DIY Rear Shock Sag Setup for Bomber Air Trunnion

Posted on
in Uncategorized

The Bomber Air Trunnion [paid link] rear shock from Marzocchi is known for its durability and exceptional performance in tackling rough terrains. Proper suspension setup is crucial to ensure that the shock functions optimally, providing the best possible ride experience. One of the most important steps in achieving the ideal setup is adjusting the sag.

Sag refers to the amount the rear shock compresses under the rider’s weight. Setting the correct sag is essential for improving bike handling, comfort, and overall performance. This guide provides a detailed, step-by-step process for setting up the sag on your Bomber Air Trunnion [paid link] rear shock.

Tools Required

  • Shock pump
  • Ruler or tape measure
  • A helper (optional, but useful)
  • A level surface for bike setup

Understanding Rear Shock Sag

Sag is a critical factor that influences the performance of your rear suspension. It determines how much of your shock’s travel is used when you’re on the bike, which directly affects the shock’s responsiveness and ride comfort. Too much sag leads to a feeling of a soft or “soggy” ride, while too little sag can result in an overly harsh ride with poor traction. Proper sag ensures that your suspension absorbs impacts efficiently, offering a balance between comfort and performance.

For the Bomber Air [paid link] Trunnion, the recommended sag range is typically between 25% and 30% of the shock’s total travel. To set this up correctly, follow the steps below.

Step 1: Prepare the Bike

Before starting the sag setup, ensure your bike is positioned correctly.

  • Place the bike on a level surface, such as a floor or a bike stand [paid link].
  • Ensure the rear shock is clean and free of any debris that could affect measurement accuracy.
  • Make sure your tires are inflated to the recommended pressure.

Step 2: Measure the Shock’s Total Travel

To determine the correct sag, you must first know the shock’s total travel. For example, if your Bomber Air [paid link] Trunnion has a total travel of 160mm, the goal is to set the sag to 25-30% of this distance.

  • Using a ruler or tape measure, measure the shock’s total travel from the top of the shock body to the bottom (fully extended position).
  • Record the total travel distance, as you’ll need it for the next steps.

Step 3: Set the Shock Pump to the Starting Pressure

Before checking sag, you must set the appropriate starting air pressure for your rider weight.

  • Using a shock pump, inflate the shock to the recommended pressure. You can find these values in the shock’s manual or Marzocchi’s guidelines for your rider weight. A good starting point for the Bomber Air Trunnion is approximately 200 PSI for a 75kg rider, but this can vary based on personal preference and riding style.
  • It’s important to note that the pressure will vary depending on the rider’s weight and intended use, so refer to your specific guidelines for the most accurate starting pressure.

Step 4: Position the O-Ring

To measure sag correctly, you need to install an O-ring on the shock shaft. The O-ring will serve as a marker for the amount of shock compression under your weight.

  • Slide the O-ring onto the shock shaft, ensuring that it is placed at the highest point of the shock body.
  • Make sure the O-ring is snug but able to slide up and down the shaft as the shock compresses.

Step 5: Get on the Bike

Now it’s time to get on the bike and achieve your riding position. Ideally, this step requires a helper to measure the sag while you are seated.

  • Put on your riding gear, including a backpack or any additional weight you typically carry during rides.
  • Mount the bike and get into your riding position. Sit in a normal riding posture, ensuring your weight is evenly distributed on the saddle.

Step 6: Measure the Sag

While you’re in position, the O-ring will be pushed downward by the compression of the shock. To determine the sag, measure the distance between the O-ring’s starting position (top of the shock body) and its final position (after you are seated).

  • Use the tape measure to measure the distance the O-ring has moved from the top of the shock body.
  • Calculate the percentage of travel that has been used. For example, if the shock has 160mm of total travel, 25% sag would be 40mm. If the O-ring has moved 40mm, your sag is perfect.

If the sag is not within the recommended 25-30% range, adjust the air pressure in the shock.

Step 7: Adjust the Air Pressure

If the sag measurement is too high (i.e., the O-ring has moved too far down), you need to increase the air pressure in the shock. This will reduce the amount of sag.

  • To increase pressure, use your shock pump to add small increments of air (usually 5-10 PSI at a time).
  • After each adjustment, recheck the sag by repeating the process described in Step 6.

If the sag is too low (i.e., the O-ring has not moved enough), reduce the air pressure in the shock to allow for more compression.

Step 8: Final Check and Fine-Tuning

Once you’ve adjusted the sag to the correct percentage, double-check your measurements to ensure consistency. You may need to fine-tune the pressure slightly for comfort and handling preferences.

  • Test the shock by compressing it with your hand to ensure it is responsive and smooth.
  • Ride the bike in different conditions to make sure the suspension is performing well under various loads.

Troubleshooting Common Setup Issues

If you encounter issues while setting up the sag, consider these troubleshooting tips:

  • Sag too deep or soft: This may indicate that the air pressure is too low. Add more air in small increments and test again.
  • Sag too stiff or shallow: If the shock feels harsh or unresponsive, reduce the air pressure slightly.
  • Inconsistent sag readings: Make sure the O-ring is correctly positioned at the top of the shock and the bike is on a level surface during measurement.

Customization and Optimization

Once you’ve set the correct sag, you may want to fine-tune the shock for different riding styles. The Bomber Air Trunnion offers adjustability through rebound and compression settings.

  • Rebound Adjustment: Adjusting the rebound allows you to control how quickly the shock returns to its fully extended position. For smoother, more controlled descents, slow down the rebound. For more responsive and quicker rides, increase the rebound speed.
  • Compression Adjustment: Fine-tuning the compression settings allows you to adjust how the shock absorbs impacts. Softer compression is ideal for absorbing smaller bumps, while stiffer compression is better for handling larger impacts.

Experiment with different settings based on your riding style and terrain to optimize the Bomber Air Trunnion’s performance.

Compatibility with Other Drivetrain Components

The Bomber Air Trunnion rear shock is designed to integrate seamlessly with a wide range of mountain bike drivetrains. However, it’s important to ensure compatibility with the frame, especially when considering different shock mount types. The Trunnion mount design is popular among modern bike frames, offering increased stiffness and improved responsiveness compared to traditional mounting systems.

When pairing your rear shock with other drivetrain components, ensure the following:

  • Rear Suspension Travel: Ensure that the rear shock’s travel matches the frame’s design and intended travel range. The Bomber Air Trunnion is available in various travel lengths, so select the appropriate option for your bike.
  • Frame Compatibility: Check that your bike frame has a compatible trunnion mount or is designed to accept a rear shock with this mounting system.

By properly setting up your rear shock sag and adjusting the compression and rebound settings, you’ll optimize your Bomber Air Trunnion rear shock to handle any terrain with ease. Whether you’re a seasoned rider or a beginner, getting the suspension setup right is the key to a smoother, more efficient ride.