i have the same thing happening in my wifes car
. and found out that the alternator wasn't putting out the amp needed to run it so it would shut off the ABS and then the light would come on, the brakes still worked but ABS did not!
dose it happen some times when you have your foot on the brake?or when you are drawing power like lights and stuff like that?
your tier size shouldn't effect that at all. i would assume it was a electrical issue more then dirt or tire size!!! try spraying some electrical cleaner in the alternator and tighten your wire connections and see what happens.alot of dirt will get in there when you are wheelin or just driveing dirt roads and wires come lose from vibration. thats what ended up worked for me. and take it to a auto zone or napa and have them test your battery and altanater its free there. thats where i would start before takeing it to a dealer or something. well that depends on the warrenty!!