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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.
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.
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 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: * 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 = 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 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.
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:
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
Here are some measurements I took - mounted dimensions are on a 16.5 X 8.25 15° bead-seat modified Hummer rim.
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.
The Look
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!
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:
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
Alpha Numeric
Metric (Euro-Metric, P-Metric)
Flotation
LT Numeric
Summary:
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! We can immediately see that the
latter is a lower profile tire. 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:
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 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. 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):
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.)
Here is a chart of Load Ranges, the corresponding Ply Rating, the approximate equivalent Load Index, approximate load carrying capacity, and nominal maximum inflation pressure. Note that the data is incomplete because these systems were never designed to readily interchange. And again, the figures in italics are APPROXIMATE and can vary widely in different tires.
Speed Rating Most off-road tires are not speed
rated, and most of us have no concern for a tire's speed rating because of the
use our tires see. That said – no tire article would be complete without
at least a mention of speed ratings – and they might be useful if you’re
shopping for tow rig tires. Example:
Speed ratings are based on laboratory
tests where the tire is pressed against a large diameter metal drum to reflect
its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in
10 minute increments) until the tire's required speed has been met. Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:
Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were made prior to 1991. Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire's service description, such as 225/50R16 89S. When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.
While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.
Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:
Repairs Even the toughest tires aren't bulletproof. And if you run them hard enough for long enough - eventually you're going to have to deal with repairing one. Punctures in the tread are easy to fix - just plug them from the outside and add a nice big patch on the inside. Don't use the dinky little plugs and patches you get at auto parts stores - they're only meant for radial tires on a car. Instead, head to the local 18-wheeler or tractor supply house and get a heavy duty plug and patch kit intended for big trucks, off-road equipment, or tractors. Sidewall damage is another thing altogether. It's what everybody dreads - and for good reason - it can be very difficult to repair. You can't simply plug or patch a sidewall gash - the flexing of the sidewall and the loads imposed on it will spit out a plug in short order. There is some hope however. The trick to a decent sidewall repair is something called a "section repair" that comes from the heavy truck and equipment tire world. A ‘section repair’ is the term for a professional, industrial repair to a damaged tire. It is normally performed only on large heavy equipment type tires that cost many thousands of dollars. The damaged area is “sectioned” or cut out and the area enlarged – similar to the way you would cut out rusted sheet-metal. A new piece of rubber, or combination of rubber and body-ply is then vulcanized over the damaged area. Technically, vulcanizing is the process of hardening rubber by combining it with either sulphur, selenium, or tellurium and applying heat. The end result is rubber with a useful level of hardness, but a sufficient amount of elasticity, or flexibility. The process was discovered accidentally by U.S. inventor Charles Goodyear in 1839 and patented in 1844. He named the process "vulcanizing" after Vulcan, the Roman God of fire. Vulcanizing in the context of tire repair refers to a process where rubber is, essentially, 'welded' by the carefully controlled application of heat, to repair punctures or damage to the tire; using a machine called a vulcanizer. There are also several types of “cold-cure”, “no-heat”, or "cold fusion" vulcanizing processes that can be used by either the professional or do-it-yourselfer. Generally, you grind out the damaged area, apply a large patch-like repair section (often called a “boot”) inside the tire and then apply some sort of cold vulcanizing chemical. After a prescribed amount of time (often up to 72 hours – depending on the manufacturer) the repair is chemically cured. In most cases, radial tires are much less readily repaired using these methods, especially if the damage is to the sidewall, because of the risk of a blowout known as a “zipper”. Recall that all the chords in all the plies in a radial lie in the same direction. This means that a split or gash in the sidewall of a radial can quickly spread – like cutting a board with an axe along the grain, leading to sudden and explosive failure. In fact, most tire manufacturers, along with the Rubber Manufacturers Association state that it is unsafe to repair (especially in a radial) a tire injury that is outside of the steel belts, or located on any part of the sidewall. However, for a trail-only, off-road, bias ply tire a professional section repair can save the tire. Here are a few pics of just such a repair I had made to one of my 42" TSL's after a viciously sharp rock punctured the sidewall:
How to Read the Sidewall There's an awful lot of useful information that is moulded into the sidewall of every tire:
The most useful of which are as follows: Service Type Most tire sizes begin with a letter
or letters that identify the type of vehicle and/or type of service for which
they were designed. The common indicators are as follows: P = When a tire size begins with a "P," it signifies the tire is a "P-metric" size that was designed to be fitted on vehicles that are primarily used as passenger vehicles. This includes cars, minivans, sport utility vehicles and light duty pickup trucks (typically 1/4- and 1/2-ton load capacity). The use of P-metric sizes began in the late 1970s and they are the most frequently used type of tire size today. 225/50R16 92S If there isn't a letter preceding the three-digit numeric portion of a tire size, it signifies the tire is a "Metric" size (also called "Euro-metric" because these sizes originated in Europe). While Metric tire sizes are primarily used on European cars, they are also used on vans and sport utility vehicles. Euro-metric sizes are dimensionally equivalent to P-metric sizes, but typically differ subtly in load carrying capabilities. T125/90D16 98M T = If a tire size begins with a "T," it signifies the tire is a "Temporary Spare" ("space saver" or "mini spare") that was designed to be used temporarily only until a flat tire can be repaired or replaced. LT245/75R16 108/104S LT = If a tire size begins with "LT," it signifies the tire is a "Light Truck-metric" size that was designed to be used on vehicles that are capable of carrying heavy cargo or towing large trailers. This includes medium and heavy-duty (typically 3/4- and 1-ton load capacity) pickup trucks, sport utility vehicles and full-size vans. Tires branded with the "LT" designation are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo. 7.50R16LT 112/107Q, 8.75R16.5LT 104/100Q or 31x10.50R15LT 109Q LT = If a tire ends with "LT," it signifies the tire is an earlier Light Truck size designed to be used on vehicles that are capable of carrying heavy cargo and towing trailers or are wider, oversized tires designed to help the vehicle drive on top of loose dirt or sandy surfaces. This includes light, medium and heavy-duty (typically 1/2-, 3/4 and 1-ton load capacity) pickup trucks and sport utility vehicles. Tires branded with the "LT" at the end of their size designation are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo. 195/70R15C 104/102R C = If a Euro-metric sized tire ends with a "C," it signifies the tire is a "Commercial" tire intended to be used on vans or delivery trucks that are capable of carrying heavy loads. In addition to being branded with the "C" in their size, these tires are also branded with their appropriate Service Description and "Load Range" (Load Range B, Load Range C or Load Range D). ST225/75R15 ST = If a tire size begins with "ST," it signifies the tire is a "Special Trailer Service" size that was designed to only be used on boat, car or utility trailers. ST-sized tires should never be used on cars, vans or light trucks. Trailer tires have extra strong sidewalls to stand up to the side-side motion of a trailer but not for the loads applied to, or the traction required by, drive or steering axles. Section Width Following the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's "Section Width" (cross section) in millimeters. P225/50R16 91S The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. This measurement is also referred to as the tire's section width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the section width in millimeters by 25.4 (the number of millimeters per inch). 225mm / 25.4 = 8.86" Sidewall Aspect Ratio Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio. P225/50R16 91S The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the shorter the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we calculate that this tire size results in a tire section height of 4.43". Internal Construction A letter (R in this case) that identifies the tire's internal construction follows the two digits used to identify the aspect ratio. P225/50R16, P225/50ZR16 The R in the P225/50R16 91S size identifies that the tire has a radial construction in which the tire's body plies "radiate" out from the centerline of the tire. Radial tires are by far the most popular type of tire today representing over 98% of all tires sold. If the R in the size was replaced with a D (225/50D16), it would identify that the internal tire body plies crisscross on a Diagonal and that the tire has a bias ply construction. If the R in the size was replaced with a B (225/50B16), it would identify that the tire body plies not only crisscross the tire on a diagonal, but that they are reinforced with belts under the tread area. This type of tire construction is called "Bias Belted." Speed Rating Today, the only tires that continue to include the speed rating "in" the tire size (P225/50ZR16) are Z-speed rated tires. In this case, following the two digits used to identify the aspect ratio are the letters ZR to identify the tire's speed rating (Z) and its internal construction (R). Since 1991, all other speed ratings are identified in the tire's Service Description (see below). Tire and Wheel Diameter P225/50R16 91S The 16 indicates the tire and wheel diameter designed to be matched together. Tires that have a rim diameter expressed in inches (P225/50R16, as well as 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26 and 28) are called "inch rim" sizes, are the most common type of tire size and are used on most cars, minivans, vans, sport utility vehicles and light duty light trucks. While not as common, two additional "unique" types of tire/wheel diameters are still in use today. Tires and wheels that have a rim diameter expressed in "half" inches (8.00R16.5LT, as well as, 14.5, 15.5, 17.5 and 19.5) are used on some heavy-duty trailers, heavy-duty light trucks and box vans. Tires and wheels that have a rim
diameter expressed in millimeters (190/65R390, as well as, 365 and 415) are
called millimetric sizes. Michelin initiated millimetric sizes for their TRX
tires that saw limited use on many different car models in the late 1970s and
1980s. All of these "unique" tire/wheel diameters were developed specifically because the tire and wheel design or intended vehicle use required them to be different than conventional tires and wheels. All of these tires and wheels feature bead profiles that have a different shape than traditional "inch rim" sizes. Tires and wheels with unique rim
diameters should never be combined with traditional "inch rim" tires
and wheels. Service Description P225/50R16 91S The 91S represents the tire's Service Description. A Service Description identifies the tire's Load Index and Speed Rating. Service Descriptions are required on all speed rated (except for Z-speed rated) tires manufactured since 1991. For more information on Load Index and Speed Rating see he individual sections in this article. Load Range LT245/75R-16E, 7.50R-15D, 31x10.50R-15C, ST205/75R15 LRC If a tire does not use the Service Description on the sidewall, it’s load range will be indicated as part of the tire’s description, as shown in the above examples, using the Load Rating letter designation system described earlier in this article. Other LT255/70R16 XL M+S XL or RF designates an Extra Load or Reinforced tire. If not specified, Standard Load (SL) is assumed and will usually not be labeled as such. M+S designates a tire rated for mud and snow use. "MAX LOAD SINGLE 2623 lbs. at 65 psi COLD" This indicates the maximum load
rating of the tire and corresponding minimum cold inflation pressure. TREAD: 2 POLYESTER + 2 STEEL + 1 NYLON SIDEWALL: 2 POLYESTER The branding in this example identifies
that molded into the rubber under the centerline of the tread lies two radial
body plies of polyester cord, two belts of angled steel cord and one circumferential
cap ply of nylon cord. It also identifies that in each sidewall at the widest
points between the tire's inner and outer sidewalls (tire section width) lie
two radial body plies of polyester cord (a continuation of the same two body
plies that were listed under the centerline of the tread). Tire FAQ What’s the best way to replace a single tire or pair of tires on a vehicle?
What is the maximum weight it should take to balance my tire? The industry standard is approx. 2% of the tire weight. So, because a 42” TSL weighs about 100lbs, 2% is 2lbs or 32ozs of lead! That’s industry standard. Keep this in mind next time you’re wondering why your 42” Swampers don’t balance well - it’s not because of the quality of the tire – it’s because it weighs so much – it’s just the physics of dynamically balancing that much rolling mass – and it’s the price you must pay for large, aggressive tires. What are tires made of? The average steel-belted radial tire is made up of:
How round is round? Generally, a passenger-car tire is considered round if it has less than 0.030" radial or lateral runout. An LT tire is considered round if it has less than 0.060" radial and lateral runout. Does it matter how I mount the tire on the rim? There are two schools of thought
on this. The wider the rim, the greater the
section width. Section width increases about 0.4” for each additional
inch of rim width (and vice versa). A narrower rim pulls the beads closer together, curving the sidewalls. This increased curvature allows the sidewall to flex more readily. It can also help with bead retention at lower air pressures, although using narrow rims is no substitute for beadlocks. Why do race teams use Nitrogen in their tires instead of air? Race cars, aircraft, and other ultra-high
performance machines use Nitrogen in their tires instead of air because, when
heated or cooled, nitrogen has a much more consistent rate of expansion and
contraction than air. What is the difference between an LT and P tire of the same size? LT tires that are load range C or
greater tend to be rougher riding and noisier than their P-Metric counterparts
and more expensive since the LTR size equivalent to the P-Metric has heavier
body ply construction and the tread lugs are generally more aggressive. How should I store unmounted tires?
What about tires on my rig in storage?
What’s so special about “ST” tires for my trailer? Why can’t I replace them with P tires with an equivalent load rating? “ST” or “Special Trailer” tires are designed specifically for trailer service, whether they are radial or bias ply. They feature materials and construction to meet the higher load requirements and unique demands of trailering. For example, ST tires are constructed for better high speed durability and bruise resistance under heavy loads and they have stiffer sidewalls that help to reduce trailer sway. Passenger car (P) or light truck (LT) tires do not have the structural components to provide stability and handle the stress and dynamics imposed by a trailered load. ST tires typically have larger chords in the body plies and the steel wire in the beads has a larger diameter and greater tensile strength to meet the additional load requirements. ST tire rubber compounds also contain more chemicals to resist weather and ozone cracking. Similarly, trailer tires are designed for use on trailer axle positions only, not for the loads applied to, or the traction required by, drive or steering axles. Are there special considerations with trailer tires that are not present with other tires? While the majority of the following factors also apply to other tires, they have special significance for trailer tires. There are two main reasons for this. First, absolutely nothing good happens when you experience a tire failure while towing a heavy load. A blowout in your car during the morning commute is bad enough – but when it happens as you’re towing 4 tons at 70mph in the dark on a curvy, rain-slick road the stakes are incredibly high! Secondly, trailer tires tend to get used, abused, and neglected or forgotten about. Because we don’t use them every day and because there’s nothing sexy about them we tend to take them for granted and not pay them the attention they deserve. We do so at our own peril!
Should I use Radial or Bias Ply tires for my trailer? It used to be that bias ply tires were considered the only way to go for trailer tires, because their sidewalls are stronger and stiffer than those of radial tires. However, recently radial ST tires have gained widespread acceptance. Both can do the job well, but there are differences. The bias ply tires will still have stiffer sidewalls and therefore be more resistant to trailer sway and so provide more lateral stability. The downside is that a bias ply tire will run significantly hotter than a radial (for reasons discussed earlier in the article). And we know that heat is one of the main enemies of any tire. Which to run is a matter of choice. Some will say that it depends on your towing habits – that you should use a bias ply for towing heavy loads because of the extra measure of stability; and that you should use a radial if you tow light loads at high speeds for long distances, because they run significantly cooler. Of course, nobody ever defines what a “heavy” load is – is it 5000lbs, 10,000lbs or more? I have run both radial and bias ply on my 7000lb trailer and can attest that, after 6 hours of towing at 65mph, the bias ply tires are hot to the touch while the radials are cool. With proper trailer/axle weight rating,
loading, tongue weight, type of hitch, trailer brakes, and size/weight of tow
rig I don’t feel that sway and stability are a problem and so my personal
preference, towing 7000lbs of trailer and buggy, is to run radials because the
cooler the tire – the less it will fatigue. Your trailer, load, and needs
may lead you to decide that bias ply are a better choice – especially
if you have issues with trailer sway. The safest answer is yes, and many manufacturers will state this. However, some believe that IF (and ONLY if) you know the exact weight of your loaded trailer you can achieve a marginally softer ride by inflating the tires to less than the maximum pressure, using a load vs pressure chart for your specific tires. I wouldn't do it myself, but such a chart will look something like this:
Super Swamper Weights ** Special thanks to MAD 4WD for providing this information on the Pirate4x4.com Forum ** Super Swamper TSL Radial
Super Swamper Bias Ply TSL
Super Swamper TSL / SX
Glossary of Tire Terms: Air Pressure: Conclusion Big, tough, proven, reliable, cool-looking, and great-performaing in all kinds of terrain. Any questions? Is the TSL still king? In my book it is - no question. In fact, there's only one tire that could ever steal me away from my 42" TSLs - and that would be a 42" TSL/SX!! References:
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