Calculator
Example Data Table
| Setup | Master bore | Slave bore | Master stroke | Pedal ratio | Foot force | Typical use |
|---|---|---|---|---|---|---|
| Street clutch | 19.05 mm | 22.22 mm | 30 mm | 5.5:1 | 180 N | Balanced effort and travel |
| Heavy cover | 20.64 mm | 25.40 mm | 32 mm | 6.2:1 | 220 N | More release force |
| Short pedal | 22.22 mm | 22.22 mm | 25 mm | 4.8:1 | 200 N | Fast movement check |
Formula Used
Piston area: A = π × d² ÷ 4
Master pushrod force: Fm = foot force × pedal ratio
Line pressure: P = Fm × efficiency ÷ master area
Slave force: Fs = P × slave area
Release force: Fr = Fs × clutch fork ratio
Slave travel: Ss = master area × master stroke × efficiency ÷ slave area
Net travel: Sn = Ss − free play
Release travel: Sr = Sn ÷ clutch fork ratio
Needed master stroke: Sm = required slave travel × slave area ÷ master area ÷ efficiency
How to Use This Calculator
- Select metric or imperial units.
- Enter the master cylinder bore and slave cylinder bore.
- Add the usable master cylinder stroke.
- Enter clutch pedal ratio and expected foot force.
- Add fork ratio, free play, efficiency, and hose loss.
- Enter target release travel and required release force.
- Press Calculate to view the result above the form.
- Use CSV or PDF buttons to save the calculation.
Clutch Cylinder Sizing Guide
Why cylinder sizing matters
A hydraulic clutch system changes pedal movement into release bearing movement. The master cylinder pushes fluid through the line. The slave cylinder receives that fluid and moves the clutch fork. A small change in bore size can change the whole feel. It can also change release travel. That is why guessing can cause poor disengagement. It can also make the pedal too heavy.
Understanding master cylinder effect
A larger master cylinder moves more fluid per stroke. It usually gives more slave travel. It also needs more foot effort. A smaller master cylinder can make the pedal lighter. Yet it may not move enough fluid. The best choice depends on the clutch, pedal ratio, and available stroke.
Understanding slave cylinder effect
A larger slave cylinder increases force multiplication. It can reduce pedal effort at the clutch fork. However, it moves less distance for the same master stroke. A smaller slave cylinder moves farther. It may not create enough force. This calculator compares both effects together.
Pressure and travel balance
Line pressure is another important check. Excess pressure can stress seals, hoses, and fittings. Low pressure may not release a heavy clutch. Travel must also be checked after free play and losses. Hose expansion, seal drag, and linkage flex reduce real movement. The efficiency fields help include those losses.
Practical setup advice
Use measured values when possible. Do not rely only on catalog bore sizes. Measure pedal stroke at the master pushrod. Check the actual fork ratio if the geometry is custom. Keep some reserve travel after the clutch releases. Too much travel can over-stroke the pressure plate. Always confirm final clearance on the vehicle.
FAQs
What does master cylinder bore change?
A larger master bore moves more fluid. It increases slave travel for the same stroke. It also raises the pedal effort because the piston area is larger.
What does slave cylinder bore change?
A larger slave bore creates more force. It moves less distance for the same fluid volume. A smaller slave bore moves farther but gives less force.
Why is my clutch pedal too hard?
The pedal may be hard because the master bore is large, the pedal ratio is low, or the clutch requires high release force. Poor alignment can also add friction.
Why is my clutch not fully disengaging?
The slave may not have enough travel. Free play, air in the line, hose expansion, short master stroke, or an oversized slave cylinder can reduce release movement.
What is a good clutch pedal ratio?
Many hydraulic clutch pedals use ratios between 5:1 and 7:1. Custom vehicles vary. More ratio usually lowers effort but increases pedal travel.
Should I choose a larger master cylinder?
Choose a larger master only if you need more slave travel and can accept more pedal effort. Check pressure and clutch over-travel before changing parts.
Why include hose expansion loss?
Flexible hoses can expand under pressure. That expansion uses fluid volume before the slave moves. The loss setting helps estimate real-world travel reduction.
Can this replace vehicle testing?
No. It gives a planning estimate. Final clutch release, pedal stop, bearing clearance, and pressure plate safety must be checked on the actual vehicle.