Italian custom suspension manufacturer, Bright Racing Shocks, has released a new upside-down fork named the Skunk. Its 130mm travel (configurable to 120-135mm) is intended for use on trail bikes designed around a 140/150mm fork. So, why the discrepancy?
Bright Racing Shocks Founder and Chief Engineer, Pablo Fiorilli, says the fork is designed to run very little sag, giving it effectively more travel than an equivalent travel fork that runs a standard 20-30% sag. The Skunk’s ACAD Damper Cartridge is responsible for this, a cartridge that Bright Racing Shocks have implemented across the F929 line of XC and Enduro Racing forks, too. Let’s take a closer look.
Bright Racing Shocks Skunk Fork
The new Bright Racing Shocks Skunk is a 120-135mm travel fork designed for trail and downcountry riding. It is an Upside Down fork, fabricated with tapered carbon uppers, 46mm in diameter at their thickest point, with 35mm stanchions made from 7000 series aluminum telescoping within them. Internal to the left leg, you will find the ACAD 8 hydraulic damping cartridge superimposed on the air spring. Housing both functional components of the fork in the same leg ensures that the damper and the air spring are subjected to the same forces simultaneously. The right hand leg is merely a guide; it has bushings of course, but these are set up in a “floating” configuration. More on that later.
- Bright Racing Shocks Fork: Skunk
- Travel: 130mm standard (120-135mm available) for bikes with a 140/150mm fork
- Application: Downcountry and Trail Riding
- Wheel Size: 29”
- Axle-to-Crown: 400mm + travel
- Use of Torque End Caps recommended
Just as bright Racing Shock’s F929 NEXT 150mm Enduro Fork is intended for bikes designed around 170-180mm forks, the SKUNK 120-135mm fork is intended for trail bikes designed around a 140mm or 150mm fork. This close-to-zero sag is is a unique feature of Pablo Fiorilli’s suspension designs, which he says allows him to design lighter, stiffer forks that deliver an effective equivalent depth of travel as compared to a relatively longer travel fork running the usual 20-30% sag. He argues that because the travel is not lost in sag, the full amount is available to absorb bumps at all times.
Some readers may well be wondering how the fork is able to track the ground properly with very little travel in reserve. We queried this with Pablo, and his in-depth explanation can be found at the foot of this article.
The ACAD Damper, now in its 8th iteration, is adjustable; both compression and rebound can be adjusted externally by dials found in the usual place. These are the only adjustments available; the air spring volume cannot be altered. That said, at the point of sale, the damper cartridge can be tuned and the air spring volume customized for each customer based on their weight, riding style and personal preferences. Bright Racing Shocks offer that custom tuning included with the price of each of their forks. Pablo tells us they usually get it right first time, but will re-tune if the customer needs any tweaks.
Of course, the aforementioned reduced sag is not the only non-traditional feature of the Bright Racing Shocks Skunk design. Clearly, it is an Upside Down (USD) Fork, but I wouldn’t consider that terribly unusual; Manitou have had much success with the Dorado Downhill Fork, and Intend Bicycle Components have their own dedicated following, including the likes of Gustav Gullholm (aka Dangerholm). These forks have, historically, received criticism for their lack of lateral and torsional stiffness. Pablo says he has overcome this drawback of the USD design with stiff, tapered carbon legs (46mm in diameter) but also through use of a floating bushing system, more akin to what you might find inside a motocross suspension fork.
Inside each leg, you will find a pair of bushings. One of these is mounted in the usual place, attached to the upper leg, sitting just underneath the wiper seal. The other is positioned, and affixed to, the top end of the fork stanchion. So, as the stanchion is pushed through compression and rebound cycles, this “floating” bushing moves directly with it. Pablo is not willing to share specifics of this arrangement.
In any case, you can appreciate how the pair of bushings become further apart from one another as the fork is pushed into its travel. When extended, the distance between the bushings is 136mm, increasing to 266mm at full compression, a distance that would normally only be possible on a dual-crown fork. This, Pablo tells us, increases the lateral and torsional stiffness of the fork. It is at its most stiff at bottom-out, and its most flexible when in an unloaded state. He says this becomes evident with improved steering precision in contrast to other USD fork designs, and also compared to many traditional forks.
You will notice that the lower portion of the carbon legs flares outward toward the wiper seal. This serves to create additional space within the carbon tubes to allow for a lubrication system that circulates 20-25ml of suspension oil in a vacuum created between the two bushings. The stanchions themselves are coated with a hard oxide, prepared in such a way as to create a micro-porous surface that absorbs suspension oil over time, lubricating themselves through use. The method is completely unique to Bright Racing Shocks, having been developed by Pablo over the last 30 years.
The Skunk is designed to run a brake caliper for a 160mm rotor, though a bracket for a 203mm rotor is also available upon request. In March, Bright Racing Shocks will also offer a bracket for a 180mm rotor.
Pablo Fiorilli’s Justification for Reduced Sag
We asked Pablo the following question, “Traditional suspension forks run 20-30% sag in order to allow the wheel to track the ground – it is as much there to smooth out holes in the trail as the rest of the travel is there to absorb impacts and and filter out small bumps. Why is the small amount of sag that the Bright Racing Shocks forks run better than this traditional design?”
At sustained speed, the portion of sag imputed to anchor the depressions in the ground is that pre-loaded portion that is identified between static sag and mid stroke. The classic static sag found on mainstream forks is mostly used to copy terrain at very slow speeds. Furthermore, that portion of sag (static) favors a false effect of “sensitivity” when stationary and therefore makes a fork pleasant to all. But this pleasantness is evident.
Speaking of high speeds (even those of a fast amateur) or high performance, the area that really works in “copying” the depressions in the ground is an area that is usually placed immediately before the “mid stroke” and is a of travel pre-loaded and “charged with energy”. That’s what I call “dynamic sag”.
Bright RS’s ACAD damper works primarily by exploiting this dynamic portion of the sag and leaving out (as a collateral factor) the classic static sag. This is where the concept introduced by Bright RS is based, which is defined as zero sag. This is actually a “concept” and not true zero sag. In fact, our forks have a minimum amount of sag but remain very supported by maintaining a high floating position on the front end. It must always be considered that the traction given by the Bright RS cartridge is high and the sensitivity on uneven ground (stones, roots, drops) always remains optimal.
If a customer prefers “classic” static sag we can do it thanks to the great versatility of our system. Normally, however, we do not do it and we do not recommend it, because the performance of our system is, in our opinion, decidedly superior.
Bright RS was born as a manufacturer of racing suspensions and therefore finds its nature precisely in this type of functioning to which you have to get used to at the beginning. What they often tell me is that I would like to change physics.
This is incorrect, I am simply giving a different way to follow physics. In the 90s, there was no mention of sag in mountain bike forks. I used fork systems where I used sag instead, in World Cup races with riders of the caliber of Frank Roman… After so many years and with over twenty more years in my evolution as a designer and developer, I understood that managing the dynamic sag instead of giving weight to the static sag guarantees greater traction. Provided you then have a suspension system with very sensitive valves and light unsprung masses.
Pricing & Availability
The Bright Racing Shocks Skunk Fork retails at €1,750 euro (excluding tax) for the standard version with Black components and the UD carbon fiber finish on the upper legs. Color customization of the crown, dropouts and stanchions is available at additional cost. Choose between Dark Red, Grey, or Licorice for the stanchions, and Red, Silver, Purple or Titanium for the Crown and Dropouts. Stanchion guards are available upon request.
Pablo says, “When you buy a Bright Racing Shocks fork you have a highly customizable piece of mechanics and many things are sometimes invented/created expressly for the individual customer. So, the advice is always to request information on customization directly via the following link”.