or the perimeter of the city.
HTH

"Stadtring" is normally a highway that circles a city. You will find them in many cities in Germany. I would leave "Stadtring" in your translation and insert the English explanation.
Please see
http://www.aquanaut.nl/route.htm
for further information.

Good luck!

See if it fits.

Just from my personal memory of highway signs in the U.S.

http://www.cato.org/pubs/pas/pa-231.html

the E-470 beltway in Denver,
I-355/FAP-340 west of Chicago, new east-west highways north
of Dallas, the Eastern Beltway and Holland E-W Expressway in
Orlando, and the Northwest Hillsboro Expressway in Tampa.

A Stadtring is not necessarily at the periphery of the city. Munich, for instance, has two Stadtringe, one around the older part of the city (called Mittlerer Ring) and the other one at the periphery (called Äußerer Ring).
Belt way might be misleading.

All of the above answers would be correct under the right circumstances. But translating Stadtring would be like translating the Ringstraße in Wien, they are proper names. Just like Dallas and several other cities have a Beltway, these are usually proper names.
Google: Bei Staugefahr auf der A43 lohnt die Anfahrt über den Stadtring
auch aus Richtung Norden (Recklinghausen und Dortmund): ...
AB-Kreuz Bottrop A31 Richtung Emden ... folgen
(Lingener Straße, Altendorfer Ring, Stadtring) Hotel liegt auf der rechten ...
Bielefelder Str. - B 61 - Gütersloh - Umgehungsstrasse - Nordring (Stadtring - 4-spurig);
Richtung Autobahn Dortmund oder Rheda-Wiedenbrück; an Ampel rechts ab ...
Vom Hauptbahnhof zu Fuß über Vetschauer Str. zur Görlitzer Str.
und zum Stadtring. Den Stadtring immer bergauf Richtung Stadion (10 min). .