SHIMANO 180mm Rotor Adapter — +20mm Post-Mount Shift for 160mm Frames/Forks, Aluminium

SHIMANO's +20mm post-mount adapter lets you fit a 180mm rotor to frames or forks designed for 160mm post mounts by shifting the caliper outward by 20mm.

This simple aluminum adapter provides a reliable way to increase braking surface without changing your hub or rotor mounting pattern. It’s intended for riders who need to run a larger 160/180mm rotor combination on a frame or fork with 140/160mm post-mount bosses. Color tones may vary by screen and Shimano may update markings or finishes over time.

How does the adapter let me use a 180mm rotor on a 160mm post mount?

The adapter moves the brake caliper 20mm away from the post mount so the pad aligns correctly with a larger rotor diameter. Installation keeps the caliper position mechanically correct, avoiding rubbing and maintaining the intended caliper-to-rotor clearance.

• Shifts caliper outward by 20mm to match 180mm rotor radius
• Works with frames/forks having 140mm or 160mm post-mount bosses
• Designed for use with 160/180mm Shimano rotors

Will this adapter work on both front and rear brakes?

Yes — the adapter is compatible with front and rear post-mount setups, making it a flexible upgrade for the whole bike. Verify rotor size and post-mount specification before fitting to ensure proper clearance and safe performance.

• Compatible with front and rear post-mounts
• Use when converting 140→160 or 160→180 rotor sizes
• Check frame/fork clearance and brake hose routing before installation

What specific rotor/post-mount combinations require this part?

This adapter is required whenever you pair a larger rotor with a smaller post-mount boss that can’t natively accept the rotor radius. Typical use-cases include fitting a 160mm post mount to accept a 180mm rotor or adapting a 140mm boss for a 160mm rotor.

• Required when using a 140mm post mount with a 160mm rotor
• Required when using a 160mm post mount with a 180mm rotor
• Designed around Shimano rotor and caliper geometries for reliable fit

Is installation complicated and what should I check after fitting?

Installation is straightforward with common tools, but correct alignment and torque are important for safe braking. After mounting, check for rotor rub, correct pad contact, and secure fasteners; test in a controlled area before regular riding.

• Fits using standard post-mount bolts and hardware (not included in all kits)
• Confirm torque specs on Shimano documentation when tightening bolts
• Spin the wheel to ensure no rotor contact and perform a short brake test

Who is this for: The SHIMANO +20mm post-mount adapter suits cyclists upgrading braking power or standardizing rotor sizes across builds — commuters, trail riders, and gravel riders who need a larger rotor but have a smaller post-mount on their fork or frame. It’s ideal for mechanics and home wrenchers seeking a compact, manufacturer-matched solution that preserves Shimano caliper alignment and brake performance without replacing frame or fork hardware.