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The Crossframe-Mixte:
When function determines the form of the bicycle
Triangulating the Utopia Kranich

a photo essay by André Jute

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The Kranich's frame style is technically a crossframe-mixte and is a modernized (and how!) recreation of Locomotief's famous Super de Luxe unisex crossframe built from 1936 to 1955. In more polite company, "unisex" was rendered as "priesterrijwiel" or "priest's bicycle" since the lowered top tube made it more dignified to ride in a frock. Yes, that really is the Locomotief logo: the Super de Luxe was their top model.

The frame is made by Van Raam in The Netherlands. Utopia had to develop their own lugs for the Kranich because even a straight-up reconstruction would be impossible as the old templates and molds were lost, and in any event the Kranich isn't so much a nostalgic reconstruction as a functional, determined development of an ancient good idea. Utopia, wisely resisting the siren song of trying to claim a bike so much developed is a faithful reconstruction, actively resist the notion of a nostalgia-bike; they prefer to speak of its functionality. The lugs are a mixture of traditional fully socketed lugs and layered lugs. A layered lug can take several forms. One consists of a sleeve socketing a tube or tubes, the sleeve being fillet-brazed to another tube, seen in the centre of the photograph above. Another layered form consists of a sleeved tube with another tube fillet-brazed to the sleeve, as at the top and bottom of the head tube in the photograph above. Utopia also uses internal lugs on some of their other cross-frames, and on the largest Kranich frame... A production-efficiency consultant would fall down dead of shock before he can deliver his report on Utopia.

The bottom bracket shell is fully lugged for the bottom tube, seat tube and chainstays and, above it, there is the beautiful lug to join the trapeze "top tube" and the seat tube.

So what makes a crossframe-mixte?
And why go to the expense of building one?

Locomotief, who obtained a patent for this design in the 1930s and proceeded to turn their unisex Super de Luxe into an unlikely bestseller from 1936 until 1955, when it must have seemed terminally old-fashioned in the bebop-cruiser age, followed no precedent with the crossframe-mixte, though the same designer created a related tandem in 1935.

The nearest other bicycle design is Pedersen's 1896 ladies' bike which depended on a rod for tension in the frame and didn't have the crosses jointed as did Locomotief (and licensee Durabo). I mention the Pedersen simply to stress the originality of the crossframe-mixte idea, not because the similarities will survive even cursory engineering analysis.

In engineering terms the Locomotief and the successor Kranich can be viewed as a two-dimensional trapeze frame with two full-length lateral mixte rails superimposed from head tube to dropouts to give the frame width: that much-desired third dimension which from width delivers stiffness out of all proportion to the extra weight. In addition, the twin mixte rails are attached to the other tubes of the frame everywhere that they cross them. In the photograph above, the mixte rails are fillet-brazed to the "top tube" of the trapeze, creating several vertical and horizontal triangles.

The ineffably elegant brace of the mixte transverse rails to the seat tube. Notice the tidy cable routing through the chainstay brace and over the mudguard. One cable carries electricity from the hub dynamo to the rear light, the other is a tube for the standard hydraulic rim brakes. The two cables under the chainstay are the gearchange cables for the Rohloff hub transmission whose yellow label is just at the edge of the photograph. Utopia was the first manufacturer in the world to specify Rohloff hub gears on their bikes.

I count 12 separate triangles or externally braced trapezoids, which for practical purposes are as good. You don't need to work a slide rule for long to support the eyeball instinct that the Kranich frame will be stiffer than an equivalent diamond frame. In this form it weighs 16.5kg, which for this class of bike, with the biggest and the best of everything, is excellent. Neither of my similarly-equipped aluminium-framed touring bikes can match that, and weight weenies can specify deraileur gears and save another couple of kilograms though I don't see the point of buying a sorglos (carefree) bike and then adding back the maintenance and wear and tear of derailleurs just to save a little weight.

•André Jute’s engineering books include Designing and Building Special Cars (Batsford, London; Bentley, Boston). He is also the creator of Jute on Amps the world's most popular DIY high voltage thermionic tube hi-fi site.

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All text and original photographs Copyright © 2009 Andre Jute.
Information and classic illustrations from two excellent historical bicycle sites:
www.oudefiets.nl and www.rijwiel.net.
Opinions are my own, of course.