Gravel Conditions

Types of Gravel*

Category 1 Gravel
Smooth, well maintained dirt roads that have either very small gravel chunks, or none at all, and are very much 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 that have a magnesium chloride treatment to keep the dust down and harden the top layer of dirt. Roads like these are often found in a number of Gran Fondos to add a little more adventure to the event.
Ideal bike: Road bike
Tire size: 25-28mm
OGG routes with this type of gravel: Scioto Trail State Park
Event examples: Haute Route Rockies, Battenkill Roubaix

Scioto Trail State Park

Scioto Trail State Park

 

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 one was to come off their line. A road bike is just fine, but more skill is needed when cornering at speed. Going up in tire size compared to an everyday road setup is recommended in order to benefit from the reduced risk of pinch flatting and pneumatic suspension a higher volume tire allows. 
Ideal bike: Endurance road bike
Tire size: 28-32mm
OGG routes with this type of gravel: coming soon
Event examples: Gravel Worlds, Dirty Devil, Boulder Roubaix, Belgian Waffle Ride, Grapes Of Wrath

 

Category 3 Gravel
Infrequently maintained roads that require a high level of skill when tackling on a road bike due to exposed rocks, tire eating rain ruts, sand bogs and any number of other unexpected challenges that could arise around the next corner. Unless a Category 3 Gravel section is added merely as a short connector, a gravel bike with 33-38mm tires that offer side knobs is the recommended equipment to achieve both speed and safety. 
Ideal bike: Gravel bike 
Tire size: 33-38mm
OGG routes with this type of gravel: coming soon
Event examples: Rebecca’s Private Idaho, Landrun 100, Crusher In The Tushar, Rock Cobbler, Gravel MOB, SPNDX Stampede, Chino Grinder

 

Category 4 Gravel
Non-maintained Forestry roads common in California would be considered Category 4 due to deep ruts, rock gardens, and potential landslides left for the next gravel rider to stumble upon. Going with high volume tires will help provide pneumatic suspension, reduce the risk of a pinch flat, and provide greater traction is in the corners and on steep, loose climbs. 
Ideal bike: Gravel bike
Tire size: 38-42+mm, or Road Plus (650b wheels with 42+mm tires)
OGG routes with this type of gravel: coming soon
Event examples: Dirty Kanza, Grinduro, Lost and Found

Route: Danville-Walhonding 41 - Bats Nest Road

Route: Danville-Walhonding 41 - Bats Nest Road

 

*Thanks to Neil Shirley for giving us permission to use his Industry Standard Guide to Gravel (ISGG)