Originally Posted by MerckxMad

There's a lot of hooey floating around here. When sizing a CX'er, the general thought is to go down one size from your road bike assuming the HT and ST angles are the same. If not, or if you are not coming into CX from the road, then, like any other bike, you want to pay attention to the length of the ST, HT and TT. The height of the BB (which is usually always higher than a road bike) has very little to do with correct fit other that it changes the HT and ST angles. The reason folks size down from road bikes has nothing to do with size of tires, BB height or standover height, but rather sizing down makes for a smaller cockpit and redistributes your weight/balance over the center of the bike to theoretically improve handling over rough stuff and off-camber parts of the course.

To get to your answer, a 54 Kona will have a 55.1 or 55.3 TT depending on the model year. It will also have a HT of 13 or 13.5mm and, of course, a 54cm ST. At least mine does. I'm 5'10" and ride a 55 road bike. I also have a 54 Kona Jake. I run a shortish stem and zero offset post to make my cockpit smaller, but the frame fits me perfectly. I hope this helps.