A C182 pilot on short final experienced a low level windshear and was unwilling to go around when directed to do so by the Tower Controller because traffic spacing decreased. After landing; the Reporter's aircraft passed the previous aircraft on the runway missing it by 50 FT.

Narrative

At approximately 12 miles out on a left base to final for Runway XX; Tower instructed me to follow a Cessna at my 12 o'clock and 3 miles. I replied that I had the Cessna in sight and would follow him in to Runway XX. The Tower Controller then cleared me to land Runway XX number 2 behind the other Cessna. At approximately 2 miles and 1;800 FT AGL; I began feeling tremendous turbulence and wind shear. Indicated airspeed was at 120 and dropped to 87 with tremendous LLWS. The Cessna in front of me was slowing up so much that I began to perform S-turns in order to keep enough spacing for landing. I continued to experience such severe LLWS that I felt my life was in danger and that I might actually make contact with the ground. My indicated airspeed had dropped and my ground speed dropped to approximately 70 KTS. At 1/4 mile from the approach end of Runway XX; Tower instructed me to go around. At that point; with the LLWS and fear of my safety; I responded 'UNABLE.' It all happened so fast that I felt I couldn't climb back up into that LLWS and maintain a safe attitude and altitude. I knew that I just needed to get down on the runway as safely as possible. I kept the other Cessna in sight the entire time and maintained distance from his aircraft. Since he was in a slower aircraft he was able to slow down quicker than I in a 235 HP 182 and I ended up passing him on the ground to the right with a little over 50 FT between us. With the Runway being 150 FT wide and with him over to the left of the centerline already and considering all the factors that led to this; I felt relieved to be on the ground safely. I believe next time I will continually ask the tower for updates on ground speeds of aircraft that I am directed to follow so that I can maintain a farther distance sooner rather than later. However; considering the LLWS and turbulence; I don't know how I could have slowed down anymore without jeopardizing my safety and life.