Spending a day in Frankfurt during a layover.

What tickets to get to get into town and use several u-bahns / s-bahns?

I was thinking of getting a day pass, but the description says valid for zone 50 only. It appears the FRA airport is in zone 5090.

Do I need to get several tickets?

Two tickets for s-bahn from FRA airport to downtown and back to FRA.

Then get a day ticket to ride u-bahn / s-bahn within zone 50?

Here's some info right from Google:

Frankfurt's transit system, operated by Rhein-Main-Verkehrsverbund (RMV; website www.rmv.de), is made up of the U-Bahn, S-Bahn, trams and buses. The two subway systems are pretty much the same, except the S-Bahn runs above ground once it leaves the centre. You can buy tickets from automatated ticket machines at all stations and major bus and tram stops. The main sights in central Frankfurt are covered by the central fare zone (press the Preisstufe 3 button on the ticket machine) although you will need a two-zone ticket to get to the airport (press the Preisstufe 4 button on the ticket machine). A single ticket is €1.55 for a short trip up to two kilometres, otherwise a single ticket is €2.05. A day pass is €4.80, while a weekly pass is €18.50.

Heya...check out my other posts re: my 10 hour layover in Frankfurt.

But I got an all day pass for the train..though only used it to get to and from downtown to the airport. It cost 7.50 Euro for the whole day. The price may have increased since I was there last time.

The directions in the airport are posted pretty clearly, and if you have any questions while trying to figure out the ticket machine, there is an info area, and also customer service people at the machines who can lend a hand.

One of the customer service people helped me figure out what stop I wanted to go to to get into downtown Frankfurt (for the shopping and sightseeing). She even pointed me to the right track.

Let me know if you have any other questions.