Ok, So on My Jamis, the frame's headtube length is 3.54 inches, I want a new frame for Christmas and The frame just so happens to be a Titus Racer-X. The Headtube Length on the Titus is 5 inches. I was wondering If I could use my Current fork (Fox F100 RL) on the new titus. If Not, Would it be better to just replace the fork legs with new ones since it will be time for a rebuild anyway or just get a new fork?
Depends on whether or not your current fork was cut. How tall are the spacers above your stem?
If you have more than 1.46 inches of spacers under your current stem, the old fork will work on the new frame, but without any spacers. Of course the stack height of the headset will come into play also, but if you have closer to 2 inches I'd say you will definitely be fine with the old fork. Anything less than 1.5 inches, I'd say the old fork is too short.
Your fork legs do not effect in any way the frame fitment. The steer tube is the key here. As stated. If you have 1.5" - 2" of steer tube above the headset on your old frame, the fork will probably fit. If not, you will be buying another fork.