In theory about 90-110 before light then you should have about 40-50 max before you are pushing but that all depends how you are riding and what weight you've got on your bike.
If you are heading into the more remote areas a lot of people tell you to fill up at every station you see as you never know how far the next one is

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or olives???
quote motonacio "this is to certify Meach is not the prat you'd think from his posts"
http://www.youtube.com/imeach