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Choosing Your Next Wheels

Posted in How To: Wheels Tires on April 1, 2011 Comment (0)
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A new set of wheels is a big purchase for any Jeeper. On an editor's budget, it means a month or two of eating Ramen Noodles and often works out to costing us more than buying a new (used) Jeep. The problem is that there are so many choices out there-from wheel size to wheel material to wheel construction-it is easy to put a foot wrong. It's really hard to pick wheels without seeing them on your Jeep, and we've had our fair share of gaffes over the years. The key is to sit back and consider the options to make an informed decision. We'll leave the looks of the wheels out of this, and instead will help you out with the construction and material choices.

Sizes
A general rule of thumb about wheel size is that the bigger you go the bigger brakes you can clear, the heavier the overall package becomes, but the less sidewall you have. We look for as much sidewall as the wheel diameter, so on a 15-inch wheel, we'd want the tire to be at least 15 inches bigger for a 30-inch tire height. Of course, you can't always have your cake and eat it too, but that basic rule holds true for all wheel sizes. A 16-inch wheel means a 32-inch tire minimum; a 17-inch, 34-inch tires; and an 18-inch, 36 inches of rubber. We find that if we play in rocks and pick a shorter tire, we end up grinding the wheels more than we'd really like to. This guideline also saves the rims from curbs when the old lady takes the Jeep shopping.

The width of the rim and the backspacing are the most often discussed sizes, and we still find that tire manufacturers recommend too wide a rim for a particular tire size or too little backspacing for a typical situation.

Most manufacturers won't recommend an 8-inch rim for a tire with a 12.50-inch overall width. The reason for that is there will be more sidewall roll on-road if you use an 8-inch rim, which could lead to stability problems if you drive your Jeep like Mario Andretti. The problem for us is that the 10-inch-wide rim just won't hold the bead as well down in the single-digit air pressures. So, we tend to look at a rim that is 4 inches narrower than the overall width for the best performance at lower pressures. A 14.50-inch-wide tire would then go on a 10-inch rim, and so forth. The only exception would be if we were going for a particular look. For example, if we wanted the wide and square look and we were willing to forgo some off-road ability to get it.

Backspacing ties into rim width as well, and both affect your scrub radius. The further the center of the tire moves away from the centerline of the ball joints the more scrub radius you will have and that leads to worse on-road handling. The other thing that will happen is that with less backspacing more force is exerted on the ball joints, wheel bearings, and tie-rod ends which leads to earlier failure of these components. A wider rim with the same backspacing will move the mass of the tire out from the ball joint center line more than a narrow rim. Remember, "less" backspacing means a larger number, which means the tire is sucked further underneath the Jeep. We try to run the largest backspacing we can that will still clear our suspension, brakes, and inner wheelwells for a given tire size. If you aren't sure, take off your existing tire and rim and determine backspacing, rim width, and tread and section width. Then with some simple math you can use a combination of blocks of wood, duct tape, and maybe even wheel spacers to determine where the tire and wheel would end up with the new rim.

Design
The single largest difference in the design of the wheel is whether it is a one-piece or a two-piece wheel. A two-piece (or more) wheel is a wheel that starts as two parts and is joined together by either bolts, rivets, welds, or other fastening means. A one-piece wheel is forged, cast, or machined as one piece.

Two-piece wheel

As you might imagine, a multi-piece wheel is typically less expensive to make and you, the end user will benefit from that. All the steel wheels on the market are multi-piece wheels and the center is typically welded to the hoop. In the aluminum arena the center is most often welded to the hoop, but there are some that are riveted still floating around. The big downside to two-piece wheels is that there is a tremendous amount of force on that juncture and that can cause for failure if it takes some damage. For example, if you bend the rim at a weld or the weld rusts out from the front, there is that much more stress put on the remaining attachments. There are some manufacturers of two-piece beadlocks, with the most common sources being Hutchinson and military surplus. Ironically, we feel that the two-piece beadlocks are stronger than their one-piece cousins and offer easier at-home tire changes.

One-piece wheels are generally thought to be stronger, but they cost more to produce. Certainly a billet one-piece aluminum rim will be stronger than its two-piece brother, even if all the alloys are the same. The one-piece forged aluminum wheel is the strongest of the bunch, since it is formed under pressure. Many beadlocks are based on one-piece wheels, with the outer bead surface machined down from the non-beadlock counterpart to accept the lock ring. Other beadlocks start out as one-piece or two-piece wheels that are modified to accept a welded-on beadlock ring.

Busted one-piece wheel

Metallurgy 101
A cast-aluminum rim is made by pouring molten aluminum into a mold at ambient pressure and then the bolt holes, center hole, and wheel mounting surface are often machined. Pouring at ambient pressure results in all the molecules going the same way in a grain like a piece of wood. We have all seen the karate masters breaking wooden planks. Usually when a cast rim breaks, it is pretty spectacular because it will fracture along the grain. Additionally, once you bend the rim, it will be very difficult if not impossible to bend back because it will likely break with that grain.

Cast aluminum rim

A forged-aluminum wheel is made by hammering or stamping hot or cold metal. The pressure exerted by hammering interlocks the aluminum molecules kind of like how the grain of a piece of plywood is interlocked. The interlocking grain makes the plywood harder to punch through. Like the plywood, the forged rim is harder to break. Usually it will bend first, and if it bends, it can often be bent back.

Steel wheels consist of two parts: the wheel center and the hoop. The wheel center is stamped from single piece of steel and the hoop is a steel extrusion that is formed into a hoop. The wheel center is then welded (in most cases) into place in the hoop based on the desired backspacing. As with other steel things, if you bend it, you can bend it back. And, typically the thicker the wheel center the longer lasting the wheel will be, especially with the abuse we dish out.

Steel wheel after a winter

Galling is bad. It is what happens to aluminum when another metal is mechanically attached to it. This applies primarily to beadlock rings. We prefer our aluminum beadlock wheels to have steel inserts for bolting the ring down so that they are repeatedly removable. Galling acts a lot like a steel bolt rusting to a steel nut: when you remove the bolt you end up stripping the threads.

Survivability
On-road, if you drive where they salt roads in the winter you have two options. Option A is to run steel wheels through the winter and get used to surface rust. Option B is to run aluminum wheels and likely end up with pitted wheels. The steel wheels will rust where the center meets the hoop because the powdercoating can't get down into that joint. Coatings on aluminum wheels such as powder, chrome, and Teflon will extend the life of the wheel. But, even the best coating on aluminum wheels will chip or scratch when used off-road. Once the coating is chipped, the pitting and oxidation of the aluminum will begin. Forget about running polished aluminum in snowy winters unless you like polishing your wheels once or twice a week. What we ended up doing was swapping rims come fall. We'd put the cheap steelies on for the winter, and the same weekend we took the hardtop off, we'd swap rims back. Then we'd clean the steelies of any rust, shoot some fresh Rustoleum on them, and put them away until the hard top has to go on again next fall.

Busted cast aluminum wheel

We already covered the metallurgy part of the equation- beyond that, for off-road it is a matter of preference: if you want aluminum and have the money, go forged. If you are going steel, find the thickest centers and hoops you can.

For ultimate longevity we prefer beadlocks with the removable outer ring. We can just toss the ring after we've chewed it up to the point of no return. However, there aren't many street-legal beadlocks on the market. We hate to say it, but many of the fake beadlocks also benefit from a thicker section width where the fake lock is, and the bolts can help protect the rim from some abuse. Besides that, if you follow our sizing rules of thumb, the rubber of the tire itself will do wonders for keeping your rim in one round piece.

Porky Rounds
The old adage of an aluminum rim being lighter than a steel rim just doesn't hold true anymore. There are some heavy and heavy-duty aluminum rims that weigh in more than a similar-sized steel rim, and many steel rims that are heavier than similar-sized aluminum rims. Why should you care? If you drive your Jeep on the street, bear in mind that every 10 pounds of rolling weight takes about as much effort for your Jeep to haul around as 100 pounds of sprung weight. In short, wheels that are 10 pounds lighter could mean that you can run full corner armor and rockers with no loss of fuel mileage. Conversely, rims that are 10 pounds heavier could be like doubling up your body armor. Let's put it this way, we've seen losses and gains of up to 3 mpg (with the exact same wheel and tire sizes) simply by swapping our tire and wheel package. If you drive your Jeep on the street, rotating weight is something you want to keep an eye on.

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