[moldcad]

I believe that- especially after modding the N55 to the region of some 380 hp - the tire widths in the stock staggered setup of M345i are too small.

If I wanted to keep the wheels, would 245/35 R18 (stock rear) in front, and 275/35 R18 fir w/o rubbing?

EDIT: oh, and BTW what are the stock rim widths in the staggered setup?

[moldcad]

Oops... Considering the stock wheel widths of 7.5" (F) and 8" (rear), and according to that site: http://www.tyresizecalculator.com/ty...dth-calculator, the current 245 at the rear is the max tire width...

[nike001]

Originally Posted by moldcad

I believe that- especially after modding the N55 to the region of some 380 hp - the tire widths in the stock staggered setup of M345i are too small.

If I wanted to keep the wheels, would 245/35 R18 (stock rear) in front, and 275/35 R18 fir w/o rubbing?

EDIT: oh, and BTW what are the stock rim widths in the staggered setup?

18x7.5f & 18x8r

I believe those wheels are maxed out with tire-width with the 225f & 245r tires. You'll need wider wheels to accommodate wider tires.

[kd0t]

245/35 will fit your 7.5 easily

275/35 might be pushing it on the 8 inch rear.

These are not recommended, but it's do-able. I ran 245/40 on a 7.5 with no issues

[moldcad]

Originally Posted by kd0t

These are not recommended, but it's do-able. I ran 245/40 on a 7.5 with no issues

Question is: will a 8" rear wheel with 275 tire really work like a proper combo in terms of lateral forces? Have no hands-on experience, but I would think no...

Opinions?

[WWM]

Not sure how entirely accurate that site is. For example, I punched in the rear wheel size for a Jaguar XFR (9.5x20) and it said 275 was the max width. That car came with 285/30R20 from the factory.

[Transfer]

I may be using my stock wheels for winter duty and looking at a wider aftermarket setup. 255 front, 275 rear would be awesome but I haven't had a chance to find out if that's doable yet. For my needs and stock power level I'll be looking at 235 front 255 rear.

Anyone with xDrive (or AWD know how) have an idea how to manage the diameters on a staggered setup? The stock staggered diameters front to rear are already 1.3% different which I thought was too much. Apparently xDrive may not be that picky?

[Zooks527]

Originally Posted by Transfer

The stock staggered diameters front to rear are already 1.3% different which I thought was too much. Apparently xDrive may not be that picky?

The number that's often bandied about for xDrive is 1%, based upon the controller having an "learning" range tolerance for tire diameters of 1%. Two things present themselves.

First, as above, the stated range is 1%. Note that there aren't any decimal places in that number. In a situation where there's only 1 significant digit, 1% and 1.3% are the same thing.

Second, dissimilarities between the front and rear axles are less critical on an xDrive car than dissimilarities side-to-side. The clutch system in an xDrive transfer case can load all the torque to the front or the back based on sensor input. This means that transfer case "wind-up" is not a given, unlike a strictly mechanical transfer case which puts some torque to both axles.

As a result, BMWs have much wider tolerance of fore/aft tire size differences than other AWD cars on the market. My old VW and my wife's Subaru, with mechanical transfer cases, are both down in the 0.2% range.

[Transfer]

Originally Posted by moldcad

Question is: will a 8" rear wheel with 275 tire really work like a proper combo in terms of lateral forces? Have no hands-on experience, but I would think no...

Opinions?

I wouldn't do it. 255 is the max I would use based on my experience with 245 and 255 on 8-8.5" width wheels. If you go too wide a tire on a narrow wheel, it's just sloppy and looks goofy. Granted, some tires are more narrow or wide and have different shoulders than tires of the same stated width, so it's a little dependent on the specific tire.

Here's a pic of Michelin PA4 245/40/18 on 18x8 that I took of my M3 winter setup:



Here is a pic of Nitto NT05 245/40/18 on 18x8.5 on my old WRX:



Here are the same Nittos next to Dunlop Z1 Star Specs. The Nittos are 245, and the Dunlops are 235:

[nike001]

Originally Posted by kd0t

245/35 will fit your 7.5 easily

275/35 might be pushing it on the 8 inch rear.

These are not recommended, but it's do-able. I ran 245/40 on a 7.5 with no issues

245 on a 7.5" wheel had to have looked ridiculous. What was your sidewall ratio? Putting a tire that much bigger than the wheel is never a good though. whether it's aesthetically or for safety.

Originally Posted by moldcad

Question is: will a 8" rear wheel with 275 tire really work like a proper combo in terms of lateral forces? Have no hands-on experience, but I would think no...

Opinions?

No. Don't put a 275 width on an 8" wheel. It'll be a balloon on the sidewalls. Some shops might even say they won't even put it on because it doesn't fit..

Put 275 on a 9.5" or 10" wheel

Originally Posted by WWM

Not sure how entirely accurate that site is. For example, I punched in the rear wheel size for a Jaguar XFR (9.5x20) and it said 275 was the max width. That car came with 285/30R20 from the factory.

General consensus: 235 is max for 7.5", 245 is max for 8", 255 is max for 8.5", 265 is max for 9", etc etc.

When you go past those is when your tire buldges out like a truck... AKA doesn't look good.

[zipphreak]

Go search in the wheels section. Alot of good information already in there. Specifically with upsizing the front tires and the issues you will run it. Along with finding the correct offsets for wheels in the rear. The information is here, google is your friend.

[Transfer]

Originally Posted by Zooks527

...

Thanks for the input. That's pretty much what I assumed. I suppose though that I won't mess with 235/255 as that's 1.6% difference. I'll just have to leave it be or go with a square setup 255 all around. Not sure if 255 will fit up front, but there is potential for better front end grip and more oversteer that way.

[kd0t]

@nike001

245/40 did not look "ridiculous" on a 7.5

[harkes]

I am running 255/35-18 on the rears. No problems. 255 is a much more standard size = cheaper.

[Transfer]

Are there any downsides to running a 225 front, 255 rear setup? How about with xDrive? The diameters are the same but makes me wonder about understeer or changes to how xDrive handles torque split.

[pikcachu]

Originally Posted by Transfer

Are there any downsides to running a 225 front, 255 rear setup? How about with xDrive? The diameters are the same but makes me wonder about understeer or changes to how xDrive handles torque split.

you will get some more understeer for sure

[F22_Will]

Im running 265/35/18 toyo R888 on my rears with no problems, hooks so much better than 245/35/18 pss...

[Bee Pee]

Originally Posted by F22_Will

Im running 265/35/18 toyo R888 on my rears with no problems, hooks so much better than 245/35/18 pss...

Any photos ?

[F22_Will]

Originally Posted by Bee Pee

Any photos ?

Correction they are 255/35/18 heres a pic i had on my phone, ill update a better one when i get home

[jmwilson125]

I got 265 on a 9" wheel and I think it looks great. According to tire rack the 275 moss will fit 9-11"

[x233]

Originally Posted by Transfer

Are there any downsides to running a 225 front, 255 rear setup? How about with xDrive? The diameters are the same but makes me wonder about understeer or changes to how xDrive handles torque split.

>> 235 front 255 rear.
It's doable but I don't recommend it. I tried it. In fact, will use it again for driving places where I'm concerned about my front tires getting ruined (like mountains and potholes in winter).
xDrive handles it all right but a) it feels like it takes more effort to get going, b) already not-so-stellar m235 handling gets worse because the fronts feels too tall and more wobbly, less precise. The positive is braking is noticeably better with wider front tires. Overall, I prefer the 225 front width.

>> 225 front 255 rear.
Do it. Just don't get the rear camber too negative. Common sense will tell you that it's going to increase understeer but what you're going to feel is a) noticeably better traction and b) more RWD behavior in turns, etc as more torque goes to the rear wheels. This will be especially noticeable in the wet, snow, aggressive driving, etc., and/or stability turned off. You'll love it. xDrive loves it, too.

>> 255/35/18 on the stock 8 inch wheel
Fits all right and handles all right. You wouldn't really notice it's "wide" unless told so. Winters are narrow so it's even less of a concern.

[Transfer]

Originally Posted by x233

>> 225 front 255 rear.
Do it. Just don't get the rear camber too negative. Common sense will tell you that it's going to increase understeer but what you're going to feel is a) noticeably better traction and b) more RWD behavior in turns, etc as more torque goes to the rear wheels. This will be especially noticeable in the wet, snow, aggressive driving, etc., and/or stability turned off. You'll love it. xDrive loves it, too.

>> 255/35/18 on the stock 8 inch wheel
Fits all right and handles all right. You wouldn't really notice it's "wide" unless told so. Winters are narrow so it's even less of a concern.

It's funny I posted that a year ago before I put my winter set on and I went with 225/255 on 18s x 8.5/9.5. I completely agree that xDrive is improved with this same diameter front/rear and wider rear tire. I don't entirely understand why it's different than my OEM staggered summer set but it is. My assessment of the xDrive behavior with this sizing is exactly the same as yours.