Tyre sizes.

[RootsBooster 24]

4 hours ago, Cyclone said:

In theory you could alter the tyre profile so that the rolling circumference was the same.

But fundamentally it's unsafe.

The exact legal wording  is that "Tyres on the same axle or on twin wheels are different sizes" are not permitted.

Although the outer diameter may be the same, the stated overall sizes of the tyres will be different, personally I wouldn't risk it.

[Top Cats Hat 10]

OK. Your original post said wheels.

 

Apart from the diameters being different, the profiles are different too. Why don't you just replace the odd tyre with one the right size? Also if you have the odd, smaller tyre on the front and not re done the tracking, the steering geometry will be out and you will start to get uneven wear on that tyre.

 

Just get it changed.

[RootsBooster 24]

25 minutes ago, Kidorry said:

The tyre size on my car are 215/16 and the spare one is 185/15". 

No, it would be completely illegal to use your spare wheel with your existing road wheels.

[Cyclone 10]

1 hour ago, RootsBooster said:

The exact legal wording  is that "Tyres on the same axle or on twin wheels are different sizes" are not permitted.

Although the outer diameter may be the same, the stated overall sizes of the tyres will be different, personally I wouldn't risk it.

Googling it, it appears that space savers are often of a different (smaller) diameter to the regular wheels.  I've no idea if that's a specific exception in law, or if they're all illegal to actually drive with.

I don't have one myself so I can't go and look, mine comes with the puncture repair spray in foam stuff.

[Top Cats Hat 10]

16 minutes ago, Cyclone said:

I've no idea if that's a specific exception in law, or if they're all illegal to actually drive with.

Yes, they are allowed in law as long as the intention is that its use is temporary and 50mph is the maximum speed driven.

 

Despite what people are saying it will NOT pass an MOT even if the wheel size and tyres are identical to the other three.

[RootsBooster 24]

1 hour ago, Cyclone said:

Googling it, it appears that space savers are often of a different (smaller) diameter to the regular wheels.  I've no idea if that's a specific exception in law, or if they're all illegal to actually drive with.

I don't have one myself so I can't go and look, mine comes with the puncture repair spray in foam stuff.

They're legal to use strictly on case of emergency, ie to get you home or to the nearest garage. If you are found to be using one for any other reason you can and likely would end up in court.

Most space savers are supplied to (more or less) match the outer diameter of the existing road wheels though, despite what the inner diameter of the rim may be.

[Cyclone 10]

So the OP probably has a spacesaver, and trying to reuse the tyre from a regular wheel simply won't work as it won't fit.

[geared 303]

Sounds like the spare is just some random wheel somebody threw in the back to get rid of it.

[RootsBooster 24]

1 hour ago, Cyclone said:

So the OP probably has a spacesaver, and trying to reuse the tyre from a regular wheel simply won't work as it won't fit.

It's a 185, so too wide to be a space saver. 

Not legal to mix with the other 3 tyres under any circumstances (as far as I'm aware).

 

[Kidorry 189]

The space saver is a brand new tyre because the car is only 18 month old. I would not dream of using it, only in an emergency.

[ANGELFIRE1 10]

7 hours ago, Kidorry said:

The tyre size on my car are 215/16 and the spare one is 185/15". 

I think if I bought a car, new or not and the spare was a different size, the sale would be put on hold while the correct wheel and tyre were sourced and supplied. It's just common sense surely.

 

Angel1.

[Top Cats Hat 10]

39 minutes ago, ANGELFIRE1 said:

I think if I bought a car, new or not and the spare was a different size, the sale would be put on hold while the correct wheel and tyre were sourced and supplied. It's just common sense surely

Not enough people do this.

 

Decent tyres can be expensive and although a spare tyre doesn't have to be road legal, on a couple of occasions I have knocked the price of a replacement spare (new or good part worh) of the purchase price.