I have just gotten a Trek Incite 8I computer (wireless) and have a question regarding setting up the wheel size. The computer, as do just about all computers, has several preset wheel size configurations to choose from including a custom setting. I have a 26" 1.6 semi slick on my MTB but the closest preset is 26 1.5. The next size is 1.9. Is the difference between 1.5 & 1.6 too small for me to worry about or should look at using the custom wheel size setting? For now I am using the 1.5 setting.