I just restored a GT mountain bike for my son. It had RoxShocks and under the caps was a hole that you could put in a inflation attachment for like a football and adjust air pressure to adjust stiffness. Not sure of yours has the same capability. Also, reading up on those type of air inflation systems, the valves go bad over time, so yours may not hold the pressure. In that case they would need to be rebuilt or replaced. Best regards, Doug