A LOOK INSIDE
GETTING THERE
We spoke to director of suspension, parts and accessories at Cycling Sports Group, Jeremiah Boobar, to get the full story of the Lefty fork...
WHY DO YOU BELIEVE SUSPENSION ON A GRAVEL BIKE IS NECESSARY?
“Suspension on gravel bikes allows riders to enjoy a significant increase in comfort and control over a rigid bike. This can allow you to feel safer and more confident, while reducing fatigue.”
WHAT ARE THE BENEFITS OF A SINGLELEGGED SUSPENSION FORK?
“Lefty’s single-leg design is really a means to an end, allowing us to use our needle bearing system, which provides the lowest friction system in cycling. The application of the needle bearing pack creates an incredibly stiff fork. In fact, a double-legged version would be too stiff. This allowed us to remove one leg to reduce weight. Once we were down to a single leg, we could make the axle part of the lower tube, which provides a great stiffness gain that we can tune for various types of riding. This unique construction method allows us to use our needle-bearing technology to make the smoothest front suspension possible.”
HOW DO YOU CONTROL THE FORK SO IT REACTS ONLY TO THE TERRAIN AND NOT THE INPUT OF THE RIDER, LIKE ‘BOBBING’ WHEN YOU'RE CLIMBING?
“Rider inputs, like standing or pedalling, compress the suspension relatively slowly compared to hitting a bump. We can have the suspension open additional oilflow paths when we hit a bump, which is asking the suspension to compress quickly. We can independently control the fork movement through adjusting how the suspension reacts to different shaft speed inputs, or how fast the suspension is asked to move. For example, if you hit a 10cm curb you are asking the suspension to move that distance instantly, which is a high shaft speed. If we put a one-metre ramp to that curb you are asking the suspension to compress at a slower speed. Inside the damper we have additional oil-flow paths that are held closed by springs. At higher-shaft speeds the need to move more oil quickly puts pressure on those springs and opens up those additional flow paths.”
WHAT IS THE SIGNIFICANCE OF THE LOW-FRICTION DESIGN?
“Friction in the chassis of the suspension has inconsistent movement depending on bump inputs. On the same bump you can get a different reaction, making the suspension unpredictable to the rider. By removing the friction from the chassis, then putting it back in the damper you can create a consistent and controlled experience on all kinds of bumps.”
WHY DOES THE FORK REQUIRE DAMPING AND WHY DO YOU NEED TO CONTROL THE FORK'S ACTION IN THIS WAY?
“When you compress a spring, you are storing energy, when you stop compressing the spring it will extend returning most of that energy. With suspension and no damper, you would hit a bump and the spring would compress, then would just shoot back and extend as fast as it can. The vehicle comes back down on the spring, compressing again, extending again and just bouncing along until finally it settles. Think of an old car with shocks that don’t work. It hits a bump on the highway and just keeps bouncing. With a damper, you are taking the stored energy in the spring and dissipating it through heat by creating friction. The friction is created by constricting the oil flowing through small holes. This friction can be precisely controlled to help the suspension react to different compression or extension (rebound) inputs to improve the comfort and control in a number of situations."
THE FORK HAS A LOCKOUT SWITCH. WHEN WOULD YOU USE IT AND HOW DOES THE BLOW-OFF FUNCTION WORK?
“The lockout shuts down all oil flow under compression. This means that the fork cannot compress. This makes the fork rigid. Many riders like to use this when they are standing and pedalling on steep paved climbs and want the most efficiency possible. When we shut off the flow to the valve, it has a spring to hold it closed. If you hit a large bump that spring compresses allowing the suspension to move. This can keep you from getting a flat or having your hands blow off the bars.”
THE STUB AXLE ON THE LEFTY FORK WILL PROBABLY GIVE SOME RIDERS THE JITTERS HOW CAN YOU REASSURE THEM?
“Well, aircraft landing gear and car front wheels are fundamentally the same architecture in that the wheel is mounted to the side of the suspension, so you have nothing to fear from the Lefty design.
“On the road and off it, the Lefty 1 certainly cuts an interesting shape in the flesh, the super-low slung back end and that different-looking single-sided fork with its purposeful dimensions and intricate brake fitting and QR system look like a glimpse at the future. It all holds together well with the brilliant metallic colour-shifting paint finish and high-grade finishing kit you’d want at this (high) price.
“We’d expect a few comments on the weight of the Topstone as on paper the 9.98kg weight doesn’t exactly scream lightweight. Even in gravel bike terms it seems weighty – when we tested the lower spec Ultegra model with a carbon fork and 700c wheels (with slimmer tyres) that weighed in at 9.07kg so adding front suspension and huge 47mm wide tyres does add a little heft. I’d say that you ignore on-paper weight as this Topstone Lefty doesn’t deserve any body shaming because within a few pedal revolutions off road it’ll have you believing that this was a UCI limit-baiting lightweight such is the effortless way that it traverses the rough. Think of it as a super-light mountain bike with drop bars that won’t sap your energy on the road.
“While 30mm may not seem like a lot, back in MTB's early days the Kamikaze downhill at Mammoth mountain saw legends like John Tomac hit speeds in excess of 50mph off-road with similar travel. Tomac also raced the World Champs downhill in 1990 on drop bars to keep his road and MTB bike positions the same!”