The Shimano BB-RS500 [paid link] is a bottom bracket from Shimano’s Road series, designed specifically for compatibility with Hollowtech II cranksets. While the BB-RS500 [paid link] itself does not include traditional limit screws like derailleurs, many users mistakenly refer to preload adjustment bolts or crank arm fixing bolts as “limit screws.” Understanding how to properly install and fine-tune the BB-RS500 [paid link]—and specifically, how to adjust the preload mechanism—can make the difference between a smooth drivetrain and premature bearing failure.
This article offers a detailed breakdown of BB-RS500 installation and the preload bolt adjustment, often misunderstood as a limit screw. We’ll explore why getting it right matters and how to do it correctly for optimal crankset performance.
Understanding the BB-RS500 Preload Bolt Function
The BB-RS500 uses Shimano’s Hollowtech II system, which features outboard bearings and a 24mm spindle. To keep the crankset secure and the bearings tensioned correctly, a preload cap or preload bolt is used on the left crank arm. This bolt ensures the crank arms are snug without overloading the bottom bracket bearings.
Although not technically a “limit screw,” this preload cap acts as a fine adjustment mechanism that determines the lateral compression of the crankset. If overtightened or left too loose, it can cause a range of issues—from creaking sounds and poor pedaling efficiency to bearing wear and crank arm play.
Why Proper Adjustment Matters
Proper preload adjustment on the BB-RS500 affects overall performance, longevity, and safety. Here’s why it’s essential:
- Prevents Premature Bearing Wear: Over-compression leads to increased friction, generating heat and causing the bearings to degrade quickly.
- Eliminates Crank Arm Play: Under-tightening causes the crank arms to shift laterally, which can damage the splines and make pedaling inefficient.
- Avoids Noise Issues: Many creaks and clicks originate from poorly adjusted preload bolts or improperly torqued crank bolts.
- Ensures Smooth Pedal Rotation: When set correctly, the crankset spins freely without lateral resistance, contributing to a better riding experience.
Preload Adjustment Procedure for the BB-RS500
Even though it’s a subtle step, the preload adjustment is one of the most critical phases in BB-RS500 installation. Here’s how to get it just right:
Initial Setup
Ensure the bottom bracket cups are installed flush with the frame and torqued to the correct specification (35–50 Nm). Both cups should be greased and installed using a Hollowtech II-compatible bottom bracket tool [paid link].
Crank Arm Installation
Once the cups are installed:
- Insert the crankset axle through the right-hand cup and bearing.
- Slide the left crank arm onto the spindle until it sits flush with the bearing seal.
Now it’s time to adjust preload.
Adjusting the Preload Bolt
The plastic preload bolt located on the non-drive-side crank arm should be gently turned using a Shimano TL-FC16 [paid link] or TL-FC18 tool. Here’s the ideal process:
- Do not overtighten: The goal is to take up bearing play—not to apply clamping force.
- Turn until resistance is felt, then stop. This usually equates to roughly 0.7–1.5 Nm of torque.
- Check for play: Rock the crank arms side-to-side to ensure there’s no lateral movement.
- Ensure smooth rotation: The crankset should spin freely without resistance or grinding.
Final Torque of Pinch Bolts
Once preload is set:
- Torque the two pinch bolts on the left crank arm to 12–14 Nm, tightening them evenly in increments.
- Never use the preload bolt to secure the crank arm; it’s only for bearing adjustment.
Common Preload Adjustment Errors
Mistakes during this process are frequent and can seriously affect performance. Watch out for the following:
- Using the preload bolt for clamping: This leads to cracked plastic caps and uneven crank arm engagement.
- Skipping preload entirely: Omitting the preload step causes crank arm play and bearing misalignment.
- Overtorquing the pinch bolts without preload: This compresses the spindle unevenly, risking long-term bearing damage.
Signs of Incorrect Preload Adjustment
Riders can identify an improperly adjusted BB-RS500 through these symptoms:
- Creaking or clicking noises during pedaling
- Wobble or play in the crank arm under load
- Tight crank rotation or stiff pedaling feel
- Rapid bearing deterioration or water ingress near the cups
Any of these signs warrant a re-check of the preload setting and crank arm installation.
Best Practices for BB-RS500 Preload Tuning
To get consistent, optimal results every time:
- Always use the correct Shimano preload tool.
- Clean and lightly grease the spindle interface before assembly.
- Torque in stages, alternating bolts when securing the left crank arm.
- Re-check preload after 100 km to account for settling.
- Replace the preload cap if damaged or overused.
Conclusion
While the BB-RS500 doesn’t use traditional limit screws, the preload cap fulfills a similar role in fine-tuning bearing pressure. Getting this adjustment right is essential for drivetrain longevity, smooth pedaling, and quiet operation. By understanding the function and following a precise installation method, you can ensure your Shimano BB-RS500 performs flawlessly for thousands of kilometers.