Here is a must have tool for the serious racer. Just hook it onto a track clip and pull toward the back of the sled and you will see how many pounds it takes to make your track move. It has a handy guide that will mark where the gauge stopped. The key to a fast 120 is a free rolling 120, the easier your sled rolls the less horsepower it will take to move it. Most stock out of the box sleds have 20+ pounds of rolling resistance, a Championship winning 120 will have around 4 to 5 pounds of rolling resistance.