Tickets for train from Frankfurt Airport to Frieburg. Buy in advance?

The train station is in the airport. The direct ICE train about 2hrs15mins. I picked a random day later in May and got a "super sparpreis" price of about 40euro vs the full fare of more than 90. So I would say booking ahead should save you some money. No need to book four months ahead, though.

I guess you mean Freiburg im Breisgau?

If yes, train is a very good option.

Info about train station at FRA airport:
https://www.frankfurt-airport.com/en/transport-and-parking/by-train/long-distance-trains-of-german-rail.html

Check train connections https://int.bahn.de/en

and different fares. With flex fare ticket you can take the next train in direction to Freiburg. Cheaper fares are for booked connection.

Train is the most direct route. The station is actually Frankfurt Flughafen, it is at the airport, you can leave from there. The station is walking distance from one terminal, but requires a free shuttle from others. Your destination is Freiburg im Breisgau. There are direct fast ICE trains, though construction on that lined has slowed the ICE trains, but it takes just over two hours to get there, even if you have a change somewhere.

You can save by buying well ahead, but then the issue is how much time do you leave between landing and the train departure? If your time is more valuable, then you can wait, and take the first available train, getting you there potentially a couple hours earlier.

Look at D Bahn https://www.bahn.de/ for ticket options and prices.

Thank you so much for the info!

You have two choices. You can go from FRA to Freiburg using regional trains. That will take from 4½ to 5+ hours, depending on how many changes of trains you want to make. The fare will be €49 for one person (€10 each for 1 to 4 additional persons) using a 2nd class, Quer-durchs-Land-Ticket. There is no discount for advance purchase of regional tickets.

Or, you can take a long distance train and make the trip in 2-3 hours, either direct or one change. The price will be about €170 for two people in 2nd class, depending on the specific train, but with these trains, there are discounts for advance purchase. I can see advance purchase Saver fares at €94-€102 for two people on Sept. 1. However, these fares are train specific, i.e., they have the date and time for a specific train printed on them, and they are not valid for any other train. That's a big issue when you are flying in from the United States on a flight that could be hours late. These tickets are cancellable, but only up to the day before the flight, not on the day of arrival. You would be wise to plan on spending one night in the Frankfurt area and traveling the next day when you can be more sure of making you train.

I did that in 2017, when I wanted to go to SW Bavaria (Pfronten, near Füssen). It was a pretty long trip by long distance train, even longer by regional trains. So I booked a hotel in St. Goar, a short distance by inexpensive regional trains, for the first two nights. We had a nice cruise on the Rhein the first day, then used a highly discounted Saver fare ticket on day three to go to Pfronten.

There is one other possibility, the best possiblity, I think. Depending on your airline, there might be something available called Rail&Fly, an offer of the Bahn, where for a little extra on top of your air fare, you get and open long distance train ticket to any station in Germany. It's an open ticket, usable on any train(s) on the day of arrival and the next day. Check with your airline or travel agent to see if they offer it.

Added: An earlier post suggested a "Super Saver" ticket. Plain Saver tickets can be cancelled up to the day before travel, so if you purchase in advance, and your plans falls through, and you don't go, you can cancel. However, Super Saver fares, once purchased are NON-Refundable. Better know you are going to make the trip.

I would suggest booking ahead and getting seat reservations.

This past Tuesday, I took the train from Frankfurt to Nuremberg. Noon departure.
As the train left its initial departure point--not Frankfurt--I got an email that my seat was changed. (They substituted a smaller train.) I went from a seat by myself in the quiet area to a side by side in the regular area. The train was packed and some people stood the entire way. I had to kick someone out of my seat but he was nice about it.

The day before my train showed low popularity.

You would be wise to plan on spending one night in the Frankfurt area and traveling the next day when you can be more sure of making you train.

This is good advice if money matters.

Lee mentions the risky Super-saver / saver fare option (train/time-specific) which you could use with some degree of certainty after an overnight stay.

If you like the prices of those (which may still be high) you can also reduce your risk of forfeiting the ticket by building in a cushion of DOWN-TIME at FRA airport prior to your scheduled train. So your flight is scheduled for 9 am arrival... you scheduled your train departure for 12:00... your flight is 90 minutes late, but you can still make it through security and to the airport train station before your train leaves at 12:00 that same day. Make sense?

In the case of FREIBURG, I think I would just ride the regional trains. whether it's 9:30 - 13:56, or 10:00 - 14:30 that you prefer to leave, the regional-trains-only ticket is 100% flexible. You can ride ANY combination of regional trains you wish that same day to Freiburg. No matter how late your flight is, you hop on the the train at the airport's Regionalbahnhof station and make your way. You will probably get to Freiburg just as quick as you would if you inserted the fixed down-time period before your scheduled saver-fare train.

The fare for two is €59 for FRA - Freiburg on the Day ticket for Germany, which covers all the regional trains you can eat in one day.