'96 Silverado vs 2009 Outback

[vteco]

I live in a world of hills. Going downhill idling, the Silverado picks up speed very quickly. The Subaru noticeably less so on the same routes. The Silverado bleeds off speed more slowly going back uphill.

The Subaru has all wheel drive. The Silverado has manual electrically engaged 4 wheel drive.

I'm guessing this is the explanation?

[vteco]

Couple other thoughts re coasting:

1.) At least with a wheelbarrow, big wheels push easier than little ones.

2.) Wheel inertia, disparaged under power, especially when needing to frequently brake, is not necessarily such a detriment when largely coasting up and down hills in our area.

Particularly if the wheels are storing energy by retarding speed which might be wasted in braking at curves, where speed buildup downhill otherwise would get excessive with small light wheels.

[vteco]

Third thought. Everybody has different conditions. If I lived in a desert, or a city, or had a long commute, every aspect of working towards reducing fuel usage might be different. I'm shooting towards optimizing a very particular niche set of conditions in a specific vehicle.

[cRiPpLe_rOoStEr]

Wheel inertia tends to be troublesome for overall efficiency, even if it could seem at a first glance to be beneficial while driving through hilly terrain. Fewer usage of the brake OTOH tends to happen once you're already driving in a more efficient way.

[vteco]

Well having read through the 100+ tips here I can say truthfully that I am already driving that way, nothing seemed new, and particularly I've been maximizing since the Subaru has instantaneous and trip average MPG readout which I've paid careful attention to for the last 6 months.

Nevertheless, the Subaru, just tested a half hour ago on a 10 mile round trip down the mountain and back, will slow down with the foot off the pedal on even a moderately steep downhill grade. I'm thinking this must have something to do with the "all-wheel drive" being computer apportioned somehow during coast.

The Silverado easily and rapidly accelerates on practically any downhill grade, pedal off. While it has 4 wheel drive, it's only when manually engaged.

This is a separate issue than wheel inertia.

I think it's not established that "wheel inertia tends to be troublesome for overall efficiency" in my own case since that overall efficiency is composed primarily of winding hill conditions, with little highway usage.

I'm going to guess that:
80% of my driving is up and down winding mountain roads at 35-45 mph speed limits
12% hilly town streets, 25 mph speed limit
5% hilly 55 mph highway speed limit
3% hilly 65 mph highway speed limit

These conditions probably have their own set of optimization scenarios. That's what I'm interested in. I think that will take an open mind to work out.