Here's a discussion of what's involved in the ring & pinion gear swap, with photos, from the Yaris side. It looks and sounds pretty difficult. I've done a lot with cars, but this is probably beyond my skill level. Too bad, as I'm ready to buy the parts ($400) or a Yaris transmission (available from $370 from junkyards). A straight transmission swap might be the way to do this.
I'm running 205-50/17s which are 25.07" tall, 5.31% taller than OEM. They lower my 60 mph engine rpms from 3096 with the OEM tires to 2931. The Yaris 3.722 final drive ratio (v. the xA/xB's 4.31) would lower the 60 mph engine rpms (with OEM tires) from 3096 to 2673. It's still higher than the 2545 rpm of the ATs.
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Darrell
Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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