Super Champ Gent's and Mod58's (twin-hollow), and Mavic E-2's were all extruded rims with hollow sections, joined by pins or sleeve. Weinmann concaves, though extruded, were usually, if not always, welded at the joint and often braked poorly as the external grinding was too deep in some cases.
Earlier aluminum 27" rims were more commonly formed from a strip of sheet. Popular rims by Weinmann, Birmalux, Fiamme, Nisi and others used this singlewall design, while 700c sewup rims were formed from sheet-derived tubing to allow their much thinner wall.
Clincher rims made from sheet strip require welding at the joint, an often troublesome spot in terms of cracking and rim evenness when braking. Subsequent closed-section, extruded clinchers eliminated these problems and reduced weight, while it should be mentioned that extruded sewup rims (Mavic Reflex) are contrarily heavier than their earlier, sheet-derived (GP4) counterparts and use an advanced welding process with machined sidewalls.
There are a few variants of early, welded singlewall clinchers, some dimpled, some with a shallow step to a dropped center, and also the Nisi Evian with a simple, gentle convex profile. All were relatively wide as I recall, about 22-25mm outside. These rims, barring the Nisis, were often very lumpy, leading me to believe that the rolling operation may have been done with a hand crank, with feed speed (and thus creep yield and profile shape) cycling several times along the rim's circumference. I hate that!
David Snyder Auburn, CA usa
----- Original Message -----
From: "Jerome & Elizabeth Moos" <jerrymoos@sbcglobal.net>
Subject: [CR]More Advice on 1970 Touring Paramount
>
> Also, this bike has Mavic G-40 27" clincher rims, much newer than the
> bike. I know a 1970 touring Paramount would have had 27" clinchers, but
> what brand? Weinmann, marked either Weinmann or Schwinn Approved? Was
> the Weinmann concave available in 1970, or is it too new?