I have shimano XT brakes with 160mm fr And rear. I want to go 180 up front. Can I use an avid rotor 185mm with and avid adapter?

Yes.

you can do whatever you want....its a free country

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'the notorious North County Sancho'

will it cause any problems?

No, it will not cause any problems. Just make sure that you center everything before you tighten it down so nothing is rubbing and there you go!

just don't let his highness do it, he'll put marine grease on it. he puts it on everything.

.....been there done that.

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Ambition is a poor excuse for not having sense enough to be lazy. ~Milan Kundera

is that why you are walking funny?

joking