Driving from Florence to Montepulciano

We drove from Florence to Volterra then to montepulciano the to Orvieto in March. My husband drove. It he had no problems with the roads. We had printed maps and had maps to use offline on our iPad. The only problem we had was there were some mud slides near Volterra and we had to detour. No problems for montepulciano though. We drove by some other towns also.

Florence to Montepulciano is mostly freeway. A1 to Roma, then exit at Bettolle, on the Valdichiana.
Outside of the freeway it will be on regular two lane highway, with plenty of curves. Not a difficult drive. Be careful at the curves, drive at the speed limit or no more than 10km over. Also roads often have no shoulders, therefore they are somewhat narrower than equivalent roads in North America.

Are you doing all these towns in one day? I would go to Montepulciano and Montalcino (we stayed there for 3 wonderful nights) and then another day go by bus to Sienna. There is too much to see in Sienna for just an hour or so and parking can be very difficult. It is easier to travel by bus there for the day.

I agree with Marie to use the car for places that are harder to access and to plan a separate Sienna daytrip by bus, if possible. The rural roads are not hard driving and the hill towns tend to have well-marked parking lots, so that you don't drive into their narrow centers.