It’s been almost 10 years since Pace produced a full-suspension frame and this time round the focus is very different from the square-tubed RC500 DH rig that last rolled out of the Yorkshire facility. Building on the overwhelming success of the RC303XCAM hardtail, Adrian Carter of Pace Cycles wanted to produce a 130mm travel full-suspension frame designed specifically for singletrack. He also wanted to maintain some overlap with the hardtail design to give the range coherence and Adrian freely admits that he wanted the RC405 to look like a traditional bike with a classic ‘double-diamond’ design. So, a short twin-link suspension set-up was the obvious choice, but which one? After much deliberation and numerous variations, Pace settled on what it calls the Free Floater design. But suspension frames shouldn’t be designed in isolation from shocks, so Pace built the Free Floater linkage around the DT HVR200 because it had a suitable spring curve. Also, there was no commercial conflict with DT.
It’s not just the rear suspension that’s unique on the RC405. Two welds bisecting the lower section of the 6066 T6 down tube are telltale signs of the internal webbing. By effectively splitting the tube in two with a reinforced section, Pace has dramatically increased stiffness and strength where the main pivot penetrates the bi-ovalised down tube. Up front an oversized head tube with semi-integrated headset provides a large enough contact area for the massive 57mm-diameter down tube. All pivots use sealed cartridge bearings and the bolts are made from hard anodised aluminium to reduce weight. Additional sealing on the pivot shafts and bearing covers should minimise downtime. Shared features with the RC303 include replaceable dropouts and a bridging gusset connecting the seat tube and top tube. All in, Pace claims that the RC405 frame weighs 6.2lb without shock and fitting hardware. If that is achievable on production frames it will be impressive as the RC405 is incredibly stiff for its weight.
To hone the geometry on the RC405 and reduce prototyping time, Pace used several head-tube inserts and custom dropouts to field-test the bike with different head angles, bottom bracket heights and chainstay lengths — finally settling on what we would call modern XC geometry. The 68.65deg head angle combined with a good front-centre length gives sharp handling but good stability. At 13.5in the bottom bracket height provides ample pedal clearance for cranking across natural off-camber trails without making the rider feel perched on the bike. The RC405 does, however, have a slight forward weight bias that took a bit of getting used to, but that could have been due to the low stem/bar height. With the links tailored to the spring curve of the shock, set-up becomes critical and if you run more than 25 per cent sag, the rear suspension bottoms too easily. With the correct amount of sag the suspension felt active, but controlled. There is very little pedal feedback in the big or middle ring, but drop it into the granny and chain torque stiffens the suspension and some feedback is noticeable. That said, it’s nothing like as pronounced as some better-known twin-link designs.
Initially Pace will offer the RC405 in three frame sizes with two finishes — anodised pewter for £1,295 and the classic white painted finish for £100 less. Both frames come with the DT HVR200 shock and by the time you read this Pace will have rolled out 10 demo bikes to its dealers. Hit www.pace-racing.co.uk.
The Free Floater twin-link suspension design can be split into two distinct areas — how the links provide a given axle path and the effect they have on the shock, so we’ll deal with them separately.
Pace wanted an initially rearward axle path to introduce some chain torque and make the rear wheel dig in more under hard efforts, and this is achieved with the lower link. The angle of the link is nothing like as steep as that found on VPP bikes and as a result the axle path is less rearward. In the mid-stroke the axle path becomes more vertical and as the travel increase the upper link becomes dominant pulling the wheel towards the frame, reducing chain growth and pedal feedback deep in the stroke. Basically the initial third of the travel is controlled by the lower link, the final third is controlled by the upper link and the mid- stroke is a combined effect of both.
By sandwiching the shock between the links, instead of mounting the lower shock eyelet to the frame the DT HVR200 shock is actuated from both ends. This tailors the compression ratio of the suspension to better suit the spring curve of the shock. As you can see from the graph, the Free Floater design helps eliminate some of the hammock inherent in all air-sprung shocks. On the bike, this translates to less suspension wallow in the mid-stroke. As the upper link comes into play deeper in the stroke it increase the leverage ratio to combat the sharp ramp up of the air spring and eke the final portion of travel for the air shock allowing the rider to achieve the full 130mm of travel. This is also why the suspension bottoms easily if you run the shock too soft.