I am thinking of installing style 128 with summer tires and looking for some advice on the tire size.

the wheels are 19x8.5 front and 19x9 rear, both 35ET.

what is the best size for our XI wagon with stock suspension?
245/35 255/40?

My understanding is that with 35 offset I will not require any spacers. correct?

 

It sounds like you'll be just ok or a little tight in the rear, depending on your suspension and the tires you select. Check the numbers in my signature for comparison. I'm sitting on KW V3s set about 0.8" lower than stock. On the rear, I had to roll and slightly pull the fenders to clear the Bridgestone 285's with a very square profile.

 

i am debating between 265/30 19 and 275/30 rear with a 245/35 front

 

It is recommended that our xDrive vehicles maintain a match between rolling diameters to within 1%. Based on the sizes you mentioned, 265 would be just under 2% different between front and rear, and the 275 would be approximately 1% (just over the limit). These numbers are only estimates based on standard calculations, so you should obtain the diameters and/or revs/mile (or likely km for you) for the tires you actually intend to get to confirm.

For 245/35-R19 fronts, a rear size of 285/30-R19 is usually your best match. In fact, the Pole Positions I run have exactly the same diameter Front and Rear.

 

will i have to roll my fenders to mount the 285/30 on stock suspension?