Someone correct me if I'm wrong but exponential is an adjustible sensitivity of your transmitter output. For example with throttle expo, if you turn it down, it will slow the power to your motor in relation to your trigger input, making the car accelerate more controlably instead of just lighting the tires. The same would go for your steering. Positive expo will give you a quicker initial steering response, and negative would slow it down in relation to your wheel input. Does this help? Maybe sombody smarter than me could explain it a little better, as you can see I have a pumpkin for a head.