I need more traction. I'm in the high so cal desert and traction is at a premium. There is some hard pack that is like asphalt and the rest is real loose. It has a 110/90-18 on it now, a Maxxis IT med compound, it's half worn out and the only way I can get any traction at all is at 10lbs. of air in it. How big of rear tire will fit? I'm looking for a rear that has large knobs that are spaced out and the bigger the better. Thanks.