+100 to all above and you can also calibrate it to known trail distances. If it is reading 26 miles when you know the distance is really 25. 6 miles, enter a lower value for the tire size . My cateye is so close with the preset for 700x23 I left it alone but I had to lower the number on my Topeak as it was reading over 2 extra miles in a 50 mile distance. If I remember correctly it said to set it at 2133 for 700x23 and 2100 is much closer for the topeak. Just experiment with it and you will be able to get it very close.