Shock Packing Down — What It Is and How to Fix It
If your rear end feels harsh, kicks sideways, or gets worse through consecutive bumps, you're likely dealing with rebound packing.
What Is Packing?
Packing happens when the shock cannot return fast enough before the next impact.
Each bump compresses the shock further until:
- Travel is reduced
- Suspension stiffens progressively
- Traction drops
The shock is being pushed down faster than it can recover. It "packs" deeper into the stroke until it has no travel left — then every subsequent bump goes straight through the chassis to the rider.
Common Causes
- Rebound damping too slow — the most common cause. The shock can't extend fast enough between impacts.
- Overly stiff rebound shim stack — clickers may not have enough range to compensate
- Excessive oil viscosity — heavier oil increases all damping forces including rebound
- Poor base valve balance — compression and rebound circuits not tuned as a system
What It Feels Like
Locks Up Over Bumps
Rear end becomes progressively harsher through a series of bumps — whoops, braking bumps, or rocky sections.
Rides Lower and Lower
The bike sinks into the stroke and stays there. You can feel the shock sitting deeper than it should be.
Loss of Grip
Rear tyre skips and loses traction because the shock can't follow the terrain. The wheel bounces off instead of conforming.
Harsh and Unpredictable
Combined with reduced travel, the bike feels harsh and unstable — especially in the last third of the stroke.
The Real Fix
Clickers can help slightly, but the real control comes from the rebound shim stack design.
You need to:
- Reduce rebound force in key velocity zones — where the shock needs to return quickly between bumps
- Maintain control without slowing return too much — too fast and the bike pogos; too slow and it packs
- Balance compression and rebound — they work as a system, not independently
Model It Properly
The Shim Calculator lets you:
- See rebound force vs velocity — identify exactly where the damping is too slow
- Test stack changes instantly — reduce rebound force in specific velocity zones
- Compare three recommended stacks and pick the one that balances control and return speed
- Run suspension simulation to validate the stack won't pack on your typical terrain
Fix Your Rebound Stack
Enter your shock rebound shim stack and see the force-velocity curve. Find out exactly where it's too slow.
Use the Shim CalculatorGet the Handbook
The Suspension Engineer's Handbook covers rebound tuning methodology, shim stack balancing, and packing prevention in detail. A$69.95 PDF download.
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