A vehicle slip state determination system serves to calculate an estimated
vehicle speed VB, an estimated vehicle deceleration in the vehicle speed
DVB, and each of wheel speed differences between right front and rear
wheels and between left front and rear wheels .DELTA.VR, .DELTA.VL,
respectively. The wheel speed difference .DELTA.VR, .DELTA.VL are divided
into three ranges, that is, range 1, range 2, and range 3 by the speed
difference upper and lower limit values JVUP and JVLO, each of which is a
linear function value with respect to the estimated vehicle deceleration
DVB. In the ranges 1 and 3, the vehicle traveling on the road with the
low friction coefficient .mu. is brought into the slip state where four
wheels are slipped. If the wheel speed difference at a predetermined
estimated vehicle deceleration deviates from a determination range
defined by the upper and lower limit values, the slip state of the
vehicle, that is, the condition where the vehicle is traveling on the
road with the low friction coefficient .mu. is determined.