Forking Good Fun

​If it’s frame building, it must also be fork building, right? But whether it’s ‘building’ or merely ‘making’ a fork, the task is one easy to avoid in a world of off-the-peg carbon-fibre forks made to suit almost any purpose from track racing to the gravel touring/bike packing scene.  Given that carbon-fibre forks not only save a lot of weight over steel but spare the frame builder the trouble of making one, why bother?

Where weight is not the primary consideration, there are several good reasons. One, which is arguably subjective, is that a lightweight steel fork – one built using traditional tapered, thin-wall blades unsuitable for disc brake fitment – offers superior ride comfort. If true, it depends as much on factors such as the length of the blades’ taper and their rake curvature as on the use of steel itself. When it comes to custom geometry that requires a fork offset and, perhaps, height, not available in an off-the-peg fork, building from scratch is the way to go. And there’s the aesthetics of it all; a steel fork may be exactly what a steel frame needs to look just right.

So today is build day and another opportunity to reflect on the challenges facing the builder about to embark on a steel bicycle fork. Most of them can be averted by using an accurate jig, but one or two are not quite so easily ignored. There are a number of choices to be made before starting work. Which fork blades? Today’s ‘standard’ road fork uses blades with a 28x19mm oval section – the ‘Continental Standard’ – but many older forks and some specialist current crown designs require the older Reynolds Imperial 29x16mm oval. The latter is stiffer in the fore-and-aft plane, i.e. under braking, while the Continental style is laterally stiffer and should, in theory, offer greater directional control.

Reynolds Continental oval blades have a shorter taper than those by Columbus, which are easier to rake. A builder looking to cater for the ‘classic’ bespoke scene might choose a Grand Bois fork crown designed for the narrower Imperial oval, along with matching blades. An even more specific request was for an ‘aero’ 650C fork with Columbus Max-style blades to complete an old Cyfac time trial bike.

An 1 1/8” steerer tube improves both strength and stiffness over the traditional threaded 1” job, which retains a following amongst tourists and is used when building a replacement fork for a classic frame. Then there’s crown design – hollow or solid, sloping, external… And dropout style – socket, plug or traditional plate; achieving a coherent overall frameset look is often the deciding factor.

These details may affect how the finished fork looks and to some extent, feels, but far more important is that it be built to the specified dimensions, including rake and height to the bearing seat on the top of the crown, which is dependent on wheel size and expected brake reach. The fork must also be correctly aligned, which is where the fun comes in.

That’s because there are several ways the fork can be ‘out’. Perhaps the most visually obvious is when the blades’ straight section is not quite in line with the steerer. This is not a problem if building a Colnago Precisa-style fork with straight blades, where rake is determined by the angle at which they leave the crown. The other main advantage of this design is that it obviates the need to bend the fork blades, which is a procedure with issues all of its own. There are two basic techniques: bend the blades once the fork is built, or before building it…

If the former, then they can be bent simultaneously, ensuring equal rake on both sides. This approach obviously requires twice the force needed to bend one blade at a time and needs a wider, more substantial bending former. It also makes it a bit trickier to gauge the blade length needed for a specific rake and crown height, although this becomes clear with repetition.

Bending the blades individually is easier in some ways – and considerably trickier in another. The hard part is not, in fact, getting them both bent to the same rake. A simple jig, which orientates the fork dropout with the steerer centre line at the required offset, makes it simple enough, provided one takes care not to go too far, to bend the blades to fit.  The difficult part is avoiding fork ‘swoop’, which is where the blades appear to veer to one side when the fork is viewed from above.

A road fork crown’s oval sockets locate the matching oval of the blades and, if one or both were even slightly off-axis as the bend was put in, the resulting curve will be displaced to the inside or outside of the fork, depending on which side the blade is used. If both blades are misaligned to the same side, then the visual effect is pronounced; if they are out by the same amount on opposite sides, the fork will look symmetrical and no one will notice… Little matches the satisfaction – and relief – to be had on dry-fitting a pair of blades and seeing them pair up nicely.

After all that, it’s simply a case of making sure that the crown is in line with the wheel spindle, that the wheel rim is centred between the blades and that the fork dropouts are equidistant from the steerer centre line. It’s all worthwhile; a good steel fork is such a pleasure to ride.

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