I ran a classic ‘ish’ 911 for a while, that had a ‘folded’ space saver wheel and tyre. True it took up less room in the boot/trunk, but from new it was bald and not street legal in the UK!
Of course the wheel that came off the car was much bigger and would only fit in the back seats. I am glad that I never had to use it.
Having had a cursory read on the subject in the MTB community, the non-expert main cause for concern would be heat build up in the car tyre and its effect on the solidified plug of sealant.
The tyre fitters hate this stuff. You take the tyre off and everything gets covered in this sticky goo. Some tyre fitters refuse to take wheels/tyres where the goo has been used because of the mess.
Very true. The sealant makes a mess of my mtb tyres, to the point that I won’t remove them until they are shredded or plain worn out. It’s then a real faff to clean the wheel rim and replace the valve. I pity the tyre fitters who have to deal with this stuff.
So glad I drive a van which came with a real spare wheel and tyre.
I have runflats on my 730. They are not the best for NVH, but with 20" wheels and 285/245s back and front I would need 2spare wheels (don’t like those Citroen 2cv-style spare wheels).
The other point is would I feel comfortable attempting to change a wheel at the side of the road given current traffic levels and the “Blind Pew” buffoons hanging onto the steering wheels of their vehicles…
The TPMS on my old BMW 530d bonged at me and I stopped on the A2 to check things out.
If you have ever had occasion to get out on the hard shoulder of a major A road or motorway, it is not a place you want to be for long. Jack up two tonnes of car, replace an offside tyre? No thank you.
About 10 years ago we rented a bedsit in Brides les Bains for the ski season. Come the end of the season the landlord came to give the appartment the once over, but got a flat tyre on his Mini on the road into Brides. So I said I’d come out and give him a hand changing it. We spent about 15 minutes looking for the spare, including several peaks in the glove box. Unbelievable that there’s no spare, unless it was hiding under the manual.
Can’t say I much fancy driving round the alps with nothing but a bit of gloop between me and the wooden crash barriers.
Copperslip is great for bolt/stud threads. Also use it on the mating surfaces of the bolts/nuts and the back of the wheel where it sits against the hub flange. This saves having to have to kick the wheel off where is has corroded to the hub when you need to remove further down the line.
No lube will cause galling of the threads and an inadequate clamping force due to the friction caused by dry threads.
It would be wise to follow the manufacturers instructions. Most I have seen specify clean dry threads. Copper slip on mating surfaces, yes. On wheel bolts with a dry torque figure, absolutely not. The torque is usually calculated to induce a stretch according to the bolt material grade. Torquing with lube will simply overstretch the bolt and risks causing failure.
I assume that the quote from Audi would have included a tyre fitted to the spare wheel whereas the Ebay price would be for the wheel only.
I’ve just taken delivery of a new car, and the only optional extra I paid for when I ordered the car was a spare wheel instead of the standard basic bottle of sealant. I’m still hopeful of being able to take my car across to the continent in the next couple of years and wouldn’t feel comfortable without a spare wheel. I got away with it on a couple of occasions with my last car (as far as Venice), but to tell you the truth I had forgotten that I didn’t have a spare wheel.
I was actually amazingly lucky with my last car which I had for around 9 years. It came only with a sealant kit which I was fortunate enough never to have to use. On the two occasions I had punctures they were slow enough that I could inflate the tyres and safely drive the car to my nearest local tyre fitter.
I’ve never had an issues with a smear of copper slip. And my threads are 32 years old. 
What I said earlier. Depending on the lubricant, usually half the dry torque .
Indeed you can get away with much including guessing at dry vs lubricated torque figures. I only point out how these things are calculated. (I may have used this information in even more critical applications.)
ARP 'rod bolts have grease supplied and a specific double torque procedure. Certainly critical!
A few months back one of those bell-shaped width restrictions leapt up and bit a big hole in the sidewall of one of the tyres on my wife’s Disco, which luckily has a proper spare and what’s more it’s in a readily available size so you can get a new one quickly. The wheel is under the car and you winch it down (and need an anti-theft plate) so we do have an old sheet in the boot. This means you can get going, but prepare to get filthy changing the wheel. Totally agree with all the other comments about runflats, ill-fitting wheel braces, rare tyres, useless and out of date goop cans, space-savers (which you need to think about when cornering) etc. Least favourite flat tyre experience was in the pitch dark at rush-hour on the M1 through Johannesburg many years ago, with a metal bar through the left rear on a front wheel drive A4. The choice between pulling over and certain death from a choice of causes or ignoring the burning and scraping, keeping on to the next junction and civilisation was made easier by this being a rental car. At least it had a proper spare under the boot floor.
I had the misfortune of parking up against one of those ‘nice’ architecturally selected curbs at a fancy office carpark I was visiting, it had and probably still has a honed top edge with vertical sides, whilst manoeuvring into a parking space at a crawl, I managed to pinch a small section of the side wall of my front right tyre against the top edge and the wheel rim, it cut a neat hole about 30mm in diameter out of the side of my tyre. “Phusssh” Fastest I have ever seen/heard/felt a tyre go down!
Lesson learn’t, keep well clear of fancy curb stones. I note that our local council is smartening up our high street incorporating these same design of curbs, we shall see how many complaints there are! The standard curb used all over the UKs roads have a smooth cast concrete side wall that leans back at a slight angle and a radius on the exposed edge. Not fancy but it is functional and saves drivers from themselves. :0)
There are some days when your luck is out. I saw a lady up in London (Cromwell Rd. IIRC) who, in the midst of the rush hour, and in moving to let a blue-lit fire engine through, scraped her rim and tyre on the kerb and the tyre came off. I felt so sorry for her.
Regarding the torqueing aspect, while it’s (obviously) a worthwhile point, some Fords make the aspect of seating and tightening wheel nuts a bit of a challenge as:
1- as above, as the car gets older some corrosion aggravates things - perhaps due to different metal surfaces in play
2- My Ford has nuts which have a pressed-over soft-metal covering (assume aluminium), which matches them to the alloy wheels but underneath is another nut head (imperial?).
The top covering, being soft, doesn’t like too much torque being applied – and if it deforms, it can be a world of pain. Worst case, the cover has to be stripped to access the nut below, which requires a hammer and screwdriver/tiny chisel – certainly not something you’d want to be doing by the side of a busy road.
3- the wrench supplied with the car is so soft-headed that it really isn’t good for multiple usage. Soft bolt heads + soft headed wheel brace = obvious issues.
The wheel nuts are almost consumable items for me, as every time I get a tyre change, I get them to put new nuts on where existing ones are showing distress – better safe than sorry.
I remember having to use a 6ft length of scaffolding pipe on the end of the lug wench to add extra leverage when removing the wheel nuts on a Series LR. After that I always used a smear of copperslip on my landrovers nuts 
OK end result - thanks for all the input and comments.
I looked around on ebay and thought safety comes first my life and passegers is worth more than saving a few pounds. So went brand new from Audi -
Spare wheel with tyre plus fitting and balancing (£300), Foam insert for tools, some of these are already in the car (£25), Jack (£95) - again the last item could have been sourced from Halfords for £25 but my old Audi jack was solid.
So peace of mind for £420.
I asked the Audi guy if he had a lot of requests for spare tyres and he said yes it’s becoming more common now once people realise they no longer have a spare as standard.
Interesting as to the overall cost - I must admit I’m so ‘old skool’, I thought checking the spare was still part of the MOT…even though I’ve just remembered my TVR had the foam which, thankfully, was never required (one of the few things which didn’t need attention!).
I suspect (would like the stats if available) that most issues result from ‘slow punctures’, so the wheel can be changed in a far more convenient location than say a busy main road - and noting many can now be repaired by plugging subject to where the issue with the tyre is.
I had a few slowies a couple of years ago and it turned out the valve seats were compromised - which can happen due to gunge getting caught in the slight trap in the rim, and also the use of some car shampoos, which tend to bite in to rubber/whatever sealant is used to seat the valves.
Haha that was wonderfully optimistic!
We’ve got a classic Mini. Full size spare in the boot. It is quite well hidden under a flap of cheap vinyl, so you could be forgiven for missing it, but even that spare wouldn’t fit in a glove box - even if the Mini had one!