Girder forks are staging a comeback – and it’s not just in pursuit of retro authenticity.
Royal Enfield have filed patent applications around the innovations, which will feature in their incoming electric Flying Flea’s old-school front suspension – explaining it doesn’t just look good, but also makes the bike better.
The girder fork dates back to the early 20th century, when simply having suspension was a luxury, but after the Second World War it was increasingly phased out in favour of newfangled telescopic forks. However, in the 2020s the idea is having a revival as brands add their own twist – and Royal Enfield’s first commercial venture into electric motorcycles , the Flying Flea C6, is among the bikes to benefit.
The basic idea of the girder fork is to hold the front wheel between a pair of rigid uprights – the girders that give the setup its name. These are attached to a set of parallel suspension links extending forward from the bike’s chassis: one above the steering tube and the other below.
The Flying Flea’s setup sticks to that convention, but its implementation departs from the past so significantly that Royal Enfield have applied for patent protection around the idea.
While there have been many variations on the girder fork idea over the years, they commonly have the spring and damper – or multiple springs – mounted between the upper and lower parallel links in front of the steering stem.
Here’s one area where the Flying Flea departs from the norm: it uses two spring/damper units mounted relatively low down, tucked into the triangular opening cast into each girder. The bottom of each shock is bolted to the girder itself, while the top mount is part-way along the lower linkage.
The company’s patent points out that by tweaking the linkage mounting positions and arm shapes, it can engineer the suspension to be either progressive or linear in its response.
The version seen in the patent illustrations and on the Flying Flea allows 100mm of suspension travel to translate to around 60mm of stroke for the shocks themselves. Mounting the springs and dampers inside the openings in each leg makes life easier for the bike’s designers and aerodynamicists, too.
With no shock in front of the headstock, there’s more freedom to mount the headlight further back, and the girders can be shifted slightly rearwards to lose the awkward dimensions seen on some girder-forked bikes. Aerodynamically, the shocks are tucked away, and air hitting the front of the bike beneath the headlight can be channelled relatively cleanly to either side.
The girders and links are connected on needle roller bearings, minimising friction for the suspension movement without introducing any fore-and-aft play under braking.
The whole lot looks to be made from a light alloy casting, reducing weight compared to more conventional girder forks.
The patent says it helps handling by reducing unsprung mass but also boosts efficiency – the overall kerb weight reduction is claimed to improve the bike’s all-important range by five per cent.
Royal Enfield’s patent says the system is particularly capable in both rugged and off-road environments where it can absorb shocks and vibrations and help reduce rider fatigue, and because the dual shock units are conventional there’s the usual scope to offer adjustable damping and preload.
The linkage-based design also means engineers can tailor the amount of anti-dive, while the twin-shock setup improves torsional stiffness.
The…