Is there a difference in ride between a 35d, 3.0 and 4.8? I'm guessing that they should be the same (relative to the sports package/adaptive drive packages).

Ride is pretty subjective.

I found the 214's on my 4.8 exceeded my expectations. It was stiff (the way I like it), but way more comfortable than a sedan with low profile tires. I don't feel the irregularities/harshness of the road as I do in my 3'er or MB E class.

The 128's (21") that I have on them now are not that big of a difference from the 20". Slightly stiffer.

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2008 X5 4.8
White w/ Black Interior w/ Bamboo Trim | Premium | Sports + 214" | Tech | Cold Weather | Rear Climate | Premium Sound | Active Vent Seats | Heads-Up | Comfort Access | 3rd Row | Aero Kit | Huper Optik Tint | Clear Reflectors