The Shimano SM-MA90-R180-P/S is a high-performance adapter engineered to mount a Post Mount (PM) caliper to an International Standard (IS) rear frame mount. Specifically designed to facilitate the move to a 180mm rotor, this adapter provides the necessary offset for riders who need more heat dissipation and leverage than a standard 140mm or 160mm setup can provide.
As part of the professional-grade "90" series, this adapter features a weight-optimized, CNC-machined construction. It is designed to be incredibly stiff, ensuring that even under heavy braking loads, there is zero flex between the caliper and the frame. This results in a crisp, communicative lever feel and consistent pad engagement, which is essential for technical trail riding and loaded touring.
IS-to-Post Precision: Converts a 51mm International Standard (IS) frame mount to accept a modern 74mm Post Mount (PM) caliper.
180mm Rotor Optimized: Specifically spaced for a 180mm rear disc, offering a significant increase in braking torque and cooling surface area.
SM-MA90 Lightweight Design: Features a premium, hollowed-out aluminum construction that reduces weight without sacrificing structural integrity.
Anodized Durability: Finished with a high-quality black anodization that resists corrosion and keeps your bike looking "factory" for years.
Rock-Solid Braking Feel: The rigid CNC-machined body minimizes caliper "twist" during hard braking, ensuring maximum pad-to-rotor contact.
Complete Safety Hardware: Comes with high-tensile mounting bolts and the Shimano safety wire system to ensure hardware stays torqued through trail chatter.
| Feature | Specification |
| Model Number | SM-MA90-R180-P/S |
| Mount Type | IS Mount (Frame) to Post Mount (Caliper) |
| Rotor Size | 180 mm |
| Position | Rear Only |
| Material | CNC-Machined Aluminum |
| Included | 2x Bolts, 1x Safety Wire |
Aggressive Trail & XC Riders: If you find yourself "cooking" smaller 160mm rotors on long descents and need the extra thermal capacity of a 180mm disc.
E-Bike & Cargo Cyclists: Perfect for providing the additional stopping power required to slow down heavier bikes or riders carrying significant gear.
Performance Restoration: Ideal for upgrading a high-quality older IS-mount frame with the latest hydraulic braking technology.
Lightweight Road Racing: Most dedicated road frames are designed for 140mm or 160mm; a 180mm rotor may be overkill and add unnecessary rotating weight.
Front Fork Mounting: This adapter is rear-specific for the frame. If you are mounting a 180mm rotor to an IS-mount fork, you will need the front-specific version (F180P/S).
The SM-MA90-R180-P/S is a "pro-tier" part, and it deserves a pro-tier installation. Before bolting it on, ensure your frame's IS tabs are perfectly clean; even a small bit of paint or grit can cause the caliper to sit slightly crooked, leading to a "spongy" lever. Like all our premium Shimano adapters, don't forget to thread the safety wire through the bolt heads—it’s the ultimate peace of mind when you're flying down a bumpy descent! Also, double-check your frame manufacturer's specs to ensure the chainstay or seatstay has physical clearance for the larger 180mm disc.
