For some years now there has been a trend in attempts to re-invent the wheel - well, certainly in the case of aerodynamic carbon clinchers.
For a long time Zipp were the go-to brand, but since the introduction of a growing number of aero wheel sets from companies like ENVE, their grip on the market has not been quite so firm. Improved braking surfaces, aerodynamic efficiency and stiffness from Zipp's competition has led to rapid developments and a need to offer something more. The culmination of Zipp's quest for the market leading aerodynamic offering is the new FireStrike.
Building on their mathematically derived FireCrest rim shape technology, borrowing from their 303 FC and with a new brake track and a host of other tech, Zipp have created a wheel that offers the rider greater confidence which in turn reinforces the improved aerodynamics.
Zipp recognised that aerodynamics are limited by rider confidence, the riders' ability to corner safely at speed and by the ability to stop - you are unlikely to go as fast as you can if you are unable to stop! For us, this particular trait of Zipp wheels (and their relative flexibility, but we'll get to that) has been something of a bugbear. Yes the Firecrest certainly improved the braking in the dry but when it came to wet weather stopping, a lot was left to be desired. Happily then, the new FireStrike addresses this issue with Showstopper, a new molded-in brake track which is not only textured to alter the friction rate and quickly disperse water but which contains Silicon Carbide. At almost 3 times harder than hardened steel, Silicon Carbide is highly abrasion resistant and ensures consistent braking performance. Indeed, Zipp claim that the surface is now equal to that of industry leading aluminium surfaces in the wet.
In addition to greater stopping confidence, Zipp have also addressed the issue of tyre deformation at the rim while cornering. For those of us who have had those cornering moments as the tyres roll around beneath us, this will be welcome news! Borrowing from the 303, the FireStrike employs a wider clinch bed, moving from 24.7mm to 26.4mm. This additional width means less tyre roll in corners and this in turn reduces the slip angle of the wheel as a whole. The benefit is two-fold: more confidence in a corner at speed (faster) and improved aerodynamics thanks to a more upright wheel - faster again!
As well as the improvements to rider-driven aerodynamic benefits, Zipp have also improved on the fundamentals. Computational Fluid Dynamics (CFD) and Frequency Atuned ABLC dimple patterns on the rim surface have once again advanced the aerodynamic balance of the wheels to yield reduced drag and improved stability over the 404 FireCrest.
The Firestrike has a slightly more blunt profile than it's predecessor and is also wider (27.8mm compared to 25.5mm). This profile change improves the aerodynamic stabiilty over the back half of the wheel by allowing the leading edge to 'hold on' to air for a longer period of time, reducing drag and improving the stabilty in a range of yaw angles.
In addition, refinements in the dimple pattern used by Zipp on their sidewalls (ABLC) has further reduced drag. Aerodynamic Boundary Layer Control (ABLC - the dimples!) allows retention of air at the surface of the wheel and although this may seem counterintuitive as it increases the 'skin drag' at the surface, it does result in lower overall drag values at every single measured data point than previous rim designs, but more importantly yields minimum drag in conditions that riders experience the most often - very few of us ride in wind tunnels! In the case of the new FireStrike, Zipp looked closely at how the air detaches from the rim and 'frequency tuned' the dimple pattern to create high frequency vortices that exist for less time. This higher frequency shedding of air is less perceivable to the rider and results in a smoother, more stable feel while turning in the wind allowing the rider to hold the aero position for longer. To ice the cake, Zipp now use a direct print graphic which perfectly conforms to the dimples, so even the graphics are faster!
The rim profile change and CFD design combined with the improved, wavy ABLC dimple pattern results, Zipp say, in a 34% reduction in side force over the 404 Firecrest in the most often encountered conditions.
As mentioned earlier, another issue with Zipp's deep section offerings has been their lack of stiffness. The Firecrest range made huge steps in this regard but has, until now, still been some way behind the best of the competition. The FireStrike wheels use 88/188v10 hubs laced with Sapim CXRay spokes. The new version of the 188 rear hub is now 20g lighter. Both the lateral and torsional stiffness of the rear wheel have been improved by using a virtual 3-cross lacing pattern and Zipp quote figures of 5% and 25% improvements respectively when compared to the widely used DT240 hub. The benefits of improved stiffness cannot be overstated: improved cornering with less deflection and possible brake rub, improved pick-up for greater acceleration and better climbing efficiency to name a few.
At 1620g for the pair, the Zipp FireStrike are far from heavy for a wheel of this depth (58mm). Zipp have added extra value to the wheels with the inclusion of Titanium Skewers, rim tapes, tubes, valve extenders, Tangente Platinum Evo brake pads and 2 individual wheel bags.
The new Zipp 404 FireStrike is definitely going to put the cat back amongst the pigeons. Aside from the better aerodynamics; the improved lacing, hubs, stiffness and braking that have been bones of contention for some, may just swing a few die-hard anti-Zipp folk out there!
ZIPP 404 FireStrike Carbon Clincher Rear : 188 Hub with 24 Spokes : Shimano/Sram : Impress Graphics Black