SHIMANO SM-MA90-R140-PS BRAKE ADAPTER 140MM A-STD
Precision Engineering for Lightweight Road & XC Performance.
The Shimano SM-MA90-R140-P/S is a high-performance adapter designed to bridge the gap between a Post Mount (PM) brake caliper and an International Standard (IS) frame mount. Specifically engineered for the rear of the bike, this adapter allows you to run a compact 140mm rotor, making it a favorite for weight-conscious road cyclists, gravel grinders, and XC racers who prioritize modulation and weight savings over sheer downhill stopping power.
Part of Shimano’s premium component range, this adapter is CNC-machined to exacting tolerances. This ensures that your brake caliper is perfectly centered over the rotor, eliminating annoying brake rub and ensuring that your pads wear evenly over time. The "90" series designation signifies its lightweight, hollowed-out design, providing a high strength-to-weight ratio for performance-oriented builds.
Key Features
IS-to-Post Conversion: Specifically designed to mount a 74mm Post Mount caliper to a frame with 51mm International Standard (IS) eyelets.
140mm Rear Optimized: Precise offset dimensions tailored for a 140mm rear disc rotor, providing a sleek, low-profile look for modern disc-road and gravel frames.
CNC Machined Alloy: Constructed from high-tensile aluminum with a weight-saving hollow design, ensuring maximum rigidity for crisp braking feel without unnecessary bulk.
Corrosion Resistant Finish: Features a durable black anodized finish that protects against the elements and maintains a professional aesthetic.
Complete Mounting Hardware: Includes the necessary high-grade steel bolts and the Shimano safety wire system to prevent bolts from loosening due to road or trail vibrations.
Low Stack Height: Designed to keep the caliper as close to the frame as possible, improving aerodynamics and protecting the brake system from external impacts.
Technical Specifications
| Feature | Specification |
| Model Number | SM-MA90-R140-P/S |
| Mount Type | IS Mount (Frame) to Post Mount (Caliper) |
| Rotor Size | 140 mm |
| Position | Rear Only |
| Material | Lightweight Aluminum |
| Included | 2x Mounting Bolts, 1x Safety Wire |
✅ Why This IS For You
Road & Gravel Enthusiasts: If you are building a modern disc-brake road or gravel bike and want the clean, minimalist look and weight savings of a 140mm rear rotor.
Weight-Sensitive Racers: Perfect for those looking for the SM-MA90 series lighter-weight construction compared to standard cast adapters.
Legacy Frame Users: Ideal for riders with high-quality IS-mount frames who wish to upgrade to modern, high-performance Post Mount hydraulic calipers.
❌ Why This May NOT be for you
Heavy Touring or DH Riders: A 140mm rotor has less surface area for heat dissipation; if you are carrying heavy panniers or doing long mountain descents, a 160mm or 180mm setup is safer.
Front Brake Mounting: This is a rear-specific adapter; IS-to-Post front adapters use different offsets, so ensure you are mounting this to the frame, not the fork.
BFC Pro Tip
The SM-MA90-R140-P/S is a "set and forget" part, but only if installed correctly. When mounting, ensure the IS-mount tabs on your frame are clean and free of paint overspray—this ensures the adapter sits perfectly flat. We always recommend using a drop of blue Loctite on the threads and finishing with the included safety wire. This is especially important on the rear, where vibrations from the drivetrain and road can cause hardware to settle. If you're upgrading from a 160mm to a 140mm, double-check that your frame has the clearance for the smaller rotor position!
