M3 tire size on 189s, DSC issue?

Transport3r · 01-01-2012, 06:20 PM

I was thinking of decreasing the understeer of my 335 by fitting the 245/40/18F 265/40/18R M3 tire sizes to it. I've searched and the conclusion seems to be that they fit without rubbing.

However it seems there might be an issue concerning the % difference in the tire circumference front to back. For the stock sizes that is 0.8%. The difference for the M3 combo is 7.5%. I've read that the M3's traction control is especially set up for this and that the 335i cannot handle over a 3% difference, but I've not been able to confirm it through a reliable source.

Even if I were to drop the rear tire to 265/35/18, the difference is already 5.7% again due to the rear being shorter than the front at that point.

Any ideas? Thanks!

anerbe · 01-01-2012, 08:15 PM

why couldn't you put 265/35R18's on? this would be a better option.

Stock rolling circumferences are linked to the vehicle's stability system. Vehicle handling systems are fine tuned with the proper sizes, and can be quite sensitive. Having such large differences will most likely effect it.

Transport3r · 01-02-2012, 08:28 AM

Quote:

Originally Posted by anerbe

why couldn't you put 265/35R18's on? this would be a better option.

Stock rolling circumferences are linked to the vehicle's stability system. Vehicle handling systems are fine tuned with the proper sizes, and can be quite sensitive. Having such large differences will most likely effect it.

I checked the difference with that size too, it's also over 3%...
I'm trying to figure out how much tolerance is in the system before the dsc freaks out. Seems like there is no easy way to get a 245/265 setup on a non M3.

remmib · 01-02-2012, 02:01 PM

265/35/18 is not a problem, and it can't be over 3% bigger since OEM is 255/35/18.

Transport3r · 01-02-2012, 02:15 PM

Quote:

Originally Posted by remmib

265/35/18 is not a problem, and it can't be over 3% bigger since OEM is 255/35/18.

I know 265/35/18 isn't a problem. I haven't found any data on someone who paired it with such a wide front tire though. the car doesn't care that it's smaller or bigger than stock, but it needs to be within a certain % of the fronts, otherwise the DME thinks one set of wheels is slipping.

245/40/18 vs 265/35/18 % difference = ((245x0.40)-(265x0.35))/(245x0.40x100%)= 5.4% -fronts are taller than rears
245/40/18 vs 265/40/18 % difference = ((245x0.40)-(265x0.40))/(265x0.40x100%)= 7.5% -rears are taller than fronts

The big question is what is the magic number where the DSC decides that whe wheels are slipping? If it's 3% neither of these setups will work.

remmib · 01-02-2012, 02:25 PM

Your math is wrong, google a tire calculator.

Transport3r · 01-02-2012, 03:05 PM

Haha, looks like tires aren't calculatied as i thought they were, thanks remmib!

245/40/18 vs 265/35/18 % difference = 1.6% -fronts are taller than rears
245/40/18 vs 265/40/18 % difference = 2.4% -rears are taller than fronts

So technically either of these setups should fall into BMW's 3% margin?
Then why did i read that M3's are especially calibrated?

will.c · 01-02-2012, 06:04 PM

I ran 245/35/18 and 265/35/18 on stock 189s (mounted at BMW). Quite a bit more grip overall, no problem at all with DSC. Slightly quicker steering response due to lower profile in the front compared to stock, but probably at a cost of harsher ride. However it felt smoother than the stock RFTs IMO. Just to share my thoughts, next time I'll rather get 235/40/18 front and address the understeer with M3 rear sway bars.

anerbe · 01-03-2012, 02:58 PM

Quote:

Originally Posted by joshuo

Haha, looks like tires aren't calculatied as i thought they were, thanks remmib!

245/40/18 vs 265/35/18 % difference = 1.6% -fronts are taller than rears
245/40/18 vs 265/40/18 % difference = 2.4% -rears are taller than fronts

So technically either of these setups should fall into BMW's 3% margin?
Then why did i read that M3's are especially calibrated?

I don't think the 3% is a hard cutoff for errors in the car. However, understanding the basics of the system accounting for difference in wheel speed to activate ABS, the higher the difference, the greater the chance for unwanted interference by the DSC system.

The factory stagger for the 335 is 0.2% different. The more you change the stagger, the higher chance for unwanted effects. Therefore, it's always better to get close to the OE rolling circumference as possible. 1.6% is better than 2.4%. Will the size difference effect be noticeable to you? Who knows.

M3's are calibrated to the different tire sizes. The DSC system is tuned to OE sizes different to the 335.

01-01-2012, 06:20 PM	#1
Transport3r Major 86 Rep 1,262 Posts Drives: 2011 N55 E90 Join Date: Sep 2010 Location: Melbourne, FL iTrader: (4)	M3 tire size on 189s, DSC issue? I was thinking of decreasing the understeer of my 335 by fitting the 245/40/18F 265/40/18R M3 tire sizes to it. I've searched and the conclusion seems to be that they fit without rubbing. However it seems there might be an issue concerning the % difference in the tire circumference front to back. For the stock sizes that is 0.8%. The difference for the M3 combo is 7.5%. I've read that the M3's traction control is especially set up for this and that the 335i cannot handle over a 3% difference, but I've not been able to confirm it through a reliable source. Even if I were to drop the rear tire to 265/35/18, the difference is already 5.7% again due to the rear being shorter than the front at that point. Any ideas? Thanks! __________________ Josh- Last edited by Transport3r; 01-01-2012 at 08:45 PM..
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01-01-2012, 08:15 PM	#2
anerbe Lieutenant Colonel 121 Rep 1,568 Posts Drives: Red E90M 6MT Join Date: Dec 2006 Location: BH, MI iTrader: (2)	why couldn't you put 265/35R18's on? this would be a better option. Stock rolling circumferences are linked to the vehicle's stability system. Vehicle handling systems are fine tuned with the proper sizes, and can be quite sensitive. Having such large differences will most likely effect it.
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01-02-2012, 02:01 PM	#4
remmib General 1571 Rep 29,202 Posts Drives: 2013 F10 520d M-Sport Join Date: Feb 2006 Location: Norway iTrader: (0)	265/35/18 is not a problem, and it can't be over 3% bigger since OEM is 255/35/18. __________________ F10 520d M-Sport Alpine White \| HRE P43SC 20x9+20x11 \| Michelin PSS 255/35+295/30 \| KW V3 Coilover \| M5 Front Sway Bar + M550d Rear Sway Bar \| 3DDesign Front Lip \| BMW M Performance CF Spoiler \| BMW M Performance Diffuser \| BMW M Performance Black Grills \| BMW M Performance Pedals \|
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01-02-2012, 02:25 PM	#6
remmib General 1571 Rep 29,202 Posts Drives: 2013 F10 520d M-Sport Join Date: Feb 2006 Location: Norway iTrader: (0)	Your math is wrong, google a tire calculator. __________________ F10 520d M-Sport Alpine White \| HRE P43SC 20x9+20x11 \| Michelin PSS 255/35+295/30 \| KW V3 Coilover \| M5 Front Sway Bar + M550d Rear Sway Bar \| 3DDesign Front Lip \| BMW M Performance CF Spoiler \| BMW M Performance Diffuser \| BMW M Performance Black Grills \| BMW M Performance Pedals \|
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01-02-2012, 03:05 PM	#7
Transport3r Major 86 Rep 1,262 Posts Drives: 2011 N55 E90 Join Date: Sep 2010 Location: Melbourne, FL iTrader: (4)	Haha, looks like tires aren't calculatied as i thought they were, thanks remmib! 245/40/18 vs 265/35/18 % difference = 1.6% -fronts are taller than rears 245/40/18 vs 265/40/18 % difference = 2.4% -rears are taller than fronts So technically either of these setups should fall into BMW's 3% margin? Then why did i read that M3's are especially calibrated? __________________ Josh-
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01-02-2012, 06:04 PM	#8
will.c Captain 130 Rep 638 Posts Drives: E46M Join Date: Mar 2011 Location: Central Jersey iTrader: (5)	I ran 245/35/18 and 265/35/18 on stock 189s (mounted at BMW). Quite a bit more grip overall, no problem at all with DSC. Slightly quicker steering response due to lower profile in the front compared to stock, but probably at a cost of harsher ride. However it felt smoother than the stock RFTs IMO. Just to share my thoughts, next time I'll rather get 235/40/18 front and address the understeer with M3 rear sway bars. Last edited by will.c; 01-02-2012 at 06:18 PM.. Reason: iPhone app was acting up....
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