Additional Information

the wt/cst that appears first is the accurate one and the others have been converted using the cst=(wtx15)-100 guide.

Fastrax Racing Pure Silicone Diff Oil 12500cst FAST61-12.5K<

RC Differential Oil – Setup & Selection Guide

Note: A full table of available oil viscosities and part numbers can be found at the end of this listing.

Pure silicone differential oil for RC cars
Suitable for gear differentials in on-road and off-road vehicles.

Oil Viscosity Information

Differential oil viscosity is measured incSt (centistokes).
Some oils are labelled in WT; these values are not directly interchangeable between brands. A commonly used approximate conversion for tuning reference is:

cSt ≈ (WT × 15) − 100

(≈ indicates approximate)
For consistent results, always use oils from the same manufacturer.

How Differential Oil Affects Handling

Thinner oil (lower cSt)
More differential action, increased steering and rotation, but reduced forward drive and stability.

Thicker oil (higher cSt)
More locked behaviour, improved forward traction and stability, but reduced steering and slower rotation.

Recommended Differential Oil Setups

General starting points for box-stock vehicles.

1:10 Touring Car 4WD (Gear Differentials)

Front: 10,000 – 30,000 cSt
Rear: 7,000 – 25,000 cSt

Suggested part numbers: FAST61-10K, FAST61-15K, FAST61-20K, FAST61-30K

Thinner oils increase corner-entry steering, thicker oils improve stability and on-power control.

1:10 Buggy / Short Course 2WD

(Rear differential only) 5,000 – 20,000 cSt

Suggested part numbers: FAST61-5K, FAST61-7K, FAST61-10K, FAST61-15K, FAST61-20K

Lower values improve rotation on low-grip tracks, higher values increase forward drive and rear stability.

1:10 Buggy 4WD

Front: 10,000 – 25,000 cSt
Centre: 20,000 – 40,000 cSt
Rear: 5,000 – 20,000 cSt

Suggested part numbers:
Front – FAST61-10K, FAST61-15K, FAST61-20K
Centre – FAST61-20K, FAST61-30K
Rear – FAST61-5K, FAST61-7K, FAST61-10K, FAST61-15K

Centre diff oil has the biggest impact on acceleration and front/rear power balance.

1:10 Short Course 4WD

Front: 15,000 – 30,000 cSt
Centre: 30,000 – 60,000 cSt
Rear: 10,000 – 25,000 cSt

Suggested part numbers:
Front – FAST61-15K, FAST61-20K, FAST61-30K
Centre – FAST61-30K, FAST61-50K
Rear – FAST61-10K, FAST61-15K, FAST61-20K

Heavier vehicles benefit from thicker centre oils to reduce front wheel unloading.

1:8 Buggy & Truggy

Front: 20,000 – 40,000 cSt
Centre: 40,000 – 100,000 cSt
Rear: 10,000 – 30,000 cSt

Suggested part numbers:
Front – FAST61-20K, FAST61-30K
Centre – FAST61-50K, FAST61-100K
Rear – FAST61-10K, FAST61-15K, FAST61-20K

Heavier vehicles require thicker centre oils for improved acceleration and jump stability.

Fastrax Pure Silicone Differential Oil Range (FAST61)

Final Note

Differential tuning is track- and driver-dependent. These values are starting points, not limits — small changes can make a big difference.