Most beautiful drives in Tuscany...

How many nights do you have between Florence and Ovieto? Two or three?
Any location near Siena will work to use as a base. To get there drive the SR222. Exit the A1 freeway at FIRENZE IMPRUNETA then take the road to Ferrone, Passo dei Pecorai and on to Greve in Chianti to Siena. From the airport to Siena, via that road, it's over 2 hours plus pit stops (at wineries).
An alternate route is to visit San Gimignano and Monteriggioni and then proceed to Siena. Once you get to your destination, visit Siena. Devote a day to the Val d'Orcia. Montepulciano, Pienza, Monticchiello, Bagno Vignoni, Buonconvento, Montalcino are some options in the area.

If you haven't driven in Italy before, don't forget that each driver listed on the rental form must have the compulsory International Driver's Permit, which is used in conjunction with your home D.L. These are valid for one year, and easily obtained at any CAA/AAA office (two Passport-sized photos required, which may be provided by the issuing office). Failure to produce an IDP if requested can result in fines on the spot!

You may also want to have a look at some of the other posts here concerning the dreaded Zona Traffico Limitato areas that are becoming increasingly prevalent in many Italian towns & cities especially Florence, which is almost saturated with automated ZTL cameras. EACH PASS through one of the automated Cameras will result in a €100+ ticket, which you won't know about until several months after you return home! This website provides more information - http://www.slowtrav.com/italy/driving/traffic_cameras_speeding.htm

There are also speed cameras, including the devious Traffic Tutor system which measures both instantaneous speed as well as average between two points.

For visiting Siena, parking can often be a challenge. If you're going to spend a night or two there, try to pick a hotel that provides parking.

Excellent Suggestions. Thank you so much. We will have basically 2 nights and 3 days. Concerning the ZTL zones, is there a way to find out exactly where those are going to be in every city? Where would be the best place to get maps?. Also, could we count on a GPS in Tuscany?

You could try drive this ...
Day 1 Take the SR222 Chianti drive to Siena
Day 2 To Montepulciano
Day 3 To Orvieto
Bit rushed though you may find.

You have to decide whether you are going to visit the UNESCO WHS cities of Siena or San Gimignano, or go to less famous and/or smaller towns. You didn't give the month of the trip, but those two cities are so crowded (and hard to park for) that I don't personally recommend them in summer. While it is not at all the "same", I found Orvieto to be a wonderful substitute for them. Three smaller towns along you way you might consider are Arezzo, Cortona, and Monteriggione. I would save at least a half day, if not a night, for Orvieto.

Because it is on your way, I'll mention how much we enjoyed the three-hour tour and gourmet lunch (E 50 p/p) at Aviognesi Winery. Advance booking required. It sounds like you should find a countryside Agriturismo, or if you can afford it, small luxury hotel like the one we used in 2016, Locanda dall'Amoroso in Sinalunga. Don't underestimate how hot it is in summer.

There is some "overhead" (detour from the main highway, parking, avoiding ZTLs, long lunch services) in each tiny town. So use Google Images and other sources to choose where you want to stop. The only way to avoid ZTLs is to watch for the signs and park "outside" the walls, usually for payment. Does your father have any mobility problems?

oh yeah, SR222 ...beautiful drive. You can pull it up on Google Maps, use Street View and "mouse drive" the entire route

Extremely helpful! We are going in October.

I was there Sept-Oct last year. Weather is great in Oct, you'll love it

IMHO the most beautiful drives are in the zone south of Siena. San Galgano, Sant'Antimo, San Quirico d'Orcia, Pienza.

I also recommend 222. Drive 222 through Greve to Radda. Radda is a lovely little hilltop town off the beaten path. It can be seen in a couple of hours. From Radda head west to San Gimignano and from there to Volterra. Consider looping back and spending the night in Sienna. Spend at most of the day in Siena, then drive down to Montepulciano.

My suggested route will take you through some of the prettiest areas in Tuscany. You can go online and get city maps of all the towns you'll travel through. They will have ZTL zones clearly marked. You'll also find ZTL's well signed when you get to the town. If you pay attention, they are easily avoided. Speed limits are also clearly marked. Just observe the speeds and you'll be fine. You don't want to hurry through the gorgeous scenery anyway!

We used our trip as an excuse to replace our aging Garmin. The model we bought has an SD card slot. We bought the maps of Italy and it worked out great. I was able to enter every place we planned to visit and save them as favorites before we left for the trip. The maps were spot on and the Garmin really helped us navigate, especially at the beginning of the trip. By the end of the trip we were familiar enough with the region and the signage that we did an entire day trip just following road markers.

We were there in December. You're going at a great time. Check for local wine and harvest festivals during the time you'll be there. They would be a great experience!

that is a great plan Doug

Forget the international DL. Been renting and driving in Italy for over 15 years and have never been asked for it.
As for Tuscany. Pick a smaller town, Montepulciano ????, and then use that as your base to explore.
It is not about the "drives" but more about the "towns" and the "people".
Enjoy your time with your Dad.
John

Natasham, I just bought Rick Steves book for Italy. For Tuscany, it has 3 beautiful drives - one is in the crete area between siena and something else. Then one doing a circle around montelpulciano. Go to your local bookstore and look up his book.