Differential

The differential controls how much the left and right wheels are free to rotate independently.

In simple terms, imagine a car going through a corner. The outside wheel needs to cover more distance (larger radius) and thus needs to rotate faster than the inside wheel. Forcing both wheels to rotate at the same speed (locked differential) is not ideal for cornering.

Conversely, imagine a car braking hard into a corner. The wheel with less weight load will have a tendency to lock earlier; connecting it to the other wheel (forcing it to rotate at the same speed) helps prevent locking.

Differential Ramp Angles

There are two independent settings: coast and drive.

Drive

  • Controls the behaviour of the differential on-throttle (under acceleration).
  • Higher values (eg 80) cause more understeer when cornering, but also less wheelspin and thus more control on corner exit.
  • Lower values allow higher cornering speed but may lead to spins under acceleration (corner exit).
  • Wheelspin on exit can increase tyre temperature throughout a race.

Coast

  • Controls the differential off-throttle.
  • Higher values (80) increase cornering ability off-throttle (corner entry) but decrease stability under braking.
  • Lower values (30) increase braking stability and efficacy (think ABS, in a way) at the price of reduced cornering on entry.
  • Very low values may lead to snap oversteer under braking; if both rear wheels lock at the same time the rear of the car will step out in a similar way to applying the handbrake.

Lower “drive” and higher “coast” values make the car more responsive to throttle inputs.

Differential Clutch Friction Faces

Clutches influence the maximum lock (wheels rotating at the same speed) achieved. They affect both coast and power differential in the same way.

In the image below, compare the lock (bottom row) achieved with the same ramp value (top row) at different discs (middle row). You will notice that the discs act as a lock multiplier (4 discs have 2x the lock of 2 discs; 6 discs have 3x the lock).

Values in the image above are taken from the real life F317 manual. We assume they are identical in our simulation.

You can use the image to tune the differential in a very simple way:

  • if you choose settings to the left you have more on-throttle understeer and off-throttle oversteer
  • If you choose settings to the right you have more on-throttle oversteer and off-throttle understeer

Differential Preload

Regardless of the mechanics (we have very little info), the preload can be used to tune the F3 behaviour.

First of all, preload has effect on both slow and fast corners in entry, mid-corner and exit. By contrast, the ramps and discs have more effect in slow corners and affect entry and exit, less so mid-corner.

Higher values (eg 100) produce more oversteer on-throttle and more understeer off-throttle.
Lower values (eg 20) produce understeer on-throttle and oversteer off-throttle.

You can increase the car reactivity on corner entry by decreasing the preload.
If you want the car to turn better on exit, instead, choosing higher preload values should help you.

More info on the differential at pages 27-28-29 of the F317 user manual, including a comparison of the lock in all the available settings.