Reynolds' elite Composites Studio division officially unveiled a more aerodynamic version of their ultralight RZR 46 wheels under the Footon-Servetto riders in the opening prologue of this year's Tour de France.
As the name suggests, the new RZR 92.2 uses a doubly deep 92.2mm rim but it's not simply a scaled-up version of the original RZR 46. According to Reynolds' director of technology and innovation Paul Lew, the 92.2 smoothes turbulent airflow over its rim surface by virtue of a precisely shaped rim that was designed largely through CFD (computational fluid dynamics) modelling.
"This is the first wheel in the Reynolds line to use what we call dispersive effect termination (DET)," he said. "We arrived at this 92mm depth by determining first what the width needed to be based on the wider 22mm tyre – which is what a lot of people want to time trial on – and then we adjusted the shape and the length in the CFD program to essentially give us the lowest drag."
As with the RZR 46, the NACA airfoil-profile carbon spokes are bonded in place along with the internal carbon nipples that aid in initial truing. This leaves a smoother transition at the interface compared to exposed external nipples for additionally reduced turbulence, according to Lew. Unlike the RZR 46, though, the 92.2 rim uses a sharper and more gradually tapering tail that omits its little brother's Swirl Lip Generator.
There's no Swirl Lip Generator on the new 92.2 due to its more aggressively tapered trailing edge
"The Swirl Lip Generator is effective on a blunt edge," said Lew, which typically leaves a turbulent vacuum of air in its wake as the separate layers of air struggle to reconvene behind. "[The Swirl Lip Generator] helps suck the air around that edge. With the tapered trailing edge you don't really get that vacuum and so you don't need the generator. This is a faster wheel in every condition we tested."
Part of that formula is a fatter 25.7mm rim width under the tyre bed plus a deeper tyre well that now also includes a channel to account for tubular seams. Unlike wide rims from competitors such as Zipp and HED, though, the RZR 92.2 uses parallel sidewalls that don't widen below the brake track. Lew claims this yields more predictable braking performance than angled sidewalls and the same aerodynamic performance as more aggressively bulged shapes.
"The highest airflow comes at the widest section [of the 92.2 rim], which is actually about 33 percent of the distance from the edge of the tyre," he said. "Wheels that tend to be toroidal in shape are trying to achieve the same thing. This does it but it gives you parallel brake surfaces."
Part of the RZR 92.2's aero formula is a wider rim section at the tyre bed
Another key change is a new brake track, which abandons Reynolds' old scrim layer in favour of a woven carbon layer that Lew says takes better advantage of today's more capable – and more specifically developed – carbon brake pads.
"Originally, Reynolds used the scrim to increase the heat because the harder pads that were designed for aluminium needed a little higher heat to get grabby but that's contrary to what you want for epoxy," Lew said. "Instead, we designed a resin, we designed a laminate, and we designed a brake pad as a system. The braking temperature with the new laminate [which will be applied across the Reynolds range for 2011] is about 100°F cooler."
As expected, the RZR 92.2 will be very light for a wheel with this deep a rim section. Claimed weight for the pair is just 1,460g (680g front, 780g rear – or nearly half a pound lighter than Zipp's 1080) using the same carbon hubs and three-flange rear configuration as the RZR 46 but a lower 12/16 front/rear spoke count instead of 16/20. Cost will remain similarly high at around US$6,000 for a set. Lew expects the RZR 92.2 to be available in the autumn.
The 92.2 hubs use a full-carbon shell with a 12/16 front/rear spoke count
Updates to RZR 46
The RZR 46 gets some significant updates as well and will actually split off into two versions for 2011. While ultralight, the first RZR 46 didn’t pass the UCI's stringent wheel impact test so Reynolds infused the formula with Kevlar. Lew says there are now two strands per spoke (a feature shared with the RZR 92.2), two circumferential strands around both the inner and outer rim edges, as well as two spiral-wound strands that encompass the entire rim.
This new UCI-homologated version ends up around 100g heavier per pair but is now legal for use in UCI-sanctioned events, and it's still extremely light at around 730g for the front and 830g for the rear. For well-heeled riders who don't ever plan on racing at that level, the lighter version will still be available, and there's a clincher planned for the 2011 model year, too.
To meet UCI standards, Reynolds had to infuse their RZR 46 wheels with 100g of Kevlar fibre