I decided the same thing too - in the Northeast, our potholes are everywhere (despite the America Revitalization Act, which has nicely repaved most of the parkways/highways I take); the 18's are also easier on the $$ and spine!
Quote:
Originally Posted by okolisr
I haven't seen this mentioned this yet, but I always learned that the main performance benefit from larger-diameter wheels (with lower-aspect-ratio tires to keep the same overall diameter) is NOT because of the larger wheel size, rather it's because of the lower aspect ratio of the tires which results in REDUCED TIRE SIDEWALL HEIGHT. With reduced sidewall height, tires do less flexing and floating while cornering, for better stability and road contact.
Here are rough theoretical calculations:
The 18" 400M wheels have 225/45 front tires (225mm x 45% = 101.25mm sidewall height) and 255/40 rear tires (255mm x 40% = 102mm sidewall height).
The 19" 403M wheels have 225/40 front tires (225mm x 40% = 90mm sidewall height) and 255/35 rear tires (255mm x 35% = 89.25mm sidewall height).
So basically, the 403M tires have roughly 12mm less tire sidewall height than the 400M. That's more than a 10% difference, and enough to increase sidewall stiffness and improve handling significantly.
PERSONALLY, despite this significant improvement with the 19" 403M wheels, I still plan to order the 18" 400M wheels. Why? Because the same reduced tire sidewall height that improves handling also makes it much more likely that I will break a wheel in one of our many St. Louis, MO year-round potholes. Not to mention the endless spine jarring when I keep my car in "sport mode" all the time.
The bottom line is that even though I do faster cornering in my BMW than 95% of drivers, I don't need the "ultimate" capability. The 18" 400M wheels are plenty good enough.
And they look great.
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