Glossary
Differential Setup Explained: Preload, Ramp Angles & Locking Percentage
Differential setup governs how torque is split between the driven wheels when they want to rotate at different speeds. A plate-type limited-slip differential uses preload (static friction), ramp angles (how hard the plates clamp under drive and overrun) and the number of friction faces to set its locking behaviour. More locking gives better traction out of corners but makes the car push on entry and mid-corner; less locking frees the car up but can spin the inside wheel.
| Change | Corner entry (coast) | Mid-corner | Exit (power) |
|---|---|---|---|
| More preload | Stable, more push | More push | More traction, more push |
| Shallower power ramp | No change | Little | More lock: traction up, understeer on throttle up |
| Shallower coast ramp | More lock: stable, pushes on entry | Little | No change |
| Open coast (90°) | Free, rotates on entry, can be unstable | Little | No change |
How the parts work
Preload springs clamp the friction plates with a fixed force, so even with no torque the wheels resist turning at different speeds. The ramps convert input torque into additional clamping force: as the engine drives the car the cross-pin rides up the power ramps and squeezes the plates; on overrun it rides up the coast ramps. The angle sets the ratio of clamp force to torque, and the number of active friction faces multiplies it.
Choosing settings
A tight, high-grip circuit with slow corners rewards traction, so run more power-side lock. Fast, flowing circuits reward a car that is neutral mid-corner, so run less lock and lower preload. If the driver complains of understeer on throttle, reduce power lock or preload; if the inside wheel spins, increase it. Record the ramp pair, preload and plate count in each setup so changes can be compared across events.
Frequently asked questions
What does a 45/60 differential mean?
The power ramp angle is 45° and the coast ramp is 60°. The shallower power angle gives more lock under drive than on overrun.
How is preload measured?
With a torque wrench on one axle while the other is held, with the diff out of the car or the wheels lifted. It is quoted in Nm or lb-ft of breakaway torque.
What is a torque-biasing differential?
A gear-type (Torsen-style) differential that uses gear friction rather than plates. It has no preload adjustment and cannot lock when one wheel is completely unloaded.
Related
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