Here's a nifty demonstration of how to modify a Lego car to go up a glass incline. It slips at 20 degrees until it's converted to a 4-wheel drive. At 40 degrees it needs grippier tires. At 50 degrees it flips upside down until its center of gravity is dropped. The modifications continue until the car is going up a 180-degree slope (i.e., upside down).