Shimano Altus RD-M370-SGS Rear Derailleur - 9-Speed, Long Cage, 34T Max, Black
The Shimano Altus RD-M370-SGS is a reliable 9-speed rear derailleur built for mountain bikes, hybrids, comfort bikes, and utility builds that need dependable shifting without unnecessary complexity. This is a long cage derailleur designed for wider gear range setups and everyday durability.
It works especially well as a direct replacement for older Shimano 8/9-speed mountain and hybrid drivetrains where riders want smooth shifting, easy serviceability, and affordable long-term parts support.
This is not a modern clutch derailleur for aggressive trail riding—it is a practical workhorse derailleur for real-world riding and service repairs.
Key Functional Details
- Shimano Altus RD-M370-SGS rear derailleur
- 9-speed drivetrain compatibility
- Long cage (SGS) for wider gear range setups
- Maximum 34T largest rear cog compatibility
- 45T total chain wrap capacity
- Standard 10x1 derailleur hanger mount
- Compatible with Shimano mountain-style pull ratio
- 11-tooth upper and lower pulleys
- Strong replacement option for MTB, hybrid, and commuter bikes
Technical Specifications
| Brand | Shimano |
| Model | Altus RD-M370-SGS |
| Drivetrain Speeds | 9-Speed |
| Cage Length | Long Cage (SGS) |
| Largest Rear Cog | 34T Max |
| Chain Wrap Capacity | 45T |
| Mount Type | 10x1 Standard Derailleur Hanger |
| Compatibility | Shimano Mountain Pull Ratio |
| Pulley Size | 11T Upper / 11T Lower |
| Color | Black |
Compatibility & Technical Notes
Good Fit: Shimano 9-speed mountain bikes, hybrids, fitness bikes, comfort bikes, and commuter builds using standard Shimano MTB shifter pull ratios.
Not A Fit: Shimano 10/11/12-speed systems, SRAM exact actuation drivetrains, modern clutch derailleur applications, or oversized cassette conversions beyond 34T without special adaptation.
This derailleur must match the correct shifter pull ratio—not just the speed count. That is one of the most common ordering mistakes.
Service / Ownership Context
For many older bikes, replacing the derailleur is often smarter than trying to rebuild a bent or worn unit. This is a dependable service replacement that keeps older bikes shifting properly without forcing expensive drivetrain upgrades.
It is especially common on bikes where the derailleur hanger gets bent during transport, crashes, or tip-over damage.
Fit & Use Signals
Best for:
- Hybrid bike repairs
- Older 9-speed MTB replacements
- Commuter bike drivetrain repairs
- Comfort bike service work
- Budget-conscious reliable repairs
Not ideal for:
- Modern wide-range MTB builds
- 12-speed upgrades
- Aggressive trail riding requiring clutch derailleurs
- Large cassette performance conversions