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Right chaps I have a little poser for you, particularly those with either knowledge of wheels and tyres or those with a geometrical bent.

I am considering buying a car and ridiculously the thing doesn't come with a spare wheel either normal size nor space saver. I am not inclined to use the rather weedy cans of spray which comes with the car in case of a puncture and I would rather have a wheel of the correct size (and therefore a tyre to match the existing ones) or a space saver with an appropriate tyre on it.

The existing wheels are 18'' in old money and the tyres are 225/45/R18. If I buy a 17'' space saver (they are all that appears to be available) what sized tyre will give me an identical radius/diameter/circumference as the exiting wheels and tyres?

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I think the nearest you will find is 225 50 17 which gives approx 3 mm difference in tyre diameter. This results in approx 9.5mm rolling circumference.

wheel-size.com will give you all the parameters by vehicle.

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Doesn't really matter if the space saver is a touch smaller (it will just spin a touch faster )  I doubt your gonna be driving about on it for weeks .

I once had to do about 150 miles on mine down the motorway  .it got me home .

And I'm pretty sure its smaller than the normal wheels /tyres .

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Mine was exactly the same , no spare wheel of any sorts only a kit with a couple of cans inside , I didn't like the idea of being down the marsh and run over a spike that no can of spray would put right so like one of the other replies I looked on Ebay and got the same wheel with a good tyre for £100 delivered from Scotland to my house , at the time Ebay were doing a promotion where they pay 20% of your purchase so it only cost me £80 , touch wood in the three years or so I have had it I haven't used the spare , but for peace of mind it is there if needed , Good luck in finding one .

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It sounds like the car you are considering might have run flat tyres? Mate told me about his wifes mini having these - any puncture means a new tyre at £180, if you use the foam then that has to be cleaned off the rim which also has high cost.

All that aside our peugeot came with a 'space saver' in a full height wheel well. The full sized identical wheel and tyre to the other 4 was £50 delivered off of ebay and of course fits in the wheel well. 

On a 17 inch rim rather than 18 inch you need to increase the sidewall height (the 45 figure out of 225/45/r18) - the exact running diameter with the weight of the car on the wheel depends on tyre pressure and sidewall stiffness so hopefully someone on here can give you a direct figure.

I can only quote the peugeot space saver which is a 125/80/r16 to replace a 225/45/r17

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Beware buying any old wheel - there's umpteen different bolt/nut spacings and wheel depths. Best look for one off a breaker, wont really matter if its scruffy if its in the boot anyway.

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Neither my Audi nor Tesla have spare tyres. The Audi has foam the Tesla nothing. I don’t have a spare on the defender either. Not too bothered as I wouldn’t feel comfortable changing wheels on a wet and windy motorway or country lane. I’d call the RAC and get them to sort it out. 

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9 hours ago, AVB said:

Neither my Audi nor Tesla have spare tyres. The Audi has foam the Tesla nothing. I don’t have a spare on the defender either. Not too bothered as I wouldn’t feel comfortable changing wheels on a wet and windy motorway or country lane. I’d call the RAC and get them to sort it out. 

I know this is silly but I would feel less of a man not being able to change a wheel in any place. If I see a woman with a flat I will stop and help change it, always hopeful but never had any reward 🤣

I have to go to building sites and off road frequently. The lads at the local independent tyre fitters all know me by name whatever car I arrive in. They even know the dogs’s names. Great guys and very good value. Normal puncture £10, sidewall sent away at £25. 

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1 hour ago, WalkedUp said:

I know this is silly but I would feel less of a man not being able to change a wheel in any place. If I see a woman with a flat I will stop and help change it, always hopeful but never had any reward 🤣

I have to go to building sites and off road frequently. The lads at the local independent tyre fitters all know me by name whatever car I arrive in. They even know the dogs’s names. Great guys and very good value. Normal puncture £10, sidewall sent away at £25. 

The tesla doesn’t even have a Jack. I’ve changed plenty of tyres in my youth and it’s more a case of the dangers involved. The police don’t advise changing a tyre on a motorway. 

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13 hours ago, Farmboy91 said:

Will a full size spare fit in the boot? 

I have a space saver for the golf and looked at getting a full size spare but a full size tyre is too big to sit in the boot with the actual boot floor shelf in. 

Mine was the same , I got over that problem by putting a length of tile batten underneath with a strip of underlay pinned on top , not something mentioned in the book that came with the motor but it do the job and the floor is only a inch higher :good:

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25 minutes ago, marsh man said:

Mine was the same , I got over that problem by putting a length of tile batten underneath with a strip of underlay pinned on top , not something mentioned in the book that came with the motor but it do the job and the floor is only a inch higher :good:

Mine has two positions for the boot floor, the bottom one gives you a full boot space, the top one isn't worth using. Even in the top position the floor wouldn't sit flat with a full size in. 

Last time I had a puncture I borrowed the wheel off my missus golf for the day lol

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I share your concerns, but I have been driving a BMW (runflats) for 13 years now.  No spare, no jack, nowhere to put a spare.  At first it bothered me, but now, 13 years and never a puncture - it doesn't even cross my mind.

Incidentally, I have a summer toy car (old Merc SLK) which has a space saver in a well in the (very small) boot.  IF you get a punctured rear tyre (bigger wheels on the back) and change it for the space saver - the punctured wheel won't even fit in the boot!  You have to put it on the passenger seat - or so I'm told, luckily I have never had a puncture.

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On 15/10/2020 at 17:35, JDog said:

Right chaps I have a little poser for you, particularly those with either knowledge of wheels and tyres or those with a geometrical bent.

I am considering buying a car and ridiculously the thing doesn't come with a spare wheel either normal size nor space saver. I am not inclined to use the rather weedy cans of spray which comes with the car in case of a puncture and I would rather have a wheel of the correct size (and therefore a tyre to match the existing ones) or a space saver with an appropriate tyre on it.

The existing wheels are 18'' in old money and the tyres are 225/45/R18. If I buy a 17'' space saver (they are all that appears to be available) what sized tyre will give me an identical radius/diameter/circumference as the exiting wheels and tyres?

Out of interest what car is it?

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22 minutes ago, Lord O War said:

No spare tyre is a huge weight saver and makes the mpg look better when they go for testing. Plus it saves them a few quid per car!

I realise every little bit of weight saved helps, but I wouldn’t call a spare wheel a huge saver. Even with a Land Rover wheel weighing 80lbs it is only the difference between a fat passenger and a lighter weight one.

3 hours ago, JohnfromUK said:

luckily I have never had a puncture.

You should get into more farm yards!

Three punctures in one month is my record.

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29 minutes ago, London Best said:

I realise every little bit of weight saved helps, but I wouldn’t call a spare wheel a huge saver. Even with a Land Rover wheel weighing 80lbs it is only the difference between a fat passenger and a lighter weight one.

You should get into more farm yards!

Three punctures in one month is my record.

About 5 yerrs ago I had builders doing major work on the house - and fully expected to get several punctures - and I only got one - in the wheelbarrow!

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