lowering the final drive, aka "nerd gear" for better fuel economy/MPG

[MightyMirageMpg]

ide like too discuss a few options, and the problems they create, with the end goal of lowering the final drive for better efficiency.

anyone who's ever driven 40mph in 5th gear on a flat road in a "non-uk spec" mirage, and reset the mpg meter, will tell you that its very easy too maintain over 70mpg, even over very long periods of steady state travel. obviously, there is gains too be had here.

idea #1. custom made set of gears for final drive.

I've emailed a few companies and received "General prices" of gear sets. i was told by multiple companies, "were not interested" but two companies have given me similar pricing. $3000 for a 1-off set, or $3600 for 3 sets. ($1200/ea)

problems: pricing. i figure even at a large efficiency gain, the pay-off is near 100,000 miles. you must remove and disassemble your transmission. speedometer will be off.

idea #2 uk-spec final drive swap, us spec 5th gear

problems: i am unable too locate a source for the parts, and again, removal of transmission, disassembly, and your speedometer will be off.

idea #3. complete transmission swap

problems: well there's obviously lots, but "its been done before" and I'm positive it can be done, but the time, labor and cost will be huge for the first man on the moon.


questions i have,

can anyone locate the part number for the uk-spec final drive gears?

does anyone understand how our cable-less speedometer works, enough so to say they would be able too correct it?

is there anyone who would be interested in getting custom gears made? I HAVE A SPARE TRANSMISSION that can be the donor for the company making them.

anything I'm overlooking? there should be no computer issues, correct?
yes i realize taller tires will help, but i can't justify sticking 40" mud boggers on the mitsu and claiming its for mpg.