Headwinds and tailwinds notwithstanding.

I'm sure my motivation for the high speed run was different from all others.

I had just purchased it used and had a 90 day warranty. If it broke, the flatbed would have dropped it in front of the showroom door and I was going to call the salesman when the Dealership opened. The drive home that night I bought it was the hardest I've EVER driven it.

We are using the same line of thinking as far as how to come to a realistic top speed. Saved your file to desktop, very useful. That's way I searched out a speed calc. that considered drag.

Isn't 5100lbs. the curb weight?

BC, the 5100 number is an estimation of a 4824 lb X5 + me + SC parts. But weight is not a crucial factor for top speed. (If it weighed 1000 lbs more, I'd need only need 9.5 more hp to arrive at the same top speed) :)

Trial by fire. :)

Yeah, rather it breaks on their dime vs mine!

I wonder if the wider tires effect frontal area, and offset?

Seems to me it would.

My run was on 255s all around, have 255s/285s now with 15mm out F and 50mm out R.

I think that it would affect frontal area, rolling resistance and Cd overall. Couldn't say to what degree. Where's an air tunnel and aero engineer when you need one!

Hahaha! Really.

I also wonder if those doing high speed runs are aware that tires shoud be inflated near max pressure. Did that prior to leaving dealership.

And balanced.

PO had BMW install new OEM Vrated B'stones prior to trade-in. Checked for any damage/punctures/plugs during purchase inspection on lift. All that matters prior to a high speed run.

You will be glad you did!