JConcepts launches BK-design 13mm shock pistons in Delrin with multiple tuning options

What was released

Why the BK piston is different

The BK piston uses a slotted, channeled geometry rather than a simple top-to-bottom pass-through. The internal channel increases the effective oil volume inside the shock body, acting like an additional chamber. Instead of relying only on holes drilled through the piston and blow-by around the perimeter, this design routes fluid through two separate channeled sections while keeping the working disturbance area submerged in oil.

Reported handling effects

According to JConcepts' team and test drivers: the BK piston translated into more overall grip and handling that feels more "with the track surface" rather than fighting it. The piston reportedly improves stability and cornering when running a lower ride-height while still coping with individual bumps and deflections during hard sweep cornering.

Materials and manufacture

Available options and part numbers

JConcepts lists the following piston options for 13mm shocks:

• 5327 — BK design, 2 x 1.5mm
• 5328 — BK design, 2 x 1.6mm
• 5329 — BK design, 2 x 1.7mm
• 5330 — BK design, 2 x 1.8mm
• 5331 — BK design, 2 x 1.9mm
• 5332 — BK design, 2 x 2.0mm
• 5333 — BK design, 3 x 1.5mm
• 5334 — BK design, 3 x 1.6mm
• 5335 — BK design, 3 x 1.7mm

Each option is described as pre-drilled for simplicity so racers can select the hole count and bore size that match their setup and track conditions.

How a racer might use these pistons

• Choose a piston variant by hole count and bore diameter that approximates your current damping feel and then fine-tune oil weight and volume.

• Consider trying the BK piston if you're seeking more consistent damping and improved grip at lower ride-height without losing ability to handle individual track bumps.

Bottom line

Delrin option that reworks internal oil flow with channeled sections and pre-drilled tuning choices. JConcepts reports improved grip and more consistent handling in testing, and offers multiple hole sizes and 2- and 3-hole configurations for racers to tune their shocks.