Tyres Sizes for BMW 1Series

[Jazy]

Hi All

I have a 2014 M120d and running 18” standard alloys. At present the tyres are run flats. The fronts are225/40R18 & rears 245/35/R18. My question is can I run 245/40/R18s on the rear? I want to put some winter tyres on but the cost of the 245/35/R18 I have been quoted are astronomical!! Any advice/ help much appreciated, J 

[Greydog]

Morning Jarrod

It is the guys with x drive cars who have to be really careful with tyre sizes. As your car is rear wheel drive as long as the tyres are the same each side you should be fine the difference in rolling radius will be negligible.

Spare a thought for us with X drive cars who need a set of 4 (often wheels as well) to avoid damage to the transmission 😥

Dave

[SilverJohn]

Hi Jarrod

Last week I posted about winter tyres and sizes etc for my 3 series.

According to my local tyre specialist, just putting winter tyres on the rear is not a good idea.

I'm in the process of buying a full set of 17" wheels and winter run-flat tyres to temporarily replace the 19" summer wheels and tyres.

Yes, this will slightly compromise the appearance of the car but as it will be used less in the winter and will be so much safer, I'm prepared to accept the difference.

Hope this helps.

John

[Guest]

5 hours ago, SilverJohn said:

Hi Jarrod

Last week I posted about winter tyres and sizes etc for my 3 series.

According to my local tyre specialist, just putting winter tyres on the rear is not a good idea.

I'm in the process of buying a full set of 17" wheels and winter run-flat tyres to temporarily replace the 19" summer wheels and tyres.

Yes, this will slightly compromise the appearance of the car but as it will be used less in the winter and will be so much safer, I'm prepared to accept the difference.

Hope this helps.

John

Aside from what my dad told me many years ago, when the UK had proper winters, I've never heard of "Winter" tyres. I have been driving for over forty years, through all weathers. I've never encountered a single issue with standard tyres. In 2019, I simply don’t believe "standard" tyres can’t be used twelve months of the year.

[Guest]

16 hours ago, Greydog said:

Morning Jarrod

It is the guys with x drive cars who have to be really careful with tyre sizes. As your car is rear wheel drive as long as the tyres are the same each side you should be fine the difference in rolling radius will be negligible.

Spare a thought for us with X drive cars who need a set of 4 (often wheels as well) to avoid damage to the transmission 😥

Dave

"who need a set of 4 (often wheels as well) to avoid damage to the transmission" ?

Sorry, can you clarify? Why would we/I/them on an XDrive need new wheels? And what damage would replacement tyres cause to the transmission?

Thanks..

[SilverJohn]

Hi Richard

Like you, I have been motoring for 40 years or so and this is the first time I've sought winter tyres.

This is because I now have a moderately powerful car with automatic transmission and wide tyres.

Cars in your Dad's and my Dad's day were far less powerful, rarely had automatic gearboxes and had relatively skinny tyres.

I've discussed this at length with a tyre specialist. The optimum snow/ice tyre has a soft compound and soft sidewalls so it will mould itself to the road surface.

Summer run flat tyres are the exact opposite.

Both BMW and Mercedes rear wheel drive cars have a reputation of being difficult to control in winter conditions.

I would rather be safe than sorry.

I don't know about the X-Drive and possible transmission damage, that's out of my knowledge range.

John

 

[Upt'North]

I think the X Drive thing refers to wear variables for axles and front to rear. I think the max difference recommended is 3 mm either on the same axle or front to rear. So if your rears are down to 2 mm and your fronts are at 4 mm, then you shouldn't just change the rears but all 4, hence confining two perfectly good tyres to the scrap heap unless you have somewhere to store your very own collection of part worns. This is assuming the new tyres will be around 8 mm. 

Upt'North. 

[SilverJohn]

I'd be interested to know the technical reason for this. It sounds potentially very expensive.

John

[Greydog]

OK I will try to clarify

(1st) Winter tyres are a legal requirement in many European Countries from October through to March, so if your planning a ski trip or similar be aware and check the regulations.

(2nd) Winter tyre compounds generally work best below 12 deg C where a standard summer compound will begin to become hard at those temperatures and below reducing their effectiveness, ie Starting Stopping and steering the stuff we rely on.

(3rd) X drive equipped cars (not just BMW) have a front and rear diff with a transfer case in the middle. If the rolling tyre radius varies between front and rear the transmission will suffer "wind up" causing damage to the transfer case but can also damage diffs as well. Not Cheap

My X5 has 20" wheels with a staggered set up  (front) 275/40R20. (rear) 315/35R20 ..so first finding winter tyres in those sizes is not easy and where you can they are expensive so I also have a set of 18" (needed to clear the brakes) wheels fitted with 255/50 R18 same size all round fitted with winter tyres. 

So my personal choice, is to swap my Summer Wheels and tyres over to the winter set in November as I regularly tow a horse trailer being able to stop go and steer with a couple of tons behind me is important. 

Yes you can drive on Summer Tyres all year round in the UK many do and thankfully get away without incident however it is a simple engineering fact they are compromised by low temperatures. How ever drive in say Germany or Poland at this time of year with out winter tyres and the risk is yours.

[Upt'North]

As GreyDog states, it's not just about snow and ice but the temperatures at which tyres best operate. 

If you live in a cool part of the UK 4 season tyres work well, and they are fitted to the wife's non BMW. My only option is full winters which is too much of a faff, when it's cold and snowy I drive Er'Indoors car on Cross Climates, now they are a good 4 season tyre. 

Upt'North.