I have had them on my Gen II non-ABS but 40mm rear caliper car for awhile. I love the R4S on my SRT-8 Jeep as they are very clean, quiet, and eased what I would characterize as an overly grabby pedal feel. But now that I have had them on the Viper for awhile I am thinking about ditching them and going back to stockers. They are making dust on the Viper. No where near the mess of the stock pads, but if I have to wipe the wheels off anyway what the heck. BUT the biggest thing is they just plain do not stop the car well compared to the stockers. Yes I hated the low speed/low pressure squeal and mess of the stocker but DANG those things were like throwing out an anchor at 100 mph. I do not feel safe stopping the car from 100+ with the Portefields (I never tried the R4 race compound). I guess in the world of Viper-tax etc $250 for that lesson was not catastrophic. Regular slow street driving I really like the R4S, but high speed I do not.