Approximately 1/3 of German Autobahn is unrestricted. As you would expect, unrestricted segments tend to happen in the more rural areas, between major cities.
Recognizing that the "end speed limit" sign really ends the speed limit is key. I have heard of the "advisory speed limit sign", but never seen one. Similarly I know somebody who took a car trip to Frankfurt, used the GPS provided speedlimits, and wondered afterwards why there was always as speed limit - the GPS announced the advisory limit as it would any other limit.
Also, the end speed limit sign only means this on highways. Or rather it really means "the speed limit is now the default for this type of road", and it happens that autos have no default speed limit on highways. So in particular, the sign means 50km/h on normal roads within towns, and 100km/h on normal roads outside of towns.
Ah, good point - I shall remind my friend ( ) of this...
Another couple of things come to mind the first time my friend drove in Germany - One is the violent braking at the last second as fast-movers do hit a speed restriction, it can bring tears to the eyes if you're travelling behind and not expecting it... The other is that speed restrictions on many turning entries/exits seem to be pitched at the "much over this speed and you'll be hard-pushed to keep the car on the road" level, and this can also cause great entertainment if you choose to ignore them.
Most new German power cars are "chipped" at 250km. Scary fast, but when I had my BMW 535, cruizing at 250km on the Autobahn, there would still be Porches and Ferraris flashing me wanting to pass.
My recomendation is not to exceed 180km unless in light traffic, and the road is clear and dry. Sundays are best, as trucks are not allowed on the autobahn on Sundays. You must also focus on your driving when at these speeds - and be prepared to make lots of petrol stops - it costs a fortune in petrol.
As previously stated, if not otherwise specified, you can drive as fast as you like on the autobahn. Take care to slow down when there is a speed limit - it is there for a reason (bend, bad road, construction work, tunnel, etc.)
I'll add - make sure that when there IS a speed limit (and pay attention to when they are posted) you actually stick to it.
They have speed traps set up frequently, and they mean their limits. Usually there is a good reason.
Also, do your math. If you are crusing at 160/180 km/hour, and a truck move in front of you to overtake another at 60 or 80km/hour, it is a very hard break - keep a sharp eye in front and check the rear view frequently for flash lights requesting passage. Once you are faster than 130km/h, one has to be alert and awake.
Having driven up and down A81 for several years now, drivers of Swiss cars on German Autobahns can be classified into three groups:
a) Germans living in Switzerland, subgroup 1) poor Ossis in old Hyundais - a traffic obstacle , subgroup 2) normal drivers that know how to drive* on an Autobahn
b) native Swiss endangering other drivers by pulling out at 110 km/h, or blocking the middle lane at 110.
c) silly expat bankers not aware of group b), pushing their GT3s/Ferraris/Continental GTs/DB9s too far given the traffic/road/weather conditions.
*Adjust your speed to traffic and weather, take into account silly behaviour of others. The normal travelling speed in dry weather, normal traffic is around 120-130 on the right lane and 150-170 on the left.
And if your are driving a fast car with powerful brakes, remember to negotiate your braking/lane change not only to keep yourself out of the boot of the car in front of you, but also to keep the guy behind you out of your boot.
...and always check that your tires are correctly inflated at the right pressure, particularly before driving on the Autobahn. It's not just a question of economy, it may save your life.
Er, while your recommendations are all correct do the 130 not come from an insurance but the German traffic laws... someone said, he has never seen the sign, here it is:
"recommended" - Richtgeschwindigkeit is a bit more than a speed limit... it also includes that you should not be driving much slower. So if you see for example an 80 in a blue square, do not drive slower than that.
Also bear in mind that as much as autobahn lives her own rules, soon after you take the offramp the normal traffic rules are obeyed. Heard lots of tourist stories from Switzerland that posh Swiss citizens are a good target by local cops who soon after seeing your foreign licence plate they will expect you to pay a hefty fine. Just be aware!