Aero gravel is here, and I’m excited. Going back to 2011, I had been interested in how aero enhanced frames and deeper wheels could make an impact on cyclocross. 3T got the ball rolling with the Exploro, which I had a chance to ride at Interbike 2016. Since then, frame makers have been bringing over internal cable routing and aero shapes to gravel and wheel makers started creating specific shapes to work with wider tires while depths have slowly crept up. And now, WTB is introducing what they believe is the answer to one of the biggest challenges to the aero gravel category, how to create a range of tires that are capable on and off road, yet still retains aerodynamic optimization. Through a partnership with Stromm, the brand behind the world’s fastest UCI-legal road bike, WTB is launching the Byway RS, Course, and Macro, creating gravel’s first aero tires.
We have already seen aero framesets hit the gravel world. Along with optimizing tube shapes and frame packs that are molded to smoothly integrate into the frame, these aero gravel frames are getting wider clearances to be able to handle larger tires to make them even more capable. Many riders are brining over more road specific items like narrower one piece cockpits that also improve the aerodynamics of the frame, but also help to put the rider into a faster position. Add in deeper, wider wheelsets, and slipperier kits and helmets, and gravel racing is becoming just as fast as racing on the road.
The challenge is that road is generally clean, and gravel isn’t so much. Just like 3T, WTB and Stromm understand that aerodynamics are different when things get dirty. Mud caking on tubes and the shoulders of tires affect how air interacts with the wheel/tire combination and how it flows around the bike. Instead of a smooth surface that the air would normally pass along with little turbulence, a dirty bike and knobby tires causes more disruptions in the air flow. That’s when they went to work.
WTB shared a white paper that was written by Ben Rothacker, an aerodynamicist at Stromm as part of the launch pack. In short, they were able to fine tune their computation fluid dynamic (CFD) modeling down from a scale that would financially be out of reach of major aeronautical companies to something that was still producing extremely accurate results or a fraction of the price. Normally, major cycling brands model out to 15-20 million cells when they are going extremely deep, but Stromm needed 500-800 million cells. By creating a lower-detail tread stand-in shape, they were able to get the details they needed of how the air interacted with the tread and then streamed behind the rim, but at a tenth of a the cost.
So back to that challenge. As clean (laminar) air passes over the tire, the blocky treads make the air much more turbulent than a traditional slick tire. Also add in the fact that gravel tires are wider than road, and that adds another layer. The other issue is that wheels rotate. A static object is much easier to test and is much more aerodynamic than something moving. Whether it is wheels, crank arms, a cyclists legs, they all create challenges as they are moving, which creates additional turbulence as air passes by.
That’s when Stromm began looking at sidewalls. Tread is off limits, because it is needed to keep the tire capable when offroad. As long as rolling resistance isn’t impacted, they were given free reign to see what improvements they could make. That’s where trip strips and vortex generators come in.
The goal of each is to help keep the air attached to the tire and rim as long as possible and reduce the low pressure pocket behind the rim, which causes drag. This also helps to smooth out the air as much as possible. The concept was proven, but turning it into a a tire that can be manufactured at scale was another story. WTB provided their insights into how rolling resistance would be affected, along with bringing the tire design and production expertise, and helped to create the prototypes.
From there, Stromm and WTB went to the Jerry Baker Memorial Velodrome in Redmond, WA. Yes, a velodrome isn’t quite where you’d expect to test a gravel tire, but it allowed them to test the aerodynamics in a repeatable environment with minimal variable. This includes things like tire and velodrome surface temperature, barometric pressure, tire pressure, body position, rider body volume changes due to perspiration, and chain tension. Their testing was so precise, they could pick up a nearby train passing by. In the end, they found they could save 3 minutes and 10 seconds over 100km at 30kph (18.6mph). And the faster you ride, the better they perform.
“Stromm applied the same real-world applicable engineering that made the fastest road bike to this tire, designing in surface features that substantially improve aero over the tire/wheel even when dirty and with no compromise to the tread. We brought all our tools to bear, running what may be the largest CFD simulations in the cycling industry to date and then doing detailed CdA measurements of clean and dirty tires with and without surface treatments to make sure what we found on the computer is working on every ride. ” – Ben Rothacker
What they created, is a tire that is fast rolling, reduces drag, while still capable offroad, has dependable flat protection, and is fast on varying surfaces of gravel.
WTB created three tires as part of their aero gravel line, the Byway RS, Course, and Macro. Each gets progressively larger and adds more tread. The new tires are designed for modern wide gravel rims with from 25mm to 32mm internal widths, with 28mm being the optimal width. Beyond the aero treatments, these are completely new tires using a new 120 TPI casing with bead-to-bead SG2 puncture protection that keeps the tires supple, yet stable in cornering. The upgraded Dual DNA rubber compound and refined low-drag center rubber keep speeds fast with should lugs for cornering grip. The new advanced manufacturing techniques help keep manufacturing tolerances ultra tight.
Byway RS 50
This is your tire when you are looking for all out speed. It has a slick center for the best rolling resistance with low-profile transition tread and shoulder knobs for grip in road and hard packed surfaces, while still providing grip when things get loose. At 620g, it is the narrowest and lightest of the group.
Course 52
If you are looking for the middle ground between fast on the road, yet still enough grip when things get more challenging, the Course 52 is your choice. Weighing in at 635g, it has more densely packed tread down the center to all the tire to roll efficiently and larger, more widely spaced knobs on the shoulders for more grip.
Macro 54
Finally, you have the Macro 54, the tire for rougher terrain and big adventure days. It’s the largest tire and had the most aggressive tread, with taller, more widely spaced knobs across the tire for maximum confidence in loose, rocky, technical terrain.
All three model are available now through WTB dealers and the website, and will come in black or tan sidewalls. Pricing is $89.95 per tire.
As a sneak peak, WTB will also be launching a new CGR carbon gravel wheelset in the near future, creating a wheel/tire system from the brand that is sure to make your ride even faster. More to come on the wheelset in the future. For now, we have a set of the Byway RS 50 and Course 52 on the way for review.
Based in Lancaster, Pennsylvania, Scott joined Bike World News as the Cyclocross Editor in 2012 before taking over as Tech Editor in 2016. He has also worked as a photographer for various pro teams and shoot races along the east coast of the US, including the 2012 US MTB National Championships, 2013 UCI Cyclocross World Championships, and 2016 UCI Road World Championships. Scott has a passion for performance and technology, with 35 years of riding and mechanic experience. He also enjoys soccer, running, teaching group fitness classes, and is the founder of Lancaster Beard Company.
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