QUOTE(sgould @ 6 Mar 2010, 23:22 )

So to get to Istanbul, I would go M25 to Dover, Calais, A26 to Reims, A4 to near Strasbourg, A35 north down the Rhein, into Germany to the A5. Up to the A8 near Karlsruhe. A8 past Munich to Salzburg. Then down to Villach on the A10 and into Slovenia. After that I have no experience, but the route looks like Ljubliana, Zagreb, Belgrade, Sofiya, Istanbul.
We have been driving to Austria regularly before we moved here. While I generally agree with sgould's route, we generally travel to Dunkirk, then either head for Lille/Mons/Charleroi/Namur/Luxembourg/Saarbrucken/Pirmasens/Karlsruhe, then as he says, take the A8 down past Munich to Salzburg, or go round the Brussels ring road (never had many problems although it is busy), then down to Namur/Luxembourg & then as before. Beware of long stretches of the A8 mainly east of Augsburg where they are widening it to three lanes and there are endless sections restricted to 80kmh (50mph).
Petrol is cheap in Luxembourg so fill up there - don't bother going off the motorway, it's the same price everywhere - but very expensive in Germany atm, around 135 cents per litre. Off the motorway in Austria you can get super unleaded for around 118 cents per litre (but it can be up to 130), the cooking is around 110 cents. Diesel is around 98-99 per litre. Motorway vignette for Austria is 7.70 euros for 10 days, the next step up is a month (not sure how much this one is) so it might be worth getting a ten-day one for each leg.
The only spare I carry is an auxiliary drive belt, I figure anything else is going to be too difficult to fix at the side of the road! Just make sure you have good breakdown insurance and get the car thoroughly checked over before you go. If you have extra load tyres, it's technically illegal to have them repaired in Austria, you have to replace them if you get a puncture.
See my other post about hotels - the Ibis & ETAP are part of the same chain, so sgould's advice about prebooking is sound, you can turn up when you arrive even in the middle of the night, but do make sure that you carry the credit card that you booked with to enable you to check in. Alternatively, you could take a directory of such hotels & just use your card to "buy" a room when you know how far you've got that day. On the other hand, it's much nicer to stay in a "proper" gasthof in Germany and/or Austria and I can make some recommendations if you want.
Finally, don't set yourself punishing schedules & targets. Driving at high speed is clearly fun, but it can be very tiring in bad weather and heavy traffic - the Munich ring road is four lanes of totally derestricted road and you do need to keep your wits about you - imagine the M25, but with aggressive drivers travelling at 100+mph - and not just the odd one or two. Take it easy and make the trip part of the holiday by seeking out some characterful overnight stops.
Have fun and as I said, PM if you want more info on anything in particular.