Good stuff, RDoc. I've never yet found a highway grade steep enough that full regen was needed to hold a constant speed on the downhills; at most, I've seen something like 30kW of regen (and usually less) with the cruise control set at 65 mph, while coming down the big mountain passes here in CO. I've read elsewhere on TMC that the standard regen algorithm is tuned to yield a deceleration of 0.1g, with a cap of 60kW, though my empirical observation is that it's more complex than that. If we assume no friction and no aero resistance, a gravitational acceleration of 0.1g is achieved on a slope of about 5.73 degrees, also known as a 10% grade. But aero resistance at highway speeds is quite a large factor, so a highway grade would have to be a fair bit steeper than 10% before full regen is required to hold a constant speed. There's a tipping point, though: at higher speeds and depending on vehicle gross weight, 60kW of regen is no longer sufficient to give 0.1g of deceleration.
Where am I going with this? Beats the hell out of me...but I do agree that for longer, steeper slopes, using regen to hold a reasonably low constant speed ends up giving you more range than using regen to hold a higher constant speed, and even more so compared to freewheeling down the mountain at terminal velocity.
