AMSOIL SHOCK THERAPY 10 MEDIUM SUSPENSION FLUID

Choose it for more damping

#10 Medium is the heavier Shock Therapy grade. Use it where more damping control and a slower return stroke are wanted, or where the component specification points to a medium suspension fluid. Heavier does not mean better for every setup.

At 40°C, #10 Medium measures 31.8 cSt compared with 15.9 cSt for #5 Light. At 100°C, it measures 7.3 cSt compared with 4.4 cSt. The damper will usually feel the biggest difference early in a ride, before heat narrows the gap.

Match listed systems and forks

Fox, Koni, Öhlins, Race Tech, and WP suspension systems are listed where more damping control and slower rebound are wanted. Harley-Davidson forks that recommend type E or type B fork oil are covered by this grade as well.

Race Tech and WP also appear under #5 Light, so the brand stamped on the shock body does not pick the fluid by itself. Use the component specification, the desired damping change, and the rebuild procedure together before the cap comes off.

Read the cross-reference carefully

The replacement list includes Bel-Ray Fork 10W and HVI 10W, Fox Racing Oil, Maxima Fork Oil 10, Maxima 111-390 Racing Shock Fluid Medium 7 wt., Klotz 10W, Spectro SK400, Redline Medium, Öhlins Fork Fluid #15, Pro Honda SS-8, and Harley-Davidson Type B and Type E.

Two entries need extra attention. Compared with Fuchs Silkolene, #10 Medium gives slower rebound. Compared with Harley-Davidson Screaming Eagle Performance Fork Oil Heavy, it gives faster rebound. Treat the cross-reference as a service guide, not a promise of identical feel.

Hold feel as heat builds

Aggressive riding heats suspension fluid until it thins, and thin fluid can make shocks feel soft and inconsistent. High-viscosity-index synthetic base oils help maintain viscosity at extreme temperatures. This grade posts an ASTM D2270 viscosity index of 206.

ASTM D892 foam results are 60/0, 50/0, and 60/0 across the three sequences. The first number is foam at the end of aeration, and the second is foam after settling. Every settled value is zero, which helps keep air from softening the stroke.

Check wear, cold flow, and packages

Under ASTM D4172 at 40 kgf, 75°C, 1,200 rpm, and one hour, the four-ball wear scar is 0.42 mm. Anti-wear agents protect shocks and forks from premature wear, while friction modifiers cut energy lost to sliding parts inside the damper.

The ASTM D97 pour point is -48°C (-54°F). Flash and fire points are 192°C (378°F) and 208°C (406°F) under ASTM D92. No winter-specific recommendation is attached to #10 Medium, because #5 Light is the grade named for winter use.

Agitate the fluid before filling. STMQT-EA is the single quart bottle, STMQT-CA is the case of twelve, STM05-EA is the five gallon pail, and STM55-EA is the fifty-five gallon drum. Use the damper manufacturer's fill and service procedure.

Verified specifications