Gearbox Simulator
5-Speed Synchromesh • Clutch • Countershaft • Reverse Idler — Simulate • Explore • Practice • Quiz
Layshaft layout: Every forward gear routes power through a common input pinion (Zin=18) meshed with the layshaft primary gear (Zlay0=28), giving a constant primary reduction of 1.556:1. The selected layshaft gear then meshes with its mainshaft gear, and a synchro collar locks that gear to the mainshaft. Reverse inserts an idler on a third axis to flip the output direction.
Centre-distance constraint: the mainshaft and layshaft are rigid parallel shafts, so their axes sit a fixed distance apart. With a single module that forces Zc + Zm = 46 for every forward pair and the primary. Reverse is exempt because its idler rides a third shaft off that plane. Fourth gear (Zc=28, Zm=18) exactly mirrors the primary pair, so its two stage ratios cancel and i = 1.000 — direct drive.
1 Overview
The Gearbox Simulator visualises a working 5-speed synchromesh manual transmission with a fully functional clutch, an animated countershaft (layshaft) gear train, and a reverse-idler gear. You can watch the input shaft from the clutch drive the countershaft, and see the currently selected gear pair on the mainshaft output.
The physics is derived directly from tooth counts and follows the classic textbook approach in Khurmi & Gupta Theory of Machines and Heisler Advanced Vehicle Technology: the overall gearbox ratio i is the product of the primary countershaft reduction and the individual pair ratio, and torque is multiplied by i with a fixed efficiency η per stage.
2 Getting Started
The simulator opens in Simulate mode in neutral. To begin:
- Set an Engine RPM with the slider (idle 800 — redline 7000).
- Set Throttle to change engine output torque. The torque curve peaks near 4500 rpm.
- Press the Clutch Pedal to decouple the input shaft from the flywheel: at 0% the clutch is fully engaged, above 5% the friction disc starts slipping, above 95% it is fully disengaged.
- Pick a Gear from R, N, 1–5. In neutral no dog-clutch is engaged and the output shaft stops. In reverse an idler is inserted between the countershaft and the mainshaft.
3 Simulate Mode
The canvas opens in the Real view: a sectioned gearbox on a workshop stand, with the clutch in its bellhousing, bearings in the case walls, shift forks and selector rails, the gear lever and the speedometer drive. Parts are painted by what turns together: input green, layshaft vermillion, freewheeling gears blue, output amber, selector violet and the reverse idler lime, with a colour key on the canvas. The small end view shows the idler, which sits behind the cutting plane. Use the Real / Schematic toggle at the top right for the colour-coded teaching diagram.
In the Schematic view the gearbox is laid out like a workshop schematic. The green input shaft enters from the left through the clutch; the yellow output shaft leaves to the right on the same axis. The red layshaft runs below — all its gears are keyed, so they turn together at one speed. The blue mainshaft gears are permanently meshed with their layshaft partners but freewheel on bushes, so they all spin all the time. Three purple synchro collars, moved by the shift-fork rail above, each serve two gears: 1↔2, 3↔4 and 5↔R.
- Input RPM equals engine RPM when the clutch is engaged, and 0 rpm when fully disengaged.
- Output RPM = input RPM ÷ gearbox ratio. In neutral every gear still turns but no collar is engaged, so the output shaft is stationary.
- Output Torque = input torque × gearbox ratio × η (0.96 for the two forward meshes; 0.94 in reverse, which adds the idler).
- Wheel Torque = gearbox output × the fixed 4.21:1 final drive. The final drive is treated as lossless, matching the worked examples.
Ratios: 1st 3.556 · 2nd 2.022 · 3rd 1.307 · 4th 1.000 (direct drive) · 5th 0.830 (overdrive) · R −3.590.
3a The 3D Gearbox
Switch View to 3D above the canvas (it opens in 3D on a computer or tablet and in 2D on a phone; your choice is remembered). The 3D view is the same gearbox installed in a rear-wheel-drive car and cut open on the car’s centre line, with the cut faces painted red: the engine bolted to the bellhousing, the clutch inside it, the gearbox in the transmission tunnel under the floor, the propeller shaft leaving the output flange, and the gear lever coming up through the tunnel into an open gate in the console.
- Change gear with the lever. Drag the knob through the gate, or tap a number on the gate. The pattern is the standard H: 1st forward-left, 2nd back-left, 3rd forward, 4th back, 5th forward-right, reverse back-right. While you hold the lever the sleeve stops at its brass baulk ring; let go and the synchromesh does its work. The gear pills and the keys 1–5, R and N work too.
- Watch the shift. Every change plays seven stages, shown in a strip at the top: clutch down, out of gear, across the gate, to the baulk ring, synchronising, dogs engage, clutch up. The lever, the selector shaft, the rail, the fork and the sleeve move together; the engaged pair glows green and the baulk ring glows amber while it slips.
- Cameras. Auto follows each gear change; Overview, Gears, Synchro, Selector, Gate (the driver’s view of the lever), Clutch, Reverse and Under go to one place. Drag to turn the view, right-drag or Shift-drag to pan, pinch or Ctrl + scroll to zoom (a plain scroll moves the page), double-tap a part to close in on it.
- Display. Casing: Cutaway, X-ray (the castings as glass) or Closed. Colour: Shafts uses the 2D colours; Pairs gives each gear pair its own hue, deep on the layshaft (the driver) and light on the mainshaft (the driven gear). Labels names the parts; Power path lights only the parts carrying the engine’s torque.
- Tap any part to see its name, tooth count, job and live speed. A tapped gear lights its partner, so the two gears of a ratio are always found together.
4 Explore Mode
Explore mode presents structured educational content in two categories:
- Basics: gear ratio, the centre-distance rule (Zc+Zm is fixed), torque multiplication, direct drive, overdrive, and the final drive.
- Components: layshaft, constant mesh, synchro collar, synchromesh cone, shift fork & rail, reverse idler, and the single-plate dry clutch.
5 Practice & Quiz
Practice mode generates problems on gear ratios, torque multiplication, output RPM, wheel torque via final drive, and clutch torque capacity. Each problem is scored and comes with a fully worked solution.
Quiz mode presents 5 randomised multiple-choice and numeric questions covering the main concepts, with a summary card at the end.
6 Tips & Best Practices
- Press the clutch fully before selecting R. In a real car the reverse idler is not synchronised, so engaging it while the mainshaft is still turning is what makes reverse graunch.
- Watch what happens to output RPM as you climb from 1st to 5th: same input RPM, output RPM increases geometrically because the ratio drops. Wheel torque falls in the same proportion.
- Sit in Neutral and watch: every gear on both shafts is turning, but the yellow output shaft is dead still. That is the whole idea of a constant-mesh gearbox — the teeth never disengage, only the collar moves.
- 4th gear is exactly 1.000:1. Its pair (Zc=28, Zm=18) mirrors the primary pair (Zin=18, Zlay0=28), so the two stage ratios cancel algebraically. Output RPM equals input RPM.
- In 5th the ratio is 0.830 — an overdrive. Output RPM is now higher than input RPM. This is why cruising in top gear keeps the engine at low RPM and improves fuel economy.
- Try engaging a gear with the clutch pedal partly down (say 40%). Transmitted torque falls in proportion to pedal travel and the readout switches to “Slipping”. (The capacity formula Tc = nμFRm is taught in Explore and Practice; this MVP scales torque with the pedal rather than solving the friction model.) In a real car this is what generates the heat that boils clutches on hill starts.
- Reverse gives i = −3.590. The output torque and RPM read negative because the shaft is rotating backwards — watch the orange idler gear that causes it.
Understanding the Automobile Gearbox — Free Interactive Simulator
An automobile gearbox (transmission) sits between the engine and the drive wheels and provides a set of selectable gear ratios to match engine speed and torque to the demands of the road. Without a gearbox, the engine could only pull the car efficiently over a narrow speed band. Our interactive simulator visualises a working 5-speed synchromesh manual transmission with an animated countershaft (layshaft), a full clutch pedal, and live readouts of RPM and torque at every stage.
Gear Ratio and Torque Multiplication
For a countershaft transmission, each forward gear routes power through two meshes in series. The gearbox ratio is the product of both stage ratios: i = (Zcs/Zin) × (Zms/Zcs2). Output shaft speed is engine RPM divided by i, and output torque is engine torque multiplied by i and by the mesh efficiency η (typically 0.98 per mesh). A low gear like 1st has i ≈ 3, giving high torque at the wheels for launch; top gear (5th) has i < 1, an overdrive that lets the engine loaf at cruising speed.
Clutch, Synchromesh and Dog Engagement
The clutch is a controllable friction interface between the engine flywheel and the gearbox input shaft. Pressing the pedal lifts the pressure plate off the friction disc via the diaphragm spring, decoupling the engine from the transmission so the driver can select a new gear. Every forward gear is permanently in mesh with the countershaft (constant-mesh design), but only the dog clutch selected by the shift lever locks that gear to the mainshaft. A synchromesh unit — a small friction cone in front of the dog teeth — matches the sleeve speed to the target gear before the teeth engage, which is what eliminates the double-declutching skill needed on older gearboxes.
Reverse and the Final Drive
Reverse gear inserts an extra idler between the layshaft reverse pinion and the mainshaft reverse gear. A forward gear passes through two meshes — input to layshaft, then layshaft to mainshaft — so the output already turns the same way as the engine. The idler makes it three meshes, and that odd number is what reverses the output shaft. Downstream of the gearbox, the final drive is a fixed reduction (typically 3.0:1 to 4.5:1) sitting in the differential; wheel torque equals gearbox output torque multiplied by the final-drive ratio.
Inside a 5-Speed Manual Gearbox — Parts and Layout
The simulator’s Real view is a sectioned rear-drive gearbox on a workshop stand, the way a training cutaway is displayed. From the engine to the propshaft, these are the parts it shows and what each one does:
- Clutch, inside the bellhousing: a flywheel bolted to the crankshaft, a friction disc splined to the input shaft, and a pressure plate clamped by a diaphragm spring. A release bearing, pushed by a fork and a hydraulic slave cylinder, unclamps it.
- Input shaft: carries the input pinion (18 teeth here), which is permanently meshed with the layshaft.
- Layshaft (countershaft): one gear for every speed, all turning together, driven by the input pinion.
- Mainshaft (output shaft): on the same axis as the input shaft. Its speed gears run on needle rollers and spin freely until a synchro locks one of them.
- Synchro hubs and sleeves: each hub is splined to the mainshaft; its sleeve slides over a gear’s dog teeth to lock that gear. A brass baulk ring matches the speeds first.
- Shift forks and selector rails: one fork per sleeve, riding in a groove in the sleeve and clamped to its rail. Three rails serve 1–2, 3–4 and 5–R.
- Reverse idler: a gear on its own short shaft between the layshaft and the mainshaft reverse gear.
- Case, bearings and extension housing: ball and roller bearings in the case walls; the extension carries the gear lever, the speedometer drive worm and the output flange to the propshaft.
The parts are painted by what turns together: input green, layshaft vermillion, freewheeling gears blue, output amber, selector violet and the idler lime. In any gear the power path reads as a colour sequence: green, then vermillion, then one blue gear locked by an amber sleeve, then amber out.
The Gearbox in 3D: a Cutaway Inside the Car
The 3D view shows the same gearbox in its real place: bolted to the back of the engine, sitting in the transmission tunnel of a rear-wheel-drive car, with the gear lever coming up into the cabin. Car and gearbox are cut on the centre line, as a training cutaway is, and every part is drawn at true scale from the simulator’s own numbers. Every gear is a generated involute tooth form (20° pressure angle) on one module of 3.04 mm, which is what a 70 mm centre distance and Zc + Zm = 46 require. The forward gears are helical (14°), cut in opposite hands on the two shafts so that they mesh along the whole face; the gears are timed from the layshaft so that their teeth interlock in every frame.
Three details show the engineering a flat drawing hides. The reverse gears cannot share a plane: their teeth add up to 43, not 46, so in one plane their tip circles would overlap by 1.5 mm; the layshaft reverse gear sits one face width forward and a wide idler meshes both. (Reverse in this gearbox is constant-mesh and synchronised like the forward gears; many gearboxes slide an unsynchronised idler into mesh instead.) The lever pivots on a ball, and its lower end turns a transverse selector shaft whose finger moves the rails: two levers in series, so the knob moves a rail the same way and 1st sits forward-left in the standard H. And the selector finger can cross from one rail to the next only when every rail is in neutral, which is the gearbox interlock: two gears can never be engaged at once.
How a Synchromesh Gear Change Works, Step by Step
Select a new gear in the simulator and the shift plays in the same six stages a real synchromesh gearbox goes through:
- Declutch — the pedal goes down and the clutch disengages, so no torque reaches the gearbox.
- Select — the fork slides the sleeve off the old gear, through neutral.
- Cone — the brass baulk ring touches the friction cone on the target gear.
- Synchro — friction drags the gear to the sleeve’s speed; until it does, the baulk ring blocks the sleeve.
- Dog — the speeds match, the sleeve passes over the dog teeth and the gear is locked to the mainshaft.
- Drive — the pedal comes up, the clutch re-engages and torque flows through the new gear.
Learning to Drive a Manual? What the Clutch and Gears Do When You Shift
This is not a driving game: there is no road and no car to steer. It shows what happens inside the gearbox each time you work the clutch and the lever, which is the part a driving lesson cannot show you.
- The bite point is clutch slip. Between fully up and fully down, the disc slips against the flywheel. Move the Clutch Pedal slider between 5 % and 95 % and the clutch reads Slipping: input speed and torque fall together. Slip is how a car pulls away; holding it wears and heats the disc.
- Why you press the clutch to change gear. With the clutch engaged, the dog teeth are loaded by engine torque and cannot slide apart. Pressing the pedal unloads them.
- Why you pause in neutral. The baulk ring needs a moment to bring the next gear to the right speed. Forcing the lever faster than the synchro can work is what makes a gearbox crunch.
- Why reverse grinds. In most manual gearboxes the reverse gears are straight-cut and unsynchronised, so reverse should be selected with the car stopped.
- Why each gear feels different. At the same 3,000 rpm, 1st gives about 23 km/h and 5th about 100 km/h in this gearbox, while the torque at the wheels falls from about 1,440 to 335 N·m for every 100 N·m of engine torque (see the table below).
Gear Ratios of the Simulated 5-Speed Gearbox
Every forward gear passes through the primary pair first (28/18 = 1.556) and then its own pair. The final drive is 4.21:1 and the tyre rolling radius is 0.31 m (a 195/65 R15). Efficiency is 0.98 per mesh; reverse has three meshes. These are the numbers the simulator’s readouts use.
| Gear | Teeth (main / lay) | Pair ratio | Gearbox ratio | With final drive | Road speed at 3,000 rpm | Wheel torque per 100 N·m |
|---|---|---|---|---|---|---|
| 1st | 32 / 14 | 2.286 | 3.556 | 14.97 | 23.4 km/h | 1,438 N·m |
| 2nd | 26 / 20 | 1.300 | 2.022 | 8.51 | 41.2 km/h | 818 N·m |
| 3rd | 21 / 25 | 0.840 | 1.307 | 5.50 | 63.7 km/h | 528 N·m |
| 4th | 18 / 28 | 0.643 | 1.000 (direct) | 4.21 | 83.3 km/h | 404 N·m |
| 5th | 16 / 30 | 0.533 | 0.830 (overdrive) | 3.49 | 100.4 km/h | 335 N·m |
| Reverse | 30 / 13, via a 15-tooth idler | 2.308 | −3.590 | −15.11 | 23.2 km/h backwards | 1,422 N·m |
Gearbox Questions and Answers
In reverse gear, how many times is the direction of rotation reversed?
Three times. Every external gear mesh reverses the direction of rotation once, and reverse uses three meshes: the input pinion drives the layshaft, the layshaft reverse gear drives the idler, and the idler drives the mainshaft reverse gear. An odd number of reversals leaves the output shaft turning opposite to the engine. A forward gear uses two meshes, an even number, so the output turns the same way as the engine.
What moves the synchromesh sleeve in a manual gearbox?
A shift fork. Each fork sits in a groove around its synchro sleeve and is clamped to a selector rail (shift rod). Moving the gear lever across the gate chooses a rail; pushing it forward or back slides that rail, and the fork pushes the sleeve toward one gear or the other. An interlock stops two rails moving at once, so two gears can never be engaged together.
Is the output speed of a gearbox always lower than the input speed?
No. In the reduction gears (1st to 3rd in this gearbox) the output shaft turns slower than the engine and the torque is multiplied. 4th is direct drive at 1.000:1, so the output turns at engine speed. 5th is an overdrive at 0.830:1: at 3,000 rpm engine speed the output shaft turns at about 3,600 rpm, and the torque is reduced in the same proportion.
Why does a manual gearbox grind, or a synchro feel sticky?
Grinding is the dog teeth meeting before the gear and the sleeve are turning at the same speed. The usual causes are moving the lever faster than the synchro cone can match the speeds, a clutch that does not fully disengage (so the input shaft keeps driving the layshaft), worn brass baulk rings that no longer grip the cone, and the wrong or degraded gear oil, since the synchro works through friction in an oil film. Reverse is usually unsynchronised, which is why it grinds if selected while the car is still rolling.
What is double declutching?
A gear-change technique for gearboxes without synchromesh. Press the clutch, move the lever to neutral, release the clutch, adjust engine speed with the throttle so the layshaft gears turn at the speed the next gear needs, press the clutch again, select the gear and release. It does by hand what the synchromesh cone does automatically, which is why synchromesh made it unnecessary for everyday driving.
Can I practise driving a manual car with this simulator?
It is not a driving game: there is no road and no car to steer. It is a cutaway of the gearbox itself. Move the clutch pedal and select gears, and you can watch the clutch slip and release, the synchro shift in six stages and the power path change from gear to gear. Seeing why the clutch must be pressed, and what the synchro is doing during the pause in neutral, makes the pedal work of a manual car easier to understand.
Who Uses This Simulator?
This gearbox simulator is designed for automotive engineering students studying powertrains, mechanical engineering trainees learning gear-train kinematics, apprentice mechanics building intuition for clutch operation, and instructors teaching manual transmission fundamentals without needing a stripped gearbox in the workshop.
Explore Related Simulators
If you found this Gearbox simulator helpful, explore our Gear Train Calculator, Planetary Gear Simulator (how an automatic transmission makes its gears), Four-Stroke Engine simulator (what drives the clutch), Clutch System Simulator (how the clutch itself is sized and why it slips on take-up), Gear Strength calculator (Lewis and AGMA tooth stress), Belt & Chain Drive simulator, Cam & Follower Mechanism, Centrifugal Governor, and Flywheel Energy Storage for more hands-on mechanical engineering practice. Every gear in a gearbox obeys the same tooth-count rule, and the gear train simulator lets you mesh simple, idler, compound and worm trains one stage at a time to see where each ratio comes from.
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