[cbreez]

You didn't mention if this was straight line lock up or corners...I like to keep things simple....looking at the disparity in tires sizes, front smaller and rear much larger and wider, it is not surprizing at all that the fronts would possibly lock up sooner. A lock up can be from overloading the tires...an easy quick solution is to shift weight rearward. A proportioning valve is mostly used for rear wheel lock up because of weight transfer in racing situations, you see it all of the time on TV,but it would work for a street application if you wanted to play with it....lot of variables here...