Upload & Sell: Off
Ridgway is a 5.5-hour drive via both I-70 and 285 (and an additional 8-15 minutes by way of Carbondale and Delta off of 70). Certainly an easy and likely a must-see destination for a three-day trip, but not if you're day-tripping from Denver, or are set on the four-hour limit; Aspen is right at four hours.
That being said, you would be kicking yourself later for going that early (around the 20th) unless you are stuck with those dates. Otherwise, aim for around October 1st if at all possible, assuming you're planning this trip for fall colors. If you're stuck around the ~20th-23rd, then the Twin Lakes area and the forest roads off of the South Mt. Elbert Trailhead out of Leadville and the Cottonwood Lake area out of Buena Vista will be in good color, as these are amongst the earliest areas in the state to turn and are great options.
If you're able to swing the later dates, then the Aspen area (Maroon Creek and Castle Creek roads) would have to make the list as well as McClure Pass (3.5 hour drive via Glenwood Springs). Just a little bit on the south side of McClure Pass is CR 265 that leads up Grand Mesa, where there are aspen forests a plenty starting about eight miles up.
Another great four-hour option is in the Flat Tops out of Yampa, which is three hours from Denver. Head up the scenic byway to Dunckley Pass (four hrs) area for some great aspen forests. This is a quieter and more relaxed area than the areas south of I-70, which have more tourists during that time of year.
Those would be my top suggestions for the driving criteria. If possible, though, definitely plan to drive to the Ridgway and Telluride areas as well if you aren't stuck in Denver.
A passenger car will be perfectly suitable for all roads listed here except further sections at the base of Mt. Elbert. If your criteria is subject to change, additional input can be given.