A customer blew it, trashed it and now is asking for a new one but don´t know the size of it

I don't think there ever was an X5 4.0l engine, so I'll assume you mean the 4.4l engine, also depending on the model package the tire size would differ. All X5's come with full spares and are usually aroond this size 255/50R19 or this size 255/55R18. Try checking the sizes of the tries that are on the vehicle right now. The spare should be the same size, but again depending on the package, BMW puts 2 different sized tires on the higher end packages. Next time if you give a little more information aboot the vehicle you can get better quality answers, such as year, make, series, and correct engine size.

What size are the rest of the tires on the car? Is it a donut tire or a regular size spare? Get that info from him first unless you already know it

And you are ? a tire shop, repair shop, bob`s uncle? You are going to sell this guy a rim and tire and don`t even have anyway of finding this out other than here. Hope you don`t do this for a living. Why not call BMW dealer? Cause that is probably the only place you will find that particular rim. as for the tire , well I`m sure you will be back trying to find that as well. If it`s too much trouble for you , then send the customer to his dealer for a new one.