4 ▁is ▁slow ed ▁by ▁ 2 9 4 mm ▁vent il ated ▁front ▁disc ▁bra kes ▁and ▁tw in - pot ▁floating ▁cal ip ers ▁and ▁ 2 9 0 mm ▁vent il ated ▁rear ▁disc s ▁and ▁single - pot ▁floating ▁cal ip ers . ▁An ▁increased ▁diameter ▁vac u um ▁assist ed ▁tan dem ▁boost er ▁gives ▁reduced ▁ped al ▁effort ▁though ▁relatively ▁firm ▁bra king ▁feel ▁( see ▁graph ). ▁The ▁system ▁is ▁diag on ally ▁linked ▁to ▁maintain ▁safety ▁in ▁the ▁event ▁one ▁line ▁should ▁fail , ▁and ▁front ▁and ▁rear ▁pressure ▁control ▁val ve ▁are ▁used ▁to ▁balance ▁bra king ▁force ▁to ▁suit ▁weight ▁distribution . ▁Max imum ▁bra king ▁dec eler ation ▁from ▁ 1 0 0   km / h ▁is ▁ 0 . 9 9 g ▁with ▁a ▁ 3 9 . 4 ▁met re ▁stopping ▁distance . ▁ ▁The ▁B 4 ' s ▁standard ▁anti - lock ▁bra king ▁system ▁is ▁Bos ch ' s ▁ 5 . 3 i ▁system ▁( which ▁is ▁made ▁under ▁license ▁by ▁N ipp on ▁A BS ). ▁It ' s ▁a ▁ 4 - channel , ▁ 3 - phase ▁system ▁with ▁the ▁front ▁whe els ▁controlled ▁individually , ▁while ▁the ▁re ars ▁are ▁controlled ▁joint ly ▁( through ▁the ▁' select ▁low ' ▁method ). ▁The ▁select ▁low ▁method ▁uses ▁the ▁rear ▁wheel ▁with ▁the ▁lower ▁coefficient ▁of ▁ad hes ion ▁to ▁calculate ▁the ▁bra ke ▁line ▁pressure ▁applied ▁to ▁both ▁of ▁the ▁rear ▁whe