Make sure the tire is properly inflated. If you know the tire pressure, but not the tire size, use that number and a pressure gauge to add or subtract air from the tire. You will need a bike pump or an air compressor to do any inflating. If you do not know the tire pressure, make a guess by pinching the tire with your thumb and forefinger, and judging the resistance. A road tire should offer a little give when you pinch it, and an off-road tire will give somewhat more.