In a previous article I had briefly mentioned some of the effects of shock absorbers. This was a very simplified view to their application in the vehicle. In this article I will go over how shock absorbers affect weight distribution and overall handling of a vehicle.
Starting off, it's important to note that shock absorbers in their purest form do not add to the spring rate of a vehicle. Therefore, stiff rear shocks cannot replace soft rear springs and vice versa. Shock absorbers function by resisting changes in the motion of your vehicles suspension geometry. Simple adjustable shock absorbers tend to only have a stiffer/softer setting. But more expensive adjustable shock absorbers can be tuned to have 2 or even 4 different adjustment settings, namely bump, rebound, high speed bump, and high speed rebound.
Since shock absorbers don't add to the spring rate of the vehicle, this means that the steady state driving conditions of the vehicle aren't affected by the shock absorbers. So if your car likes to consistently under or over steer in a corner, shock absorber settings is not likely the suspension parameter you want to be touching. If however the vehicle under/over steers during the initial turn in response of the vehicle or when the vehicle goes over bumps/depressions, then shock absorber settings is likely what you want to adjust. In other words, spring rates=static weight transfer, shock absorbers=transient weight transfer.
Much like adjusting spring rates, the stiffer you make the shocks the faster weight will transfer. If you stiffen the rear shocks your vehicle will have a greater tendency to over steer during initial turn in. This is due to a faster weight transfer in the rear. Likewise, if the front end is stiffer the vehicle will tend to under steer during initial turn in due to a faster weight transfer up front.
Bump stiffness and rebound stiffness work together to resist a vehicle rolling in a corner. If your bump stiffness is too high compared to the rebound stiffness the weight will be transferred by lifting the chassis at the inside wheel rather than dropping the chassis on the outside. This will lift your vehicles center of gravity and this in turn will degrade your cornering capacity. As a rule of thumb, bump stiffness should be about 65% softer than rebound stiffness.
Low speed settings are generally used for adjusting the turn in of the vehicle while the high speed settings are used to allow the vehicle to handle bumps and imperfections in the road better. This means that in corners the shocks will generally operate stiffer allowing for a faster and more controlled weight transfer, and when a bump or depression is encountered the rapid suspension movement will lower the resistance shock absorber thus allowing the suspension to remain in contact with the ground and transfer less of the bump/depressions effect to the chassis. Reducing bump/depression effects is great because it will allow for a smoother and more controlled ride.
Another effect of damping to look out for is under/over steer when bumps or depressions are run over. If you don't have shocks with a softer high speed settings the vehicle will tend to under or over steer whenever imperfections in the road are met (depending on your setup). If you prefer having the vehicle safely under steer during turn in, then set the front absorbers to be stiffer than the rear. Generally speaking a little under steer isn't too much of a problem, you'll lose a little more traction in the corner but it's less dangerous. However, if your vehicle is tuned to have a bit of extra turn in response by having stiffer rear absorbers, the vehicle may then have a tendency to scare you in the bumpy bits by causing momentary over steer.
So far we have discussed a lot of front/rear adjustments; these are generally made for road courses where a similar left/right turn is desired. If however the tuning is made for a speed way car (i.e. only left hand turns) left/right adjustments may also be made. By increasing the left bump/rebound stiffness settings compared to the right side, your vehicle will transfer more weight on the left hand side during braking/accelerating, this reduces the weight transfer on the right hand (laden) wheels and improves grip when accelerating/decelerating.
I hope this article was written clear enough to help demystify how shock absorbers work. If you have any questions feel free to ask below.