Dirty drivetrains don't just look bad — the grit and old lube packed between chain rollers and pins acts like a grinding compound that accelerates wear on your chain, cassette, and chainrings. Park Tool's CB-4 Bio ChainBrite is a plant-based degreaser formulated to cut through that buildup without the harsh fumes or material damage you get from petroleum-based solvents. The formula is 100% biodegradable and uses full-strength application — you don't dilute it with water, which means the solvent concentration stays high enough to actually dissolve caked-on grime rather than just pushing it around.

CB-4 is designed to work inside Park Tool's CM-5.3 Cyclone Chain Scrubber and the CM-25 Professional Chain Scrubber, where it fills the reservoir and the rotating brushes force the solution through the chain's inner surfaces. You can also use it as a general-purpose degreaser with a scrubbing brush on cassettes, chainrings, derailleur pulleys, and other drivetrain components. The formula won't harm alloy, plastic, rubber, or carbon fiber parts, so you don't need to worry about damaging seals or housings when cleaning around bottom brackets, derailleurs, or brake calipers.

The 16 oz bottle with its flip-top lid pours cleanly into the chain scrubber reservoir without spilling. One fill of the CM-5.3 reservoir handles a standard cleaning session, and you can get multiple sessions out of a single bottle depending on how dirty your drivetrain runs between cleanings. If you've been reaching for dish soap or automotive brake cleaner to degrease your chain, CB-4 is the purpose-built alternative — it breaks down lubricant films without leaving residue that interferes with fresh lube application, and the bio-based solvents rinse away with water when you're done.