Carbon vs Steel Fork

[DebW]

The bottom bracket height on Isis is 10.3 and Classic 10.4, which I consider vitually identical. Please clarify why the slight difference in chainstay length is important for loaded touring. Is it just to be sure that my feet can clear rear pannier bags, cuz Isis comes with rear rack stays and I have never had a problem with that, or would it have a significant effect on bike stability under load.

With only 1/4 inch difference in chainstay length it probably won't be noticable. There are 3 reasons for longer chainstays on touring bikes: pannier-foot clearance, pannier weight stability (ie. you don't want weight behind your rear hub), and a softer ride on rough ground (but there are other factors here as well). The more foot clearance, the larger pannier bags you can carry. Traditionally, a touring bike also had a lower bb to lower the rider's center of gravity (actually the opposite is true for your 2 bikes). You obviously aren't talking about a bike that is built exclusively for touring with a really long wheelbase and poor acceleration, but a do-everything bike for light tours and fast rides both. If you were comfortable touring on your old classic, looks like the new Isis should fill the bill as well.

Another question, do you think center pull canitlivers or long reach side pull breaks are best? I know I should be discussing this with the frame builder, but since he is just retrofititng my bike with couplers and doing the fork, he doesn't seem interested in being real chatty about it all, I presume relative to a customer for whom he is building a complete bike.

You can probably get by with either brake type if you're not carrying really heavy loads over really hilly terrain. But cantis are best for loaded touring. Does the new frame have canti bosses on the rear, or can you get them added? You also need cable-hangers for centerpull canti's, usually attached among the headset spacers on the front and on the seat post bolt or to a braze-on on the rear. Get the braze-on if you can.