Still the King? 42" TSL Review and Tire Tech By Bill "BillaVista" Ansell Photography: Bill Ansell & Terry Brummel Copyright 2006 - BillaVista Offroad Tech (click any pic to enlarge)

Introduction

Ahhh....tires!

Tires, tires, tires!

Is there any other component on your rig that elicits such an emotional response, such heated debate, such pride, as its tires? Pull up to a trail ride or event and what's the first thing you notice about the other guys' or gals' rigs? Watch closely and what's the first thing they stroll over and look at on yours? It's not the motor or the gearing or the suspension...it's the tires. And for good reason...whether street-driven or trailered, buggy on 42's or Jeep on 31's - your tires say a lot about your rig.

Whether in mud, snow, or rocks, tires can make or break your rigs performance so it's obviously pretty important to choose the right tires. The ironic thing is, unlike many other components, there's precious little hard data available to compare tires. With engines, axles, and suspension we can talk of horsepower, torque load capability, anti-squat, valving, and spring rates. With tires we're much more reliant on experience, word-of-mouth, gut feel, and reputation.

To complicate matters, in the past several years there has been a marked increase in the number and different types of tires available for your hardcore 4x4. There are old players with new offerings, there are narrow-focus competition tires, there are even new companies more traditionally associated with sports cars selling offroad tires. And with pro competition, sponsorships, marketing deals, advertising, and the Internet full of "experts" it can all get pretty confusing pretty fast.

With this article I aim to give you some ideas to help you decide where to spend your tire dollars. It used to be the off-road crowd were divided into two camps - those that had Super Swampers - and those that wanted them. In essence, the "Swamper" was King. So now I'm going to answer the question: "For an all-round, hardcore, off-road tire - is the Swamper still King? "

Before I go any further, I should point out that this article is aimed at the hard core enthusiast. It's for the individual who places a premium on off road performance - above all else. Whether street driven or trailered; Suzuki, Ford of buggy - it's about serious off-road ability and not about quiet ride, mileage, or tread-wear warranties.

Basic Tire Tech

Before I get into the why's and wherefore's of my favorite tires we should first go over a little basic tire tech. Not only because, as usual, we need to be sure we're talking about the same things, but also because knowing precisely what a tire is made of, how it's made, how it works, and what the differences are between types has a surprisingly large effect on how we view our tires - and ultimately what we decide to buy. I know, I know, you're thinking, "What's to know - it's a tire for God's sake - surely even BillaVista couldn't over-complicate it!" And you'd be wrong ;-)

What is a tire and what does it do?

On the face of it, this bit's actually quite simple. A tire is just a rubber air bladder that contains pressurized air to support the vehicle's weight, right? Well, yes...but it also transmits acceleration, braking, and cornering forces to the road or trail, and acts as a spring between the trail and the wheel.

It's able to do all this because of the way it's constructed. You see, a tire isn't just a rubber balloon - it has a carcass made of plies (or layers) that give it shape, strength, and stability (otherwise when filled with air it would just expand in a wobbly and useless round fashion like a balloon tire in a kids picture). It has a steel bead to clamp it to the rim with sufficient friction to transmit acceleration and braking from the rim to the trail and vice versa. It has tread blocks to grip the road and trail, tread voids to shed mud, snow and water, and it can have cap-plies or steel belts under the tread to stabilize the tread and reduce punctures. The plies themselves are made of chords of fibrous material (polyester, fiberglass, nylon, rayon, steel mesh, kevlar, etc.) woven together and coated with rubber. It is the plies in a tire that give the tire shape and strength and prevent it from expanding like a balloon, thus allowing the build up of load supporting pressure.

What are the parts?

The major parts of a tire are as follows:

Body: The body, also known as the carcass or casing, is the core of the tire. Made up of body plies, it is beneath the tread and inside the sidewalls.

Chords: Lengths of fibrous material (polyester, kevlar, nylon, etc.) that lie at the heart of a ply.

Ply: A fibrous, fabric layer made from chords woven together and coated with rubber.

Body Plies: Layers of rubber-coated fabric that form the body of the tire.

Cap Plies: Optional extra layers of fabric used for circumferential reinforcement in high-speed tires.

Bead: High-strength, rubber-coated, steel cable that clamps the tire to the rim.

Tread: A compound of many natural and synthetic rubbers and other components that contacts the road.

Tread Lug: Raised segment of the tread.

Tread Void: A gap or space in the tread to allow the shedding of mud, snow, and water.

Sidewall: The rubber between the tread and the bead, it provides lateral stability for the tire and protects the body plies.

Shoulder: The area where the tread and sidewall meet.

Inner liner: The innermost rubber layer in a tubeless tire that helps to make it air-tight.

Steel Belts: Belts of steel mesh that lie under the tread to provide puncture resistance and keep the tread area flat for maximum road grip.

Edge Cover: Optional special circumferential reinforcements above the steel belts found in high-speed tires. Also called belt edge strips.

Essentially, a tire is made as follows:

- The beads are formed from steel cable
- Body plies are made from rubber-coated fabric cords
- The carcass is made from body plies stretched from bead to bead
- Optional steel belts and/or cap plies are added on top of the casing (depending on design)
- The tread and sidewall rubber are moulded on
- The inner liner is added.

Dimensions

To have a meaningful discussion about tires, in addition to knowing the names of all these parts, there are some important dimensions of a tire that we must know. These are illustrated and described below:

Overall Width:
The distance between the sidewalls of a tire when it is, mounted on the design rim*, inflated, and unloaded; including any protruding side ribs, raised lettering or decorations.
Section Width:
The distance between the sidewalls of a tire when it is, mounted on the design rim*, inflated, and unloaded; exclusive of protruding side ribs, raised lettering or decorations.
Tread Width:
The width of a tire's tread at the point where it comes into contact with the road, i.e. the width of the contact patch.
Section Height:
The distance from rim seat to outer tread surface of a mounted, inflated and unloaded tire.
Rim Diameter:
Diameter of the rim measured at the bead seats.
Rim Width:
Distance between the two opposite inside edges of the bead seats.
Overall Diameter:
The diameter of the inflated tire, mounted on the design rim*, unloaded.
Note: Overall Diameter = Section Height X 2 + Rim Diameter

* Since a tire's section width and diameter changes depending on the width of the rim on which it is mounted (the tire gets wider and taller if mounted on a wide rim, and narrower and shorter if mounted on a narrow rim), each tire is measured on a specific rim width, called the "design rim". For tires with aspect ratios between 50 and 80, the design rim width is usually 70% of the tire's section width. For tires with an aspect ratio less than 50, the design rim's width is normally 85% of the tire's section width.

Aspect Ratio: There is another dimension of a tire that is useful to know - though strictly speaking it's a calculation rather than a true dimension. It's know as the tire's Aspect Ratio.

Aspect Ratio = Section Height divided by Section Width

Aspect Ratio is the relationship of a tire's height to width when mounted and inflated on a rim of correct size. Aspect ratios are expressed as a two digit percentage such as 80, 70, 60 etc. This number, as a percentage, means the height of the tire's sidewall (its Section Height) is x% of its width. Aspect ratios are also often referred to as the tire's 'series'. For example, if section height/section width is 0.60 (60%), the tire is a 60 series tire.

Why do we care about a tire's Aspect Ratio? Because the height to width relationship determines the shape of the tire on the rim, and, more importantly, determines the performance characteristics of the tire. If the sidewall height of a tire is reduced slightly, the sidewall stiffness is increased greatly. Higher Aspect Ratios deliver greater deflection under load and a softer ride. Lower aspect ratios deliver a wider footprint, quicker response, less slip angle, lower flex rate, less deflection and a harsher ride. Also, typically, a high aspect ratio tire will have a long, narrow footprint, while a low aspect ratio will have a short, wide footprint. At least that's all true in the street-car world. Things are a little different for us because the amount by which we air down our tires overdides the Aspect Ratio in determining the tire's footprint and responsiveness.

Construction - Radial, Bias Ply, and Bias Belted

There are 3 basic types of tires, named for the 3 main ways of constructing a tire, differentiated by the way the body plies are oriented. They are:

Bias Ply tires,
Radial tires, and
Bias Belted tires.

Bias Ply

The body plies in a bias ply tire are laid down at an angle (or bias) to the centerline of the tread, and are stacked one upon the other in a multi-layer criss-cross fashion. These criss-crossing layers are generally oriented 32 to 40 degrees from the centerline of the tread. Since the chords that make up the plies are fibers, they are strong in tension but have no strength in compression. This is why the plies are laid down at a bias and on top of one another - to give the tire its strength in both directions - and is also why there are always an even number of body plies in a bias ply tire. The body plies are frequently made of nylon chords but other materials can be used. Nylon is very strong but is also very stiff. These stiff, strong layers must essentially scissor against each other as the tires flexes which builds heat, causing the tire to run hotter than a radial. Over time, heat degrades a tire. That said - this building of heat is really only an issue in sustained road driving at speed. Bias ply tires also do not have cap plies or steel belts under the tread - as a result, when the tire is loaded by the vehicle the chords are stretched and the entire body supports the weight. Since there are no other layers under the tread, the tread tends to be slightly rounded, creating a smaller contact patch (relative to a same-size radial) that reduces road handling. Because of our practice of airing down this reduced contact patch is of no concern off-road. On the other hand, since bias body plies run from bead to bead there is no transition from a circumferential belt to sidewall - the tread and sidewall construction are the same. As a result, tread can be wrapped around and down the sidewalls of a bias ply tire for extra traction and protection - the perfect example of which is the TSL/SX - a tire not offered in radial design.

Intreco Tire's Super Swamper TSL/SX - photo courtesy Interco Tire Corp.

Extensive sidewall tread on the TSL/SX - possible because of its bias ply construction.

The overlapping, criss-cross plies of a bias ply tire results in a carcass and sidewall that are thick, stiff, and strong. This very strong sidewall more easily withstands trail hazards and punctures than a radial design (where all the chords run in the same direction, are generally made of weaker, more flexible polyester, and there are fewer plies). This is not only because the multiple plies result in a great thickness (making it harder to penetrate completely), but also because of the alternating angles of the bias ply. If an injury does occur in the sidewall of a bias ply tire it is much less likely to completely rip or tear (called a "zipper") than radial tire. Imagine it like this: take 2 wooden boards and glue/bond them together with the grains running in the same direction. Now strike the top edge with an axe - they will split readily....the zipper! Now, bond the same two boards together again, but this time lay one on top of the other at an angle (a bias) of 30-40 degrees. They will now resist splitting completely when struck with the axe - just like the overlapping body plies in a bias ply tire (when abused offroad - not hit with an axe, of course!)

A bias ply tire can be aired down lower than an equivalent radial tire. This is because the heavy-duty sidewalls of a bias ply tire also help support the load more than in a radial. Remember that the plies criss-cross across a bias ply tire. One layer is strong in the weak direction of another. As the tire is compressed and flattened by the load, some of the cords are put under tension where the great tensile strength of nylon results in the sidewall supporting the load in conjunction with the air pressure inside the tire - the result being we need less air pressure in the tire to support the load.

Bias ply construction also presents two additional characteristics - neither of which are of any real concern in a hardcore trail rig. Due to their weight and lack of steel belts or cap plies, bias ply tires tend to be less fuel efficient for highway use than radial tires. Also, nylon has a tendency to take a set when statically loaded, especially when cold, resulting in the "square tire" syndrome.

Radial

There are two main differences in the construction of radial tires compared to bias ply tires that account for their dramatically different on and off-road performance characteristics: the orientation of the body plies and the addition of steel belts and/or cap plies under the tread.

In a radial tire the body plies are laid down perpendicular to the center line of the tread - they appear to radiate from the center line - hence the name "radial". There are also usually many fewer body plies than in a bias ply design - up to a maximum of 3 compared to the up to 16 used in a bias ply tire. In fact, a radial tire needs only one body ply, and thus is not only less stiff, but runs much cooler, and weighs less. If more than one body ply is used , successive body plies are layered over the existing ones with all the chords being parallel. In addition, the body plie(s) of a radial tire are generally made of polyester which is softer and not as tough or strong as the nylon common in bias ply tires.

Radial tires also use a wide variety of cap plies and/or steel belts under the tread. These belts are placed in successive layers circumferentially around the casing, under the tread. They are independent from the body plies, are made from a variety of materials (including steel, fiberglass, and nylon) that are different from the materials used in the body plies, and so cause a discontinuity where the sidewall and tread meet. Each belt adds an additional layer in the tread area but leaves the sidewall area untouched.

This belted radial design, this discontinuity between sidewall and tread, results in the tread being independent from the sidewall - the steel belts provide a stable foundation for the tread allowing the sidewall to be more flexible. In a radial tire sidewall flexing does not alter tread pattern. As the tire flattens out under loads or impact, the sidewall plies just bend, adding very little resistance.

The following diagrams illustrate the difference between bias ply and radial tires in terms of the effect of sidewall flexing on tread stability and contact patch.

The combination of the radial pattern, softer polyester material, and use of belts (independent tread and sidewall) gives a radial tire more sidewall flex which allows the tire to absorb road shock and noise thus producing a much smoother ride. The softer polyester chords also resist flat-spotting much better than the stiff nylon chords in a bias ply - especially in the cold. On-road it also results in the load being distributed equally across the contact area as well as better traction with less heat build up resulting in longer life and improved fuel economy. By restricting tread movement during contact with the road, the belt plies improve tread life. In addition steel belts protect the casing under the tread against high-speed impacts and punctures.

However, the sidewall is generally weaker on radial tires than on bias tires when it comes to puncture and damage resistance. Part of this is due to fewer body plies and less rubber being used, and part is due to the fact that, in a radial tire, even a small injury can lead to massive tear because the body plies have all their chords running parallel to one another.

Also, since the radial sidewall adds very little stiffness (indeed is designed to be much more flexible), as can be seen in the distinctive radial tire "bulge", the load is almost entirely carried by the air and thus radial tires cannot be aired down as low as bias ply tires carrying the same load.

In addition, the discontinuity between tread and sidewall in a radial tire is the reason radial tires don't have substantial sidewall tread. Because the radial design depends on thin, flexible sidewalls it defeats the purpose to add significant rubber tread to the sidewall, and doing so would cause a lot of heat buildup from radial sidewall flexing. In any case, even if some form of tread is added to the sidewall of a radial their will still be a break in the transition from tread to sidewall.

Other components found in a radial tire but not in a bias ply are bead chaffers and cap plies - usually built into performance tires to enhance cornering and stability at high speeds.

Bias Belted

Bias belted tires are a hybrid combination that have criss-cross bias body plies like a bias ply tire, combined with cap plies / steel belts like a radial tire. Frequently the belts and body plies are made from different materials. For example, a polyglass tire may have polyester plies and fiberglass belts. Bias belted tires have a wider tread area than the bias ply - providing better traction and stopping power. They also have more flexible sidewalls than the bias ply, resulting in less internal heat buildup during driving and consequently greater tread life. On the surface they may seem like an ideal compromise - a way to combine the benefits of both radial and bias ply design. However, they of course also combine the weaknesses of both designs. I believe this is the reason they have never really caught on and are all but nonexistent in the market place - very few bias belted tires are manufactured today. This is probably due to the fact that both bias ply and radial tires fit their niche, accomplish their goals, so well that the potential consumer of either is not willing to compromise either with a hybrid tire. Those seeking tough, durable off-road tires with maximum sidewall strength and tread will choose bias ply tires - those seeking on-road performance, tread-life, and handling will choose radial tires.

Which One to Choose?

Virtually all street/car tires sold are radials due to their superior handling, ride quality, and wear. Radial construction allows the tire to better flex and absorb the irregularities of the road surface. The radial design also produces much less friction resulting in cooler running tires and much longer tread life.

But bias ply tires refuse to disappear from the market. The overlapping, criss-cross reinforcement design of bias ply tires makes them very durable. Since the sidewall is as strong as the rest of the body, it can withstand lateral loads, twisting, and bending which would cause a radial to split - especially in an aired-down tire. This strength and durability of the bias ply construction is also a benefit in high torque conditions like when a spinning tire suddenly gets traction. Also because of the one-piece tread/sidewall design, much more aggressive and functional tread can be added to the sidewall of a bias ply tire.

The following diagram and table summarize the strengths and weaknesses of radial and bias ply construction:

Summary

Bias ply tires are the clear choice for serious off-roading because of their sidewall strength, aggressive tread, and ability to be run at low single-digit pressures. For serious, hardcore trail riding, the strength and durability of the bias ply trumps all - after all, when you're wheeling brutal terrain miles from nowhere the best tire is the one that still holds air!

Radials are the best choice for on-road driving because of their softer ride, improved handling, and longer tread life.

If you drive both on- and off-road you have to decide which is more important - the road manners of the radial or the toughness of the bias ply. Me - I'll compromise road manners for trail performance every time. If you're compromising, whichever you choose, there are a couple of precautions to note:

- When running a bias ply tire on the street, strict attention must be paid to tire pressures. The stiff sidewalls can easily disguise an under-inflated tire. Street driving even slightly under-inflated bias ply tires can be hazardous because the scissoring body plies already build a lot of heat - this is exacerbated by under-inflation to the point that the tires can quickly build enough heat to cause ply separation and catastrophic tire failure.

- Radials tires, of course, also need correct air pressure on the street. Excessive heat in a radial tire leads to sidewall cracking, zipper blowouts, and the tread separating from the casing (those rings of tread, or "alligators" you see on the side of the highway are most often the result of radial truck tires, especially retreads, suffering this heat-induced tread separation). Off-road, radials will require more air pressure than bias ply tires to avoid excessive sidewall bulge resulting in sidewall splitting or the sidewall getting pinched between the rim and a rock.

Purchase Considerations

So now that we know the basics, we know enough to make our tire purchase decision ...well, almost!

The last thing to cover is a few ideas on the specs we need to consider in selecting a tire.

Once again I must emphasize the subjective nature of this . This is largely due to two things - the first is the fact that our hardcore offroading needs in a tire are completely and dramatically unlike any other tire users' - from race cars to motorbikes to tractors - there's no one else's use that even comes close to matching our needs. This is closely related to point two - which is: Ours is still a relatively "new" and "emerging" sport - a sport still in its infancy. As a result - there still aren't multi-million dollar competitive series and huge corporate sponsors - the kind that can fund the engineering and R&D required to really get to the bottom of things with hard empirical data. Let me give you an example. The racing world probably knows the most about tires - at least the tires they use. This is the result of many years of well funded and highly competitive, highly focused, research and development. As such - racers, the good ones at least, know about how a few degrees ambient temperature difference, a different track, or a 1/4 lb worth of pressure will affect their tires and therefore their car's handling. They use durometers and pyrometers and heat sensors and chemicals and dry nitrogen and 1/4 pound increments in pressure to tune their tires and extract every ounce of performance from them. Heck, even tractor drivers can research agricultural papers that discuss, in scientific detail, concepts such as ballasting and grip coefficients with certain implements - factors that affect their tire's performance.

We, on the other hand, have no such thing - whether it's lack of funding, knowledge, expertise, or motivation - we don't discuss durometer readings and other scientific, empirical measures - we tell campfire stories! Even rock crawling teams, along with the rest of us, still rely quite heavily on statements that are ambiguous at best - statements such as "I saw those tires in action at <location x> and man, did they ever hook up" or "So and so's tires were the best - they hooked up all day".

All of which is to say that what follows is more subjective than my usual writings. I'm ok with this. I'm confident in my observations based on many years of experience.

So here are the factors to consider when choosing a tire:

• Size / proportion
  • Probably the first and most important consideration is what size tire to run. It has to be big enough so that a week later you aren't wishing you'd upsized. But you also need to have the motor, clearance, and axles to run the size you want. Another consideration is the "proportion" of the tire - both to your rig and it's own height to width. This is one of the main reasons I chose 42" TSL's. Not only do I think they're perfectly proportioned (44s are too "fat" and 40s just not big enough) but they fit my rig perfectly - I can turn them with ease with a V8 SBC, and my built 1-ton axles handle them well without being overkill. They're simply a great size for hardcore buggies and trucks alike.
• Tread
  • This will largely be determined by where you wheel. Most of us not only have to wheel a wide variety of terrain, but enjoy doing so. This means most of us need an aggressive tread that does well in rocks, mud, water, snow, etc. The tried and true Three Stage Lug design of the TSL's fits this bill extremely well.
• Toughness
  • Unless you're lucky enough to be either sponsored or extremely wealthy this is a HUGE concern. Like I said before - at the end of some of the brutal trails I run, the best tire is the one still holding air! Fashionable new radials made by import-car tire companies mounted on huge bling rims may look cool in the parking lot (or not!) - but at the end of the day I'll take a heavy, brutal, tried and true bias ply beast any day.
• Stickiness
  • Especially for those of us that love the rocks - how soft or "sticky' a tire's tread compound is is an important consideration. However, in the real world of hardcore trail riding it's probably not as important as the tire's toughness - not to me at least. It may be fashionable to talk about wanting "competition compound' sticky tires - but unless you like buying new tires every season they're not the best bet for trail riding. I look at it the same way I did when I rode bikes - sure, talking about having the softest race-compound tires is cool, as is showing them off at the coffee shop parking lot - but it sucks replacing them all the time or having the get torn up or wear out half-way through a tour (or trail)
• Appearance
  • Don't kid yourself - this is really important - especially when you're dumping cubic yards of dollars in large tires. I know you want to think you're all about form over function - but there's no shame in wanting your rig to look good too. This is, of course, a very personal thing - everyone has their own tastes - just remember - you have to love your rig - every time you look at it - not wince and launch into an explanation of how the tires really work well...honestly...they do...

Review

So we know all about tires and what they're made of. And we know the things we need to consider when purchasing tires. Here's why I chose 15/42-16.5LT Super Swamper TSL's

The Tires

Wow - five 15/42-16.5LT TSL's actually fit in a mini-van!

Here they are mounted, compared to my old 325/85R16 Michelin XML's

The difference in performance is night and day. The old XML's were a good tough tire but my TSL's are FAR superior - they throw mud better, they are softer and stickier, and they grab and hold rocks MUCH better.

Here are some measurements I took - mounted dimensions are on a 16.5 X 8.25 15° bead-seat modified Hummer rim.

Here you can see that the tires are made of four nylon plies - that's four actual body plies (not the 'ply rating' which is a form of load rating - see the "load rating" section later in this article). They're also Load Range "C" with a max load of 2680 lbs at 30 PSI. That's equivalent to a 6-ply rating. The sidewalls are a whopping 3/4" thick!

Specified rim size is from 9.75" to 12" wide, and 16.5" in diameter.

The boy sure looks pleased with "his" buggy's new tires!

Air Pressures

Being big, tough bias ply tires, these TSL's work really well off-road across a huge range of pressures. This gives me a lot of flexibility for tuning them to different terrain and trails. The following pics show the tires at different pressures. Keep in mind that the figures are not some absolute numbers - there's nothing magical about 4 PSI - what works best depends entirely on the weight of your rig.

0 PSI. Ok, you can't really drive at 0 PSI (yes, I tried - it was hilarious - the whole rig just lurched drunkenly about - that what I'M supposed to do around the campfire!) But the bottom pic here is an excellent example of why we air-down in the first place - look at the size of that contact patch - it's like a mini tank track!

The Look

You can't deny these tires look great on this rig too.

Remember what I was saying about proportions?

Not only are they a great proportional tire in terms of their height and width...

...but they're just right on my rig too. Nothing else would be this right.

They even look good when they're in the air!

The Performance

Mud

There's no denying the TSL is a great tire in the mud - one of the greatest ever. The huge lugs and massive voids self-clean as well as any tire out there. I keep telling myself (and others) that I'm a rock-crawler, that I hate mud...but the truth is - it's actually a heck of a lot of fun - especially with the kids onboard yelling "WEEEEEEEEEEEE!!". And having kick-ass tires to fling the goo really rocks!

Here's a series of pics showing me powering out of a deep mud-hole. Sometimes it's hard to catch the mud-flinging action on camera but the last 2 pics show how well the tires can chuck the sloppy stuff!

It's a great feeling to have confidence in your tires when blasting through deep mud and water...especially when you don't know just how deep it is and the kids are egging you on!

Mixed Trails

An awful lot of trail riding is done on mixed trails - some rocks, some mud, some roots and stumps, some dirt, some water... a bit of everything. It's here that the TSL REALLY shines. It's a truly great "all-terrain" tire - I know of no other that does as well in such a wide variety of terrain. There may be tires that do a single job better than the TSL (the Bogger in mud, for example) but no tire does such an great job in ANY terrain. Particularly on slippery, muddy, rocky trails - the TSL kicks ass!

In The Rocks!!

No matter how great a tire is everywhere else - it's performance in the rocks is a make-or-break deal to me - and to most of you reading this too. If a tire sucks when rock crawling it just can't be a great tire. The 42" TSL's do not disappoint. Most of these pics were taken on the most extreme trails available at Paragon Adventure Park in Hazleton, PA by my good friend and excellent photographer Terry Brummel (thanks Terry!) I've wheeled on or with just about every tire out there- and it's my considered opinion that the Super Swamper TSL ranks with the best when it comes to gnarly rock crawling. The toughness, the sidewall strength, the ability to run low single digits, the massive outer lugs, and the tire's soft compound make it a champ in the rocks - here's a look at why:

It takes a tough tire to take this kind of deforming and constantly come back for more.

Note the marks on the sidewall. This is not a poseur tire! This is a tire that gets ridden hard and put away wet - and it works!

Toughness

This next series is just one illustration of how tough the TSL is. Believe it or not, this wasn't a setup. We were on a tight, wooded trail with lots of trees - I hate trees - and we were digging and turning and weaving in and out all day. In this particular spot, though you can't see it in the pics, there were large trees on the left and right - forcing me to drive over this stump. And not just any stump - but one chewed by a good ol' Canadian beaver - I swear I'm not making this up - that's what the li'l buggers do, and man does it leave the stumps sharp. Once again, it's great to have tough tires you can trust to hold up to this kind of abuse - there's not many tires you can run over a sharply pointed stump at 4-5PSi in a 5000 lb rig - but the TSL's laughed and asked for more.

Stickiness

If there's a hot buzzword in offroad tires these days - "stickiness" is it. It seems everyone wants the stickiest tires available - just like the pros have. Well, maybe nearly everyone. Coz I don't. I live in the real world - the one without corporate sponsorship, the one without new tires every event or even every season. In fact - most of us live in a world where a new set of 42" tires is only in the budget maybe once every few years.

When you live in this "real" world - you want performance - but your tires have to last too! I've been running my TSLs for 8 or 9 months now - and not only are they plenty soft and sticky the way they are, not only do they perform great in all kinds of terrain, but if they were any softer I'd be in danger of losing my mind! As these next pics show - after only a single recreational "season" they already show plenty of wear - I've been beating them pretty hard after all. I can't imagine them being softer and therefore even more worn! For my money, I think they're a pretty good balance between performance and durability.

More Tire Tech

Tire Sizing Systems

There are many tire sizing systems still in use today, some dating back to the 1930’s and others having come into use only since the 70’s and 80’s. I will explain each one, as you are likely to see any and all of these systems when shopping for off-road tires (Interco themselves use four different systems: Alpha-Numeric, Metric, Flotation, and LT-Numeric).

Numeric

Earliest system, dates back to the 30’s when there were few tire sizes available (or needed)

Example:

9.15-15

9.15 is the section width in inches
15 is the rim diameter in inches

Notes:
- Using this system you can’t tell the OD of the tire without knowing the Aspect Ratio
- In the 1950s and early 1960s, the standard aspect ratio was 82-84%
- Around 1970, bias ply tires moved to a 78% aspect ratio
- In the 70’s the "standard" aspect ratio dropped to 75%
- Today, Aspect Ratios of 65%, 60% and even as low as 35% are available.
- If you know the AR of the tire in question you can calculate the OD as: (Section Width x Aspect Ratio) x 2 + Rim Diameter (eg. in the above example, if we knew the Aspect Ratio were 78%: (9.15 x 0.78) x 2 + 15 = 29.3" )
- If you don’t know the AR, the only way to tell the OD is to consult the manufacturer’s specifications.

Alpha Numeric

This system began to appear in the late 1960’s. It adds the Load Rating and Aspect Ratio information, but mysteriously drops the Section Width.

Example:

H78-15

H – load rating
78 – Aspect ratio in %
15 – diameter in inches

Notes:
– This is an almost useless system as we don’t know, nor can we determine, the section width or OD of the tire.
– When radial tires began to appear, an R was added to the designation but this still doesn't’t help us determine size:

Example:

HR78-15

– There are some charts available that list common Alpha-Numeric sizes and the equivalent OD and Section Width of the tire, in inches, but these must be used with caution as they are by no means universal. Here is one such chart:

L78/15 = 30x 9.5
N78/15 = 31x 9.5
P78/15 = 33x10.0
Q78/15 = 36x11.5
Q78/16 = 36x10.5
R78/15 = 37x12.5
R85/16 = 37x12.0

-Though the alpha-numeric system doesn’t tell us the OD, we can, however, tell the relative size of tires using this system. Here’s why:

There are only two ways to increases the load carrying capacity of a tire

1) Increase the max pressure it can hold (by altering its construction/composition) or
2) Increase the size of the tire so there are more Square Inches for each Pound of air pressure to push against (a tires load in Pounds is roughly it’s max pressure (PSI) multiplied by the number of Square Inches of its contact patch)

E.g. Load = 50 P/SI x 30 SI = 1500 lbs

The alphabetic load rating system was originally based on this principle, with higher letters being assigned to larger tires able to carry more load. For this reason, we can also say that, for tires using the alpha-numeric system, the higher the letter, the larger the tire. For example, we can see from the preceding chart that an N78/15 (31x9.5) is smaller than a Q78/15 (36x11.5)
- Again, the best way to determine the dimensions of an Alpha-Numeric tire is to consult the manufacturer’s specifications.

Metric (Euro-Metric, P-Metric)

The Metric system first appeared in the 1970’s and was called the Euro-Metric system because it began in Europe. It is the first system that tells us virtually all we need to know, though some information must be calculated from the figures given.

Example:

235/75R15

235 is the section width in mm
75 is the Aspect Ratio in %
R denotes radial construction (D = (diagonal) bias ply construction; B = belted bias construction)
15 is the rim diameter in inches

To calculate the complete dimensions:

First change section width to inches by dividing the mm by 25.4

235/25.4 = 9.25” wide

Then calculate the OD in inches by multiplying the Section Width by the Aspect Ratio (to get the height of the sidewall), doubling it, and adding the diameter of the rim

OD = ((9.25*.75)*2)+15 = 28.87 ~ 29”

Therefore a 235/75/R15 is a 29” x 9.25” R15

Notes:

- This system has becom widely known as the “P-Metric” system as a P appears at the beginning of modern designations to indicate a “Passenger car” tire. Although the system is also used for light truck and special trailer tires.

Examples:

P235/75R15
LT 275/70R16
ST 205/75R14

- System allows rapid comparison of the AR or “profile” of the tire
- Unlikely to ever see anything but an R in P and LT tires, but may see a D or B for certain special tires like ST tires
- The D.O.T. decided to add the "P" to P-Metric to denote that it was designed for passenger car use for load carrying capacity limits.
- Note that P and LT tires are often rated slightly different. If P-rated tire is used in an LT application, you need to de-rate the sidewall load capacity by 9% - 10% according to many tire makers.
- The best system so far, but not perfect (for us) as it requires calculations to give the complete dimensions which we need (because we run such a VAST range of different sizes)
- Early metric sizes may be shown without the AR number

Example:

165SR15

This is because the metric system was implemented in Europe when tires were still chiefly bias ply, available only in a limited number of sizes (due to construction technology of the time) and all using a standard aspect ratio of "82". Therefore, originally it was not necessary to include the AR in the sizing system. With the advent of radial tire construction, tire manufacturer’s were suddenly able to construct better performing street tires by increasing the section width and reducing the sidewall height of the tire. In doing so, they began making tires with aspect rations lower than the “standard” 82% and so it became necessary to include the AR in the metric tire sizing system

Flotation

The Flotation Sizing system is used for larger, wider tires (LT tires) used on trucks and SUV’s – so named because these tires are supposed to “float” over soft surfaces. It is a convenient system for us as it gives the whole picture at a glance.

Examples:

39.5x13.50-16LT
36x12.50R15

36 = OD in inches
12.50 = Section width (NOT tread width)
R = denotes radial construction (absence of the R denotes bias ply construction)
15 = rim diameter in inches
LT = Light Truck tire (may or may not be present)

Tread width may be published by manufacturer, but for us will vary enormously anyway with load and low air pressures.

LT Numeric

For LT tires there also exists another useful system – the LT numeric system – based on the old Numeric system but with the useful addition of the OD.

Example:

9/34-16LT

9 is the approximate section width (in inches)
34 is the approximate overall tire diameter (in inches)
16 is the rim diameter in inches)
LT designates a Light Truck application

Notes:

- This system is used only for bias ply tires.

Summary:

Numeric – old and practically useless (unless you’re just shopping for an exact replacement tire from the same manufacturer for your tractor, small trailer, or wheelbarrow). Tires in these sizes will be bias ply.

Alpha-Numeric – only slightly less useless than the numeric system. Might be of some use to those competing in certain sanctioning bodies with rules based on what is written on the tire. E.g. getting away with an aired-down Q-78/15 in a 35” and under class. May be used for radial and bias ply tires.

Metric – has all we need to know, but calculations must be made. Not common in the sizes hardcore wheelers need (38” OD and up). Used with radial and bias ply tires, indicated by an R,D, or B in the designation. Older metric sizing on bias ply tires used a standard, unstated AR of 82%.

Flotation – Most useful “at a glance” info for us, used with both radial and bias ply tires where a radial will always have an R in the designation but a bias may just have no letter. May or may not include the designation “LT” at the end.

LT-Numeric – Similarly useful as the Flotation system, if a little more complicated to read. Used only for LT tires, and only for bias ply construction.

Both the Flotation and LT-Numeric sizing systems tell us the basics of what we need to know. My preference is for the Flotation system as it tells me the info in an easy to read format in the order that I most care about – OD, then width, then rim diameter. Then again, it might just be because that’s the system I grew up reading (and often dreaming) about!

However, it’s not perfect either – in fact, the metric system does offer one advantage – and that’s “at-a-glance” comparison of the “profile” of different tires. E.g.. If we look at:

235/75/R15 and 235/65/R15

We can immediately see that the latter is a lower profile tire.

Traditionally, we wheelers haven’t cared much about a tire’s profile. We just wanted tall tires, either wide or narrow depending on preference. However, in recent years, with the widespread use of single and double beadlocks allowing low single-digit air pressures (to increase contact patch and therefore available traction) combined with the ever increasing need for performance, stability, and predictability demanded by today’s competitive and recreational rock crawling we have begun to take note of the effect of a tire’s profile on it’s performance.

Interestingly, unlike car guys who use an aspect ratio comparing the tire’s sidewall height to its width – we are more concerned with a tire’s sidewall height compared to its overall diameter. Because very large diameter tires (e.g.. 44”), especially on smaller diameter rims (eg. 15”) give a tire a very tall sidewall, often at very low pressure the sidewall will flex excessively so as well as getting a larger contact patch (which is what we want) we get less lateral stability (hindering the ability to stick a technical line in the rocks), unpredictable handling, and increased damage to sidewall injuries (by driving on the sidewall and/or “sidewall pinch” injuries (where the pressure is so low the sidewall essentially collapses and is pinched between the rim and the rocks)). To avoid these troubles we need to run a little more air pressure – we need to find the sweet spot for our rigs weight and our terrain. Of course, this sweet spot is going to be different for different tire sizes on different rims and different tire constructions (radial vs bias ply) – and comparing these (to arrive at the best tire/wheel/pressure combination for us) is where all current sizing methods fall a little short.

If it were up to me we would introduce a new extreme offroad sizing method that would incorporate all the info in the flotation system, along with the aspect ratio (sidewall to width) as well as a dimension I’ll call "profile ratio". This profile ratio would be similar to the aspect ratio except that instead of comparing the sidewall height to the width, it would compare it to the OD (and therefore take into effect the rim diameters effect on the tires performance). It would be calculated as ((OD - Rim Diameter)/2)/OD.

Where AR is read as “The tire is x% as tall as it is wide” the PR would be read as “the sidewall is x% of the tires OD”.

The system would look like this:

42x15(85/30)D16.5LT

where:

42 = Tires overall diameter mounted on approved rim width, inflated to max psi, unloaded.
15 = Tires section width mounted on approved rim width, inflated to max psi, unloaded.
85 = aspect ratio (sidewall height/width x 100%)
30 = profile ration (sidewall height/OD x 100%)
D = Bias Ply (R=radial, B=Bias belted)
16.5 = rim diameter in inches
LT = Light Truck designation.

Imagine how useful this could be. For example, lets say you want a 42” tire (in my opinion we’re always likely to decide on OD first and foremost – basing that decision on either the largest we can fit or the axles will handle; or on what the comp class rules are). To help you compare the different offerings, lets list all the 42” tires Interco offers in the “Big 4” (the 4 most serious off-road options – i.e. TSL, SX, Bogger, And Irok) using my system and see what it tells us.

You can see that there are options with Aspect Rations ranging from 80 to 96 and Profile Ratios ranging from 29-32. Now, all we need to do is develop some sort of system for quantifying the relative performance of tires with different AR's and PR's! Not so easy to do! Probably the best we can do is rely on experience and anecdotal evidence, and combine that with a knowledge of different common tire's specs. But it would at least be a place to start.

Load-carrying Capacity

A tire's maximum load is the most weight the tire is designed to carry. Since a tire's load carrying capacity is related to the tire's size and how much inflation pressure is actually used, maximum loads are rated with the tire inflated to an industry assigned inflation pressure.

Additionally, load ranges are used to separate tires that share the same physical size, but differ in strength due to their internal construction. "Higher" load ranges are used to identify tires that have a stronger internal construction, and therefore can hold more air pressure and carry more weight.

Each load range has an assigned air pressure identified in pounds per square inch (psi) at which the tire's maximum load is rated. Listed below are the air pressures at which maximum load is rated for popular P-metric and LT tires:

P-metric
Standard Load (SL): 35 psi
Extra Load (XL): 41 psi

Light Truck
Load Range C (LRC): 50 psi
Load Range D (LRD): 65 psi
Load Range E (LRE): 80 psi

P-metric tires used on passenger cars are rated to carry 100% of the load indicated on the tire's sidewall. However, if the same P-metric tires are used on light trucks, (pickup trucks and sport utility vehicles for example), their carrying capacity is reduced to 91% of the load indicated on the tire's sidewall. This reduction in load results in causing light truck vehicle manufacturers to select proportionately larger P-metric sized tires for their vehicles to help offset the forces and loads resulting from a light truck's higher center of gravity and increased possibility of being occasionally "overloaded."

For example, P235/75R15 P-metric sized, standard load tires used on cars and light trucks would be rated to carry the following maximum loads at 35 psi:

Cars - Full Value - 2028 lbs.
Light Trucks - 9% Reduced Value - 1845 lbs.

A tire’s load-carrying capacity can be indicated in several different ways. They are:

Load Index – a number between 0 and 279 corresponding to a maximum load in lbs. Most often seen in P-metric and LT-metric radial tires.

Load Rating – a single letter between A and F indicating a tire’s RELATIVE load-carrying capacity i.e. the letter does not correspond to an exact capacity or even range of capacities. All we can tell is that an E rated tire will have a greater capacity (and therefore presumably a more rugged construction / possibly stronger sidewall ) than a C rated tire.

Ply Rating – an even number between 2 and 12, this is an older system, identical to the alphabetic load rating system, and having NOTHING to do with the actual number of plies in a tire’s construction i.e. a 10-ply rated tire could be made from a single ply. This is misunderstood and misused all the time. The key to avoiding confusion is to always make sure you use the words “ply rating” when referring to the load carrying capacity of a tire. Most radial passenger tires have one or two body plies, and light truck tires, even those with heavy duty ratings (10-, 12- or 14-ply rated), actually have only two or three fabric body plies.

Specific Load / Sidewall Imprint – max load and pressure spelled out on the sidewall. E.g. “Max load 1250 lbs at max pressure 30psi cold”. When shopping for tires where actual load capacity is a concern (e.g. for your tow rig) this is the best system to use.

Note that neither the Load Rating nor Ply Rating systems correspond to exact load numbers. In fact, depending on manufacturer, size, construction, single- or dual-configuration, etc. tires with the same load range or ply rating can have widely varying actual load-carrying capacities. For example, from various charts, I have seen the following ranges (note the overlap):

B - 1100-1520 lbs
C - 1765-2205 lbs
D – 1930-3000 lbs
E - 2470-3042 lbs
F – 3415-5205 lbs
G – 3415-6610 lbs
H – 4806-7830 lbs

Rather, the Load rating and Ply rating systems are useful only for relative comparison between tires. For example, all we can really tell is that an E rated tire will have a greater capacity (and therefore presumably a more rugged construction / possibly stronger sidewall ) than a C rated tire.

Here is a chart of common Load Index numbers:

Tire Load Index (number) and Load Capacity (lbs.)