AMSOIL SHOCK THERAPY 5 LIGHT SUSPENSION FLUID

Choose it for quicker rebound

#5 Light is the thinner Shock Therapy grade. Use it where less damping and quicker rebound are wanted, or where the component specification points to a lighter fluid. It changes damper behavior; it is not a general upgrade over #10 Medium.

At 40°C, #5 Light is 15.9 cSt while #10 Medium is 31.8 cSt. At 100°C, #5 Light is 4.4 cSt while #10 Medium is 7.3 cSt. Those measured numbers tell you more than the grade name when a fork or shock needs a specific feel.

Match the fork or shock

Bilstein, Custom Axis, Kayaba, Penske, Race Tech, RydeFX, Showa, and WP suspension systems are listed where less damping and quicker rebound are wanted. Read that as component guidance, not a blanket approval for every shock those brands sell.

The application range also reaches snowmobiles, dirt bikes, motorcycles, ATVs, UTVs, cars, trucks, circle-track racing, and other recreational or racing vehicles. The vehicle type does not pick the grade. The fork or shock specification does.

Use the winter-grade advantage

#5 Light is the Shock Therapy grade recommended for winter use. The ASTM D97 pour point is -53°C (-63°F), five degrees colder than the -48°C (-54°F) figure for #10 Medium. Pour point is a lab flow number, not a minimum riding temperature.

Cold fluid makes suspension feel stiff until the damper cycles and warms. A lighter winter grade helps the first strokes move closer to the intended setup after the machine sits outside overnight. Still confirm the component spec before changing viscosity.

Fight fade, foam, and wear

Hard riding heats suspension fluid and thins it, which can turn crisp damping into a soft, inconsistent feel. High-viscosity-index synthetic base oils help hold viscosity as temperature swings. This grade posts an ASTM D2270 viscosity index of 209.

ASTM D892 foam results are 50/0, 40/0, and 50/0 across the three sequences. The first number is foam after aeration, and the second is foam after settling. Every settled value is zero, so the foam that formed collapsed before it could keep hanging around.

Under ASTM D4172 at 40 kgf, 75°C, 1,200 rpm, and one hour, the four-ball wear scar is 0.44 mm. Friction modifiers, anti-wear agents, and seal conditioners help protect shocks and forks, reduce friction, and cut the chance of leaks.

Fill it like a damper fluid

Agitate the bottle before filling so the additive package is evenly mixed. Use the damper manufacturer's procedure for volume, air gap, bleeding, and rebuild interval. A few extra milliliters can change ride height and feel, so measure instead of guessing.

STLQT-EA is the single quart bottle and STLQT-CA is the case of twelve. STL05-EA is the five gallon pail and STL55-EA is the fifty-five gallon drum. The fluid also meets hydraulic specifications including Denison HF-0, HF-1, and HF-2 and DIN 51524 Part 2.

Verified specifications