Pondering a Differential Gear Change

[The Mindless Philosopher]

I've been kicking around the idea of an eventual differential gear change from 3:23's to 2.78's or something along that line on my 385 HP ZZ4 trike for the sake of picking up 2 or 3 extra MPG's on the freeway, if I can net that much? Hard to say. The RPM difference would be around 400-500 at 70 MPH, which isn't really a whole lot. Of course, the gap would widen at 75 MPH, which is the limit on most of our state's major routes.

Moving in the opposite direction, my Mustang lost 4 MPG freeway when I went from 2.78's to 3.55's. Dropping from 31 to 27 MPG was not that big of a hit in exchange for quicker acceleration, especially since I gained city MPG's due to the ability to skip-shift to higher gears around town, so it evened out pretty well.

Back to the trike: I don't know if a gear swap would really gain a similar difference as the Mustang lost, unless maybe I go to 2.50's like my brother did on his 350 HP LT1 Corvette? Even so, with only an 8.5 gallon main tank and a 3.5 gallon auxiliary, I might get an extra 30 miles (?) per fill-up between the two? That's not a whole lot, but the desert southwest can be a scary place on a gas guzzler. I always carry extra just in case, because some of the more remote fuel stops (historic Route 66 and old highway 80 in AZ) are seat-of-the-pants. I've been there on the Hoss; I know! BUT...I made it back, so it's not like it's a dire situation. I'm just not sure a gear swap would be worth it, though it would be a world easier than a TH350 to 700R4 swap, at least at this point where my means are concerned. I love the open road, but man, I hate literally not being able to pass up any gas stations in the desert southwest!

[502wingman]

I had a 2008 Tahoe for many years. In 2012 we rented a Suburban for a big trip with four people and lots of luggage. The transmissions after 2009 came with an extra gear and the Suburban turned about 500 rpm less at the same speed than my Tahoe. Even fully loaded the Suburban improved about 3-4 mls/gal.