changing tire size and ECU/abs problem

lgirard

Guys,

My 2009 Z is mostly used on track. This summer I had the bad idea to change the tire size on my 370Z tire size, thinking I would increase handling. I bought a set of RE71R. 265-35-19 in the front and 285-35-19 in the rear. That's when all of my problems started. I soon as I hited the track with this setup, the ABS would overly interveen which cause braking distance to be much longer. I month a a half later, I chated with a tire specialist who told me that he had seen similar beaviour on GTR when tire diameter between front/read are outside a certain range (+- 3% according to this guy). I then tested his theory by removing the ABS relay and braking came back as strong and powerfull as it was before I changed tire size. I can drive the car without ABS on dry pavement but I would like to keep ABS on wet tracks. My question is: Does anyone knows/understand what is the algorithm used by the ECU to drive the ABS module and what are all the parameters to take into consideration. As an example, I bought back a set of RE71R 245-40-19 (OEM size) and I kept my 285-35-19 in the back. Doing calculation proved that the front to rear wheel size ratio is with 1%. It improved the ABS behavior but it is still kicking in to much, to early. WHY?????
Can anyone help ?