help-do i need an 18 inch spare?????

[bmw-newbie]

hi,

i want to fit 18 inch alloys around my 325 coupe (2001) and have two questions which I'm hoping you can help with (please!)...

1) Can I still use my 16 inch spare if i fit 18 inch alloys all the way around or do i need to get an 18 inch spare?

2) Are replica alloys just as goods as the official ones?

Please help I'm a complete newb at all this...thanks!

[docevi1]

if you put 18" alloys on with thin tyres and have the same rolling radius as a 16" with tall tyres then you'll get away with it - so long as you drive slowly.

Remember however, big wheels = more top speed, but crucify acceleration (torque at wheels = torque @ engine * gear * diff / wheel radius). You'll also get a much harsher ride.

www.chris-longhurst.com/carbibles/index.html?menu.html&tyre_bible.html is the site you want

[Rob_F]

I reckon you're going to get the piss ripped out of you by a load of car snobs who don't understand why you want to put big wheels on your car, and think their opinions are right and yours are wrong. Ignore them.

You may want to try BMW specific forums about what wheels are good/bad with replicas. (Alpina?)

I would assume there is no legislation about carrying a certain size spare as some cars don't even have them. It should run on a small wheel as the tyre will have a higher sidewall so the difference will not be that great - but i'm not an expert. Might be worth dumping it and chucking in a can of tyre sealant instead. That way you'll save the weight of your ICE install, so you're no worse off when you stick the subs in (Am i on the right lines here? )

Cheers,
Rob.

[Rob_F]

docevi1 said:

if you put 18" alloys on with thin tyres and have the same rolling radius as a 16" with tall tyres then you'll get away with it - so long as you drive slowly. Remember however, big wheels = more top speed, but crucify acceleration (torque at wheels = torque @ engine * gear * diff / wheel radius). You'll also get a much harsher ride.

Of course if they are the same rolling radius your second point isn't valid... However big wheels, especially the cheaper brands, may well be heavier than your originals, which will blunt performance.

Cheers,
Rob.

[docevi1]

well, that is true Rob. Meant more as if you're changing the rolling radius

[Rob_F]

I know exactly what you meant mate, i was just being a pedant as i'm bored

Rob.

[docevi1]

why are you likening yourself to a thing that hangs off a chain?

my english is crap, so I'm one to type

[fridaypassion]

carry a standard spare and a couple of cans of tyre weld, my megane 225 doesnt even come with a spare!

[Mr E]

My car came with 16" wheels. And a 17" spare.

I now have 18" wheels. And a 17" spare.

Rolling radius is close enough.

[NormanD]

If you do have a smaller spare DON'T drive on it to fast or you will wind up the diff to much.

Some cars you can fit a larger tyre in the well but will take up more hight, worth checking and getting an odd one on eBay etc

[iguana]

bmw-newbie said:

2) Are replica alloys just as goods as the official ones? Please help I'm a complete newb at all this...thanks!

Dpends who makes it, some replicas are cheap, nasty & absolute cack, some are fine.

[iguana]

Forgot to add- as the others have said- no you don't need 18 inch, but same rolling radius is very handy.

This tyre calculator link is very useful to work stuff out-

www.partsemporium.co.uk/tyre%20size%20calculator.htm

[festernath]

docevi1 said:

why are you likening yourself to a thing that hangs off a chain? my english is crap, so I'm one to type

...a PENDANT?

[bmw-newbie]

Guys,

Thanks for all the responses. The tyre calc (www.partsemporium.co.uk/tyre%20size%20calculator.htm) sets out there is only a 5mm difference between the two.

Being a complete newb at all this I thought there would be a 2 inch difference!

Thank god for the internet and more intelligent souls like you !!!

I'm now going to spend my £200 saved on an oversized exhaust that will shake the house (only kidding !!!)

[Stevenj214]

doesn't matter the size - suspension will compensate.

just think of the smaller wheel like a 'spacesaver' wheel and limit your speed to 40mph

[Rob_F]

festernath said:

docevi1 said: why are you likening yourself to a thing that hangs off a chain? my english is crap, so I'm one to type ...a PENDANT?

lol...

Rob.

[phil hill]

AFAIK (from what I've been told by DoT vehicle inspector): You can have what-ever size spare wheel you like, so long as it's correctly inflated and has adequate tread. This is reflected in both construction and use, and the MoT test.

However, if you fit the spare to the vehicle, and have a mis-match of wheel size across an axle, you are contraviening construction and use, and are committing a road traffic offence. If you check out all the "Skinny" space saver wheels, you will find they match the diameter of the standard wheels even though the width is much reduced.

In a final twist to the story, it doesn't say you actually have to have a spare wheel to comply with contruction and use, only if you do it must be legal. So if in doubt, take the spare out before the MoT and you cannot fail for it !!