We’ve all been there. That is, we all started with no driving experience, no mechanical skills, and no off-road prowess. Some of us are better than others with natural abilities, but most all of us have made some mistakes or missteps when it came to building an off-road vehicle.
It’s part of the learning process we endure, but poor decisions can take their toll in time and money. A lot of good off-road performance is about balance and right-sizing. In general, bigger tires go with greater shock damping and beefier axle components. Proper gearing allows efficient use of engine power, without excessively burdening the transmission. Wise component choice and some planning can go a long way toward a successful vehicle build.
We’ll share with you some thoughts on how to choose to modify or build a rig. Hopefully this food for thought will save you some headaches and make your vehicle projects go just a little smoother.
It’s usually necessary to install some lift to fit much larger tires on most vehicles. However, adding excessive lift beyond that needed to allow the tire to fully travel upward means raising the ride height and can adversely affect handling and make the rig top-heavy. We even like the idea of trimming fender sheetmetal for tire clearance in some cases. This means getting the room you need for the taller tires without drastically affecting the suspension or center of gravity. Sometimes, that’s the way to go.
Improper Axle Gearing
Moving to bigger tires means your engine turns slower for a given speed and may knock it out of running in its efficient torque range. This can lead to sluggish acceleration, reduced fuel mileage, and increased transmission strain. Regearing the axles to match a significant change in tire size can help remedy these issues. Your buddies may not see the money you poured inside your differential so it doesn’t make your truck look any cooler. But, once you hit the rocks, sand, or your favorite mud hole, your truck will shine in performance.
No TAD in Axles
Depending on your kind of ’wheeling and how you use your off-road rig, you may benefit greatly from a Traction-Aiding Device (TAD). These include limited-slip and locking differentials of various designs. Again, like axle gearing, the unit is out of sight inside your axle, but the benefit shows when it comes time to apply maximum traction to an obstacle or other terrain. Today, there are automatic and selectable lockers. Adding hard lockers means you are more solidly binding the axleshafts, which can lead to greater strain on axle components, so you’ll want to consider possible upgrades needed there. Limited-slips allow the shafts to have some slip, so they are kinder to the axleshafts but less effective in providing ultimate traction.
We all know that bigger tires offer greater ground clearance and roll over obstacles easier than small tires. But, even if you have the room to stuff big meats under your rig, there’s reason to pause and consider. Bigger, heavier tires place more strain on your entire drivetrain. You’ll experience slower starts to get the greater inertia of a taller tire rolling, and stopping distances will lengthen as your stock brakes deal with slowing that heavier rolling tire. The larger rubber mass will also tax your stock shocks harder when they start bouncing over rough terrain. But, build it right for big tires, and you’ll be happy with the results.
Poor Wheel Choice
Wheels seem pretty simple. However, thoughtful choice of diameter, width, and backspacing (or offset) can be important for off-road applications. In general, a shorter sidewall translates to less sidewall flex, greater steering stability, and often a stiffer ride. Taller sidewalls allow for more flex in the tire carcass and tend to soak up bumps more readily. A good rule of thumb when choosing tires you want to use off road is to never have a wheel that is more than half the diameter of the tire (i.e., 40s on 20s, 35s on 17s, or 30s on 15s). This allows you to keep sidewall height down to a point where the sidewall is not excessively squirmy yet retains good flex and sidewall distance to soak up bumps that severely deflect the tire carcass.
Narrow wheels can provide better sidewall protection and bead retention, while wider wheels spread the tire tread to a fatter footprint. Wheels on IFS trucks have much more backspacing than those that originally came on straight-axle trucks. Using wheels with much less backspacing on an IFS truck will push the tires far outside the fenders.
Poor Tire Choice
Tires can speak volumes for the look of an off-road vehicle and gnarly treads look cool. However, tire choice can make the difference in how well your truck handles on and off the highway. Aggressive mud treads work great if you spend a lot of time in the deep goo or pursue serious rock crawling. However, they are typically less friendly on the highway and the reads grow ever more uneven as the lugs wear or become torn. Many times, a performance all-terrain tire fits the bill well, but choosing a tire that is not aggressive enough may leave you searching for traction in places. Consider tire weight, tread pattern, load rating and sidewall strength for your intended application.
Poor Shock Sizing
Your cool lift may raise your truck and make room for meatier treads, but you’re lacking in suspension performance if you fail to size your shocks correctly. In the best case, you simply rob yourself of valuable suspension travel. In the worst case, your shocks end up being the hard limit to your suspension travel until the bodies are hammered from excessive bottoming, or pulling apart due to overextension. Properly engineered kits can have the right matching shocks. But, in many cases, it may be time well spent to crawl under your rig and make some shock travel measurements to choose the right shocks you need.
Plenty of off-roaders have misjudged the performance result they expected to get from a simple or budget lift. If you’re looking to increase your ability in the dirt, you’re often better off spending some more dollars up front on a quality suspension. Many IFS lifts are kits that simply use a set of fabricated brackets to relocate the front suspension mount points farther from the main frame and body. While this generally gives you greater room for larger tires, it probably doesn’t improve on the suspension travel or ability to properly dampen heavier tires. By the same token, tall block lifts do nothing for suspension improvement and lead to greater axle wrap.
Suffering Mod Woes
Vehicle manufacturers spend considerable effort to design and build trucks and 4WDs so components are reliably matched in strength and work well together. When we start modifying a vehicle, we can upset that match, resulting in new weak links. For example, when we add new suspension and bigger tires, we may be left with a vulnerable steering system. A steering system designed to work with 29-inch tires may be far overstressed with the new 37s. It pays to be cognizant of these trickle-down effects so you can be aware and plan for other mods that may be needed.
Lacking a Plan
Most of us don’t have the luxury of building our dream off-road rig right off the bat. We often build it up gradually as time and funds allow progress. So, we often graduate through various suspensions, drivetrain parts, and tires as we build up bigger and better. Building with foresight and some semblance of a plan, you may be able to avoid having to rebuy or completely replace components, and avoid some costly mistakes. If you’re building up a project over a period of time, you can take advantage of buying some parts used, or waiting for parts sales. With a plan and shopping list in hand, you can watch for deals and buy them as they come.