Interactive teardown
A car is seven machines
working on the same problem.
Burn a controlled explosion a few thousand times a minute, turn it into rotation, choose how much of that rotation to trade for push, point the result where you want to go — and be able to stop. Every model below runs on the same geometry and physics the real parts do: drag the steering wheel and the tie rods solve for themselves; soften the dampers and the tyre really does leave the road.
Anatomy of a car
A rear-wheel-drive layout, cut open. Everything highlighted is a system with its own section further down.
Almost every car ever built is the same chain of conversions. Chemical energy in the tank becomes heat in a cylinder; heat becomes pressure; pressure becomes a push on a piston; the crankshaft turns that push into rotation; the gearbox and final drive trade rotation speed for torque; and the tyres turn torque into a shove against the road. Roughly a quarter of the fuel's energy reaches the wheels. Most of the rest leaves as heat, which is why the cooling system is as big as it is.
The layout drawn here — engine at the front, gearbox behind it, a propshaft down the middle to a driven rear axle — is the classic one. Most small cars today put the engine sideways at the front and drive the front wheels, which deletes the propshaft and moves the differential inside the gearbox, but every part below still exists and still does the same job.
The four-stroke engine
One cylinder, two crankshaft turns, four jobs. Scrub the crank angle to freeze any moment of it.
Why two turns, not one
A cylinder can only do one thing at a time, and it has four things to do: breathe in, squeeze, burn, breathe out. That needs four piston strokes, and a piston makes two strokes per crankshaft revolution — so the full cycle takes 720° of crank. The camshaft that opens the valves therefore turns at exactly half engine speed. Watch the two cam lobes: each one comes round once for every two turns of the crank.
The spark comes early
Ignition fires at about 20° before top dead centre, while the piston is still coming up. Flame takes real time to cross the chamber — a millisecond or two — and at 3 000 rpm the crank moves 18° in a millisecond. Light it at the top and peak pressure would arrive too late to be useful. Light it early and peak pressure lands just after top dead centre, where the crank has the leverage to use it.
Compression is the whole trick
Squeezing the mixture into about a tenth of its volume before lighting it raises both the temperature and the pressure the burn starts from, and that is where most of an engine's efficiency comes from. The limit is knock: squeeze too hard and the mixture detonates on its own before the spark, which hammers the piston. That limit is what petrol's octane rating measures, and why a diesel — which compresses air alone and injects fuel at the top — can run at twice the compression ratio and be markedly more efficient.
Reading the loop
The pressure-volume chart in the panel is the cycle's report card. The area enclosed by the loop is the work done on the piston each cycle. Anything that makes the loop taller or fatter — more air, more compression, better burning — makes more power from the same engine.
From crankshaft to tarmac
Clutch, gearbox, propshaft, final drive, differential. Try pulling away in 5th — the engine will stall, and the reason is visible.
An engine has a narrow useful range
A petrol engine makes nothing below about 800 rpm and comes apart above about 7 000. Between those it is genuinely useful over maybe a 3 000 rpm band. A car, meanwhile, has to work from walking pace to motorway speed — roughly a 30:1 range. The gearbox exists to bridge the gap. Each gear is a lever: reduce the speed by a factor and you multiply the torque by the same factor, minus a few percent lost as heat in the teeth.
The clutch is a deliberate slip
At rest the wheels turn at zero and the engine cannot. Something has to absorb the difference, and that something is a friction plate squeezed between the flywheel and the pressure plate. Pull away too fast and you stall; slip it too long and you burn it. Watch the "clutch" readout: while it says slipping, the difference between the two speeds is being converted straight into heat.
Constant mesh, not sliding gears
The gears in a modern box never move apart. Every pair is permanently engaged and turning; what changes is which output gear is locked to the output shaft, by a sliding collar with a small cone clutch — the synchromesh — that first matches the speeds. The animation shows the selected pair changing size because that is what changing ratio means, even though in the real box the other four pairs are still spinning alongside.
The differential's trick
In a corner the outer wheel travels further than the inner one. Lock them together and one has to scrub. The differential lets them differ while still splitting the torque: the crown wheel always turns at the average of the two wheel speeds. Use the cornering control and watch the left and right readings separate while the crown wheel carries on unchanged.
Turning speed into heat
Braking is a heat transfer problem wearing a safety hat. Switch ABS off on snow and hold the pedal down.
Why hydraulics
Brake fluid does not compress, so a small piston pushed a long way at the pedal becomes a large piston pushed a short way at the caliper, with the force multiplied by the ratio of their areas. That is Pascal's principle doing the work of a very long mechanical linkage, around corners, through a flexible hose, to all four corners of the car at once. A leak or a bubble of air breaks the chain instantly — air does compress — which is why brake systems are split into two independent circuits.
Where the energy goes
A 1 400 kg car at 100 km/h carries about 540 kJ of kinetic energy. Stopping it in four seconds means shifting roughly 135 kW into the discs — the output of a decent engine, running backwards, into four lumps of cast iron. That is the real reason discs are vented and drilled: not grip, but surface area.
The slip curve
A tyre grips best when it is slipping slightly — about 10 to 15 % — not when it is rolling perfectly and not when it is sliding. Past the peak, grip falls away. A locked wheel sits at 100 % slip, gives up roughly a third of its available grip, and steers nowhere at all, because a sliding tyre cannot tell one direction from another.
What ABS actually does
It does not brake for you. It reads each wheel's speed, notices one about to fall off the peak of the slip curve, and releases that circuit's pressure for a few milliseconds — up to about fifteen times a second. The pulsing you feel through the pedal is the pump putting the pressure back. Its biggest contribution is not usually distance: it is that a rolling wheel still steers.
Rack, pinion and Ackermann
Drag the steering wheel. The two road-wheel angles are not scripted — they are solved from the linkage.
A gear that unrolls
A rack is a gear with an infinite radius. The pinion on the end of the steering column meshes with its teeth, so turning the column slides the rack sideways, and the rack pushes one tie rod while pulling the other. It is about as direct as a mechanism gets — which is exactly why it replaced the older recirculating-ball boxes in almost every car.
Under three turns, lock to lock
The steering ratio is how many degrees of steering wheel buy one degree of road wheel: typically 14:1 to 20:1. It is a deliberate trade. A quicker rack is more responsive and heavier in your hands; a slower one is calmer and needs more winding in a car park. Note in the readouts that the ratio is not constant — the linkage's geometry changes as it moves, and it goes slower near full lock as the tie rod and steering arm approach a straight line.
The inner wheel turns more
In a turn, both front wheels circle the same centre point, which sits on the line of the rear axle. The inner wheel is on a tighter circle, so it must be steered further — around 3 to 5° more at full lock. Turn both wheels the same amount and one of them is being dragged sideways across the tarmac, which scrubs tyres and squeals in car parks.
Geometry instead of cleverness
Rudolf Ackermann's patent of 1818 solves this with no moving parts at all: angle the steering arms so that lines drawn through them meet at the centre of the rear axle, and the difference appears by itself. Switch the toggle off to straighten the arms and watch the Ackermann error climb — that number is a tyre being scrubbed.
Keeping the tyres on the road
A real two-mass model, integrated a thousand times a second. Fit worn dampers and watch the tyre load hit zero.
Comfort is the side effect
A suspension's real job is keeping a constant, useful load on each tyre. A tyre can only generate grip in proportion to what is pressing it down, so every moment the load goes light is a moment the car cannot accelerate, brake or steer as hard. Ride comfort is a very welcome by-product of doing that well.
Two masses, not one
The body — the sprung mass — floats on the springs at about 1 to 1.5 Hz, which happens to be roughly walking pace and is the frequency humans find least sickening. The wheel, hub and brake — the unsprung mass — bounce on the tyre's own springiness at around 12 Hz. They are almost independent problems, and a damper has to handle both. It is also why engineers fight so hard to cut unsprung weight: a light wheel can follow a bump the body never needs to feel.
The damper is not a spring
A spring stores energy and gives every bit of it back; left alone the body would oscillate for a long time. A damper resists velocity, not displacement, by pushing oil through small holes, and turns that energy into heat. The damping ratio ζ is the dial: near 0 the body floats and never settles, near 1 the suspension is so stiff in motion that the wheel is slammed into every bump. Road cars sit around 0.25 to 0.35.
Watch for zero
Set "worn dampers" and pick the washboard road at around 50 km/h. The wheel hits its own resonance, the tyre load reading dives, and every time it reaches zero the wheel is briefly airborne — carrying no braking, no cornering and no drive at all.
Getting rid of the heat
Block the radiator, sit in traffic on a hot day, and see how long the thermostat can hold the line.
A third out of the exhaust, a third into the coolant
Of the energy in the fuel, roughly a quarter to a third reaches the wheels. About a third leaves with the exhaust gas, and most of the remainder has to be carried away by the coolant — tens of kilowatts of it under load. The water pump moves it, the radiator hands it to the air, and the fan stands in for airflow when the car is not moving.
The thermostat stops it working too well
A radiator sized for a hard climb on a hot day would keep the engine far too cold the rest of the time. A cold engine has thick oil, poor fuel vaporisation, more bore wear and worse emissions, so the thermostat holds the coolant in a short bypass loop until it reaches about 85 °C, then opens progressively to let it through the radiator. Cold-start the model and watch the bypass carry everything until the thermostat cracks open.
Why it is pressurised
The cap holds the system at around 1 bar above atmospheric, which lifts the boiling point of the coolant from about 108 °C to roughly 125 °C. That margin is what lets an engine sit at 95 °C without any risk of local boiling around the hottest parts of the head. It is also why opening the cap on a hot engine is dangerous: dropping the pressure lets the whole system flash to steam at once.
Feedback, not control
Nothing in this loop is commanded. The thermostat is a wax pellet that expands when hot. The fan is a switch with hysteresis. The system finds its own equilibrium, and when you take a piece of it away — block the core, stop the car, load the engine — the temperature simply climbs until something else gives.
Starting, charging, burning
Hold the crank button. Then flatten the battery and try again — it will turn, just not fast enough.
The chicken-and-egg problem
An engine cannot start itself: it needs to already be turning before combustion can keep it turning. The starter motor solves that by throwing a small pinion into the flywheel's ring gear and spinning the crankshaft to about 200 rpm — enough for the cylinders to draw in a charge, compress it and fire. It draws 150 to 200 amps to do it, which is why the battery cable is as thick as your finger and why the lights dim while you crank.
The battery is a starter battery
Once running, the engine drives an alternator through a belt, and the alternator supplies everything: ignition, injectors, lights, fans, the lot — plus whatever it takes to put the cranking charge back. Its regulator holds the system at about 14.2 V, comfortably above the battery's own 12.6 V, which is what makes charge flow back in.
Spark and fuel, timed together
The coil is a transformer that turns 12 V into tens of thousands, which is what it takes to jump the plug gap in a cylinder full of compressed mixture. The injector opens for a few milliseconds at a time. Both events are timed against crankshaft position, and both move with load and speed — the engine management adjusting ignition timing degree by degree, cycle by cycle.
Why a flat battery still clicks
Below about 20 % charge there is enough energy to pull in the solenoid — that is the click — and usually enough to turn the engine slowly, but not enough to reach cranking speed. Compression leaks past the rings faster than a slow crank can build it, so the cylinder never reaches firing pressure. Turn the charge down and hold the button to watch exactly that happen.
One machine after all
Every one of these systems exists to serve the tyres. The engine supplies torque, the gearbox makes it the right size, the differential lets both driven wheels use it, the steering aims the contact patches, the suspension keeps them loaded, the brakes take it all away again, and the cooling and electrical systems exist so the rest can keep running. Change any one of them and the others have to be re-thought — which is why a car ends up feeling like a single design decision repeated in seven different materials.