Girder Forks

General Configurations

The overall assembly of the individual parts of a typical Girder suspension system can be quite varied. For example the links can be situated on the ‘inside’ or the ‘outside of the main fork legs. The links themselves can be fabricated from tubing or from flat bar stock or from castings. It’s not uncommon to see more than one link attachment method used on a single girder. You’ll sometime run across units that use continuous pivot shafts in the forks but rigid link pins on the yokes and vice versa. You’ll also see units where the upper links may be mounted inside the fork legs while the lower links are mounted outside. On some customs you’ll see forks with only one central upper link and two lowers or one central lower and two uppers. Occasionally you’ll find a fork where the shock or shocks are mounted below the lower yoke and attach to the rear legs in a modern adaptation of the old Vincent configurations.

Folks are finally catching on to the fact that a good mono-shock mounted lower in the forks reduces the height of the bikes center of gravity and permits one to use very short links while cleaning up that area ahead of the steering stem.

Hardware and Connections as to Appearance

Earlier we alluded to the fact that in the realm of chopper building there are often trade-offs, adjustments and compromises made that create a balance between strength, practicality, form, function and simple appearance considerations until just the right balance of critical factors, tempered with artistic judgment result in a final design concept that not only ‘works’ but also looks good at the same time.

All of us at one time, or another, have walked through a bike show and seen machines that defy the imagination. We’ve also made mental notes about which particular bikes were really ‘roadworthy’, or could actually be driven on a daily basis and which one’s were pure ‘eye-candy’.

If you decide you want to build Girders your design talents will be pushed to the limit since I cannot possibly imagine where artistic judgment and good engineering sense are put more to the test than in building one of these front ends that will not only handle the real road on a daily basis but look good while doing it.

From my personal perspective I rank fork system strength and functionality foremost and try to figure out a way to make it all look attractive and proportional with the rest of the bike secondarily. To be able to do this you have to have the raw materials and other components in hand to make valid decisions based upon not only sound engineering principals but also artistic visual comparisons of various potential assemblies. In other words you have to be able to actually see, feel and ‘experience’ the parts you want to experiment with. You just can’t pick parts from a catalog and expect anything to look proportional. You’ve got to have the stuff in your hands before you begin the design and fabrication process. As much as I like ‘plans’ this is the one area where real parts will far outweigh anything you see on paper.

Fortunately buying a lot of parts for a potential Girder project isn’t all that expensive and to start with you really only need a single ‘example’ of each item for each component assembly you’re planning to experiment with and you don’t need fancy top of the line parts to start with during the planning and mock-up stage.

To give you an example of what I’m talking about try this little experiment. Take two sections of 1” tubing about 36-inches long and polish one to a bright luster. Paint the other one with black paint, to simulate powder coating, and put them side-by-side. The polished tube will look considerably ‘narrower’ or smaller in diameter than its painted counterpart. If it were chromed it would look even thinner.  In this instance if you were after a certain ‘look’ for a set of forks that were to be powder-coated you would have selected slightly smaller tubing, 15/16” DOM for instance, so it would have the same visual ‘weight’ or ‘size’ as a skinny looking piece of chromed 1” tubing.

The picture below illustrates a variety of common fasteners and fittings that you might be using on a Girder fork system. The steering neck and stock rocker bolt are to provide scale.

Figure 11

The larger bolts in the upper left-hand corner are 5/8” cap screws and in the next row are half-inch and then down further 3/8” fasteners. The bronze bushing range in size from half-inch to ¾-inch in inside diameter and the washers and spacers shown are all grade-8. Some of the cap nuts are nickel-plated and some are stainless steel.

As you can see there is a huge ‘visual’ difference in size and mass between a 5/8” cap nut (acorn nut), for instance, and a one-half inch cap nut even though ‘on paper’ there is only a one-eighth inch difference in diameter and a lot of people would opt for the larger fastener for safeties sake even though it would look pretty out of place on a girder made from 7/8” tubes for example.

DOM Tubing Schedule

The table below lists some of the more commonly used sizes of DOM tubing that you might need if you’re building Girder forks.

Keep in mind that this isn’t a comprehensive list of tube sizes just the more commonly available size combinations that work well with Girder fabrication.

To Be Continued………………………………………

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