Your vehicle's axle gearing is determined by the amount of teeth on the ring and pinion gears, which in turn dictates how many times your driveshaft needs to rotate the wheels once. So if you're a serious off road driver you may want to look at regearing to maximise your drive experience.
When why should you regear your vehicle?
If you do plenty of motorway driving on small to medium tyres, you may want to consider regearing to a "taller" set of gears in order to boost your maximum speed and fuel efficiency. Conversely if you mainly off road or have larger tyres fitted, you may want to regear to shorter gears.
When your vehicle has larger tyres, some factors work against achieving optimal performance, such as the diameter of the tyre, rotational mass, rolling friction and weight of tyres. That's because the diameter of your tyres feeds into how hard your drivetrain needs to perform to move the vehicle.
The thing you need to remember is that it's the axle which turns your wheels and they are only a few centimetres in diameter, so the bigger the tyre, the more work it has to do. So by regearing to a shorter gear, you boost the force delivered to the axle with less strain on the engine.
What cost would you be looking at to regear your vehicle?
There's a bit more to replacing your vehicle's ring and pinion gears than just purchasing a set of ring and pinions. You also need to think about bearings, seals, bolts and the differential cover gaskets. Getting the whole kit together may cost you in the region of $600 to $1200.
If you can't do the work yourself, of course mechanic costs will vary between suppliers, but for a ballpark idea you can expect a ring and pinion gear set fitted for something between $500 and $700 per axle. If you go for a total regear, you can expect to pay several thousand dollars.
How to regear your own vehicle
While in most cases we would highly encourage learning DIY work on your vehicle, unless you've previously worked with wrenching on your vehicle - for example oil and filter changes - when it comes to regearing we highly recommend taking it to a good mechanic or even better a diff and gearbox specialist.
Here's a simplified step by step guide of the work involved in regearing.
Drain the differential's gear oil
Remove the axle shafts
If not replacing main caps, mark to make sure you know which side they came from
Clean all new parts get rid of metal shavings in the carrier
Coat all new bearings and seals with fresh gear oil
Install the ring gear on the carrier, making sure there is proper shimming backlash
Install the pinion gear apply the carrier bearing, checking for proper bearing preloads
Replace the assembly into the differential housing