Reference
Car glossary: automotive terms explained
147 terms from across the lessons, each defined in plain language and linked to the lesson that explains it properly.
147 terms shown
A
- Ackermann geometry
- Linkage layout that makes the inner wheel steer more than the outer so both roll about a common centre.
- Explained in:Steering Systems
- Antifreeze (glycol)
- Lowers the freezing point, raises the boiling point and carries corrosion inhibitors that protect the engine's metals.
- Explained in:Engine Cooling System
- Average crash deceleration
- For a stop from speed v over crush distance s.
a = v² / (2s) - Explained in:Chassis Construction
B
- Balance shaft
- Counter-rotating weighted shaft(s) that cancel an engine's residual shaking forces, typically turning at twice crank speed in a four-cylinder.
- Explained in:Engine Layouts: Inline, V and Flat
- Bite point
- The pedal position where the plate first grips the disc and torque starts to flow to the gearbox.
- Explained in:The Clutch
- Body (ride) frequency
- How fast the body bounces on its springs. Passenger cars are usually tuned to roughly 1–1.5 Hz.
f_body ≈ (1 / 2π) × √(k_ride / m_s), k_ride = k·k_t / (k + k_t) - Explained in:Suspension Basics
- Brake fade
- Loss of braking effectiveness as pads and discs overheat or brake fluid boils.
- Explained in:Mechanical Sympathy
- Brake torque
- The turning effort the pads exert on the disc: the friction of both pad faces acting at the effective radius.
T = 2 μ_pad F_clamp r_eff - Explained in:Disc Brakes
C
- Camber gain
- The change in the wheel's lean as it moves up and down. A shorter upper arm tilts the top of the wheel inward in bump, keeping the tyre flatter on the road when the body rolls.
- Explained in:Suspension Basics
- Camshaft speed
- Each valve opens once per 720° cycle, so the camshafts turn once for every two crankshaft revolutions.
ω_cam = ω_crank / 2 - Explained in:The Four-Stroke Cycle
- Caster and trail
- Rearward tilt of the steering axis places the contact patch behind it, producing self-centring.
- Explained in:Steering Systems
- Centre differential
- Lets the front and rear axles turn at different average speeds in permanent all-wheel drive.
- Explained in:Drivetrain Layouts
- Cetane number
- A measure of how readily a diesel fuel auto-ignites; higher cetane shortens ignition delay and softens combustion noise.
- Explained in:Diesel Engines
- Coefficient of friction
- Ratio of maximum horizontal force to vertical load at the tyre.
F_max ≈ μ × F_z - Explained in:Tyres and Grip
- Coefficient of performance
- Heat moved divided by work input; car A/C systems typically achieve around 2–3.
COP = Q̇_evap / W_comp - Explained in:Air Conditioning
- Cold-cranking amps (CCA)
- The current a battery can deliver at −18 °C for a set time while staying above a minimum voltage.
- Explained in:Battery and Starter Motor
- Compression ignition
- Fuel ignites because the air it is injected into is already hotter than the fuel's auto-ignition temperature.
- Explained in:Diesel Engines
- Compression ratio
- Cylinder volume with the piston at the bottom divided by the volume with it at the top.
r = (V_swept + V_clearance) / V_clearance - Explained in:Diesel Engines,The Four-Stroke Cycle
- Constant mesh
- Every forward gear pair stays in mesh all the time. Changing gear only changes which free gear is locked to the mainshaft.
- Explained in:The Manual Gearbox
- Constant-velocity joint
- A joint whose driving contacts lie on the plane bisecting the shaft angle, so output speed always equals input speed.
- Explained in:Driveshafts and CV Joints
- Contact patch area
- Approximately the wheel load divided by inflation pressure.
A ≈ F_z / p - Explained in:Tyres and Grip
- Crank torque
- Torque produced by a gas force F on the piston. Zero at both dead centres.
T = F·r·sin(θ + φ) / cos φ - Explained in:Pistons, Connecting Rods and the Crankshaft
D
- Damping force
- A damper's force depends on how fast it is moving, not on how far it has moved. Valving shapes the curve so it is firm at low speeds and softer at high speeds.
F_d ≈ c × v - Explained in:Springs and Dampers
- Damping ratio
- Damping compared with the critical amount that just stops overshoot. Below 1 the mass overshoots and oscillates; above 1 it creeps back slowly and the suspension feels stiff over quick bumps.
ζ = c / (2 × √(k × m)) - Explained in:Springs and Dampers
- Dew point
- The temperature at which air becomes saturated and water vapour starts to condense.
- Explained in:Air Conditioning
- Diagnostic trouble code (DTC)
- A stored code identifying which monitored signal went out of range — a symptom, not necessarily the failed part.
- Explained in:Diagnosing Warning Signs
- Differential speed rule
- The carrier (crown wheel) speed is always the average of the two output speeds.
ω_c = (ω_L + ω_R) / 2 - Explained in:The Differential
- Direct drive
- The input shaft is locked straight to the mainshaft; no gear mesh carries the load.
i = 1 - Explained in:The Manual Gearbox
- Downforce
- Negative lift that pushes the tyres onto the road, increasing grip without adding mass.
- Explained in:Car Aerodynamics
- Drag coefficient (C_d)
- A dimensionless measure of how efficiently a shape moves through air, independent of size.
- Explained in:Car Aerodynamics
- Drag power
- Power needed to overcome drag; it grows with the cube of speed.
P_d = ½ ρ C_d A v³ - Explained in:Car Aerodynamics
- Driveline wind-up
- Stress built up when axles are locked together but need to turn at different speeds, as in part-time 4WD on tarmac.
- Explained in:Drivetrain Layouts
- Dual circuit
- Two independent hydraulic circuits so a single leak cannot remove all braking.
- Explained in:Brake Hydraulics
- Duration
- How many crank degrees the valve is off its seat. Here 230° for each valve (illustrative).
duration = closing angle − opening angle (mod 720°) - Explained in:Valves, Camshafts and Valve Timing
E
- Electrical power
- Power delivered equals voltage times current.
P = V × I - Explained in:Alternator and Charging
- Electromagnetic induction
- A changing magnetic flux through a coil induces a voltage; faster change means higher voltage.
E = −N dΦ/dt - Explained in:Alternator and Charging
- Energy and range
- Range is usable battery energy divided by consumption.
range = E_battery / consumption - Explained in:Hybrid and Electric Drives
- Energy into heat
- A stop converts the car’s kinetic energy into heat in the brakes. The disc’s temperature rise depends on its mass and the heat capacity of iron.
E = ½ m v², ΔT ≈ E / (m_disc c) - Explained in:Disc Brakes
- Engine braking
- Using the drag of the engine, in gear with the throttle closed, to slow the car without heating the brakes.
- Explained in:Mechanical Sympathy
F
- Final drive ratio
- The fixed reduction between gearbox output and wheels, applied in every gear.
- Explained in:The Differential
- Firing frequency
- Each cylinder fires once every two revolutions, so at N rpm one cylinder fires N/120 times per second.
f = N / 120 - Explained in:The Four-Stroke Cycle
- Firing interval
- Crank angle between successive power strokes in an evenly firing four-stroke engine.
θ = 720° / n - Explained in:Engine Layouts: Inline, V and Flat
- Flame front
- The thin, moving boundary between burned and unburned gas. Turbulence from the intake port wrinkles it and makes it spread faster.
- Explained in:Spark Ignition and Combustion Timing
- Free play
- The first part of the pedal travel, which only closes the gap between the release bearing and the diaphragm fingers.
- Explained in:The Clutch
- Freeze-frame data
- A snapshot of key engine parameters recorded when a fault code was set.
- Explained in:Diagnosing Warning Signs
- Friction circle
- Combined braking/accelerating and cornering forces cannot exceed the tyre's total grip.
√(F_x² + F_y²) ≤ μ F_z - Explained in:Tyres and Grip
- Fuel trim
- The ECU's percentage correction to its calculated fuel quantity, based on oxygen-sensor feedback. Short-term trim reacts quickly; long-term trim learns slowly.
- Explained in:Fuel Injection
G
- Gear ratio
- Driven teeth divided by driver teeth, which equals input speed divided by output speed.
i = z_driven / z_driver = n_in / n_out - Explained in:Gear Ratios and Torque Multiplication,The Manual Gearbox
- Grip-limited deceleration
- The tyre can only push on the road as hard as its grip allows, so the best possible deceleration is set by the road and tyre, not by the brakes.
a_max = μ_road g - Explained in:Disc Brakes
H
- Half-speed camshaft
- The camshaft makes one turn per four-stroke cycle.
θ_cam = θ_crank / 2 - Explained in:Valves, Camshafts and Valve Timing
- Handy conversion
- Power in kilowatts from torque in N·m and engine speed in rpm.
P[kW] = T[N·m] × rpm / 9549 - Explained in:Torque and Power
- Heat carried by coolant
- Heat flow equals mass flow times specific heat times the temperature change.
Q̇ = ṁ × c_p × ΔT - Explained in:Engine Cooling System
- Heat pump
- A refrigeration cycle run to deliver heat into the cabin, moving more heat than the electrical energy it consumes.
- Explained in:Air Conditioning
- Hooke's joint speed ratio
- Instantaneous output/input speed ratio of a universal joint at angle β and input position θ.
ω₂/ω₁ = cos β / (1 − sin²β · sin²θ) - Explained in:Driveshafts and CV Joints
- Hydraulic force multiplication
- Output force scales with the ratio of piston areas; the price is proportionally more input travel.
F_out = F_in × (A_out / A_in) - Explained in:Brake Hydraulics,Disc Brakes
- Hydrodynamic lubrication
- A rotating journal drags oil into a narrowing gap, generating pressure that holds the surfaces fully apart.
- Explained in:Lubrication System
- Hygroscopic
- Tending to absorb moisture from the air — why brake fluid is replaced on a time basis.
- Explained in:Routine Maintenance
- Hygroscopic fluid
- Glycol brake fluid absorbs water over time, lowering its boiling point; hence periodic replacement.
- Explained in:Brake Hydraulics
I
- Ignition timing (advance)
- How many crank degrees before TDC the spark fires. More advance is needed at higher rpm because the burn takes roughly constant time.
- Explained in:Spark Ignition and Combustion Timing
- Indirect gear
- A gear that runs through the layshaft: its ratio is the constant-mesh reduction multiplied by the speed-pair ratio.
i = (z_head / z_pinion) × (z_main / z_lay) - Explained in:The Manual Gearbox
- Injector pulse width
- How long the injector is held open each cycle; fuel delivered is roughly proportional to it once the opening delay is subtracted.
m_fuel ≈ q × (t_pulse − t_dead) - Explained in:Fuel Injection
- Interference engine
- An engine in which valves and pistons would collide if valve timing were lost, making timing-belt failure destructive.
- Explained in:Routine Maintenance
- Inverter
- Power electronics that convert battery DC into controlled three-phase AC for the motor, and back again during regeneration.
- Explained in:Hybrid and Electric Drives
K
- Kinetic energy
- Energy of motion, which a crash structure must absorb; it grows with the square of speed.
E_k = ½ m v² - Explained in:Chassis Construction,How a Car Works: The Big Picture
- Kinetic energy lost in braking
- Every stop converts the car's kinetic energy into brake heat; anticipation avoids wasting it.
E_k = ½ m v² - Explained in:Mechanical Sympathy
- Knock
- Spontaneous ignition of unburned end gas ahead of the flame front, producing sharp pressure waves and an audible metallic rattle.
- Explained in:Spark Ignition and Combustion Timing
L
- Labouring (lugging)
- Demanding high load from an engine at very low speed, which stresses bearings and the driveline.
- Explained in:Mechanical Sympathy
- Lambda (λ)
- Actual air-fuel ratio divided by the stoichiometric ratio. Below 1 is rich, above 1 is lean.
λ = AFR_actual / AFR_stoich - Explained in:Fuel Injection
- Latent heat
- Heat absorbed or released when a substance changes phase without changing temperature; evaporation absorbs it.
- Explained in:Air Conditioning
- Limited-slip differential
- A differential that resists speed difference between its outputs, biasing torque towards the wheel with more grip.
- Explained in:The Differential
- Lobe separation angle
- Cam-degree spacing between the intake and exhaust lobe centre-lines.
LSA = (intake centre ATDC + exhaust centre BTDC) / 2 - Explained in:Valves, Camshafts and Valve Timing
- Lock-up clutch
- A friction clutch inside the converter that joins engine and gearbox directly to eliminate slip losses.
- Explained in:Automatic Transmission
- Longitudinal load transfer
- Load moves from the front axle to the rear when accelerating (and the reverse when braking).
ΔF = m × a × h / L - Explained in:Drivetrain Layouts
M
- Mean piston speed
- Average piston speed for stroke S (m) at N rpm. A common way to compare how hard engines work their pistons.
v̄ = 2·S·N / 60 - Explained in:Pistons, Connecting Rods and the Crankshaft
- Monocoque (unibody)
- Construction in which the body shell itself carries the structural loads.
- Explained in:Chassis Construction
- Motion ratio and wheel rate
- When the spring is mounted part-way along an arm it moves less than the wheel, so the stiffness felt at the wheel is lower than the spring's own rate.
k_wheel = k_spring × MR² - Explained in:Suspension Basics
N
- Natural frequency
- The rate at which a mass bounces on a spring when disturbed. The body bounces slowly (about 1–1.5 Hz in cars); the much lighter wheel hops quickly (around 10–15 Hz).
f = (1 / 2π) × √(k / m) - Explained in:Springs and Dampers
O
- Octane rating
- A fuel's resistance to knock. Higher octane allows more compression or more advance before knock begins; it does not contain more energy.
- Explained in:Spark Ignition and Combustion Timing
- Ohm's law voltage drop
- Voltage lost across a resistance carrying current; tiny resistances matter at cranking currents.
V = I × R - Explained in:Battery and Starter Motor
- Oil film thickness (trend)
- Thicker films come from higher viscosity and speed and lower load, which is why lugging at low rpm is hard on bearings.
h ∝ (η × ω) / load - Explained in:Lubrication System
- Open-circuit voltage
- Battery voltage at rest with no load, a guide to state of charge (≈ 12.6–12.7 V full, ≈ 12.2 V about half).
- Explained in:Battery and Starter Motor
- Open-differential torque split
- An ideal open differential gives each side half the input torque regardless of grip.
T_L = T_R = T_c / 2 - Explained in:The Differential
- Output torque
- Torque is multiplied by the ratio, less the losses in the meshes and bearings.
T_out = T_in · i · η - Explained in:Gear Ratios and Torque Multiplication
- Overdrive
- A ratio below 1 : 1, so the output turns faster than the engine.
i < 1 ⇒ n_out > n_in - Explained in:The Manual Gearbox
- Overrunning clutch
- A one-way clutch that lets the starter drive the engine but not the reverse.
- Explained in:Battery and Starter Motor
P
- Pascal's principle
- Pressure applied to an enclosed fluid is transmitted equally throughout it.
p = F / A - Explained in:Brake Hydraulics
- Peak versus sliding grip
- A braking tyre grips best at a small amount of slip and less once it slides, so a locked wheel decelerates the car less than one held near the peak.
a_lock = μ_slide g < μ_peak g - Explained in:Anti-lock Braking (ABS)
- Phasing
- Aligning the yokes of two universal joints so that their speed fluctuations cancel.
- Explained in:Driveshafts and CV Joints
- Planetary (epicyclic) gearset
- Sun, planets on a carrier, and ring gear in constant mesh; holding or driving different members gives different ratios.
(S + R) ω_c = S ω_s + R ω_r - Explained in:Automatic Transmission
- Planetary reduction (ring held)
- Driving the sun with the ring held and taking output from the carrier gives this reduction ratio.
i = 1 + R / S - Explained in:Automatic Transmission
- Plunge
- Axial sliding in an inboard joint that accommodates changes in shaft length as the suspension moves.
- Explained in:Driveshafts and CV Joints
- Power
- Torque times angular speed. A gearbox changes the mix but cannot increase the product.
P = T · ω = 2π · n · T / 60 - Explained in:Gear Ratios and Torque Multiplication,Torque and Power
- Power-split hybrid
- A hybrid in which a planetary gearset combines engine and motor-generators, decoupling engine speed from road speed.
- Explained in:Hybrid and Electric Drives
- Powertrain
- Everything that creates and delivers drive: engine or motor, transmission, driveshafts, differential.
- Explained in:How a Car Works: The Big Picture
- Pressure cap
- A spring-loaded valve that keeps the sealed system above atmospheric pressure, raising the coolant's boiling point.
- Explained in:Engine Cooling System
- Primary balance
- Cancellation of inertial forces that vary once per crankshaft revolution.
- Explained in:Engine Layouts: Inline, V and Flat
Q
- Quality (fuel-quantity) load control
- Diesel power is set by how much fuel is injected into an unthrottled air charge, so the engine runs lean at part load.
- Explained in:Diesel Engines
R
- Ratio spread
- Lowest gear ratio divided by the highest: how wide a range of road speeds the gearbox covers for one engine speed.
spread = i_1st / i_top - Explained in:Gear Ratios and Torque Multiplication
- Ratios in series
- When gear pairs follow each other, their ratios multiply.
i_total = i_1 × i_2 × … - Explained in:Gear Ratios and Torque Multiplication
- Rectifier
- A diode bridge that converts the alternator's three-phase AC into DC.
- Explained in:Alternator and Charging
- Regenerative braking
- Using the motor as a generator to convert kinetic energy into stored electrical energy.
- Explained in:Hybrid and Electric Drives
- Ride rate
- The overall stiffness supporting the body: the suspension spring (at the wheel) and the tyre act in series.
k_ride = k × k_t / (k + k_t) - Explained in:Springs and Dampers
- Road load
- The forces resisting motion: aerodynamic drag, rolling resistance and gradient. Surplus tractive force accelerates the car.
- Explained in:How a Car Works: The Big Picture
- Road speed
- Engine speed divided by the overall ratio gives wheel speed; times the tyre's rolling circumference gives road speed.
v = 2π · r_w · n_engine / (60 · i_gear · i_final) - Explained in:Gear Ratios and Torque Multiplication
- Road-speed vs engine-speed symptoms
- Whether a noise or vibration follows road speed or engine speed points to the driveline/wheels or the engine respectively.
- Explained in:Diagnosing Warning Signs
- Rod angle
- How far the connecting rod leans from the cylinder axis.
sin φ = (r / l)·sin θ - Explained in:Pistons, Connecting Rods and the Crankshaft
- Rod ratio
- Rod length divided by crank radius. Lower ratios mean larger rod angles, more side thrust and more second-order vibration.
λ = l / r - Explained in:Pistons, Connecting Rods and the Crankshaft
S
- SAE grade (e.g. 5W-30)
- The W number rates cold performance; the second number is the viscosity class at 100 °C.
- Explained in:Lubrication System
- Secondary balance
- Cancellation of inertial forces at twice crank speed, caused by connecting-rod angularity. Inline-fours are unbalanced here.
- Explained in:Engine Layouts: Inline, V and Flat
- Severe service
- Shorter intervals for short trips, towing, dusty roads or long idling, which accelerate oil and component wear.
- Explained in:Routine Maintenance
- Slider-crank piston position
- Distance from the crank axis to the wrist pin for crank radius r, rod length l and crank angle θ.
x = r·cosθ + √(l² − r²·sin²θ) - Explained in:Pistons, Connecting Rods and the Crankshaft
- Slip angle
- Angle between the direction a wheel points and the direction it actually travels; it creates cornering force.
- Explained in:Tyres and Grip
- Slip heat
- Power lost as heat while slipping: the torque being passed on times the slip speed.
P_heat = T · (ω_engine − ω_disc) - Explained in:The Clutch
- Slip speed
- How much faster the flywheel turns than the clutch disc while the clutch is slipping.
Δn = n_engine − n_disc - Explained in:The Clutch
- Spring rate
- How much force it takes to compress a spring by a unit distance, usually quoted in N/mm.
F = k × x - Explained in:Springs and Dampers
- Sprung and unsprung mass
- Sprung mass is everything carried by the springs (body, engine, occupants). Unsprung mass moves with the road: wheel, tyre, hub, knuckle and brakes, plus part of the arms and springs.
- Explained in:Suspension Basics
- Steerability
- A tyre can only produce cornering force while it is rolling. Keeping the wheels turning is what lets an ABS-equipped car steer during an emergency stop.
- Explained in:Anti-lock Braking (ABS)
- Steering ratio
- Steering-wheel angle divided by the resulting road-wheel angle.
i_s = θ_wheel / δ_road - Explained in:Steering Systems
- Stoichiometric ratio
- The air-fuel mass ratio at which all fuel and all oxygen can react; about 14.7:1 for petrol.
AFR_stoich ≈ 14.7 - Explained in:Fuel Injection
- Stopping distance at the grip limit
- Once braking is limited by grip, the stopping distance depends on the friction the tyres achieve, so holding the tyres near peak grip stops the car shorter than sliding.
d ≈ v₀² / (2 μ g) - Explained in:Anti-lock Braking (ABS)
- Stopping time and distance
- At a steady deceleration the car stops in a time proportional to its speed and a distance proportional to its speed squared — double the speed, four times the braking distance.
t = v₀ / a, d = v₀² / (2a) - Explained in:Disc Brakes
- Stroke
- One piston trip between TDC and BDC — half a crankshaft revolution. The word also means the distance travelled, which is twice the crank throw.
S = 2r - Explained in:The Four-Stroke Cycle
- Suspension travel
- How far the wheel has moved relative to the body. Positive is bump (compression), negative is rebound (extension).
s = z_u − z_s - Explained in:Suspension Basics
- Swept volume (displacement)
- The volume the piston sweeps in one stroke. Multiply by the number of cylinders for engine capacity.
V_s = (π/4) · B² · S - Explained in:The Four-Stroke Cycle
- Synchroniser (synchromesh)
- A hub, sliding collar and friction cone ring that match a gear's speed to the shaft before dog teeth lock them together.
- Explained in:The Manual Gearbox
T
- Thermostat
- A temperature-operated valve that holds the engine at its design temperature by controlling flow to the radiator.
- Explained in:Engine Cooling System
- Time per crank degree
- At N rpm the crank turns 6N degrees per second, so an advance of Δθ degrees is this many seconds.
t = Δθ / (6·N) - Explained in:Spark Ignition and Combustion Timing
- Toe
- The angle of the wheels relative to the car's centreline viewed from above; small amounts strongly affect stability and tyre wear.
- Explained in:Steering Systems
- Top and bottom dead centre (TDC / BDC)
- The highest and lowest points of the piston's travel, where it momentarily stops and reverses. Crank angles are usually measured from TDC.
- Explained in:The Four-Stroke Cycle
- Torque
- A twisting force about an axis, measured in newton-metres.
T = F × r - Explained in:Torque and Power
- Torque capacity
- The most torque the clutch can carry before it slips: friction coefficient times clamp load times mean facing radius times the number of friction faces.
T_c = μ · F · r_m · n (n = 2) - Explained in:The Clutch
- Torque converter
- A fluid coupling with a stator that lets the engine idle in gear and multiplies torque when the turbine is slower than the impeller.
- Explained in:Automatic Transmission
- Torsional stiffness
- Torque needed to twist the body by one degree between front and rear axles.
- Explained in:Chassis Construction
- Tractive force
- The forward push the driven tyres exert on the road.
F = T_wheel / r - Explained in:How a Car Works: The Big Picture
- Transaxle
- A gearbox and differential combined in one housing, standard in front-drive cars.
- Explained in:Drivetrain Layouts
- Tyre load
- The vertical force between tyre and road. The tyre behaves as a stiff spring that can push but not pull, so its load drops to zero when the wheel lifts off.
F_t = k_t × (z_r − z_u + δ_static), F_t ≥ 0 - Explained in:Suspension Basics
V
- Valve lift
- How far the valve moves off its seat. Flow area grows with lift until the port itself becomes the restriction.
- Explained in:Valves, Camshafts and Valve Timing
- Valve overlap
- The crank angle during which both valves are open together, around exhaust/intake TDC.
overlap = IVO (° BTDC) + EVC (° ATDC) - Explained in:Valves, Camshafts and Valve Timing
- Valve states
- Each wheel circuit in the modulator has an inlet and an outlet valve. Hold traps the pressure, release lets some out, reapply lets it back in.
hold → release → hold → reapply - Explained in:Anti-lock Braking (ABS)
- Viscosity
- A fluid's resistance to flow. It falls sharply as oil warms, so grades specify behaviour both cold and hot.
- Explained in:Lubrication System
- Voltage regulator
- Controls rotor field current to hold the system voltage at its setpoint.
- Explained in:Alternator and Charging
W
- Warning-light colours
- Red: stop safely and investigate. Amber/yellow: attention needed soon. Green/blue: information only.
- Explained in:Diagnosing Warning Signs
- Wheel hop
- The unsprung mass bouncing between the suspension spring and the tyre. If it is poorly damped the tyre repeatedly unloads and can leave the road.
f_hop ≈ (1 / 2π) × √((k + k_t) / m_u) - Explained in:Springs and Dampers
- Wheel slip
- How much slower the tyre’s surface is moving than the road beneath it, as a fraction of vehicle speed. 0 % is free rolling; 100 % is a locked, sliding wheel.
s = (v − ωr) / v - Explained in:Anti-lock Braking (ABS)
- Wheel torque
- Engine torque multiplied by the overall gearing, less driveline losses.
T_wheel = T_engine × i_gear × i_final × η - Explained in:Torque and Power
- Whichever comes first
- Service items have both a distance and a time limit because fluids and rubber age even when a car is little used.
- Explained in:Routine Maintenance