Rim (not tire) clearance for caliper brakes?
 

I am wondering how far the arms on newer short-reach caliper brakes open up, I have rims that are about 25-26mm wide (touring/hybrid rims), and I would like to use them on a newer road frame. Curiously, I can't find any info about that spec on the Shimano website. I'm hoping that I don't have to buy narrower rims to use with the new frame I just bought. I am specifically referring to rim clearance, not tire clearance.

Does anyone know how wide they open? If I had some here, I'd do it myself, but I don't have any yet. I am looking at lower end Shimano (Tiagra, 105) or Tektro calipers.

Also, do long reach calipers open wider?

Sorry if this is a common question, but I used the search and can't find any info.

I guess that I don't understand the question.

With the tire installed, the tire is generally a bit wider than the rim. Consequently, tire clearance is what determines whether you can install the wheel between the brake arms. As a general rule, a fully inflated 28mm tire will just barely squeeze between road caliper brake pads with the QR open and provided the pads aren't set up too close to the rim. With no tire, there's no issue.

Reach is an entirely different issue. Reach relates to the pads aligning with the wheel's brakeing surface. You don't have a choice on brake reach. You have to buy the calipers that match your bike frame.

I just measured a couple of sets of spare caliper brakes in my parts box and the maximum width between the brake pad faces with the springs fully relaxed was 32 to 35 mm. So that is the absolute widest object they will clear.