20" Tyre Sizes

[dgm]

In my efforts to source 20" winter tyres at a reasonable price for the X5 I've picked up a pair of 295/45/20 Pirelli Ice and Snow tyres at a bargain price.  To keep the rolling radius correct my intention is to put these on the rears and 265/50/20 (amended from original post) on the front.

Now I realise that the increase in height of the tyre over the standard 315/35/20 and 275/40/20 is about 22.5 mm and the speedo will under read by nearly 6% and I'm willing to live with that.  What I want to know before I pull the trigger on the fronts is if anyone has tried this combination and how did the car feel with them on?

I've found examples of American owners running this combination with seemingly acceptable results but nothing from the UK.  I can get Yokohama winters in the correct sizes for circa £1000 but I think that's too much to be honest.

[X5Sport]

FYI, it is illegal within the EU to have an under-reading speedo.  The UK rules allow for a 10% +/- 2mph over-read (hence the Police allowing for up to 79mph as still being technically 'legal') but under-reading is a no-no.  Your vehicle will no longer comply with its type approval........quoted below:

The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

If (and it's a very big 'if') you got stopped (or there was an 'incident') and someone in authority knew what they were looking at, you could find yourself in trouble.  A 6% error is insignificant at 30mph, but at motorway speeds you could be in unplanned 'bother'.

Is that profile likely to cause any 'winding-up' of the transmission?

It's your call, but............

[snipez999]

There's got to be a good reason why BMW themselves do not supply 20" versions of their winter tyre/wheel sets.........

Check out what they recommend for your car here (and it will doubtless be 18 or 19 inch):
http://www.bmw.co.uk/bmwuk/owner/winter ... tAodGSEA6g

[dgm]

Interesting point X5Sport, I'm not concerned about the legal aspect but if there's any prospect of damaging the transmission then I won't do it.  Any other views on this?

snipez999, as I've got too many wheels and tyres stored as it is I'm not going to be buying another set of wheels for the X5 and my winters are going to be 20".  I don't really subscribe to the view that BMW knows best with their winter tyre recommendations and to prove the point I've been very successfully running 265/30/19 winters on my Z4MC for several years.  Another point is that until very recently there were no 315/35/20 winters available in non run flats, that has changed with the Yokohama winters.

[snipez999]

Fair dos.  I did not fancy taking RFTs (which I have) off and on again as I understand they don't like it too much; bought a very lightly used full set of 232s sitting on the requisite 19s off a BMW dealer, for a song.

I also quite fancied a set of black wheels so had my winters sprayed/lacquered; look good. 

Hope you enjoy your new tyres, car will look smart sitting that bit higher

[Turks]

[quote="dgm"]
In my efforts to source 20" winter tyres at a reasonable price for the X5 I've picked up a pair of 295/45/20 Pirelli Ice and Snow tyres at a bargain price.  To keep the rolling radius correct my intention is to put these on the rears and 265/40/20 on the front.
[/quote]

Are you sure about this? Your rolling radius is well out if you put these Tyres on which could damage your Diff's etc.

You need to put 265/50/20's on the front to make a decent match and you will be just tipping 6% as you say on the speedo.


Turks.

[dgm]

[quote="Turks"]
[quote="dgm"]
In my efforts to source 20" winter tyres at a reasonable price for the X5 I've picked up a pair of 295/45/20 Pirelli Ice and Snow tyres at a bargain price.  To keep the rolling radius correct my intention is to put these on the rears and 265/40/20 on the front.
[/quote]

Are you sure about this? Your rolling radius is well out if you put these Tyres on which could damage your Diff's etc.

You need to put 265/50/20's on the front to make a decent match and you will be just tipping 6% as you say on the speedo.


Turks.
[/quote]

That's what I mean, the rolling radius will be the same between front and rear with these sizes, not that I will maintain the current rolling radius.

I've read a lot about these taller tyre sizes since I posted this and there seem to be a lot of people running the sizes I've quoted in the States without issue. At least one member on here ran with these sizes as well.  If you have any reference to back up your concerns about damage to the diffs then please point me in the right direction.  These sizes seem to be commonly sold on tyre and wheel packages, again in America.

[Turks]

265/40/20 as you put in your OP has a wall height of 106mm (less than OEM) and you were talking about matching that with a rear 295/45/20 which has a significantly different wall height of 132.75mm. With this combination, the fronts will be running many more revolutions than the rears meaning the diffs will need to slip - it may even think that you are losing traction and you keep gettin the DSC kicking in all the time.

What I said was you need to match the 295/45/20 rears with 265/50/20 which have a wall height of 132.5mm - an almost perfect match.


Turks.

[dgm]

[quote="Turks"]
265/40/20 as you put in your OP has a wall height of 106mm (less than OEM) and you were talking about matching that with a rear 295/45/20 which has a significantly different wall height of 132.75mm. With this combination, the fronts will be running many more revolutions than the rears meaning the diffs will need to slip - it may even think that you are losing traction and you keep gettin the DSC kicking in all the time.

What I said was you need to match the 295/45/20 rears with 265/50/20 which have a wall height of 132.5mm - an almost perfect match.


Turk.


[/quote]


Apologies, you are spot on.  That was a typo by me that until now had gone unnoticed (now amended).  I meant to type 265/50/20 and indeed that's what I've ordered.

[Turks]

Great, I was hoping that it was a typo and that you hadn't purchased the wrong sizes.

I have just been looking at getting the Yoko's - cheapest I have found is on Black Circles for just a touch over £1100!


Turks.

[dgm]

[quote="Turks"]
Great, I was hoping that it was a typo and that you hadn't purchased the wrong sizes.

I have just been looking at getting the Yoko's - cheapest I have found is on Black Circles for just a touch over £1100!


Turks.
[/quote]

Ears Motorsport were doing them for about £940 plus delivery the last time I looked, still pricey though.

[Turks]

Thanks


Turks.