I did a trip from South Carolina to Montana and back last September on 19" Diamaris.

I wouldn't do it again.

In your case, you are talking about going in October. I would put (at least All Season tires - and maybe even winters) on before the trip because you never know when the snow will come and trap you.

Last September (Mid - Edit, Checked my records - trip was actually at start of September), I had to cut my trip through Yellowstone short because the park was closed in by snow.

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2006 X5 Sport 4.4i