I have used a full sized front wheel as a 'spare' on my older M5. Just sits in the boot.

I do like the idea of being able to swap a tire and have, basically, unlimited range until I get a new replacement....basically 2 or 3 days for a tire to be ordered and shipped to a tire shop along my route, or where I am located.

If you are going the spare tire in the boot route. Make sure it is secure and tied down tight. 6o lbs loose projectile will make a mess of the vehicles occupants.
A lot of cars with runflat have the old area for the spare filled with sub-woofers or air suspension compressors. Rendering that old storage area useless.

The X5 has the space under the boot floor for a spare, the floor is locked down, not the most secure of locking devices that I have seen, but none the less, will stop the spare from flying around, especially with a couple of suitcases and all of the paraphernalia that gets put into the car, just in case, and never gets used... all sat on top of the floor covering the spare etc Luckily there are also some places, one of which is large enough to stow my bottle jack, and a few extra tools as well as those very few items that BMW supply, I will have to find a boot tidy or something similar to put the extra bits that I like to carry, don't want tools and the like floating about in the back, and it should keep the boot area tidy for when I am not carrying the 3 tonnes of needless holiday luggage that my Mrs will insist is taken with us, two pairs of shorts, a few t-shirts, a spare pair of trainers and maybe a sweat shirt just in case it drops below 30C, that's my packing done :-) unfortunately the wife and youngest sprog are very different :-( I expect that the xBox will be in there somewhere too

I now, just have to find a matching front wheel, Ebay seems to have sets of 4 that have been kerbed or want silly money for a single rim. At least I have 2 or 3 months to find one, before setting off on our trip.

I am not sure which model of Continental tyre they have ordered, I spoke to the tyre bloke that I use and he recommended them, and they should be delivered tomorrow, but because I have also asked for a full geometry set up to be carried out on the car, he couldn't fit it in until Saturday morning.

o/p - your tyre bloke should be able to find you a one off rim. It does not need to be a BMW brand. As spare? Who cares. Get your bloke to get you a rim and use one of the old front tyre to put on that rim. An 18" rim here runs about 2oo bucks, surely your bloke should have an option at 140 sterling-ish.
Mind you.... a 20" tyre may not fit under the floor???

1. I was speaking of my full size front tire in an M5 boot (aka trunk) which by definition means it is NOT in a passenger compartment. ;) If you are keeping a spare in the cabin (like the X5) then yes, you need to secure it. And really you should secure luggage, etc as a matter of course. Most dont.

2. A full size front tire/wheel will NOT fit in the E70 X5 spare tire compartment. The only thing that fits is the custom compact (skinny) spare. An 18", 19", 20", 21" rim ALL will **not** fit in this location. Has nothing to do with the rim size.

3. Buying a loose BMW 18 or 19" wheel is usually pretty cheap- personally I really like the quality that comes from OE rims.

So, from what you are all saying, it looks like it is going to be a narrow "get you home" wheel or it wont fit under the floor...... there is a company that sells these complete, rim and tyre for about £150 each. Maybe I will have to go down that route then, I don't want a wheel sitting in the luggage space, I need all the space that I can for carrying the wifes hair drier and the lads xbox etc...... nothing is ever easy.

Correct.

However with 'get you home' possibly being 4000 miles, it will be a 'get you to where the tyre will be delivered in a day or two'.

;)

Oh, I usually keep 'the best tire' from my old set of tires when replacing rubber. It sits at home in storage. (A point of contention with the wife in the barn...5 cars, spare tires, a set of track rims and tires....). However if I have a blow out, or other unrepairable damage, the old tire gives me that option if t makes sense. If it is a fairly new set of tires, I'll buy a new replacement- but if they are down to 60%. I'll use the old one. FWIW

If I was still running on "run flats" I would be in the same situation, the only difference is that I may have to get my hands dirty while I put the narrow tyre on, but I have saved a load of money and I expect getting a normal tyre will be easier than getting a run flat to where ever I might be, and I can travel a bit further, all be it at a much slower pace, to get to a town rather than driving a limited distance on the run flat before it could possibly give up, still having to drive at a slower pace..... anyway, decision has been made, and I am now off to get the new boots fitted, I will update you with the outcome.... thanks again for all of your help and advice :D:thumbup::D:thumbup::D

Well the new boots are on and I have given them a few miles to see how they are. First impressions are that they are very quiet compared to the Duellers and the ride is a lot less harsh when going over bumps etc, at speed they feel good too. So, I am very pleased with them so far, now just need to get myself a spare to fit in the boot and that is another thing crossed off the list ready for our trip in July.

Thank you all for your advice and putting up with my, no doubt, endless questions.

For my "spare" I picked up this rim AND tire for right around $200 new at Tire Rack.

http://i67.tinypic.com/kd5qvc.jpg