what's the best diff fluid weight for 8B/8T for racing and why?

[jhautz]

You can adjust the characteristics of the differentials by using thinner or thicker silicone
oil within their cases.

• Changing the oil in the front differential affects overall steering response.
• Changing the oil in the center differential affects the front-to-rear drive.
• Changing the oil in the rear differential affects cornering traction and overall steering.

Front
Thinner

• Increases steering into corners (off-power)
• If oil is too thin the steering may become inconsistent,
especially it can lose forward traction (and steering)
during acceleration out of corners

Thicker

• Increases stability into corners during braking
• Increases steering on-power at corner exit

Center
Thinner

• Front wheels unload more during acceleration
• Decreases on-power steering (reduces oversteer)
• Easier to drive on rough tracks
• If a high-power engine is used you could waste too
much power and sometime “cook” the oil in the center
differential because it “overloads”
• More off-power steering

Thicker

• More all-wheel drive effect
• Better acceleration
• Increases on-power steering (reduces understeer)
• Better suited on high-bite, smooth tracks
• Car can be more nervous to drive especially if a high
power engine is used - you might need to be smooth on
the throttle

Rear

Thinner

• Increases cornering traction
• Increases steering into corner

Thicker

• Decreases rear traction while cornering
• Reduces wheelspin