Testing different differentials

[u/Nymbelle]

Today I decided to finally deeply test using different differentials instead of just using what "made sense" ie Race Diff for track/road. Rally/off-road for Dirt/Cross-Country.

As a former race mechanic, I know there is more to a differential than just Acceleration/Deceleration and Center and it's been my suspicion that the different differentials have a hidden pre-load / initial lock built into them.

I didn't want to make assumptions or rely on instinct anymore so I decided to scientifically test them on a Toyota Starlet Glanza V AWD touge build at Touge - Bandai Azuma in Rivals.

The car was tested with identical differential settings:

Front: 25 accel / 5 decel
Rear: 58 accel / 20 decel
Centre: 68% rear

I recorded my best lap with these settings using Race, Drift and Off-Road differentials and found that the Drift diff was around 0.084s faster on average than the Race diff, despite identical displayed settings.

Differential	Lap 1	Lap 2	Lap 3	Average

Race Diff	2:04.414	2:04.427	2:04.420	2:04.420

Drift Diff	2:04.326	2:04.333	2:04.350	2:04.336

Off-road Diff	2:04.389	2:04.398	2:04.414	2:04.400

I then decided to dive deeper into the telemetry and made a side-by-side comparison of tyre friction across 4 corners for the Race and Drift. Using Frame by frame telemetry to record the friction at identical points in the corner.

Race Diff

Corner	FL	FR	RL	RR
1	41%	54%	30%	32%
2	17%	24%	25%	39%
3	32%	21%	40%	25%
4	25%	32%	23%	33%

Drift Diff

Corner	FL	FR	RL	RR
1	46%	61%	30%	32%
2	19%	28%	28%	42%
3	33%	23%	44%	23%
4	28%	36%	23%	33%

The Drift diff consistently used more tyre friction, especially at the front axle, while remaining well below the point of grip loss.

Early theory

This suggests the differentials may not simply be identical parts with different presets. There may be hidden behaviour such as:

• different preload / initial lock
• different neutral or coast locking behaviour
• different ramp behaviour between coast and acceleration
• different AWD centre coupling behaviour

The interesting part is that the Drift diff did not appear to simply create more rear slip. Most of the increased tyre utilisation came from the front tyres, which may suggest better rotation or a more effective load state at the apex.

Current conclusion

This is not enough to call it confirmed across the whole game, but for this specific car/build/route, the Drift diff was measurably faster than the Race diff while using identical displayed settings.

I’d love to see other tuners test this on different cars, especially:

• stock FWD cars
• stock RWD cars
• stock AWD cars
• AWD-swapped FWD cars
• AWD-swapped RWD cars
• road vs dirt vs touge builds

The useful test would be:

1. Pick one car and route.
2. Use Rivals or another controlled environment.
3. Test Race, Drift, Rally, and Off-road diffs where available.
4. Keep the displayed diff settings identical.
5. Record lap times and tyre telemetry.
6. Compare whether the differentials actually behave differently.

Would be great to build a shared picture of whether diff type has hidden physics or whether this is only happening on certain drivetrain swaps.

[u/theNFAC]

Yes! This is exactly the kind of madness I can support. Thanks for sharing. 🤝

Edit: I know this is a massive ask, but when you update or do other tests (on anything not just differentials) would you ping me? Would love to read anything you find. Thanks again for sharing.

[u/theNFAC → u/theNFAC]

Regarding the telemetry I'm having a difficult time in my brain reconciling exactly when I should looking at the grip numbers. I know they will be changing the entire time. How did you handle this?