What tyre size is fitted to the 18" M Sport?

[aliti]

Hi Guys,

I was just going through the specs on the 123D again while I wait for delivery, (yes I can't wait). I noticed that it tells me that it comes with 215/40/18 front and 245/35/18 rear.

If you look at the standard 16" fitment though, to keep the same diameter the tyres should be 225/40/18 front and 255/35/18 rear?

For those that have already received there cars, what size did the tyres on the 18" wheels actually come in?

If they are actually a 215/245 setup, why would BMW go slightly undersize and would this have a great inpact on revs and spedometre readings?

Maybe I am just being too paranoid?

Thanks for your feedback in advance.

[BigBoss168]

My 135i came standard with 215/40/18 fronts and 245/35/18 rears. From what I have read, it is entirely possible to fit 225/40/18 fronts and 255/35/18 rears, and a lot of members who have replaced the runflats appear to have done so. Yes there is an impact on the speedo readings but again from what I have read it is supposedly around 1%.

[BrokenVert]

225/40 R18 front and 255/35 R18 are perfect tire sizes on the standard wheels

I have been running these sizes for the past 40k km without issue

[aliti]

It just seems strange that BMW wouldn't fit a 225/255 combination in order to keep the overall diametre the same thereby eliminating this 1% error in readings.

This would also mean that when the speedo is showing that we are travelling at 100km's we are actually not. This would also mean that the odometre (in terms of distance travelled) will also be incorrected with the odometre showing more than what the car has actually travelled.

Anyway, when the tyres comes due for replacement I will definitely go with the 225/255 set-up. I think for now I just have to look forward to the delivery of the vehicle first.

[chylld]

Originally Posted by taipan168

My 135i came standard with 215/40/18 fronts and 245/35/18 rears

Me too. But not looking forward to replacing them $$$$

I think 1% speed error is a price BMW paid from a cosmetics standpoint to make the tyres look 'meaner' i.e. less bulgy? Although 1cm tread width is 0.5cm either side which I doubt would make that much of a difference...

[BigBoss168]

Originally Posted by aliti

This would also mean that when the speedo is showing that we are travelling at 100km's we are actually not

I tested my speedo with a GPS unit and it over-read by about 5 km/h anyway.

[Lukkyphil]

Originally Posted by taipan168

I tested my speedo with a GPS unit and it over-read by about 5 km/h anyway.

So you mean at a speedo indicated 100kmh the GPS showed you were doing 95kmh?

[chylld]

Originally Posted by Lukkyphil

So you mean at a speedo indicated 100kmh the GPS showed you were doing 95kmh?

yes... my gps shows the same, it over-estimates by about 4-5%. so when i think i'm doing the speed limit (according to the speedo) i'm actually going slower this is commonplace for manufacturers to avoid liability when you get a ticket i think.

interesting my cruise control is half-way between the two.

[Taymaishu]

Originally Posted by chylld

yes... my gps shows the same, it over-estimates by about 4-5%. so when i think i'm doing the speed limit (according to the speedo) i'm actually going slower this is commonplace for manufacturers to avoid liability when you get a ticket i think.

interesting my cruise control is half-way between the two.

Correct, my Subaru used to read 8% out. When testing coming into Melbourne i sat square on my dial's 100km/h, and the radar read 92km/h.

You can also get a rough estimate from the odometer test signs on the Hume Hwy.

[sparoz]

225/255 here . I trade my tires in when it had 1000km, only paid about $700 for the swap. Just doing my books and the mobility kit was $135.

[aliti]

Hi sparoz,

Why did you trade your tyres in?

Also where did you buy your mobility kit from?

[BigBoss168]

Originally Posted by Lukkyphil

So you mean at a speedo indicated 100kmh the GPS showed you were doing 95kmh?

Yep, exactly. I set my cruise at exactly 100 km/h and the GPS indicated a consistent 95 km/h. Not as bad as my old Boxster which used to over-read by 10 km/h.

[sparoz]

Originally Posted by aliti

Hi sparoz,

Why did you trade your tyres in?

Also where did you buy your mobility kit from?

My local Bob Jane. Mobilility kit from Coastline BMW.

[Scoobs]

Anyone running 255/40/19's on the rear ? Was hoping that the CSL rep's of my 3er would fit on the 1er. Have read that some are achieving this without rubbing.

Be good to hear from someone local doing it succesfully

[aliti]

Hi Scoops,

The fitment from factory 245/35/18 has an approximate overall diameter of around 628.65 mm. The 255/40/19 has an approximate overall diameter of 686.56 mm.
That is approximately a difference of 8.44%. That is too of a difference to fit to a 1er. Your gearing would be totally out as well as your speedo and look just wrong.
If you wanted to fit 19" rims an appropriate tyre size to fit the 1er would be 255/30/19 which would give you the right overall diameter and keep your gearing and speedo constant.

[MickyD]

radical thought..... maybe, just maybe, BMW has enough of a clue to adjust the speedo parameters for the size of the tyres fitted at the factory.....

[aliti]

Just out of curiosity.

Has anyone had a look at the tyre placard on the door frame to see what is the actual tyre size listed that should be fiited?

[BigBoss168]

Originally Posted by aliti

Just out of curiosity.

Has anyone had a look at the tyre placard on the door frame to see what is the actual tyre size listed that should be fiited?

Yes, it just lists all the possible OEM sizes and the appropriate tyre pressures. That said, if you look in the tyres forum they list the maximum possible tyre sizes, which for the 1-series coupe is 225/40/18 front and 255/35/18 rear. Anything else needs mods to avoid rubbing (apparently).

[aliti]

What I was trying to get at was:

If the tyre placard lists the 225/40/18 and the 255/35/18 as the standard listed replacement, then the fitting of the 215/245 combo technically makes the car un-roadworthy.

[AussieRacer]

aliti, look here for all your answers regarding OEM tyre sizes for the 123d:
http://www.realoem.com/bmw/showparts...34&hg=36&fg=30

[aliti]

Thanks AussieRacer
Looking at the list, I hope I end up with the Bridgestone's and not the Dunlop's.