Over the years, I've driven from Buffalo, WY. on 16 and 14 in a 'C' pulling a Jeep Wrangler four down. 16 is the easiest, but even 16 has pullouts to check your brakes. Not mandatory but highly recommended. Remember that going UP is just slow, but going DOWN is an adventure. If you ride your brakes, you can boil your brake fluid. Then you're a coaster. I drove 14A in just my Jeep Wrangler once to see how it was. I swear there were turns where I could see my own rear license plate through my front window. (slight exaggeration).
But I'm older and wiser, and also not in such a hurry. I now stay on I-90 all the way to Bozeman, MT, then south to the entrance at West Yellowstone, MT. and stay at Grizzly RV park during my visit. FHUs and lots of space between sites. Only a 1/2 mile to the park entrance every day. If you hit the entrance in the early morning, there's no line to get in. New arrivals don't get to the gate until later in the day. Certainly, its more expensive than inside the park, but West Yellowstone has a couple of grocery stores and gas stations that compete. You can also visit the Grizzly and Wolf Discovery Center in West Yellowstone. A private operation, but that's as close to either animal than you ever want to be.
