This is a link to a very well written article about fork offsets as it relates to mountain bikes. We are currently not making mountain bikes but the mechanics are the same for any bike or motorcycle for that matter.
I was put in mind of an incident that happened a while back at our factory here in Jacksonville Florida. A disgruntled and disheveled customer arrived at our doorstep complaining that his EMORY frame was misaligned and that it was impossible for him to ride down the street with no hands (perhaps with his mom on the sidewalk – I was thinking to myself – “Look ma no hands”) anyhow I digress…..
Rather than dismiss my surfer / hippy brother I decided to respectfully take his complaint seriously. I produced a straightedge that we use in our tool and die shop and placing it first on one side of the frame and then the other. It showed, and was evident, that the frame was straight.
Not good enough. He insisted that the bike pulling to the side was the result of bad workmanship. I told him that he had to ride down the middle of the street as the roads have a high spot in the middle for rain to run off but he was having none of it.
OK, I had the bicycle disassembled and placed on our cast iron straightening table first one side and then the other while measuring the difference with a micrometer. He was right. The difference was about .002 thousands of an inch (about the width of a human hair). Finally he was convinced. We reassembled the bike (no charge) and he left happy and presumably only rode in the middle of the road no hands from then on.
Back to offset or rack and trail. So, I explained that to him as well, demonstrating that when our front wheel was rotated 180 degrees the bike did not rise up and down, which is as it should be. The link above goes into great detail but basically that’s what we want; a nice neutral feel. Now one more thing: When folks are placing weight, in the form of fully loaded panniers extending the forks does give a bit more stability but otherwise we’ll stick with a nice safe neural feel. Great for riding down the MIDDLE of the street no hands!