79pmooney

+1 Front center roughly equals Wheel base - chainstay length. (I say roughly because there is an about 2" difference in height between the hub axles and the bottom bracket so this isn't quite exact but it is close. If you ignore published front centers and just use this calculation, you can quickly see what bikes work for you and which don't. To do this:

Measure the axle to axle wheelbase of a bike that works for you. Measure the BB center to rear axle. The difference is now the calculated front center. Now it's easy. Most bike specs publish both wheelbase and chainstay length.

Yes, you can also get there (and more exactly in theory) using the frame geometry but - the seat tube angle determines where the top tube starts. So where the top of the head tube is depends on both seat tube and top tube. Now you draw that line of the head tube angle and offset that by the fork rake. You are looking for a number where a few mms matters a lot. This method trusts 5 of the specs to be right on over about 1 1/2 meters of tubing.

And for all this, even with my simple calc, we have to trust the specs or bring our tape measure or shoes. Specs are published months before the first bike of that year rolls of the line. Changes happen. Carbon fiber means once the mold is made, no more changes for the frames off that mold, but - molds get replaced, there are varying levels of oversight between design offices, often on different continents, and manufacturing plants, different languages, etc.