Expensive pan scraper tires are subjected, during the bowl loading cycle, to wheel slip far beyond that actually needed to produce optimum machine draft force. Virtually all scraper operators routinely spin the wheels vainly attempting to produce more draft force than traction will permit. Available traction depends on terrain and tire load, which change unpredictably during the loading cycle, and it is difficult to load as rapidly as possible without slipping the unseen tires. The Wheel Slip Monitor provides two prompt and intuitively understandable operator warnings when any tire exceeds a preset slip rate: a beeping tone sounds accompanied by a flashing light and both beep rate and light flashing increase in direct proportion to the slip rate of the worst wheel. Development and field testing are described and it is shown how the Wheel Slip Monitor makes practical the acquisition of certain unique tire test data. The potential advantages of automatic wheel slip control are discussed.