At Tyre Review, we understand there are a lot of terms, acronyms, names and phrases that most people don’t know or understand when it comes to the world of tyres, wheels and vehicles.
We’ve compiled a list of frequently used terms to save you time and help you understand some of the techy bits on our site.
Plus, you never know when the knowledge will come in handy for a trivia night.
Wheel alignment - The process of ensuring all wheels are close to perpendicular to the ground and parallel with the vehicle, within manufacturer’s specifications. You can read our in-depth article on wheel alignments here.
All Terrain Tyres
Anti Roll Bar
Also known as an anti sway bar, this resists the urge of a vehicle to tilt towards the outside of a corner when turning.
Vehicle approach angle - An imaginary line between the lowest point of the car ahead of the front wheels and the tyre. Approaching an object taller than this angle will cause the vehicle to hit that object before the tyre has a chance to make contact. Similar to Departure Angle.
Tyre aspect ratio - Aspect ratio is a two-digit number expressing what percentage of tyre width is the height of the sidewall. For example, a 50 profile tyre has a sidewall height 50% as tall as the width of the tread.
Asymmetrical tyre tread - Describes a tread pattern where the inside and outside of the tyre tread is different and designed to be used only in the labelled orientation.
Tyre Bagout - Commonly referred to when talking about lowering Tyre Pressures for offroad use. Bagout, or bag out, or bagging out, is the phenomenon where a tyre sidewall expands sideways when a tyre is run at lower pressures. Bagout contributes to the larger surface contact area, or Contact Patch that is desirable when driving on soft surfaces.
Tyre balancing - The process of fitting lead weights to a wheel to avoid any vibrations from an imbalance caused by heavy or light spots in the wheel and/or tyre.
Tyre Bead - The part of the tyre that immediately seats against the wheel.
Tyre belts - Tyres are internally reinforced by layers of steel, nylon or polymers. These layers are arranged in belts.
Tread block - Raised portions of a tread pattern designed to make contact with the ground.
Wheel camber - camber is the inwards or outwards tilt of the wheels when looked at from the front of the vehicle. Negative camber means the wheels lean in at the top. Positive camber means the wheels lean outwards at the top.
Tyre carcass - The main body of the tyre. This is then covered with tyre tread, and an air tight inner liner, making a tyre.
Tyre contact patch - The surface area in which a tyre touches the ground at any given time.
Tyre curb guard - Also known as a wheel protector, this is a raised portion of tyre sidewall designed to help prevent wheel damage from curbs, debris or other scuffs. Damage to this part of the tyre does not affect tyre integrity.
Vehicle departure angle - An imaginary line between the rear tyres of a vehicle and the lowest point of the vehicle behind the rear wheels. When reversing up to an obstacle or leaving an obstacle, any object steeper than this angle will be impacted by the body of the car. Similar to Approach Angle, but on the opposite end of the vehicle.
Tyres with a directional tread are designed to be fitted to a vehicle so they rotate in a specific direction. Running directional tyres backwards often results in poor wet weather performance and excessive tyre noise.
Tyre and fitment - A term used to describe how a wheel and tyre combination is situated in relation to the bodywork of a vehicle. For example, a 4x4 with large tyres that stick out past the body of the vehicle would be described as having aggressive fitment.
Tyre flat spot - Describes non-uniform circumference in a tyre. This can be caused by long term storage, locking up the brakes during an emergency or manufacturing defects.
Flotation tyres are typically tyres run at lower pressures and have massive contact patches to avoid sinking into soft terrains such as sand and mud.
Tyre tread grooves - Tread grooves are longitudinal gaps between the tread ribs of a tyre. Typically they are uninterrupted by Tread Blocks.
Highway Terrain Tyres
Otherwise known as HT tyres, these are optimised for on-road use and typically have low noise, wet weather performance and durability characteristics.
Also known as Aquaplaning, describes when a tyre can not move water out of the way fast enough while driving. The tyre loses contact with the road along with total loss of grip from that wheel. The risk of hydroplaning increases as a tyre wears down.
Tyre imbalance - When the mass of a wheel and tyre is non-uniform, a vibration may be felt while driving. This is usually resolved by balancing the tyres to the wheels.
Load Carrying Capacity
Tyres are rated on how much weight they can support at certain air pressures. This is listed along with tyre size information on the sidewall of the tyre. Tyres are given a load rating index.
A numerical code that relates back to a chart where the load index of the tyre is specified in kilograms.
Low Profile Tyre
Tyres with a low aspect ratio have shorter sidewalls, or a lower profile when looked at from the side. Generally, tyres with an aspect ratio of less than 50 are considered low profile.
Mud Terrain Tyres
Also known as MT tyres, these typically have aggressive, self-cleaning tread patterns and perform excellently off-road.
Wheel offset - Offset is a measurement of where the mounting face of the wheel is situated in relation to the width of the wheel. Most factory wheels have the mounting face biased towards the outer face of the wheel and are thus positive offset.
Original Equipment (OE)
This is a term used to describe manufacturer-specified equipped parts such as tyres, light bulbs, engine oil and more.
A condition where a vehicle turns more rapidly than expected, often caused by lack of traction under the rear of a vehicle, compared to the front.
Pitch Circle Diameter - Describes the layout of the studs or bolts that hold a wheel onto a vehicle. Often written as (number of studs/diameter of imaginary circle studs are laid out on), eg 4/100 or 6/139.7.
Tyre Placard - A small sticker or plaque indicating important information about your vehicle that is often found in the drivers door jamb.
A term used to describe changing to a larger diameter wheel whilst going to a lower profile tyre, keeping roughly the same diameter.
Internal layers of rubber and reinforcement materials used in a tyre.
A term used to describe how much friction is generated by a tyre simply rolling along a road surface. ‘Eco-friendly’ tyres typically prioritise low rolling resistance to help improve fuel economy.
Run flat tyres - Tyres with a special construction that allows them to hold their shape and support a vehicle while no air pressure remains in the tyre. Punctured run flat tyres can be driven on for short periods at lower speeds to a service center for replacement.
Tyre sidewall - The vertical section of tyre between the wheel and the tread pattern. The sidewall is visible when the tyre is mounted on a vehicle.
Tyre tread sipes - Tread sipes are thin slits cut into tread blocks. These are designed to improve grip, as a larger tread block can flex more with carefully designed siping.
The difference between the direction a tyre is travelling and the direction it is pointing.
Not all tyres are created equal and they are engineered with maximum speeds in mind. These speed ratings are specified on the sidewall in the same location as the tyre size information.
Vehicles with differently sized front and rear tyres are described as having a staggered fitment.
Most vehicles will have multiple wheel nuts or bolts holding each wheel to the hub surface. When tightening these up, it’s recommended to follow a star pattern to ensure equal pressure and minimise the chances of a wheel coming loose. Do all the fasteners until they’re hand tight, and then make a final pass to the correct torque specifications.
The collective name for all the components under your vehicle that allow it to move smoothly over rough and irregular surfaces.
Tie rods connect the ends of the steering rack, which can only move linearly side-to-side - to the steering knuckle.
Toe is a term used in suspension alignments. Toe is where the front of the wheels point either towards the middle of the car (toe in) or towards the outside of the car (toe out) when looking at the vehicle from above.
Every fastener on your vehicle has a specific recommended tightness. This is the torque specification.
The measurement between the outer edges of two tyres at opposite ends of an axle-line.
Tread Wear Indicators
A raised feature inside the tread groove in a tyre. When the rest of the tread wears down level with this indicator, the tyre is legally bald and must be replaced.
Short for Tyre Pressure Monitoring System. A system that will alert you if your tyre pressures are either too high or too low. Can be fitted from the factory or there are universal kits you can retrofit to older vehicles.
Tyre tread life - The length of time and/or kilometres between a tyre being new to worn out and due for replacement.
All modern road going vehicles use pneumatic tyres, which are tyres filled with gas, most often plain old air. Air pressure is measured in pound-force per square inch (PSI), kilopascals (kPa) or bar. Correct pressures for the application are essential for prevening premature Tyre Wear.
Tyres come in all sizes and are designed for all purposes. Luckily, tyre sizing and the necessary labelling schemes are tightly regulated to help you get what you need for your vehicle.
The tyre tread slowly erodes away through constant contact with road surfaces, eventually causing tread to get shallower and disappear entirely.
Understeer is the condition where the vehicle goes straight instead of turning as sharply as intended. Caused by a lack of traction under the front wheels of a vehicle compared to the rear.
Short for Uniform Tyre Quality Grading. A testing standard where tyres are compared to a known control sample and rated on treadwear, traction and temperature metrics.
Tyre Valve - The small device through which tyres can be inflated or deflated. Just about every road vehicle will use the same style ‘Schrader’ valve.
When a vehicle accelerates, brakes, or turns corners, each wheel is subjected to heavier and lighter loads as the suspension shifts, this is referred to as weight transfer.
Please see alignment.
The distance between the centerline of the front wheels and the centerline of the rear wheels. Generally, long wheelbase vehicles are more stable over bumps and while towing. Shorter wheelbase vehicles are more sporty feeling and easier to maneuver in smaller areas.
Width of a wheel fitted on a vehicle. Car, 4x4 and motorbike wheels are measured from tyre bead seat to bead seat, rather than overall width.
The reluctance of a vehicle to continue in a straight line. A wandering vehicle will require constant attention and corrections, for example, to stay in a lane on a highway.