Join Date: Apr 2008
Location: St. Pete, Florida
Head tube and seat tube length are completely unrelated. If you're currently riding a 55cm frame and it fits, then chances are a 60cm is too big for you. You need to find a frame that fits YOU first, then figure out if you can reuse your existing fork. The key dimension to look at is Effective Top Tube. Saddle height adjustment can let you get away with a wide range of seat tube lengths, but ETT controls reach an you only have a few cm of adjustment (by changing stem length) before you are "forcing" the fit and compromising weight distribution and handling.
Now, to answer your original question ... if the HT is the same length AND uses a similar headset, then you can probably re-use your fork. However, 1cm of spacers doesn't give you a lot of margin to play with. Hopefully you have some additional spacers above the stem. What you're looking for is total stack height, which is the HT length plus headset stack plus stem height plus any spacers you want to run. That total has to be less than the length of your fork's steer tube from crown race to top.