They say that anybody can restore a rare old car, but that it takes a real man to make a hot rod out of it. To some extent the same could be said for modifying perfectly good tires, grooving them in an effort to make them work even better. Either modification-car or tire-involves taking a chance, because there's no guarantee that the end result will be as good as the original.
Tire manufacturers must design treads that deliver decent longevity and handling on paved roads, usually at the expense of trail performance. It's one of many compromises made in tire manufacturing, but it's one we can do something about. What we'd like to accomplish is primarily to increase the conformability of the tread area. Ideally, in the process we also get a contact pressure that's better suited for the vehicle and terrain. We can do this by altering the tread a bit through a process called tire tuning, which involves cutting new, deeper, or wider grooves in the existing tread. Tire tuning has nothing to do with "tuner cars," those pesky low and loud little imports that zoom around at the level of our driveshafts. It's called tire tuning because that's what you do-tune the tire tread to make it work its best on the trail.
Modified with a groover, the...
Modified with a groover, the 35x15.0-15 Swamper on the left has been tuned to work better on the trails when on a light vehicle. There are now more biting edges and the tread area can flex much better. Other performance enhancements aside, the tuned tire is 3 pounds lighter than the uncut version.
The Benefits
There are definite advantages to tuning a tire for trail use. They include increased tread conformability and the creation of more biting edges. A tire with more flex in the tread area rolls more easily over rough terrain since it can better conform to trail obstacles, and consequently it provides increased traction and improved ride quality. Because the tread can move more when tuned, it is possible to get traction and ride equal to a standard tire while running higher inflation pressures, if you so wish. Or, you could enjoy even more flexibility at your normal trail pressures. Either way, the range of adjustability is increased, thanks to the relaxing of tensions across the tread area. Light vehicles with large tires are the most likely to benefit from tuned tires. Large 4x4s generally have enough weight to make as-delivered tires conform, especially when aired down.
Having more biting edges on a tire tread is rarely a bad thing, and, much like siping, each cut in a tuned tire adds extra bite. Basically, you can get all-terrain grip from a mud tire but without losing the mud tire's mudding qualities. Likewise, making some additional cuts could make a mild tread more all-terrainy, while still offering flotation in soft stuff. With more biting edges and better conformability, most tuned tires end up working better on the trail. Bias tires generally respond the best, getting a really nice round tread arch when the tread is freed up. Radials are built to not flex and squirm in the tread area and use stiff steel belts that instead add contact-patch stability and make them excel on pavement, so the carcass construction itself prevents much of the potential tread movement regardless of tread layout. Still, radials also can benefit from tire tuning. Being designed not to conform like a bias tire, they can use all the help they can get in the flex department-for trail duty, on a light vehicle.
It is common to see the chevron-shaped...
It is common to see the chevron-shaped center blocks on Swampers cut in half, but here each one was made into three equally sized blocks. Notice that the so-called tie bars (at the end of each shoulder lug and between the center blocks) also were removed, further freeing up the tread area. Not extending the cuts in the shoulder lugs all the way out helps keep the lugs from chunking off.
The Drawbacks
Two things are pretty much guaranteed to happen when tuning your tires. First, the warranty is void once the first cut is made, and technically the tire is no longer street-legal once it's modified. Chunking, where parts of (or entire) lugs come off, also is more likely with tuned treads, especially if little or no thought was applied to how the shoulder lugs were grooved.
That you can't buy tires already made for maximum trail performance is simply because the tire companies must take longevity, noise, rolling resistance, operating temperature and steering response into consideration when building tires for the masses. Those tread blocks were designed the way they are for many reasons, but maximum traction or conformability weren't the main priorities. Tuned tires will wear faster, be noisier, and require more power to turn, plus they'll run hotter and handle worse on the street. Tire manufacturers have to make tires that will work even under the worst conditions, which would be for heavy vehicles on pavement, at speed. Tuned tires shine at the opposite end of the spectrum.
In reality, the drawbacks apparently aren't all that negative, compared to the benefits. Grooved tires were a very rare sight when Four Wheeler first ran a story on tire tuning some eight years ago. These days you see tuned tires all over the trails, and it makes perfect sense when considering that the drawbacks are pretty much limited to street use.
The Procedure
Making cuts in rubber isn't particularly easy-not when you want it to get cut, anyway. That's why there are special tools for the purpose, called tire groovers. Using a heated and very sharp U-shaped blade, a groover slices through tread blocks with relative ease. Good tire groovers have several heat settings and the trick is not to use any more heat than necessary-when there's smoke there's a blade overheating. Since the blades cost from 50 cents to $1.50 each, it's best to use the lowest heat setting possible. Once you get more familiar with the procedure, higher settings can be used, if the speed of cutting is increased accordingly. Expect to waste a few blades before getting the hang of it. You may want to practice on a junk tire before modifying your good trail treads.
 This Australian Treadtech...  This Australian Treadtech T-2000 groover is representative of what works well for tuning trail tires, and can be found in the USA for just over $300. With a wide range of heat settings, it can be used for making small and delicate cuts as well as for taking out large portions of a tread block in a single pass. Too much heat ruins the blade, not enough makes progress real slow. |  Groovers use a very sharp...  Groovers use a very sharp U-shaped blade that is heated to enable it to slice rubber. Pushing on the handle with the blade against a tread block makes the contact (right behind the blade) close, putting current through the blade, which in turn heats it up. Blades are available in several sizes, and by adjusting the depth and width where they mount in the groover they can be used to make various shapes of cuts. |  Seen from the trail's point...  Seen from the trail's point of view, this tire really doesn't have much tread left for gripping when enveloping an obstacle. By tuning the tire, there will be additional biting edges to help create traction. Or, if the tire then conforms so much better that it closes those new voids, too, that'll also help with getting more traction. Either way, you'll gain. |
Before making the first cut, have a plan. You definitely need to figure out what you want to cut ahead of time. Since the process is irreversible, think first and cut later. Long before plugging in the groover, we drew some potential cutting lines on paper, using an enlarged photocopy of the tread pattern from an ad. These ideas were bounced off some people that really know tires and the art of tuning them. The revised version was then drawn on a tire, using chalk, and we could ponder the recommended grooving versus what we'd wanted to do. Not being complete idiots, we went with what the experts felt would work best.
Be really careful when setting...
Be really careful when setting the depth of the blade. Cutting into the cords will weaken the tire significantly so stay level with, or above, the stock tread depth.
Remember that you can always cut more later on, but once a cut is made it is permanent. It's perfectly OK to make an asymmetrical pattern, for example, leaving the outside shoulder lugs more intact for better cornering. Also, the front and rear tires can be tuned differently.
Once you get going, you'll find that the first five or six inches of tread tuning is great fun-but you soon realize that there's eight feet or so to go. And then three more tires. Knowing that the effort was well worth the resulting improvements helped us keep going, but whittling away a few ounces at a time until the piles of small rubber pieces on the floor totaled 12 pounds was, well, work. You may want to groove just one pair of tires at first and try them out on the trail before attacking the other two. It'll help tell if you tuned them too little, about right, or (gulp) too much for your application.
At 5 psi the difference between...
At 5 psi the difference between the stock and tuned tires was nearly 1 1/2 inches, and at 3 psi the tuned tire has completely enveloped the rock, and then some (making the gauge read 4 psi). Some bias tires will grow about an inch in diameter when fully inflated as the tuned tread flexes better both ways.
Setting the tire down on a...
Setting the tire down on a 5-inch-tall rock provided proof that tire tuning relaxes the tread and allows more flex-at least on this tire. At 10 psi most of it is already enveloped in the tuned tire, while at this pressure the stock tire sat more than one inch higher.
The Results
After being tuned as shown in this story, these 35x15.5-15 Super Swampers work great-at least they do on a vehicle weighing less than 3,000 pounds, with about 4 psi in the front tires and 3 in the rears. Traction on rocky trails was much improved since the tires could conform far better than before, and the new gripping edges surely didn't hurt. We were told not to cut the shoulder lugs all the way out to the edge, which could be why no chunking whatsoever has taken place. On the other hand, the tires haven't spun much on rocks since they were tuned. A very aggressive design, these tires still wanted to dig down when on soft surfaces. At the Tierra Del Sol Desert Safari, for example, they often left two deep ruts behind rather than just going up and over like a milder tread could. Since the tuned Swampers work so well on rocks and other firmer trail surfaces, we'll leave them as is, rather than try to make sand tires out of mudders. A few hundred miles of pavement driving, at about 10 psi, haven't left any bad impressions-not in us, or the tires. Sure, they're a bit noisier and have noticeably higher rolling resistance now, but we could air up a bit more or stay off the pavement altogether if those things were issues. The bottom line is that these tires work far better on the trail than they did before being tuned-at least on this particular vehicle. And since we really like things that help trail prowess, even if it compromises street manners, tuned tires are definitely a cut above untuned tires, in our opinion.
Contact Pressure-Friend or Foe?
As specialized as tires are these days, they're still quite compromised. One size may fit them all, so to speak, but there is only one ideal contact pressure for any given terrain. If the 35x15.50-15 Swampers shown in this story were mounted on a Suburban, each square inch of tire tread contacting the ground would have to support a fair amount of weight-pounds per square inch. Lowering the tire inflation pressure puts more of the tread in contact with the ground, thereby lowering the contact pressure although the vehicle weight is unchanged.
If those same 35x15.50s were on a much lighter Samurai, the contact pressure would obviously be lower than it was with the Suburban, and at any given tire inflation pressure. Most likely, there wouldn't be enough contact pressure for optimum traction with such a large tire (footprint) on a Samurai, regardless of inflation pressure, and is one situation where tire tuning could help immensely.
If your tires tend to spin on top of the trail surface, you may want to try increasing the contact pressure. This can be accomplished either by airing up a bit (there goes the ride quality), running a more aggressive or narrower tire (costly experiment), or try tuning what you've got (no going back with this one). Should your tires want to dig down more than go forward you may already have too much contact pressure for the terrain, and/or a tread that's too aggressive. Try airing down even more (very cost effective), use a less aggressive tread pattern (looks aren't everything, really) or use a wider tire.
Grooving the tread effectively increases the contact pressure since there's less rubber remaining to meet the ground. While you can easily increase contact pressure with tire tuning, keep in mind that there can be too much of a good thing. You'll have to experiment to find out what works best for your vehicle, with your tires, on the trails you drive.
Where to Buy a Groover
If you're feeling groovy about the idea of cutting up good tires and would like to get the needed equipment, don't bother looking in the hardware store. You'll find several sources for tire groovers on the Internet, including Ideal, Rillfit and Treadtech units. We found one for as little as $51.95, and a cheapy is the way to go if you're only going to tune one set of tires. At the opposite end of the scale, a nice Rillfit was advertised for $475. Your local tire dealer is usually a good place to order a groover, since they buy their supplies from companies that handle most anything tire-related. Or you could order one yourself from Tech Inc., P.O. Box 14310, Lenexa, KS 66219, 800/255-1002.