Tires
Tires are definately the easiest way to improve offroad performance. Even a set of basic all-terrains will take the truck from stuck in the mud to the end of the trail; realistically, tire size is not as important as tread pattern and
siping.
For everything other than mud, clay or rock crawling, a simple all-terrain with heavy factory siping, deep lugs and a sturdy sidewall will do very well, particularly for daily driver (DD) rigs, or expedition rigs that must drive long distances on paved roads to reach a trailhead.
Mud tires perform well on any surface except wet or icy pavement or rock.
Siping and/or
grooving can overcome this limitation and significantly improve both dry and wet traction on any large-lugged tire. In general, mud tires are a poor choice for a rig that sees 90%+ pavement mileage due to the decrease in mileage and inclement weather traction, unless the owner is willing to void the manufacturer's warranty by modifying the tread blocks for better adhesion. A siped, grooved mud tire performs extremely well offroad due to self-cleaning lugs, mechanical keying (not including keying due to deformation at low pressure), and improved lug surface deformation.
When choosing tire size, shift preference to height, not width, since contact patch size is much more dependent on
height than width.
Airing Down
Reducing the air pressure in the tire improves traction by lengthening the contact patch, improving mechanical keying, and reducing the likelihood of breaking traction on a loose or slick surface. In bottomless sand or snow, lower pressure allows the vehicle to float rather than sink. Excellent examples of flotation can be found at
Arctic Trucks, and trucks specifically built for the beaches of Hawaii. Airing down is best done with a small rim and a large tire--while a 31R20 can be aired down (anything can be aired down), the increase in traction is offset by the likelihood of pinching the tire against the rim, and the wider rim generally required for a lower profile tire also increases the possibility of unseating the bead of the tire from the rim at offroad pressure. To maximize the ability to air down offroad, run the smallest rim that will fit the truck, and a rim width at the narrower end of the manufacturer's recommendation for the planned tire size--this also requires careful planning to allow sufficient clearance between the sidewall and upper control arm to prevent rubbing when the carcass flexes under normal driving.
To decrease air down time, several manufacturers offer adjustable check valves which thread to the stem, marked so they can be preset to a particular pressure in advance, deflating the tire to a known pressure automatically. For the drive home, dedicated air compressors and CO2 tanks are easy to install and/or carry, and can be extremely efficient and easy to use. CO2 tanks are by far the quickest, most convenient, simplest and least expensive solution for refilling tires, but are far larger than an air compressor and generally require space in the bed. Compressors capable of the flow rate of CO2 tanks generally cost twice as much, and in addition to mounting points require wiring and plumbing. The benefit to a compressor is mounting location (engine compartment, inner bedside airspace, frame rails, etc.), and a supply that won't run out as long as there's a power source. The best solution is to carry a small CO2 tank for refilling tires (speed, simplicity) and a small compressor (endless supply, redundancy) for operating lockers, and plumbing the system so either can supply tires or lockers. When choosing a compressor, be aware that the majority of "roadside emergency" kits are intended for emergencies involving small tires near civilization and will not have a duty cycle appropriate for refilling four 33" tires in a reasonable time. Here's an informative
article with all the gory details.
Lockers
Your 4WD with open differentials is actually a 2WD. Take a look at this
article for an explanation, or put a truck with open differentials in an off-camber situation where opposite tires are in the air, or the more common situation where two wheels are on ice. As soon as one wheel on an axle loses traction, the entire axle becomes dead weight, a common offroad situation with the limited articulation available on even a modified IFS vehicle. Read up on
Eaton's website about the differences between limited slip, mechanical lockers and selectable lockers. Eaton is also the parent company for Detroit lockers,
here is the entire product line and intended applications. For a daily-driven rig that sees difficult trails, the best solution is a selectable locker. At the moment, the only selectable locker available for the stock Toyota Tundra rear differential is the ARB air locker.
Traction Ladders, 2x4s, Rock Stacking and Other Quick Fixes
Occasionally, despite improved articulation, better tires and locked differentials, the truck gets bogged down in sand, snow, mud, loose dirt or doesn't have the stability required for a locked ascent of an obstacle that leaves a tire or two in the air. Traction mats, bridging sections or traction ladders usually solve any of these problems. Though
floor mats or even the bed mat can be used in desperation, a few 2x4s or 2x6s don't take up much space, have multiple uses, and can be used to extract the truck from deep sand. If an obstacle is too tall or a hole is too deep, rocks can be stacked to create a ramp or a bridge, as long as there are rocks available. In loose, wet or icy conditions, wood and rocks are either too slick or hard to find. The best overall solution is a traction ladder--a combination of the traction available from a dedicated mat (but not flexible), and the strength of a bridging section but hopefully without the weight. Fiberglass makes a great traction ladder, since the material is able to elastically deform, it's lighter and requires less storage volume than a steel bridging piece or the old air force metal runway strips, it's easy to spray with bedliner to keep the edges from splintering and to provide even better traction, the grid pattern provides flotation as well as traction to both tires and on the ground, and they're even useful in camp. A 5x1.5 foot section fits across the bed and below the rails, and a 2"x2" grid with two inch depth provides enough strength to support a Tundra. Call around or search the web for suppliers, ask about scrap sections. A pair of traction ladders are much more effective in sand, snow, mud and loose terrain than wood or rocks, and provide a self-recovery option if winching isn't possible and a strap isn't available. In sand, mud, snow or loose soil, put the ladders under the front wheels for a good ten feet of traction as well as momentum. A piece of rope attached to the ladder at one end makes it easier to find after a recovery.