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      04-13-2014, 11:37 AM   #1
6seriesgc
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Recommended tire setup for 640xi?

Hey guys....I currently have stock 19s (245/40-19) run flats and would like to upgrade to wider tires. My wheels are the 351M all season, so the length of the wheel is measured at 8.5.

Is it recommended to have a square setup or can I go stagger.

For either option, what is the widest I can go in front? I was thinking 275-35-19 all around but unsure if this will causing rubbing.

Im leaning more toward 255-40-19 (f) and 275-35-19 (r)...or...265-35-19 and 275-30-19. Any issues with this configuration on the 640xi?
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      04-13-2014, 02:34 PM   #2
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if you don't already have a staggered set up, I am assuming you are 8.5 inches wide all around. Wheel width is your limitation. I wouldn't put anything wider than a 255 on an 8.5 inch wheel. You'll get a lot of sidewall bow which isn't ideal and looks weird too.

So without changing wheels, you're looking at 255/40-19 all around. Assuming you are changing to non-RFT, the weight savings and tire design will make more of a difference than the width.
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      04-13-2014, 03:29 PM   #3
6seriesgc
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so there would be drastic sidewall bow still even although i am off by .5 inch? the 275's from continental are for 9-11 inch wheels.
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      04-14-2014, 05:53 AM   #4
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Given the low profile, there's not a lot of distance from the rim bead to the maximum section width. On a 275/30 for instance, assuming the max section is about an inch from the road, you only have about 2 inches to "grow" from rim width to section width.

With an 8.5" rim and 275 (10.8") the sidewall will buldge about 1.2" wider than the rim (per side) and then have to "fold" back to tread width. IMO that looks funny and I doubt it's an ideal situation. I would guess mounting would be problematic, as would sidewall stress and heat build up. Not to mention potential for tire curb rash. I would stick with the tire manufacturer's recommendation on rim width - especially on low profile tires.
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