New BMWs, tire diameter and traction control question

[CarsSuck]

Hey all,
I'm wondering what the consequences of changing overall wheel diameter are on a new BMW, say a 2012 135i. The front tires are only 215s and the rears are 245. So ideally, a square setup would go on. I haven't looked into all the details, but a little more rubber would be nice on the front, its just so damn harsh with the run-flats.

So what do these changes do to ABS and DTC and what not? Can it be reprogrammed for a different setup?

TIA,
Will

[nrubenstein]

Small differences are OK. Large changes will start causing DSC/DTC to behave oddly. Obviously, this is only the delta between axles that matters.

Also, the 1 is, IIRC, pretty heavily constrained on front tire selection.

[mrcheezle19]

my buddies dad runs 225f 255r conti extremes I believe, the ride is incredible over the run flats. There's no issue when any of the traction control or abs

[Irish1]

You can run NON run-flats 235s on the front of the 135i with no problem and you'll balance out some of that inherent understeer. Running non run-flats front and rear is the best first upgrade. On my 08 Z4 30si Coupe the first thing I did was pull the run-flats off and put a set of Michelin PS2s on it and bump front tire width. The run-flat tires on the 1 Series are crap. Send your pal over to 1 Addicts for more detailed information on suspension and tire upgrades on the 1's.

[10Toes]

What's traction control?

[Wh33lhop]

Small differences are OK. Large changes will start causing DSC/DTC to behave oddly. Obviously, this is only the delta between axles that matters.

Also, the 1 is, IIRC, pretty heavily constrained on front tire selection.

I don't think it behaves oddly or differently, it will just tell you to go fuck yourself (light up your dash and disable itself) if it can't figure out what's going on. The generally accepted rule is if the front and rear diameters are within 3% of each other you are ok.

[lambo]

What's traction control?

Sounds like some of that witchcraft business...I want none of it!

[u3b3rg33k]

I think we need some miata tirecalc numbers up in here. so far we've got section width only, yes?

[jlevie]

There will be no affect on ABS or DTC if the rolling diameters of all of the wheels is the same, or very nearly the same. That diameter can be different from stock with no affect. However on cars with wheel speed sensed low pressure tire warning a change in rolling diameter from stock can result in nuisance warnings.

[CarsSuck]

Yeah, its all hypothetical for the near term. The car only has about 7k on it, so I think we're gonna wait until the OE tires are used up. But it's not too early to start thinking.

Car has the M-package 18" wheels. My initial thought was just buy a used set of rears for a square setup, but I'm beginning to doubt that will fit. Option 2 would be fitting a slightly wider front tire, getting closer to equal width with the rear and being less stretched. Option three is having a second set of wheels, which seems inevitable given that all the other cars have extra shoes as well.

And here is where i admit its my parents' car. But Im gonna try to sway them in the best direction. This car is for the street, but it will likely see a little track time. We all agree it understeers too much and even I think its overly harsh on manholes and the like. So, with those modest goals in mind, does anyone have a recommendation?

[CarsSuck]

I think we need some miata tirecalc numbers up in here. so far we've got section width only, yes?

So 18" is it, no options there. 215/35/18 = 245/35/18 O.D. The wheels are 7.5"/8.5" f/r. Obviously, i should just test fit a rear wheel on the front.

Apparently people go to 225/255 widths. I doubt that would have the desired effect.

I was just wondering if these new BMWs were sensitive to having a non stock tire configuration. Its so computerized, i dont know how it works. I also didnt realize the front and and rear were the exact same diameter.

[u3b3rg33k]

Chances are if an OEM picks (a) tire size(s), their computer can handle it, equal diameter or not.

[mrcheezle19]

ps2's

[Irish1]

Square'em up!

Finding another set of 8.5 inch rear wheels for the front and running 245/35X18 tires at all four corners is the best idea. There's lots of suspension work that the 135i would benefit from to really make it a neutral car. E90 M3 steering and control arms fit, are lighter, and have better geometry. The first step I would make is working on rear bushings: TC Kline found the 1-Series rear suspension bushings were way too soft. 1 Addicts Forum is a great resource.

So 18" is it, no options there. 215/35/18 = 245/35/18 O.D. The wheels are 7.5"/8.5" f/r. Obviously, i should just test fit a rear wheel on the front.

Apparently people go to 225/255 widths. I doubt that would have the desired effect.

I was just wondering if these new BMWs were sensitive to having a non stock tire configuration. Its so computerized, i dont know how it works. I also didnt realize the front and and rear were the exact same diameter.

[glucklich21]

I'm running Nitto Invo 235/35/18 on the front and 265/40/18 on the rears of my 335i. I have no problems. Now with camber worn front tires traction control about lost its shit going around a corner. It felt like the car was fighting itself, but that's a different story. ;)