ATV Mud Tires – An OC Overview
In support of our recent review round-up that looked at some of the best ATV mud tires on the market, we have brought together some extra information to help you in your search.
Truth be told, we had so much content in that top 10 reviews that we had to cut it short. We like to bring you the most comprehensive reviews that we can, but when the word counts clock over 5000 – well, you guys don’t have the time to read all of that.
So what follows is the stuff we left out. The directors cut if you will.
So without further delay, let’s jump in and learn more about ATV mud tires…
ATV’s & Recreational Driving
Recreational driving allows one to enjoy off-road adventures. This is made possible by the tires of the automobile which can be driven on rough, uneven, and non-tarmacked terrain where mud or sand particles would otherwise make normal car tires to skid or slide on the surface.
Likewise, these tires are designed to be fitted on specialty vehicles built for off-road driving. These automobiles are called all-terrain vehicles (ATVs) as they can be driven on different types of uneven, non-tarmacked terrains.
Evidently, one of the construction features that differentiates ATV from standard cars is the design of their tires.
Also, because this article focuses on a special category of ATV tires that are designed for road-cruising on muddy surfaces, there is need to differentiate these tires – collectively known as mud ATV tires – from standard tires.
Let’s take a closer look…
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A closer look at the ATV Tire
A tire is basically a ring-shaped hoop that surrounds the rim of the wheel. It has 2 primary yet interrelated, functions.
The first one is to provide traction that allows a vehicle to be driven over a surface. The second function is to transfer the axle load through the wheel and onto the ground surface. Even so, how is this axle load transferred to the tire?
In-vehicle design, a drive axle is designed to fit into the center hub cavity of the wheel hub assembly (or unit). Each end of the axle shaft is broached or machine-milled before its surface is shaped into long gear-like teeth called splines.
These are external splines, and they are chamfered so as to reduce stress concentration that normally result from high load (weight) being placed on sharp edges.
At the center of the hub assembly, a matching machine process is used to create internal (or female) splines.
This permits the male splines of the axle to mate with the female splines of the hub unit, thus allowing for torque – in form of rotational inertia caused by rotary motion – to be transferred from the axle and into the hub unit.
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The hub unit
Therefore, as the axle rotates, the hub unit also rotates at the same speed and direction (of rotation). On the outer (wheel-facing) surface of the hub unit are the brake drum unit with its mounting (bolt) holes that allow the wheel to be bolted onto the hub assembly.
This also means that the brake drum is coupled with the wheel, and that both rotate as a single unit. This brake drum has a set of brake pads (shoes) that can be pressed outwards – using a hydraulic mechanism – against the machined inner surface of the drum, and this causes it to stop moving, and subsequently the wheel and tire stop.
The job of the axle
Because each drive axle has 2 ends, then 2 wheel hub units are needed per axle, and this translates to 2 tires per axle. Most vehicles just have the front and rear axles, and this means that they have a total of 4 wheels and 4 tires.
Relatedly, the vehicle weight rests on these drive axles, and these loaded axles also serve to transfer the load on the undercarriage to the wheel hub.
Therefore, each axle not only transfers rotational torque, but also transfers the weight of the vehicle to its wheels via the wheel hub assemblies.
Consequently, the tires bear the weight of the entire vehicle. Expectedly, this requires the tires to be made from strong elastic materials, with the most preferred materials being natural rubber or synthetic rubber.
The outer edges of the wheel have an integral rim that holds the tire in place. Most heavy-duty wheels are constructed from machine-pressed and welded steel, while medium-duty wheels are made from light-weight alloys that contain magnesium and aluminum.
Regarding the change of direction of the applied force, these wheels cause the rotational torque of the axle (force) to change direction along a tangent into a straight, unidirectional, and vertically applied force that the tires bear.
It is this straight applied force that pushes the wheel forward when accelerating forwards, or pulls it back when reversing.
This also means that the applied force on the tires acts vertically on the surface, and this introduces another engineering challenge that is described below.
Why Tires Get Stuck
If the surface area of the tire that is in contact with the surface is small, then the applied (tire) force would generate a high pressure – as opposed to a large tire surface area – that can cause the tire to deform the surface, and if the pressure is extremely high, then the tire can dig into the surface which can cause it to become stuck.
In this case, if one accelerates the vehicles, it increases the rotational torque on the axle, and this subsequently increases the applied force on the tire, and consequently the pressure on the surface is amplified; and the tire further digs in, and the vehicle sinks into the terrain.
This explains why tires designed to be used on soft surfaces of sandy and loose-soil terrains, as well as muddy terrains need to have large surface areas in contact with the ground. Otherwise, they would cause the vehicle to get stuck in the road.
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There are 2 secondary functions of the tire:
To begin with, the tire serves to absorb shock so that the driver driving a vehicle on an uneven surface can enjoy a smooth ride; as well as prevent the vehicle from jumping up when it hits a bump.
Secondly, the tire is designed to provide a footprint that matches the vehicle load to the bearing capacity of the road so that the road surface is not deformed when a tire rolls over it.
This means that a heavy vehicle can be only driven safely on a gravel road when a particular type of tire is used, and if different tires are used, then it would deform the road.
For rubber tires to serve the aforementioned secondary functions, they need to be pneumatically inflated as this allows them to easily absorb shock, while the pneumatic pressure inside the tires can be regulated so as achieve the required (tire) footprint.
Originally, the tire was conceived as a dressing of the wheel.
This concept is even reflected in its etymology as the noun tire is a truncation of the word attire; and just as an attire dresses the body and protects it, so does the tire dress the wheel and protects it from damage caused by direct contact with the road surface.
Therefore, the right spelling is tire, though the noun tyre has gained currency in British English.
As mentioned earlier, a tire is designed to provide traction that allows a vehicle to travel on the ground surface.
In engineering, this traction is accurately described as a tractive force because it is a force that generates motion between the tire and the tangential ground surface by taking advantage of dry friction and shear force of the soil (the maximum force that a clump of soil can sustain before it deforms or disintegrates).
As expected, in muddy environments, the sheer force of the soil is considerably minimized, while the magnitude of dry friction is very low. This means that less tractive force is needed to move a vehicle, as opposed to driving on a dry road.
In physics, pressure is defined as the force applied perpendicularly (in this case, the tractive force) to a specified area.
As mentioned earlier, high pressure could cause the tires to dig into the surface, and even sink a vehicle in a muddy pond.
When riding in muddy surfaces, the area where the tire traction forces are applied is the total surface area of the tires in contact with the road.
Therefore, there are two ways for reducing pressure on the road (road pressure) when traveling in muddy surfaces; make the vehicle light-weight so that a low amount of load is transferred to the drive axles, or increase the tire area that is in contact with the road.
Additionally, according to kinetics as explained in classical mechanics, if the velocity of the vehicle is increased (that is, acceleration occurs), then the amount of tractive force is proportionally increased; while the tractive force is proportionally reduced when deceleration occurs.
This means that traveling at high speeds on muddy surfaces increases the odds of the tires getting stuck in the mud. This aspect of kinetics can be combined with the understanding of pressure to better explain how ATV mud tires are designed.
To begin with, these mud tires are designed to be fitted in relatively light-weight recreational ATV such as quadricycles or three-wheelers, whose weight is much lower than ordinary cars.
There are also 6-wheeled ATVs. Secondly, the wheels and tires of these ATVs are large in proportion to the vehicle size.
Therefore, these ATVs can generate low pressures that make it safe to ride them without getting stuck in the mud.
Likewise, it means that the maximum tractive force needed for safe driving is relatively high. Moreover, there is another functional utility to the low vehicle weight and large tires, the ability to drive at relatively high speeds on muddy surfaces without getting stuck.
According to kinetics, high tractive forces are generated by high vehicle speeds; and maximum safe tractive force is high, then these ATVs can be accelerated (to specified limits) on muddy surfaces, and it is this freedom to accelerate that makes cruising on the mud an enjoyable experience.
What is more, the designs of ATV mud tires are optimized for use in muddy surfaces as is described below.
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To begin with, ATV tires are divided into 2 broad categories; tubeless and tubed tires. This is because they are pneumatic tires which need to hold air at high pressure within an enclosed space of fixed volume.
It is this pressurized air that carries the weight of the vehicle, as well as cushions the tire when it is rolling. This air can be held in a tube placed inside the tire, or it can be held in place by the (tubeless) tire itself.
Regardless of the way ATV tires hold pressurized air, their basic design and construction features are almost the same.
Tire Material and Hysteresis
As described earlier, tires are made from processed rubber which takes two forms vulcanized (polymerized natural) rubber or synthetic rubber.
This processed rubber material forms the elastomer (a portmanteau of elastic and polymer) of the tire. This elastomer gives the tire its elasticity and malleability that allows it to regain its shape after deformation.
The other major component of the tire is its ply which gives it the strength (especially the high tensile strength needed) to bear the vehicle load.
This ply is simply a series of cords that are embedded in the elastomer in a specific pattern. These cords are made of a composite of steel and fibers. These fibers can be natural fibers like silk or cotton; or synthetic fibers mainly kevlar or nylon.
The elastomer forms the surface of the tire in contact with the road, and thus the quality of material determines the rolling resistance, as well as how long the tire can last (as its use causes wear and tear).
In the case of ATV mud tires, the rolling resistance is the measure of friction that prevents the tire from moving (or rolling) on the surface.
As expected, a high rolling resistance is associated with poor fuel efficiency as fuel combustion is necessary to generate power just to overcome the rolling resistance so that the vehicle can start moving. Likewise, it is associated with elastic hysteresis.
Elastic hysteresis is the dissipation of heat that occurs when a loaded deformed elastomer is being unloaded.
This means that the load of the vehicle weight and axle rotational torque causes the elastomer to be deformed, and when this load is gradually lifted off the tire and the elastomer regains its shape due to its elastic property, then heat is generated.
This heat is the excess energy released during the unloading process, which shows that loading requires more energy than unloading.
According to the theory of elasticity in the field of solid mechanics, the deformation (also called strain) of an elastic material is proportional to the force (best described as stress) applied on it.
Consequently, based on the law of conservation of energy, the energy associated with the stress of the deformation must be released when the tire elastomer regains its shape.
However, hysteresis shows that more energy is needed during loading and that this excess energy is converted into heat energy during unloading.
Why is this so?
The reason for this is that the internal friction (between polymer layers) of the elastomer material needs to be overcome before the tire can be deformed (change shape), and the loading energy must provide this force, which also contributes to rolling resistance.
Therefore, low hysteresis means that the tire cannot be deformed by normal vehicle loads, and this tire can easily roll (low rolling resistance) on the road as a solid non-elastic tire that can transfer shock directly into the drive axle and vehicle body.
This not only contributes to an uncomfortable ride, but this kind of tire also wears off quickly. Thus, a good ATV mud tire must have moderate internal friction (moderate hysteresis) that allows it to behave as an elastic tire.
Ultimately, this hysteresis gives the elastomer its springing and damping functions that allow the tire to function as a shock absorber.
Mud Tire Construction
The most common elastomer material used is a copolymer of butadiene – a rubbery polymer with low hysteresis and low rolling resistance, and hence easily prone to wear – and styrene, which is a glass-like polymer with high hysteresis, high rolling resistance, and good wear resistance.
The styrene-to-butadiene ratio determines the grip and wear-resistance properties of the tire, as well as allows for optimization of its rolling resistance so that it can operate well on a muddy surface that normally has low friction.
Each tire is therefore constructed from two materials, the ply material, and the elastomer material.
And that concludes our overview of the ATV mud tire. We hope you didn’t get too bogged down with the physics, some of it can be quite complicated.
However, with a better understanding of what the tire does, how it is constructed, and how it actually works, we believe you are in a better position to buy the right tire for you.
Still having problems with your search, then head over to our top 10 mud tire review round-up for more helpful information.