What is the difference between hydro shocks and nitro shocks?

Answer 1

Hydraulic and gas charged shocks have the same amount of oil, the difference is the gas charge.

A hydraulic shock has equal amounts of dampening force in both directions. Gas charged shocks usually are pressurized with Nitrogen. Hydraulic shocks have a tendency to fade as the oil heats up and gets agitated by the shock, creating air bubbles. These air bubbles cause the shocks dampening ability to fade. The nitrogen charge keeps the air bubbles under control, so they can not affect the shocks performance. A gas shock will extend on its own due to the gas charge.

General rule of thumb is that hydraulic shocks ride better, nitrogen charged shocks are stiffer, but last longer and don't have shock fade problems.