DIY Rear Shock Sag Setup for Bomber CR Trunnion

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The Bomber CR Trunnion [paid link] rear shock by Marzocchi is a high-performance suspension component designed for aggressive trail riders and enduro enthusiasts. Getting the sag setup correctly is critical to achieving optimal performance and comfort. This guide will walk you through the step-by-step process of setting up the rear shock sag for the Bomber CR Trunnion [paid link], ensuring that you achieve a balanced and responsive ride.

Understanding Rear Shock Sag

Rear shock sag refers to the amount of compression the shock experiences under the rider’s weight. It is essential to set the sag correctly, as it directly influences the bike’s handling, traction, and overall ride quality. If your sag is too little or too much, it can affect the suspension’s ability to absorb impacts effectively, leading to poor performance and discomfort.

For the Bomber CR Trunnion, getting the sag right is crucial for maximizing its performance on rough terrain. Proper sag ensures that the shock operates within its optimal travel range, allowing it to provide the necessary support and damping.

Tools Required

  • Shock pump (with pressure gauge)
  • Ruler or caliper
  • Marker or tape for measuring sag
  • Torque wrench [paid link] (for re-tightening bolts)
  • 15mm wrench (for trunnion mount)

Steps for Setting Up Rear Shock Sag on Bomber CR Trunnion

Step 1: Set the Correct Air Pressure

The first step in setting up the rear shock sag is to ensure the shock is inflated to the correct pressure. This pressure is typically determined by your weight and riding style. Marzocchi provides a pressure chart with the Bomber CR Trunnion shock, but it can be adjusted slightly based on rider preference.

  1. Remove the shock from the bike or ensure the bike is on a stable surface.
  2. Attach the shock pump to the valve on the rear shock.
  3. Set the recommended air pressure as per the chart, or adjust based on your comfort and weight. The shock should feel firm but not rock-hard.
  4. Inflate or deflate until the desired pressure is reached. Be sure to check that the air pressure gauge on the pump reads correctly.

Step 2: Measure the Rider’s Initial Sag

Before adjusting, you need to measure the rider’s current sag setting. Follow these steps to get an accurate reading:

  1. Prepare your bike by placing it on a flat surface. Ideally, have someone assist you to ensure the bike stays upright.
  2. Mark the starting point: Use a marker or tape to mark the center of the shock’s stanchion. This will serve as the baseline for measuring sag.
  3. Set the bike up with the rider in full gear, as you would typically ride. This includes helmet, hydration pack, and any other gear that affects the rider’s total weight.
  4. Sit on the bike in a neutral position and allow the suspension to compress under your body weight. It’s essential to remain still and let the suspension settle for 15-30 seconds.
  5. Measure the sag by checking how much the shock’s stanchion has moved from the initial mark. The measurement should be taken at the mid-point of the shock’s stroke.

Step 3: Calculate the Proper Sag

The recommended sag for the Bomber CR Trunnion typically falls between 25% to 30% of the shock’s total travel, but this can vary based on rider preference and intended use.

  1. Calculate the total shock travel: Check the specifications of the Bomber CR Trunnion to determine its total travel.
  2. Calculate 25% or 30% of the total travel: This will give you the desired sag measurement.
  3. Compare the actual sag: If the sag is less than the desired percentage, you need to decrease air pressure. If the sag is more than the target, you will need to increase air pressure.

Step 4: Adjust the Air Pressure

If your sag measurement is off, it’s time to make adjustments:

  1. Increase the air pressure if the sag is too deep (greater than the recommended 30%). This will make the shock stiffer, reducing the amount of sag.
  2. Decrease the air pressure if the sag is too shallow (less than the recommended 25%). This will soften the shock, allowing for more sag.
  3. Repeat the sag measurement after making adjustments. It may take a few iterations to achieve the perfect sag setting.

Step 5: Fine-Tuning for Optimal Performance

Once you have the basic sag setting in place, it’s important to fine-tune the shock to your riding preferences:

  1. Check the rebound settings: After adjusting sag, make sure the rebound damping is set correctly. The Bomber CR Trunnion has easy-to-use rebound adjustments, which should be set so that the shock returns to its original position at a comfortable speed.
  2. Test ride: Take the bike for a short ride on varied terrain to test the suspension. Pay attention to how the bike behaves in different conditions. Does it feel too soft or too stiff? Adjust accordingly.
  3. Dial in compression damping: If you feel the bike is bottoming out too often, you can increase compression damping. Conversely, if the shock feels harsh, decrease compression damping for smoother performance.

Troubleshooting Common Issues

While setting up your rear shock sag, you may encounter a few common problems. Here are some potential issues and how to address them:

Issue 1: Shock Bottoming Out

  • Cause: Too little air pressure or too soft a compression setting.
  • Solution: Increase the air pressure or adjust the compression damping to prevent the shock from bottoming out.

Issue 2: Harsh Ride

  • Cause: Too much air pressure or too stiff compression setting.
  • Solution: Decrease the air pressure or soften the compression damping for a smoother ride.

Issue 3: Unstable Rebound

  • Cause: Incorrect rebound damping setting.
  • Solution: Adjust the rebound dial to slow down or speed up the shock’s return, depending on the riding conditions.

Customization and Optimization

The Bomber CR Trunnion rear shock allows for significant customization to optimize performance. Here are some key adjustments to consider:

Compression and Rebound Damping

  • Fine-tuning both compression and rebound damping will allow you to better match the shock’s performance to your riding style and terrain.
  • Experiment with low and high-speed compression settings for improved control during both fast descents and technical sections.

Air Volume Adjustments

  • Some riders may benefit from increasing or decreasing the air volume in the shock, which changes the spring curve and the shock’s response at the end of its travel.
  • This can help improve the overall feel of the bike, particularly for those riding on more aggressive trails.

Volume Spacers

  • If you find that the shock is too linear or too progressive, you can adjust the volume spacers. Adding or removing spacers allows for fine control over the shock’s behavior through its travel.

Compatibility with Other Drivetrain Components

The Bomber CR Trunnion rear shock is compatible with a wide range of bikes equipped with a trunnion mount. However, it’s essential to ensure that your bike’s frame and linkage are designed to work with this shock. The correct mounting hardware and spacing must be used to avoid installation issues.

Additionally, consider the overall weight distribution of your bike when setting up the shock, as this will influence how the rear suspension interacts with the front fork and drivetrain components.

Conclusion

Proper sag setup is crucial for getting the most out of your Bomber CR Trunnion rear shock. By following the steps outlined in this guide, you can achieve optimal performance, comfort, and control. Remember that sag settings can be adjusted based on personal preference, but maintaining the recommended range will ensure your shock functions at its best. Regular maintenance, including checking the air pressure and adjusting for changes in rider weight or riding conditions, will help you enjoy a smoother, more responsive ride over time.