in California runs the same pattern, standard passenger vehicle on the pavement, high-clearance 2WD once the gravel starts. Neither route needs a transfer case. What it needs is ride height, the kind a stock pickup or body-on-frame SUV has and a sedan doesn't.
Guadalupe Rim Road and Figueroa Mountain Road only ask for ride height. Cinnamon Pass and Engineer Pass, both in Colorado's San Juan Mountains, ask for the drivetrain itself, and ride height alone won't get a vehicle over either pass. Both guides spell it out bluntly: "stock 4WD with high clearance and low range, aggressive tires recommended," and then the line that matters most: "stock SUVs handle the route in dry conditions, AWD crossovers do not." The "stock SUV" in that line means a body-on-frame 4x4 like a 4Runner or a Wrangler, not a crossover-style SUV like a RAV4 or a CR-V. Those fall on the "AWD crossover" side of that same sentence no matter what the window sticker calls them. That's the gap that catches people, and the reason for it is the transfer case. A stock 4WD SUV has a low-range gear that lets it crawl a steep, rocky grade at walking speed with maximum torque to each wheel. An AWD crossover doesn't have that gear. Its system shifts power between wheels for traction on pavement or light snow, not for grinding up a climb like Cinnamon Pass, and most crossovers sit lower to the ground to begin with.
Sage Creek Rim Road through Badlands National Park needs a standard high-clearance vehicle in dry conditions and turns impassable once the gravel becomes gumbo in the rain, a reminder that weather changes the answer more often than the vehicle does. The Chain of Craters Backcountry Byway carries the same caveat just as bluntly: high-clearance recommended, impassable in wet weather. A route's vehicle requirement is often really two requirements, one for dry conditions and a stricter one, sometimes no vehicle at all, for wet ones.
Distance from help can matter as much as the weather does. El Camino del Diablo in Arizona calls for high-clearance 4WD, then keeps going: extra fuel, water, a full-size spare, and self-rescue gear, because there are no services and minimal cell coverage along the route. The clearance question there turns out to be the easy part. The harder one is whether a driver can get out unassisted if something breaks two days from the nearest tow truck.
None of this is a reason to distrust a difficulty rating so much as a reason to read past it, into the language attached to that particular route. The vehicle requirement on a route's guide page is written for that route, not as a generic warning label, and it usually says exactly which end of "high-clearance" applies: 2WD or 4WD, dry-only or wet-capable, a clearance question or a self-sufficiency one. Read that sentence before the trip, not the phrase.