What should we be prepared for in driving rental car from Munich airport to Innsbruck , Austria

I would suggest you go on Google Maps and figure out which way you're wanting to go. You can go the autobahn to the east and then south to Innsbruck--the long way. We go west of Munich and entered Austria at Garmisch. It's the more beautiful way to go.

I don't change sim cards. We have T Mobile, and I just sign up for 1 month of their international service. My smartphone works just like in the U.S..

You can pick up an Austrian vignette in Garmish or just inside Austria at a drive in market/gas station. You'll want it when you get on one of their controlled access highways.

Their roads are very well paved and driving in Austria is no problem. There are speed limits which are reasonable, and it's not a dfificult place to drive in.

I can't comment on a rental car. The route I usually take from A9 is through Munich on the Mittlere Ring. Usually a lot of traffic and confusing routing. Many speed cameras. Something you do not want to drive tired, jetllagged and unfamiliar with driving in Europe. Once you reach A95 towards Garmisch-Partenkirchen things get easier. Most of A95 has no speed limits. Some new bypass around Garmisch-Partenkirchen that will keep you out of most of the town proper. You'll bypass around Mittenwald on secondary roads and enter Austria bypassing Seefeld and travel down into the Inn valley. If you stay off of the Austria autobahns there is no need for a vinyett. Obay the speed imits as there are many speed cameras. Like Germany, in Austria secondary road speed limit when not posted is 100 kph and In towns is 50 kph. Austrian Autobahn speed limit when not posted is 130 kph. In Innsbruck there are street trams that can make driving interesting.

Are you arriving in Munich after a transatlantic flight? If so, don’t expect to get much sleep if any on the flight over. Instead, take a train from München Flughafen Terminal to Innsbruck that requires a transfer (2h 15m).

Speed limits are clearly posted and should be taken seriously. Cameras are everywhere. Same with the Austrian Vignette. Do NOT drive on an Austrian highway without one, not even for the shortest trip.

I always take a few minutes to get familiar with the cars controls… wipers, lights, etc. and even drive around the parking lot or garage a bit to get used to the cars controls.

You can buy the Austrian Vignette (toll sticker) after leaving the Munich airport at any highway gas station. mchpp route is the one we have used. We like stopping in Mittenwald for a break. It’s too pretty not to. Signs are very well marked with the names of the towns/cities the road is heading towards. Such as this example.

https://depositphotos.com/356533178/stock-photo-road-signs-austrian-motorway-salzburg.html

The Austrian Vignette is sold in Germany also. Look for the sign. Almost any gas station after leaving Munich airport will have them for sale.

https://www.traveltyrol.com/austrian-vignette/

thanks guys for the swift response.

Since im coming from Dubai i would be needing a sim card for google map during the road trip.

Is it advisable to take sim card from airport , i have heard that once people buy the sim and leave the airport even after 2 hours the data would not be working.

other things I don't think have been mentioned -

If you are hiring the car in Germany and want to return it in Austria you will pay a high (often between 500€ to 1000€) international drop fee. This would be in effect in most countries.

It sounds like you plan to get the car and drive right after 7 hours in the air. You'll be tired. Train will take a relaxing 2 and a half hours (one easy change in Munich, the airport station is right at the airport), driving perhaps 15 minutes longer but by the time you have rented the car and found it in the lot, and then stopped to get the Vignette, and possibly a break you will probably take an hour longer than the train or worse. Especially if the tired causes problems.

You will need an IDP (don't know where you get in Dubai) in both Germany and Austria.

Concerning SIM cards I would recommend to get it in Innsbruck if needed, as they are cheaper in Austria.

Just use offline navigation and download the required maps upfront.
For free offline car navigation I use the “HERE We Go” App, for walking/hiking I prefer OsmAnd.

Make sure you photograph all sides of the car before driving off.

The route through Garmisch and Mittenwald has a short but extremely steep descent, it is easy to overheat brakes a bit. If you are not into mountain driving the other (highway) route is easier to drive.
In Tyrol the highway top speed is dynamic, it changes according to pollution probability but often is 100 km/h, a bit on the slow side. As you will see, it is religiously obeyed as radar checks are very frequent.

... a short but extremely steep descent, it is easy to overheat brakes a bit.

If this happens then you did not drive correctly. You must shift to such a low gear that you rarely need to brake when going downwards. Even in a car with an automatic gear you can force it accordingly. (Similarly you have to do this when going up to prevent overheating of the engine.)

In all mountain countries you learn this for obtaining your drivers license.

There was a time when the Zirlerberg ramp became a recurring topic on the old rec.travel.europe newsgroup; I drive it twice or thrice per year, but I remember discussing it with a Munich fellow who did it twice or thrice per week. The descent is a couple of kms. long and very steep (18%). You have to use the engine to slow down or you will blow your brakes, but if you are following other cars or - worst but frequent case - you are stuck behind a very slow truck, you will discover your gear ratio may be not optimal and you will be forced to use brakes anyway.

Not to throw more wood on the fire but... I have never had a problem driving down into the Inntal. Actually, never gave it a second thought. I would not let it stop me from completing the drive. I have always had newer capable cars though, and I am used to driving mountain roads. Great views that can be distracting on a good day too. There are places to stop. If you have only driven flat roads all your life, then I would exercise some caution. You certainly do not brake the whole way down! People drive it with campers and trailers etc.