Choosing the Right Rubber for your Rig

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My favorite letter gets reprinted about once a year in each of the 4WD magazines. The name changes, and the exact model Jeep varies, but the basic story is always the same. It sounds something like this: I’m a high school student with no money and I’m dreaming of putting 44” Swampers with a 12” lift on my uncle’s old 4 cylinder Willys. What is the best way to do this without spending more than $200?

We talk about a lot of things on the trail during Iron Range Offroad Adventure Weekends. The classes are broken up into training modules that get covered at different stopping points along the trail. We start in the parking lot talking about safety and environmental responsibility. As we wind our way through the park, we discuss driving techniques for different terrain, how 4WD works (and why we get stuck), different extraction techniques, vehicle maintenance, and vehicle upgrades

Choosing the Right Rubber for your RigUpgrades are a popular topic. Jeeps are an amazing starting point for customization. You can buy virtually everything aftermarket…frames, engines, fiberglass bodies, axles, suspension kits, wheels and tires, bumpers, seats…I’ve often considered building my next vehicle (brand new) from parts. I’m not sure how I would register it, but I’m certain I could get everything I need delivered right to my door.

The single most important decision you are going to make in the entire upgrade process is tire size. Many other upgrades will be directly affected by it. Understanding the logic behind tire size will help you make smarter decisions and have a more cohesive vision of what your “completed” trail rig will look (and perform) like. This decision considers many factors:

– What kind of wheeling do you want to do? Mud, sand, rocks, trails, or even competition?
– Where do you want to go? Close to home or across the country?
– What is your budget? Bigger tires might mean thousands of dollars (read on…)
– What is your experience level?

If you are driving a stock vehicle, you are right around a 30” tire diameter. You probably have an all-terrain type tread with is not super aggressive offroad, but that’s because the manufacturer had to take into account highway driveability and road noise. The stock tire and wheel fits the fenders, delivers reasonable acceleration, acceptable fuel economy, and a manageable lifespan for other critical components. In short, it’s a long series of compromises that deliver “trail-rated” capability within a vehicle that can legally travel down a federal highway.

Choosing the Right Rubber for your RigOne argument in favor of sticking with a “near stock” tire size has to do with safety. The axles, brakes, suspension, and steering were designed for the stock application. Engineers tend to “overdesign” somewhat (a preponderance of lawsuits might have something to do with that), but there is a limit to how much upgrading you can do before you exceed the design limitations.

Oversized tires require a lot more braking capacity to stop the additional rolling mass. Upgrading brakes (larger calipers, slotted or drilled rotors, etc.) can certainly help, but the additional sized strains everything…not just the brakes. Turning bigger tires might exceed the engineering of the steering components. If a tie rod fails, a pitman arm breaks, or a steering box shears from the frame, stopping won’t be your only problem. Larger tires also put additional strain on axleshafts and u-joints. Clogging a trail while you replace broken parts (especially parts that failed because of over-sizing the tires rather than under-engineering the rest of the drivetrain) is not only bad etiquette, it is just plain stupid.

Another argument in favor of near stock tire size is fuel economy. To fit the bigger tires, you need to create space, and that usually means a suspension lift. In stock form, a Jeep has the aerodynamic characteristics of a brick. With a lift, that brick simply becomes taller. When you consider the additional effort required to roll those bigger tires, and the fact without also changing axle ratios you have taken the engine out of it’s most efficient RPM at cruising speed, it is no surprise that fuel economy suffers. With gas prices expected to go up, many people are looking for ways to get more miles per gallon, not fewer. And if this vehicle is a daily driver, you are paying for this higher cost every day…in every mile you drive.

Speaking of money, take a look at how quickly the price of the tire goes up as it gets bigger. Then multiply that by 4 (or 5 if you have a full size spare). Mounting and balancing big rubber is not something every tire shop has the equipment or skill to do. Budget that into your decision before you spend your hard earned cash.

Big tires create other concerns as well. If the tires stick out past the fenders, you might get extra attention from law enforcement. Make sure the fenders cover the tires and you are not out of compliance on bumper height restrictions. In addition, be careful that all lights and turn signals are functioning and mirrors are in place. There is no reason to give an overzealous officer obvious reasons to write more citations.

Here is the final point in my case for near stock tires. Bigger tires require bigger trails. You will find yourself seeking out “extreme” or “black diamond” trails. What are you going to do on smaller trails? Trails that might be closer to home and more likely to be visited by your “not quite ready for extreme” friends. Take it from a guy who went there and came back. The toughest trails challenge everything. I found myself breaking things I thought were upgraded to unbreakable status, and wrenching (and not wheeling) all the time. It requires better technique to drive a trail with stock sized tires, and I found that to be a lot more fun than simply spending money to roll over rocks in a straight line.

Jeeping is a great way to spend time with your family and friends, and it certainly allows for a great deal of individual expression. Think long and hard about what you want from your Jeep, then buy the right parts to make it a safe, reliable, and comfortable rig. You (and your passengers) will be glad you did. And if you’re that high school student dreaming of 44s under the Willys…read this column again, and keep dreaming!

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