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12.18.2013
Rock Crawling | Part 1 The Basics

the-basics-of-rock-crawling

Rock crawling in a 4×4 can be intimidating for even the most seasoned drivers; let alone someone who’s never stalled on a 45° incline of shale. My first real rock crawling experience was during the 2012 Easter Jeep Safari in Moab. Up until that point my off road experience was limited to my experiences in the military. I didn’t know what to expect in Moab except that it’d be the most challenging rock crawling that i’ve ever done. I knew my TJ was ready for the trail, but was I?

My anxiousness compounded itself once I arrived in Moab to discover that it had snowed – in April, and that the Bushwacker team was hitting the hardest trail of the week first – Behind the Rocks. I’d always heard that rock crawling was technical and hazardous without care, but now I had to factor in the snow – the term Moab “slick rocks” was never truer. Needless to say I was a bit anxious on the trail, but the jitters soon worked themselves out once I realized that rock crawling is simply a state of mind: slow and steady wins the race. Since then i’ve been fortunate enough to hone my crawling skills twice more in Moab, as well as in the Sierras, Rockies, and Cascades. From my experiences i’ve found that these general rules will keep you and your 4×4 safe:

  1. Know what you’re capable of – if you don’t feel comfortable negotiating an obstacle then don’t do it; there’s no shame in taking a bypass.
  2. Know what your vehicle is capable of – you may be ready for an obstacle, but is your vehicle? Having your drivetrain grenade on the trail hurts in more ways than one.
  3. Trust your gut – if an obstacle approach doesn’t feel right then back off and reassess, it’s much quicker than having to do a recovery.

And as always, Murphy’s Law applies to any off road adventure – that’s why it’s paramount that you never wheel alone. With that being said, let’s break into the basics of rock crawling.

Lift & Tires

flexing with flat flares

Choosing a tire depends on the frequency that you off road, the average trail you encounter, and how much your vehicle can fit. We were able to fit 35″ tires with flat flares on a stock ride height Rubicon and wheel confidently through Big Bear, CA, but that won’t be the case for everyone. For those starting out in a TJ, a modest yet capable combination is a 4″ lift with 33″ tires. For JK’s, a good combination is 3″ with 35″ tires. For all other makes I would recommend 4″ to start.

The great thing about starting small is that you can typically avoid additional modifications like extending the driveline or installing a slip yoke eliminator. The trade off is that you’ll most likely need a transfer case drop down bracket, which will lower your skid plate clearance by about an inch. You’ll want to do this to keep your driveline as close to its original angle as possible. Otherwise you’ll feel driveline vibration, and potentially break u-joints.

Picking tires for your 4×4 can be overwhelming since there are so many brands and styles to choose from. Typically a mud terrain tire is preferable for rock crawling because of the aggressive shoulder tread and large sipes (channels). Here at Bushwacker we’ve used Mickey Thompson MTZ’s with great success, but if you’re looking to keep your 4×4 as a daily driver then look no further than the Falken Wildpeak A/T, which has received countless accolades for its off road capability.

The important thing to remember when choosing a lift and tire combo is that you need to give your tires room to travel up and down; so choose a lift that can clear your tires. You can also add a set of Bushwacker Flat Flares to open up your wheel well, and give your suspension the ability to flex completely. Bushwacker Flat Flares for Jeeps eliminate the overhang from OEM flares, and allow your tires to travel with rubbing.

Gears

dana 44 schematic

The importance of re-gearing your ring & pinion when upgrading to larger tires cannot be overstated. Your 4×4 was built at the factory with the appropriate gears to turn a specific tire. The factory gears aren’t designed to handle the additional pressure that comes with oversized tires. Crawling with oversized tires and stock gears is a surefire way to grenade a drivetrain. By gearing lower (numerically higher) you’re trading speed for torque. This added torque relives the transmission and axles from doing all the heavy lifting.

I chose 4.56 gears for 33″ tires because they would give my TJ adequate power without sacrificing too much fuel efficiency. A 4.56 ratio means that the driveshaft will turn 4.56 times to one full tire rotation. With a numerically higher ratio your engine will feel more powerful, but it will hit its top speed faster since it’s turning more RPMs. Take a look at this gear ratio to tire size chart if you’re unsure of what gear ratio you need.

A note on Dana 35’s & C-Clips: If you have a Dana 35 or other axle with a c-clip, then it’s highly recommended to invest in a c-clip eliminator. With a c-clip, the axle shafts are retained by a small clip, and aren’t directly bolted to the axle housing. The axle shaft will slide out from the housing if this tiny clip breaks.

Crawl ratio

2013 Jeep Wrangler Rubicon With 35" Tires

Although not critical, it’s good to know your crawl ratio so you can gauge your 4×4’s crawling capability. Crawl ratio is the lowest gear ratio the vehicle is capable of. It considers the ratios of the transmission, transfer case, and axles – (transmission first gear ratio x transfer case low gear x axle gear = crawl ratio). So my TJ’s crawl ratio is approximately 48 (3.83 x 2.72 x 4.56 = 47.5), which is capable, but has room to improve. Simply put –  the higher the crawl ratio, the more low end torque you’ll have, which means more power to hurdle over large obstacles. For manual transmissions a high crawl ratio will mean you’ll stall less. Check out Novak Conversions for details on the most common 4×4 transmissions and transfer cases.

The Jeep Wrangler Rubicon

Aside from all the cool badging and trim, the Rubicon is the only Wrangler model (aside from the J8) that includes the robust NVG 241OR RockTrac transfer case. Currently the 241OR can only be found in Wranglers, and is one of the reasons why Wranglers are considered to be the best OEM 4×4. The 241OR is known for its 4:1 low gear ratio, which gives owners a great crawl ratio in a modest package. If I had a RockTrac in the TJ then my crawl ratio would jump from 47.5 to 69.8, which is quite a difference in performance.

Lockers, what’s the diff?

In a nutshell, lockers provide additional traction by transferring power equally to all four tires regardless of which has traction. There are several types of locker, but we’re going to cover the two most common – air and electric. Also known as “selectable” lockers, the primary difference between air and electric lockers is how they’re actuated. Electric lockers operate off a switch while air lockers require a switch to engage an air compressor that charges an airline to actuate a piston within the unit. You can read our pros and cons between air and electric lockers here.

I would recommend selectable lockers to anyone getting into rock crawling for the first time. In my opinion, lockers provide the biggest performance upgrade since they will get your vehicle through obstacles you might not consider otherwise. The issue with “auto” lockers or limited slips is that they engage without warning, and for daily drivers on M/T’s this can cause issues on slick surfaces.

Below is a visual comparison of my TJ attempting the same obstacle in Big Bear, CA. You’ll notice that without lockers the Jeep transfers 100% of its power to the traction-less tire on the drivers side:
Rock crawling

Here we see the lockers engaged and distributing power equally to all four tires:

rock crawling

Now that we’ve got the verbiage out of the way we can start talking techniques.