I posted this in the road forum but am not getting much response:
I went on a group ride yesterday with my new computer (trek incite ach digital) and while in the group I was looking around and saw that my computer had been reading the same speed as others at times and different at other times and when I stopped I asked what the distance and average speed were of another guy and mine was way above what his was. My question is why would a computer do this and can I fix it? My wheel size is set correctly.

Sounds like you might need to mount the magnet a little closer to the sensor. It's also possible you have interference issues. Make sure there are no obstructions between the sensor and the computer. I prefer wired computers for that very reason.