Gearbox Simulator
5-Speed Synchromesh • Clutch • Countershaft • Reverse Idler — Simulate • Explore • Practice • Quiz
Live Formulas
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 pair, including the primary. 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 shows the gearbox in cutaway side elevation, laid out exactly 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 multiplies the gearbox output by the fixed 4.21:1 final-drive ratio.
Ratios: 1st 3.556 · 2nd 2.022 · 3rd 1.307 · 4th 1.000 (direct drive) · 5th 0.830 (overdrive) · R −3.590.
4 Explore Mode
Explore mode presents structured educational content in two categories:
- Basics: covers gear ratio, torque multiplication, meshing kinematics (v = ωr at the pitch point), efficiency cascade, and the final drive.
- Components: countershaft, synchronizer cone, dog clutch, reverse idler, single-plate dry clutch, diaphragm spring.
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
- Set the clutch pedal to 100% before pressing R after driving forward — otherwise the fault chip will complain that the sleeve is grinding.
- 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%). Output torque is limited by clutch capacity rather than by the engine, and the readout switches to “Slipping”. 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 countershaft reverse pinion and the mainshaft reverse gear. Because a forward gear pair already reverses direction once, the extra idler flips it back to opposite — the output shaft now spins backwards, and the car drives in reverse. 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.
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
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