[elhigh]

I just got done making a run to Chattanooga over the weekend, about 260-280 miles round trip. It was pretty warm and steamy, and of course at highway speeds riding with the windows down is just too blustery and noisy.

I found that it was impossible to maintain 60mpg (indicated) at 60mph on the flat with the AC on. Couldn't do it. AC off, the instant indicator would jump up to a tick above 60, AC on it dropped to a tick below. I have no more precise measurements to offer than that, and I didn't think to repeat the test along the same stretch of I-75 on the way back - besides, the median between north- and southbound was so far that the slope of the road couldn't be guaranteed to be the same.

DAC (Downhill AC) allowed me to pulse-and-glide the air conditioning, turning it on only for the downhill stretches. It reduced my glide a bit but not enough that I was about to give up the cooling.

When I got home I had averaged 60.5 (indicated) for the entire trip. The real world numbers are invariable 7-10% less than the indicated ones, but for a real time barometer it gets the job done.