[quackbury]

And don't forget to pop the trunk lid when driving around town. The sail effect is easily good for a 2 hp savings if you have a tail wind. Haven't figured out a way to get it to work on upwind tacks, though....

Also, skinny tires offer less rolling resistance - why not put donut spares on all 4 wheels? You couldn't drive over 50 mph, but then think of all the wind resistance you wouldn't have to overcome? (Especially with said tail wind...)

 

[quackbury]

On a serious note, just realized your car is an E39. Don't know how many miles you have on it, but if the injectors are clogged it will hurt your fuel economy. You may want to try running a bottle of Techron through the system. (BMW may even have their own brand of injector cleaner they recommend). There is always a tendency to save a few dollars a fill up by going with a budget gasoline brand like Hess. The budget brands don't add as much detergent additives as Mobil, Exxon, Sunoco, etc., so your injectors will clog quicker.

Also may want to change the filters in your air cleaner while you are at it, unless you know the previous owner did that recently. And I second the tire inflation pressure comment.

Have I redeemed myself for my previous pie-in-the-face comment?