Lightweight Wheels: Add More or Less Damping?

[Shazaam]

Neither.

One advantage in reducing unsprung wheel weight is that a lighter wheel can accelerate up and down faster when it encounters an uneven road surface. This allows the tires to stay in better contact with the road surface at higher speeds and with more uneven surfaces.

Let’s assume for the moment that your bike with heavier OEM wheels as been set up properly, That is, let’s assume that you’ve already installed the correct stiffness springs for your body-weight, you’ve properly adjusted their preload to obtain the correct ride height, and you’ve adjusted your dampers to achieve critical damping.

A critically-damped suspension system approaches equilibrium as fast as possible without any oscillation, and in the shortest time, after hitting a bump. This is best because it give a rapid recovery without producing either a harsh or bouncy ride, and will gives the best wheel tracking of uneven road surfaces by maximizing the time in contact with the road and therefore maximizes tire grip.

If the suspension doesn’t have enough damping, the bike feels unsettled because it takes a number of bounces (oscillations) before the suspension settles back down (reaches equilibrium) after hitting a bump. If the suspension has too much damping, the bike feels stiff and unyielding because it takes a long time before the suspension recovers from hitting a bump. If you hit a second bump before recovering from a first, the suspension “packs-up” and transmits higher impact forces to the bike and rider, and the wheel cannot track the pavement.

So now let’s look at your dampers to see what you’ve done.

Ducati dampers made by Ohlins and Showa use clickers to obtain motion control of LOW SPEED oscillations of the damper and incorporate a shim stack that opens at high damper piston velocities. The movement of the bike in it’s suspension is low speed. The movement of the wheels is high speed.

Here’s how the system works. The clicker adjusts the position of a needle valve that changes the size of the fluid flow orifice. As the piston moves faster in response to higher speed bump motions, this orifice would quickly go into orifice limitation, but it doesn't because the damper has a shim stack that begins to open up more oil flow area and take over control of damping.

To visualize a shim stack imagine a thin washer that covers a ring of holes and is backed by a small diameter spacer, then a second washer. As the damper piston accelerates, first the thin washer deflects easily, but as it bends up more, it contacts the second washer. This stiffens its resistance. Various combinations of washers of various thickness and diameter, with spacers, can be used to make damping closely proportional to velocity.

Unfortunately, this proportionality doesn't extend smoothly down to low velocities. To handle low-speed oil flow, therefore, a separate, adjustable orifice is provided. This orifice is adjusted by screwing a tapered needle into or out of it, and this is held at the desired setting by a spring detent. As you rotate the screw, you feel the detent click. This is the 'clicker', or external adjuster on your damper.

So, the motion of the wheel in response to pavement unevenness is high speed and dealt with by the shim stack which is not under control of the clickers. When you add lightweight wheels into a proper suspension set-up, the wheels will track better but changing the clicker settings will upset your overall handling and have no effect on your shim stack flow characteristics.