Navigating with GPS and a bike in the Stuttgart area? No problem anymore: VVS Fahrradroutenplaner
I’m just impressed! I’ve been using this many times now. And in combination with Google Earth, it’s perfect tool to get everywhere in my area.
Just a little tip: In Google Earth you can let mountain look 3 times higher, than they really are. That way it’s much clearer to see, if one track is easy, normal, difficult, or almost impossible to do by bike.
You can set it up under:

Google Earth: Tools->Options->Tab:3D View->Elevation Exaggaration

Look for “Terrain Quality” in the lower part of the screen:

You just drop a GPX-Track into Google Earth and tip the surface in a way, where you can see the embossment best.
If you see the track isn’t easy, just try another way. Use Google’s Earth built in tools to edit the track to your needs.