Aero Gains for Wide Gravel Tires

Enve is launching the new G SES wheel lineup today, claiming to have finally solved the gravel aero puzzle. Dubbed “the world’s most aerodynamically efficient gravel wheel,” the new line spans three distinct wheelsets that mirror the road-going SES 4.5 and 6.7. Each is specifically engineered to recapture lost efficiency, saving riders up to 25 watts while running high-volume modern gravel tires.

The Problem with Gravel Aerodynamics

Over recent years, we’ve seen two parallel avenues of exploration in the gravel world. On one side, speeds are increasing, making aerodynamics more important than ever. At the same time, those higher speeds mean that rolling resistance and the ability to absorb massive hits from the road surface are equally critical. The problem is that the second goal presents a major issue for the first.

The best way to absorb energy from the road surface is through more air volume. That means bigger tires, which allow riders to roll faster across rough terrain. However, those massive tires also present a massive frontal area to the wind.

These two opposing forces create a conflicting feedback loop. Better rolling resistance and impact absorption let riders go faster. But the faster you go, the more aerodynamics matter, and the more those wide tires hold you back. So, how does this get solved?

The Zipp Solution

Every major wheel brand knows the challenges in this space and are working to fix it. This is an aero problem that is solvable but it takes the right wheel design. Most options on the market still play it safe.

The issue isn’t just the massive frontal surface presented to the wind—that won’t change. The real challenge is keeping the air attached to the rim so it can smoothly come back together after passing the tire. To do this effectively, a wheel must leverage the Rule of 105.

The Rule of 105 dictates that to effectively recapture airflow and eliminate turbulence, a rim’s external width must be at least 105% of the measured tire width. When that rule is ignored, the air detaches from the tire as it hits the rim and spills to the sides as a turbulent, watt-stealing mess. Achieving that 105% ratio is easy enough when your tire is 23mm. It’s trickier at 28mm, and at 50mm, it becomes a huge engineering hurdle.

Zipp was the first to address the problem with the Zipp 303 XPLR. The brand approached it by creating what is really just a massive wheel. The 303 XPLR is 54mm deep to give the air enough space to reattach, and it dramatically expands the rim bed to a 32mm internal width. This stretches the tire casing, reducing the turbulent “lightbulb” shape and keeping the sidewalls relatively flush with the rim edge.

The problem with the Zipp solution is that tires keep getting bigger. The 303 XPLR SW maxes out at a 40mm external width. According to the Rule of 105, Zipp’s 40mm rim mathematically fails the moment you mount a tire wider than 38mm. While it is an improvement over traditional rims, it still struggles to maintain aerodynamic efficiency as tires grow. Where a 40mm tire once made sense, 50mm is rapidly becoming the standard, and Zipp’s wheel design struggles to keep up.

Enve went bigger

Enve started the tech briefing for these wheels with a discussion about the Zipp wheels. Zipp is the primary competitor, and Enve claimed that while they are good, they don’t go far enough. To address that issue, the flagship wheels being launched today are the Enve G SES 6.7 PRO.

This wheel takes what Zipp started and goes farther. To satisfy the Rule of 105 for high-volume rubber, the 6.7 PRO utilizes a 35mm internal width and pushes the external width out to 42.60mm. That wide footprint is paired with a 60mm front and 67mm rear rim depth. The aerodynamic results are significant: Enve claims the 6.7 PRO saves 8 watts at 32 kph and 25 watts at 48 kph against a baseline shallow wheel.

To give some context on those numbers, the baseline is the 21mm deep Enve AG25. That wheel is great for numbers but it’s irrelevant as a point of comparison. Compared to the Zipp wheel, at 32kph with a 48mm tire, Enve is claiming a 3.5% efficiency advantage for the G SES 6.7 PRO. Enve also compares the wheels to the SES 4.5, which was always billed as an all-road wheel and is quite close to a number of other aero gravel wheels, and in that case shows a 2.8% efficiency gain.

Also of note, Enve did the test with slicks and claims that treaded tires are slower across the board. However, Enve notes that the aerodynamic advantage of the new wheels remains consistent whether you use a slick or a treaded tire. Slicks, and higher speeds, make it easier to see the differences and make for better headlines, but riding slower and with tread will show the same advantages at lower watts.

Enve also claims that both the 6.7, and shorter 4.5, address another issue with gravel wheels that spread the tire this widely: impact protection. As the tire spreads out and the sidewall straightens, it’s faster but there’s less protection for the rim bead. Enve has always provided a rounded out rim bead to reduce sidewall cuts with impacts, but the new wheels use a 3.8mm hookless bead design for even more impact protection and the team punished them through additional impact testing.

Weight becomes a problem

The reason that every company doesn’t just make a huge wheel to match whatever today’s new max tire standardizes on is weight. The Zipp wheels likely stop where they do because at 1,452g already Zipp felt the aero efficiency loss was worth the weight savings. ENVE pushed past those aero efficiency issues, but weight still becomes an issue and ENVE has options for this.

At the tip of the spear, the ENVE G SES 6.7 is only available as a PRO model because at 1,580g (Includes tape, valves, and HG Freehub), ENVE felt like that was the line in the sand. Any heavier and it became too much of a liability. The PRO hub uses a lighter hub shell to save 60 grams (total weight is 281g split as 87g/194g) compared to the standard hub. It also pairs the lighter shell with a flashy silver outer, silver spokes, and ceramic bearings.

Despite those changes, the G SES 6.7 PRO still won’t make sense for every rider or every course. Courses with more climbing, or riders who want to trade aero for not only weight but rounder sidewalls, have the option of the G SES 4.5 PRO and G SES 4.5.

The shallower wheels are patterned off of the SES 4.5 road wheel and use an internal width of 30mm paired with a depth of 49mm front, 55mm rear, and an external width of 37.6mm. The aero efficiency difference between the G SES 6.7 PRO and the G SES 4.5 (at 32 kph and with 48mm tires) is a 1.7% loss with the smaller wheels.

With the 4.5 option, ENVE is also offering a choice. There’s a PRO model or a standard hub model, with the PRO hitting the scales at 1,480g vs. 1,565g for the heavier non-PRO model.

Pricing, tire compatibility, and availability

Zipp is very clear about exactly what tires work with the XPLR wheels. Enve is more lenient. The published minimum tire is 40mm for the 4.5 wheels and 44mm for the 6.7 PRO, with a max pressure of 50 psi across the board. Enve also shared that “If the delta between inner rim width dimension and tire width is below 10 mm, there is a higher probability for pinch-flats” and, as usual, “In the case that tire and rim max pressures are different, the lower of the two pressures becomes the default max pressure for the system.”

All three options are built in the US and are available today at Enve dealers or via the Enve website. The wheels are backed by Enve’s limited lifetime warranty against material and workmanship defects, as well as a separate limited lifetime crash replacement program.