Short answer
Can I ride a 45 km/h scooter on the Mittlerer Ring in Munich?
Only partly. The tunnels are off limits on a 45 km/h scooter, and so is the Donnersbergerbrücke. Where there's no blue sign, coming from Dachauer Straße for example, you're allowed on.
Not allowed
Tunnels and Donnersbergerbrücke
Allowed
Stretches without the blue sign, e.g. from Dachauer Straße
Watch for this sign
The blue sign with the white car marks a Kraftfahrstraße. Only vehicles registered for more than 60 km/h are allowed on it, and a 45 km/h scooter isn't (§ 18 StVO).
If you see the sign at an entrance, ride past and take another street. That way you're riding legally.
Why I built nonstop
I ride a 45 km/h scooter in Munich myself and started out with Google Maps. “Avoid highways” only avoids them when it feels like it. On the way to the Allianz Arena I nearly ended up on the Autobahn anyway. And there was no way to exclude Kraftfahrstraßen at all.
With nonstop you enter a start and a destination and get the fastest and the shortest route that's legal at 45 km/h. It's free, and there's no account. If a street is wrong, tap it and block it. Or allow it if you know you can ride there, your device keeps both.
Try it on your next ride.
Common questions
Can I ride the whole Mittlerer Ring on a scooter?
No. The tunnels and the Donnersbergerbrücke are Kraftfahrstraßen, so they're closed to 45 km/h scooters. Where there's no blue sign, like coming from Dachauer Straße, you're allowed on.
Is “avoid highways” in Google Maps enough?
Not quite. Google itself tells riders of mopeds and motorcycles under 125cc to turn on “avoid highways” and “avoid tolls”. Its help doesn't mention Kraftfahrstraßen, and a 45 km/h scooter isn't allowed on those either. nonstop avoids both.
What's the fine if I ride onto a Kraftfahrstraße anyway?
The German fine catalogue sets a €20 warning fine. It's the same amount on the Autobahn.
Do I need an emissions sticker on the Mittlerer Ring?
No. The Mittlerer Ring is part of Munich's low emission zone, but two- and three-wheeled motor vehicles are exempt from the sticker rule.