Extragoode:
Check out
www.ringpinion.com Randy’s Ring & Pinion has a very wide selection of R&P sets. Know what your axles are as the R&P sets are for specific axles. Get the “R&P kit” as this kit includes new bearings and seals.
As for bigger tires, I can give you one piece of advice: If you increase tire diameter, your MPG will DECREASE. Repeat DECREASE. This seems counter-intuitive but it is borne out by empirical data reported by literally hundreds of people.
Three things cause MPG to go down as tire diameter increases.
First is that the rotational moment of inertia increases with the square of the diameter. This means you have four bigger “flywheels” you have to spin up everytime you pull away from a stop. If you were an over-the-road trucker – a creature of the superslab – this would not be very important. They get up to speed and keep rolling at the same speed for hours on end. I daresay you don’t drive that way. You do some stop-and-go. Big wheels stick it to you at every light.
Secondly rolling resistance seems to go up with tire diameter. I am screwed with my 16 inch wheels. The highest MPG cars tend to have clown-car tiny tires. Rolling resistance matters a lot at slow speeds.
Third, bigger diameter tires raise the vehicle up and open up more underside air flow issues. Bigger diameter tires may require a lift which further compounds the problems.
Changing the R&P should cost you in the neighborhood of $1,000 per axle. Almost any good jeep shop can do this specialized piece of work. Setting hypoid gear backlash is not a business for the shade-tree mechanic.
Another approach (often favored by 4x4 types) is to install an aftermarket overdrive. The names in overdrives are US Gear and Gear Vendors. The US Gear unit fits between your transmission and transfer case, where the Gear Vendors fits to the back of the transfer case. The GV automatically disengages when you engage the transfer case. You could operate in “4x4 overdrive” with the US Gear but I don’t know why you’d want to. The US Gear unit gives you a 20% overdrive (ratio = 0.8:1) where the Gear Vendor gives you a 22% overdrive (ratio = 0.78:1). Both overdrives are far stronger than any vehicle you own. An overdrive will set you back between $3000 and $4000 installed.
Changing your gearing is indeed a salty proposition but it is without question the most powerful ecomod you can do. By changing my rear axle from 3.73 to 3.08 (an 18% reduction) I gained 3 solid MPG – a 17% improvement. BTW, 1700 RPM @70 MPH. Going to a lower numerical ratio works by reducing your engine frictional HP. If anything it would be more effective on your normally-aspirated gas engine than on my turbo-diesel, as you have to do a lot more air pumping using engine power.
Would I do it again? Hell yes. In fact I intend to do it again on my truck this summer. I intend to install a US Gear unit to gain a seventh gear and an overall 2.46:1 ratio for 1350 RPM @ 70 MPH.
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