Shock FAQ

[johnc]

"Shock Absorber" and "Damper" are the same thing with Damper being the more correct term.

 

Dampers do exactly that, they dampen the energy stored in the springs when springs are doing their job absorbing shocks and supporting the chassis of the vehicle. If the large amount of energy stored in a spring is not controlled, the spring will oscillate causing dangerous handling traits. A Damper converts this stored energy into heat by moving a piston(s) through hydraulic fluid.

 

Dampers work in two directions:

 

"Bump" or "Compression" - when the damper is compressed as the result of a wheel hitting a bump or the car rolling onto the damper in a turn (the outside of the car in a turn).

 

"Rebound" - when the damper extends after the wheel passes over a bump or as the result of the car rolling away from the damper in a turn (the inside of the car in the turn).

 

Inside the damper valves on the piston(s) control the rate of flow of hydraulic fluid thus controlling the rate at which the damper compresses or extends. This valving is speed sensitive so a fast impact triggers special blow-off valves that allow the damper to compress quickly while slow speed changes (like those encountered while the chassis is rolling in a turn) are more restricted. More sophisticated shocks allow adjustment of the valving through disassembly and changing shims and fine tuning of the valving can often be done through external adjusting controls.

 

The rate of flow as it relates to speed can be plotted on a chart and usually assumes some type of curve. Damper dynos exist to measure and diagram the damping curves. These curves can be progressive (most common) or digressive (better but more expensive and rarer).

 

Typical external adjustments are:

 

Single Adjustable, Bump and Rebound - Both bump and rebound valving are adjusted simultaneously along a set curve. The Tokico Illumina 5 way adjustable damper is an example of this type.

 

Single Adjustable, Rebound - Only Rebound valving is adjusted. The Koni 8610 is an example of this type.

 

Double Adjustable, Bump and Rebound - Bump and Rebound valving have their own adjustment. The Koni 8611 and Ground Control's Advance Design are two examples of this type.

 

Triple and Quadruple Adjustable - Low and High Speed Bump and Low and High Speed Rebound valving are adjustable on these very sophisticated race only dampers. Penske and Ohlins are two examples of these types of dampers.

 

How do Bump and Rebound settings affect handling:

 

BUMP

 

Too much Bump control makes the car harsh riding and changes in attitude are very sudden (snap oversteer, skating, sliding). Chassis roll is slow to develop and make cause the car to skate in corners.

 

Too little Bump control makes the car seem sluggish. The car pitches a lot and rolls to the oputside of a corner very quickly. It feels like its falling over on its outside front on corner entry and outside rear on corner exit.

 

REBOUND

 

Too much Rebound and the tires don't return to the ground quick enough. Inside tires tend to get lifted. Over a bumpy track the car may actually jack down. Braking will be skittish.

 

Too little rebound and the car oscillates after bumps. The car will not put power down well and transient response will be slow.