From the dirt roads of Colorado’s Haute Route Rockies, to the unforgiving Flint Hills of the Dirty Kanza 200 and gran fondos with gravel sections, events which take riders out of their pavement comfort zone have never been so popular. With this boom, we hear many questions about what equipment – wheel, tire size, and even bike type – riders should take on these new adventures.

The first thing to note is that, unlike the pavement, which is all much the same, gravel and dirt roads vary greatly with geographic location and each type has its own ideal equipment. In order to help end the confusion, gravel riding superfan and frequent ENVE Journal contributor Neil Shirley created the Industry Standard Guide to Gravel (ISGG). It defines gravel road difficulty into simple categories and aligns recommended equipment with each. It’s already grabbing attention. Building on the ISGG, we’ve added our insights on what is the ideal ENVE wheel for each gravel category.

As this is only a guide, there will be a number of other factors to think about when considering your set-up. Your skill level and the event’s ratio of dirt to pavement are two notable aspects. Riders who are less confident riding a drop-bar bike off-road are advised to opt for a more conservative approach and step up one category in equipment. The dirt/asphalt ratio is also key, and The Belgian Waffle Ride is a great example. It features a few off-road sections that would fall under Category 3 and 4, yet because the majority of the route is pavement and easier gravel, the event is considered as Category 2. It’s about striking a balance between efficiency on and off the road.

ISGG

Category 1 Gravel

Smooth, well-maintained dirt roads that have either very small gravel chunks or none at all, and are very road bike friendly. These roads are in better condition than many paved roads in the U.S. and are hard packed, offering little more difficulty than riding on tarmac. There are a number of roads like this in Colorado onto which a magnesium chloride treatment is applied to keep the dust down and harden the top layer of dirt. Cat 1 roads are found in a number of gran fondos and add a little more adventure to the event.

Ideal bike: Road bike
Tire size: 25-28mm
Event Examples: Haute Route Rockies, Tour of the Battenkill

ENVE Insight:  

For this type of riding we want the same aerodynamic efficiency and confidence as on the tarmac. Speeds are often quite high and only minor adaptations are required to standard road equipment in order to achieve a fast pace, while maintaining comfort and overall confidence. For Cat 1 Gravel, our SES 3.4 or SES 4.5 AR road wheels fit the bill perfectly.

Category 2 Gravel

Expect potholes, washboard and probably loose, blown-out corners. There is likely to be gravel outside of the main tire tracks that could cause an extra challenge if your line deviates. A road bike can still cut it, ideally one with greater tire clearance, but more skill is needed when cornering at speed. Increasing the tire size beyond your everyday road set-up is recommended to reduce the risk of pinch-flatting and to benefit from the smoothness of a larger air chamber.

Ideal bike: Endurance/All-Road bike
Tire size: 28-32mm
Event Examples: Gravel Worlds, Dirty Devil, Boulder Roubaix, Belgian Waffle Ride, Grapes of Wrath

ENVE Insight:

The wheelset recommendations made for Cat 1 gravel hold true here as well, although it really starts tipping in favor of the SES 4.5 AR due to its 25mm inner width and its aero profile, both optimized for 28-30mm tires. Because the SES 4.5 ARs were designed for Team Dimension Data to race at Paris-Roubaix, it’s been a very popular option for Category 2 roads. A 28mm tubeless tire on that rim often measures 30mm or greater once inflated. This offers a higher volume, a larger contact patch, better rolling efficiency on rough surfaces, and allows for lower tire pressure. Depending on rider weight, you can safely drop as low as 50psi.

Category 3 Gravel

Infrequently maintained roads that require a high level of skill, made difficult by exposed rocks, rain ruts, sand bogs, and many other unexpected challenges that could arise. Unless a route’s only Cat 3 gravel section is merely a short connector, it’s recommended to step up to a gravel bike on 33-38mm tires with side knobs for the best speed and safety.

Ideal bike: Gravel bike
Tire size: 33-38mm
Event Examples: Rebecca’s Private Idaho, Land Run 100, Crusher In The Tushar, Rock Cobbler, Gravel MOB, SPNDX Stampede, Chino Grinder

ENVE Insight:

This is the point at which our M525 mountain bike cross-country wheel should be selected. Even though the inner rim width matches that of the SES 4.5 AR, it’s designed for greater resistance to impacts and pinch-flats. The M525 features our patent pending Wide Hookless Bead that has dramatically decreased pinch-flats (more than a 50% increase in impact is needed to pinch-flat the M525 versus the previous M50). Anyone who has spent a lot of time riding gravel knows this is critical. If you’re planning to use an M525 or other mountain bike wheelset on your gravel bike be mindful of the hub spacing and cassette compatibility.

Category 4 Gravel

Non-maintained surfaces with deep ruts, rock gardens, and potential landslides left for the next gravel rider to stumble-upon make these the most challenging of gravel roads. Sticking with high volume tires will help to cushion the ride, reduce the risk of a pinch-flat, and provide greater traction in the corners as well as on steep, loose climbs.

Ideal bike: Gravel bike
Tire size: 38-42+mm, or Road Plus (650b wheels with 42+mm tires)
Event Examples: Dirty Kanza, Grinduro, Lost and Found

ENVE Insight:

We think terrain like this is perfectly suited to a mountain bike, but to each his own. Given the right bike, such as an Open U.P., 3T Exploro, or other frame designed around the use of Road Plus (650b) wheels, there could be a real advantage to the smaller wheel, bigger tire format on extremely rough terrain. The M525 in 27.5” would be the choice here, with a number of tire options available ranging from a slick, to a full-blown 2.1” mountain bike knobby. That said, even sticking with a 700c x 40mm set-up would allow most riders to get into the 30-35psi range where you achieve a decent ride quality without much concern of pinch-flatting.

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