It's a simple formula that most four-wheelers are intimately familiar with: The deeper your crawl ratio, the more control you have out on the trail, particularly on steep, nasty obstacles. The more serious the four-wheeling you want to do, the lower your crawl ratio needs to be. So, where to begin? It's understood that lowering differential gearing is only a way to offset increased tire size, and it will greatly impact highway driveability and gas mileage if you try to go too low. Don't be suckered into thinking that a new set of ring-and-pinion gears will solve your problems; it's just an initial step.
No, the only real way to obtain a good, deep crawl ratio and still have a multipurpose vehicle you can drive at speed is to look to the transfer case. True, the gear ratios in your transmission have an influence, especially in First and Second where you're likely to spend a lot of time off-road, but the gear reduction takes place in the T-case. So you're left with two choices: Replace the gears inside your case with a lower ratio set or replace your T-case altogether.
The first option tends to be cheaper than the second but requires that you (or a shop) have the mechanical skills to perform the swap. This has long been a popular option with Dana 300 owners because this case is gear-driven, virtually indestructible, and new 4:1 gears will run you less than a grand. At the other end of the spectrum, you have groups such as Advance Adapters, Novak, Marlin Crawler, and others that have a myriad of options for replacing your current T-case setup and can provide the kind of technical assistance necessary to achieve the kind of crawl ratio you're looking for.
In this month's issue, we take a look at three different transfer case setups that will significantly lower your crawl ratio. The first is a wish-list of parts that any four-wheeler would covet: a Jeep Grand Cherokee with an Atlas II mated to a Klune-V. This combination offers an incredible range of gears to choose from to accommodate almost any type of terrain. Surprisingly, the setup is almost exactly as long as the NP242 that came out of the Jeep, so there are very few other modifications that need to be made.
The next T-case setup we look at is the Rock Box from Advance Adapters. This cool little case is actually an auxiliary T-case that bolts between the stock transfer case and transmission. Although it is designed for the Toyota Land Cruiser contingent, with its 3.44:1 Low range, we suspect it will only be a matter of time before some clever Jeeper adapts it to his or her rig.
Finally, we take a look at Tera's latest offering: an NP231 with 4:1 gears already installed. This case will be a direct drop-in for many Jeeps on the trail today and is a reasonably cost-effective way to achieve the deeper crawl ratios you've been after.
These three setups offer something for just about everybody. So sit back, start reading, and think about all the trails you'll be able to conquer with those low, low crawl ratios.