This is Penske’s Triple Adjustable shock, as run on Pro Street bikes. It offers separate high and low speed compression adjustments. This allows you to tune the shock separately for starting line, and down track, as well as or fine tuned adjustment. It also has rebound, spring preload, and additional ride height adjustment to raise and lower the rear of the bike. This model is a piggyback, the reservoir is mounted directly to the shock, and has a faster response time.