A Going Train is the gear chain inside a clock or watch that carries power from the mainspring or weight down to the escapement. Its central component is the centre wheel, which turns once per hour and drives the minute hand directly while passing power onward through the third wheel to the escape wheel. The Going Train's job is to step the slow, high-torque input from the power source up to the fast, low-torque rotation the escapement needs. A typical mechanical wristwatch Going Train spans a 4,000:1 ratio between barrel and escape wheel.
Operating Principle of the Going Train
The Going Train, also called the Clock Train in older horology texts, works by stepping rotation up through 3 to 4 successive wheel-and-pinion pairs. The mainspring barrel turns slowly — roughly once every 6 to 8 hours in a wristwatch — but it carries enormous torque. The escape wheel at the far end of the train needs to spin much faster, typically 6 to 10 revolutions per minute, but with very little torque demand. Each wheel meshes with the pinion of the next arbor down the line, and because pinions carry far fewer teeth than wheels (usually 6, 7, 8, or 10 leaves against 60 to 80 wheel teeth), each stage multiplies speed by roughly 8x to 12x.
The geometry is unforgiving. If a pinion has 8 leaves and a meshing wheel has 64 teeth, the centre distance must hold to within about ±0.02 mm or the depthing goes wrong — too deep and the train binds under load, too shallow and the teeth skip when the mainspring is fully wound and torque peaks. You will see this on the bench as a clock that runs fine at half-wind but stops dead at full wind, or a watch that gains 30 seconds a day when fully wound and loses 60 seconds a day near the end of the power reserve. That last symptom is what watchmakers call poor isochronism, and a worn or badly depthed Going Train is one of its most common causes.
The other failure mode you will run into is pivot wear. Each arbor rides in jewelled or brass bearings, and as those pivots wear oval, the wheel drops slightly, the depthing changes, and tooth-to-leaf engagement becomes inconsistent. A movement that has run 20 years without service usually shows pivot wear on the third and fourth wheels first, because they spin fastest under load.
Key Components
- Mainspring Barrel (Great Wheel): Stores energy and acts as the first wheel of the Going Train. In a typical wristwatch the barrel turns once every 6 to 8 hours and carries 60 to 80 teeth driving the centre wheel pinion. Barrel torque variation between fully wound and run-down is typically 30 to 40 percent — the source of most isochronism error.
- Centre Wheel: Mounted on the centre arbor, this wheel turns exactly once per hour and carries the minute hand directly on its extended pivot. It usually has 64 to 80 teeth meshing with the third wheel pinion. Its rotation rate is the timekeeping reference for the dial side of the movement.
- Third Wheel: An intermediate step-up stage between centre and fourth wheels. Typically 60 to 75 teeth on the wheel, 8 to 10 leaves on the pinion, giving roughly an 8:1 ratio. It carries no hand and exists purely to bridge the gear-ratio gap.
- Fourth Wheel: Turns once per minute in most wristwatches, which is why the small seconds hand sits on its arbor in classical layouts. In a centre-seconds movement the fourth wheel sits off-axis and an indirect drive carries the seconds hand to the dial centre. Pinion typically 8 leaves.
- Escape Wheel: The last wheel of the Going Train and the input to the escapement. In a 28,800 vibration-per-hour wristwatch the escape wheel turns at roughly 6 RPM. Tooth count is locked to escapement design — typically 15 teeth for a Swiss lever, 20 for some chronometer-grade designs.
- Pinions: The small toothed members on each arbor that receive drive from the previous wheel. Pinion leaves are usually 6, 7, 8, or 10 — never higher in a Going Train because pinion-leaf count drives the step-up ratio. Tooth profile is typically a modified cycloidal form to maintain conjugate action through the entire mesh.
Where the Going Train Is Used
The Going Train is the backbone of every mechanical timekeeper ever built. Whether you call it the Going Train in a Swiss watchmaking school or the Clock Train in a 19th century English horology textbook, the same chain of wheels and pinions appears in everything from longcase clocks to marine chronometers to mechanical wristwatches. The architecture changes — number of stages, tooth counts, arbor layout — but the function is identical: step the slow, torquey input from a power source up to the fast, light rotation the escapement needs.
- Wristwatch movements: The ETA 2824-2 automatic movement uses a 4-wheel Going Train running at 28,800 vibrations per hour, with the fourth wheel turning once per minute and driving an indirect centre-seconds hand.
- Longcase clocks: An English 8-day longcase clock by Thomas Tompion uses a 3-wheel going train driven by a falling weight, with the centre wheel turning once per hour and the escape wheel matching a 1-second pendulum at 30 RPM.
- Marine chronometers: The Mercer Mk II marine chronometer uses a fusee-driven Going Train to flatten mainspring torque variation and hold rate to within ±0.5 seconds per day across the power reserve.
- Tower clocks: The Great Clock at the Palace of Westminster (Big Ben) uses a heavy-gauge Going Train with cast-iron wheels driving a double three-legged gravity escapement, isolating timekeeping from the drag of the striking work.
- Carriage clocks: A French 19th-century carriage clock by Drocourt uses a compact Going Train laid out horizontally between two plates, with a platform escapement mounted on top of the movement.
- Quartz hybrid movements: The Seiko Spring Drive replaces the escape wheel with an electromagnetic glide brake, but retains a conventional Going Train from mainspring to fourth wheel — the wheel-and-pinion stages are mechanically identical to a fully mechanical caliber.
The Formula Behind the Going Train
The fundamental Going Train calculation determines the overall ratio between the mainspring barrel and the escape wheel. This sets how fast the escapement runs for a given barrel rotation, which in turn determines power reserve and beat rate. At the low end of typical practice you will see ratios around 1,500:1 in slow-beat longcase clocks where the barrel turns rarely and the escape wheel runs at 30 RPM. At the high end, modern high-beat wristwatches hit 4,500:1 because the escape wheel runs at 8 to 10 RPM while the barrel still only turns once every 6 to 8 hours. The sweet spot for a robust commercial wristwatch sits around 3,500 to 4,000:1 — enough step-up to give 6 RPM at the escape wheel from a daily-wind barrel, but not so steep that pinion-leaf stress becomes a service-life problem.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Rtotal | Overall step-up ratio of the Going Train from barrel to escape wheel | dimensionless | dimensionless |
| Tn | Tooth count of the nth driving wheel (barrel, centre, third, fourth) | teeth | teeth |
| Pn | Leaf count of the nth driven pinion | leaves | leaves |
| fesc | Rotational frequency of the escape wheel | rev/s | RPM |
| fbar | Rotational frequency of the mainspring barrel | rev/s | RPM |
Going Train Interactive Calculator
Vary the wheel-and-pinion stage ratios and centre wheel rate to see the total train ratio, fourth wheel speed, escape wheel speed, and barrel period.
Equation Used
The total going-train ratio is the product of the four wheel-and-pinion stage ratios. With the centre wheel turning once per hour, the fourth wheel and escape wheel speeds are found by multiplying by the downstream stage ratios and converting rev/hr to rpm.
- Each stage ratio is wheel teeth divided by driven pinion leaves.
- Centre wheel speed is entered in revolutions per hour.
- Losses, friction, backlash, and escapement load are not included.
- Adjacent gears reverse direction, but only speed magnitude is reported.
Worked Example: Going Train in a chiming bracket clock movement
Specifying the Going Train for a quarter-chiming English bracket clock with a half-second pendulum. The mainspring barrel is sized to turn once every 12 hours at nominal wind, the escape wheel must turn at exactly 7.5 RPM to match a 30-tooth dead-beat escape wheel ticking twice per second, and you have 4 wheel-and-pinion stages between barrel and escape wheel. Tooth counts: barrel 96, centre wheel 80, third wheel 75, fourth wheel 70. Pinion leaves: centre 8, third 10, fourth 10, escape 7.
Given
- Tbarrel = 96 teeth
- Tcentre = 80 teeth
- Tthird = 75 teeth
- Tfourth = 70 teeth
- Pcentre = 8 leaves
- Pthird = 10 leaves
- Pfourth = 10 leaves
- Pescape = 7 leaves
- fbar = 1 rev per 12 hours rev/h
Solution
Step 1 — compute each stage ratio individually:
r2 = 80 / 10 = 8.0
r3 = 75 / 10 = 7.5
r4 = 70 / 7 = 10.0
Step 2 — multiply the stages together to get the total step-up at the nominal operating point:
Step 3 — use the barrel rate to find the nominal escape-wheel rate. Barrel turns once per 12 hours, which is 1/720 RPM:
That overshoots the target of 7.5 RPM, so the train as specified is too steep. To hit 7.5 RPM exactly you need Rtotal = 5,400 — drop the third-wheel ratio from 7.5 to 5.625 by changing the third pinion from 10 leaves to a wheel/pinion pair giving the right number, or reduce the fourth-stage ratio.
Now examine the operating range. At the low end of the typical bracket-clock barrel rate — barrel slowing near end of run, say 1 rev per 14 hours due to friction load — the escape wheel drops to roughly 8.6 RPM with the original train, and the pendulum loses amplitude. At the high end — fully wound, barrel running 1 rev per 11 hours under peak torque — the escape wheel hits about 10.9 RPM and the pendulum overswings, banking against the crutch. The sweet spot is the corrected Rtotal = 5,400 driving 7.5 RPM, which holds the escapement in its design amplitude band of roughly 4 to 6 degrees swing on either side of vertical.
Result
The nominal Going Train ratio as specified is 7,200:1, giving an escape wheel speed of 10 RPM — too fast for a half-second pendulum and a sign the tooth-count selection needs revising to 5,400:1. Across the realistic barrel-rate range you would see escape wheel speeds from 8.6 RPM (run-down, sluggish) to 10.9 RPM (full wind, overbanking), a 27 percent swing that is far too wide for a clock expected to hold a few seconds per week. If your measured escape wheel rate sits 5 to 10 percent off prediction, the most likely causes are: (1) wheel tooth count miscounted by one — easy to do on a 75-tooth wheel under a loupe, and a single tooth changes the ratio by 1.3 percent, (2) pinion leaves chipped or burred from a previous service, dropping effective leaf engagement and causing the train to skip rather than mesh smoothly, or (3) excessive end-shake on the third arbor letting the wheel walk axially and disengage partial tooth contact at low torque.
Going Train vs Alternatives
The Going Train is one architectural choice among several for transmitting power to a regulating element. Compared to alternatives like a Clock Train using a fusee, or a fully electronic stepper-driven hand setup, the conventional Going Train sits at a particular point on the cost, accuracy, and longevity curve. Here is how it stacks up against the two most common alternatives a designer or restorer actually evaluates:
| Property | Going Train (conventional) | Fusee-equipped Going Train | Quartz stepper motor drive |
|---|---|---|---|
| Daily rate accuracy (typical) | ±5 to ±15 sec/day | ±0.5 to ±2 sec/day | ±0.5 sec/month |
| Escape wheel speed range | 6 to 30 RPM | 6 to 30 RPM | Not applicable (direct stepper drive) |
| Manufacturing cost (relative) | 1.0× | 3 to 5× | 0.05 to 0.1× |
| Service interval | 5 to 7 years | 8 to 10 years | Battery only, ~2 years |
| Service life (with maintenance) | 100+ years | 200+ years (Tompion clocks still run) | 20 to 30 years (PCB life) |
| Isochronism (rate variation across power reserve) | Poor — 30 to 40% torque swing | Excellent — fusee flattens torque | Perfect — constant electronic drive |
| Repairability by trained watchmaker | Excellent — standard parts | Excellent but specialist | Poor — IC-dependent |
Frequently Asked Questions About Going Train
That symptom is poor isochronism, and it is almost always a balance-spring or escapement issue rather than the Going Train itself — provided the train is actually clean and properly depthed. The mainspring delivers 30 to 40 percent more torque fully wound than near run-down. A correctly designed regulator (balance + hairspring, or pendulum) should be largely indifferent to torque, but a hairspring with poor terminal curves or an unequal-arm balance amplifies the torque variation into a rate variation.
Quick diagnostic: time the watch on a timegrapher at full wind and again at 24 hours into the run. If the rate spread is more than 8 seconds per day, suspect the hairspring before the train. If the spread is under 4 seconds per day but the rate is still wandering, that is when you start looking at train pivots and depthing.
This is a cost-versus-result decision. A fusee is mechanically the cleanest way to flatten mainspring torque — it is why every marine chronometer used one — but it adds 3 to 5× to the manufacturing cost, eats space inside the movement, and demands a chain or gut line that itself becomes a service item.
Refining tooth profile (cycloidal correction, polished pinion leaves, optimised depthing) buys you maybe 20 to 30 percent rate-stability improvement for a fraction of the cost. If you need to hold under ±2 seconds per day across the entire power reserve, the fusee is unavoidable. If you can live with ±5 seconds per day, refine the train geometry and tune the hairspring instead.
Going Train ratio sets where the hands point relative to escape wheel rotation — not the absolute timekeeping rate. Absolute rate comes from the regulator: pendulum length in a clock, or balance/hairspring in a watch. A 4 minute per day error (about 0.3 percent fast) is far too large to be a train depthing issue and points directly at the regulator.
In a wristwatch, slide the regulator pin toward the slow mark. If you are already at the limit, the hairspring is probably magnetised — demagnetise it first, that fixes maybe 60 percent of mystery fast-running cases. In a clock, lengthen the pendulum: 4 minutes per day on a half-second pendulum means about 1 mm of length adjustment.
The train freewheels under almost no load, so it can hide problems that only show up when the escapement loads it. The most common cause is a tight mesh somewhere — usually pinion leaves that are not properly polished, so they grab when they have to transmit real torque. The second most common is a bent pivot you cannot see by eye but that catches the bearing under axial load.
Diagnostic: pull the escapement back off, give the barrel half a turn, and watch the train spin down. A healthy train should coast for 10 to 15 seconds and the fourth wheel should reverse direction once or twice as it stops. If it stops dead in 2 seconds, you have a tight mesh or a bad pivot somewhere — work back from the escape wheel one stage at a time.
Three wheels minimum if your barrel turns slowly enough — typical of weight-driven longcase clocks where the barrel turns once a day or less. Four wheels is standard for spring-driven watches and clocks where the barrel turns every 6 to 12 hours. Five wheels appears in long-power-reserve movements (8-day watches, month-going clocks) where the barrel turns even more slowly and the total ratio needed exceeds about 10,000:1.
Rule of thumb: each stage gives you roughly 8:1 to 12:1. Beyond 12:1 in a single stage you are running pinion-leaf counts of 6, which loads each leaf hard and shortens service life. So when your required total ratio crosses about 10,000:1, add a stage rather than steepening the existing ones.
They are the same mechanism. Going Train is the modern term used in Swiss and English watchmaking schools and in any post-1900 horology textbook. Clock Train is the older term, common in 18th and 19th century English clockmaking literature, and you will still see it in service manuals for antique longcase and bracket clocks.
One distinction worth knowing: in a striking clock, the Going Train specifically refers to the timekeeping train, as opposed to the striking train or chiming train that drives the bells or gongs. A traditional English bracket clock has three separate trains side by side, and only one of them is the Going Train.
References & Further Reading
- Wikipedia contributors. Clock. Wikipedia
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