[BayM340]

Hey Everyone,

My 21' M340i xDrive came with the 792M All-Season RFT Turanzas (225/40/19 all around).

I just got a set of 8.5" 792M rear wheels thx to our friend Evan @GetBMWParts.... and as soon as I take delivery I'm swapping the Turanzas, and ditching the square setup.
Turanzas are going in a bon fire pit, and AS3+s are taking their place (before summer rolls around for a set of 4S).

After notifying my dealer of this "event", the service department came back and said they did something similar to another customer's 21 M340 xDrive, and that @ 40MPH Traction control was cutting power when they made the swap from square to staggered. The diameter delta on that staggered setup should be less than .5% so that shouldn't be happening right?

Curious if anyone else with a 21 M340i xDrive has gone from square to staggered, and has run into anything similar? The service folks mentioned they had to throw 255/30/19s??? in the rear to make it work... Something doesn't sound right here as that is asking for differential issues...

Thoughts??? My understanding is that 225/40/19 F 255/35/19 rear should be just fine... I've seen many others with 19' and 20' models transition without issue. Any input is appreciated.

Cheers,
AB

[obscurehero]

Fairly certain that's what mine is running OEM

[BayM340]

Originally Posted by obscurehero

Fairly certain that's what mine is running OEM

Staggered 19" OEM wheels have tires with those parameters, correct (Assuming your response is to: 225/40/19 F 255/35/19 R). My car isn't staggered from factory as it has All-Season RFTs on the 792Ms. It's 8" all around.

I'm questioning why there would be any issues with "Traction Control, ABS, and all of the other "stuff" that's supposed to be "going off"... "(Dealer's words, not mine) if I stagger it. Setting the right tire pressure settings in iDrive should be all I need to do...

I was just curious if anyone with a 21' has done this. I know other users on this forum with 2020s that have staggered by getting bigger rear wheels without issue, and have ditched that factory square All-Season RFT setup...

I'm curious if I'm getting bs because they just don't want to put on the wheels and tires I sourced on my own and not through Service/Parts?

[marco000]

How does this go in the end?

Curious if you are able to get the staggered setup from bmw service.

It feels strange if there's traction issue considering you can order 225/255 on xdrive. Wonder if there's a different tuning on the xdrive based on the wheel/tire sizes. (It would be surprising if there's actually different tuning)

[jeegunkim]

I have xDrive and went from the stock square setup to staggered setup. New tire sizes are 245/35/19 for the front and 275/30/19 for the rear. No traction control issues. No transfer case issues. Just gotta stay within that 1% threshold.

[G22b58]

Do you have a link for the 1% rolling difference guideline to not inflict excessive wear to the transfer box?
Is it possible to get more precise data from the tire manufacturer on the rolling circumference of the tire models you use (and not rely on the nominal tire dimensions)?
I would hesitate to start off with a 1% difference and then add other uncertainties like thread wear. It might be possible to analyze the rolling speed (average) from monitoring the ABS sensors during a typical drive, but I don't know what equipment to use. (It doesn't seem possible with BimmerLink.)

[jeegunkim]

Originally Posted by G22b58

Do you have a link for the 1% rolling difference guideline to not inflict excessive wear to the transfer box?
Is it possible to get more precise data from the tire manufacturer on the rolling circumference of the tire models you use (and not rely on the nominal tire dimensions)?
I would hesitate to start off with a 1% difference and then add other uncertainties like thread wear. It might be possible to analyze the rolling speed (average) from monitoring the ABS sensors during a typical drive, but I don't know what equipment to use. (It doesn't seem possible with BimmerLink.)

[G22b58]

Thanks jeegunkim. I was hoping for a more of a BMW official source, and in my calculation of his sizes (just the nominal values) gives me a good matching of only 0.08% difference while he reports 0.4%. I don't understand why.

[ultrared93]

Originally Posted by G22b58

Is it possible to get more precise data from the tire manufacturer on the rolling circumference of the tire models you use (and not rely on the nominal tire dimensions)?

Michelin's USA website provides the number of revolutions per mile in their tire specs. I would think that would be a more precise figure to use than diameter.

[KP-NJ]

Be lurking around for a while and 7 months ago pulled the trigger on a dealer demo '21 M340ix with square 791m 19" wheels & 225 RF P7 tires.

Long story short; got curb rash on one wheel and a bubble from a pothole on another. Need to get both fixed, but was thinking of just ordering 2 x 19x8.5 791m with 255/35/19 tires for the rear and match the staggered OEM setup - although this would be with RunFlats which I don't particularly care for. Has anyone done the same or similar switch? Are the 255/35 run flats total garbage in terms of ride quality?

Ps> anyone with a pair of 791m 19x8.5 wanting to sell? I'm in New Jersey.