Winnats Pass in the Peaks, forget ‘cars of the day’, cars of today have to go up in 1st!
Snakes Pass From ladybower is ~6 miles and ~300m, especialy when combined with (from sheffield train station) Broomhill to manchester road, snakes pass to glossop, glossop to chapel, chapel to castleton (rushup edge), then back through hayfield and up the hill over to hunters bar.
Mapmyride.com will tell you what category any road falls into, anoyingly it stops counting the moment it levels off, so what you think of as one continuous slog with a minor respite halfway it only see as two smaller climbs.