Hand numbness can spoil the most wonderful long distance ride. A cyclist’s hands can get numb from vibration and pressure.
The first step is to eliminate as much vibration as possible near the source (road surface). Supple, wide tires, run at moderate pressures, are key. Flexible fork blades and suspension are less effective at absorbing high-frequency vibrations, but they can absorb bigger bumps. Cushy handlebar tape is ineffective at absorbing vibrations, but it can reduce pressure.
Why are vibrations easiest to absorb at the source? It is relatively easy to stop a few grams of tire contact patch from moving up and down. This insulates the rest of the bike from the vibrations at the road surface. If your tire doesn’t absorb the vibrations, then your entire front wheel moves up and down a few hundred times every second as it rolls over rough pavement. These forces are then too large to be absorbed elsewhere.
Imagine somebody throwing a peanut at you: It is easy to catch with one hand. Now imagine having to catch a 5 lb weight – much harder. That peanut at the road level becomes a 5 lb weight at the handlebars, if the whole front of the bike vibrates.
Pressure can cause nerve damage in your hands, making them numb or tingly. When you look at the nerves in your hand, you see that there are only a few nerve endings in the base of your thumb, making this area ideal for resting on the handlebars.
The “on the ramps” hand position (behind the brake hoods) supports your weight with the base of your thumb, and therefore tends to be very comfortable (see photo at the top). This works best with handlebars that have flat ramps to support your hands well in that position.
Moderately soft handlebar tape can help distribute the pressure of your hands as they rest on the handlebars. Also, your hands should rest on the bars, rather than grip them tightly. Wrap your fingers around the bars loosely for safety on rough roads.
Beyond that, it helps to switch hand positions from time to time, so that you don’t put pressure on the same spot for too long. Furthermore, raising your handlebars or tilting your saddle nose slightly upward will prevent you from sliding forward and putting more pressure on your arms and hands. (However, tilting your saddle upward may cause other problems for some riders…)
Numb hands can lead to lasting damages. With the right technique and equipment choices, numb hands usually can be avoided even on rides as long as Paris-Brest-Paris (765 miles non-stop).