I am lucky that where I get my E85 for the E50 tune I run in the Ranger stays pretty consistent, but in the winter it varies from E70 to E80 and of course I take that into account when mixing. Late spring and summer it stays consistently E85. I usually get about $1 worth to test every couple of weeks, but mixing is always stressful because the Ranger just has an analog gauge with no way of knowing for sure the exact gallons left. I am always pretty close, but sometimes off more than others. Anyone here have any tips or experiences with mixing for E50 (or E30 and whatever) you would like to share?