Gravel riding seems to be this whole new category of riding that's sort of just appeared out of nowhere these last few years. It's gaining in popularity for sure, and almost every major bike manufacturer has at least one gravel-specific bike in their lineup now, but they can vary from one to the next pretty wildly. There's no real definition as to what gravel riding actually is, but that might not even be a problem. Bear with me now as I attempt to explain gravel riding, and hopefully neither of us comes out more confused than before.
Gravel riding can cover many extremes of riding, from super smooth unsealed roads.
Who is gravel riding for?
Gravel riding is for everyone, really. Gravel riding is all things to all people, and no I'm not being intentionally vague here. There are different schools of thought on what gravel riding really means to different people, and the types of bike they want to ride are going to be different too, but we can talk about the bikes later. In short, gravel riding is about as all-encompassing as the phrase "mountain biking".
To many people, gravel riding is like road cycling but without the cars. Cars are without doubt the worst and most dangerous part of road cycling - eliminate them, and your ride could be much more pleasant and safe. We all know the bliss that comes with riding a smooth, empty ribbon of tarmac. Now that we have appropriate bikes, it's easy to hit the gravel forestry roads, or purpose-built gravel tracks in comfort and get a great ride in without worrying about who else you're sharing the road with. In many places all over the world there are smooth logging, mining roads etc. where with a bike with some slightly wider tires you can ride almost as fast as on the road. You may need to ride some tarmac to get to or in between the gravel roads, and so it's useful to have a gravel bike that's almost as efficient and fast as a regular road bike but with some extra off-road capability. Many of these roads also lead to really cool places that you might otherwise never get to, and who doesn't love a good adventure?
Some rides such as the Great Divide really call for a lightweight XC mountain bike.
The 'other' type of gravel riding is the people that want to get really 'out there', maybe on some decommissioned service roads or just really chunky, hard to access roads or paths that can take you somewhere really remote and special. The sort of place where something resembling a road bike is going to be difficult to ride, but you might not consider it mountain biking in the same sense that you might consider riding Fromme laps. Maybe adventure riding is more accurate? For these people maybe an XC hardtail is more what's needed. A lightweight XC bike can be almost as fast as a road bike with fat knobby tires but a lot more capable and confidence inspiring to ride when the going gets rough.
There are also some other scenarios that are worth thinking about - gravel racing is one, and the needs are pretty specific - where you might be riding all day long and need a bike that's fast, yet stable. Confidence inspiring, yet light weight. It's a tricky thing to get right. The opposite end of the spectrum is bike touring - quite often it can be more fun off road, certainly more adventurous. The type of roads/trails you want to ride and how much you want to load up might influence the type of bike you want ride. For instance the Great Divide Trail has a lot of gravel road and tarmac, but is so rough and technical in sections that most people ride it on a mountain bike.
There are singletrack and doubletrack trails that work great on a drop bar gravel bike, such as the Sea To Sky trail.
What is a Gravel Bike?
Okay, so we're still a little fuzzy about the concept of gravel, but hopefully this will clear things up. Being able to define what a Gravel Bike is goes a long way to helping us understand gravel riding. The idea of what we call a 'gravel bike' is actually reasonably well defined. The bike industry has been accused by many people of 'inventing' gravel riding as a new segment to try to sell us more bikes. While it's true that the bike industry wants to sell bikes (we all need to make a living), and the riding itself hasn't really changed, the gravel bike is a relatively new type of bike, and this is because of a bunch of technical innovations that have significantly improved bike design but also (and not necessarily deliberately) blurred the lines between mountain bike and road bike.
Cervelo's Aspero is a lightweight and capable machine that really blurs the lines between traditional bike genres
The things that define a 'gravel bike' are simply recent technological advances that have made it possible to produce bikes that are both efficient and capable, similar to the "enduro" trend on the flat bar side of things. These innovations are namely disc brakes, tubeless tires and clutch derailleurs, all of which have been commonplace on mountain bikes for some time, and have slowly gained acceptance in the road cycling world. The other major innovation would be modern frame building technologies in both carbon and aluminum.
Disc brakes have been around for a while, but recent frame-building technologies, such as modern carbon layups, have enabled frame builders to build frames stiffer, lighter and stronger than ever, meaning frames can be light enough to be fun to ride and robust enough to take a beating, all the while negating the weight penalty associated with disc brakes. Thru-axles also help to make things stiffer again and make disc brakes much more practical. The use of disc brakes means that gravel bikes can have much more powerful and reliable stopping in all weathers, ideal for the rigours of gravel riding where extra stopping power is definitely needed.
Gravel bikes and many modern road bikes have big clearance for knobby tires thanks to the acceptance of disc brakes.
The use of disc brakes mean that frames now can be built with much more clearance for wide tires, making riding on gravel much safer and more comfortable. Tubeless tire technology from mountain biking means that tubeless tires are now more reliable than ever and are a great idea for applications such as gravel riding. Being able to run such fat tires tubeless actually makes them much more efficient as they have less rotating mass and lower rolling resistance. Not only this but higher volume tubeless tires means lower pressures and more grip, as well as fewer punctures. Rejoice!
The most common sizes for gravel bike tires range from 700x38-42c. 650b x 47c is also a fairly common size, as the outer tire circumference is about the same as a 700x33c, so you can usually fit them in a 700c frame and it gives a much more compliant ride. Some bikes, such as the Santa Cruz Stigmata even have the option of coming with 650b gravel-specific wheels.
Drivetrain technologies coming from mountain bikes include 1x drivetrains, enabling us to ditch the front derailleur and further increase tire clearance, and clutch derailleurs. Clutch derailleurs are what have enabled 1x drivetrains, meaning you're almost guaranteed not to drop your chain on rough surfaces, meaning drivetrains are much more reliable and less maintenance (not to mention less annoying) for those bike rides over rough terrain, and means a front chain guide/derailleur is no longer necessary. The advent of 12sp drivetrains also means that we can have essentially the same range of gears as a 2x10 drivetrain without having that front derailleur, so you don't have to sacrifice gear spread for tire clearance.
Modern drivetrains with clutch derailleurs mean we can now have much more reliable drivetrains AND a wider range. Win/win!
Drivetrain options range from Sram 1x11 road groupsets, and their new AXS wireless technology means you can now run a drop bar lever with their 12sp mountain derailleur and cassette with a huge 520% range as there are no cable pull or compatibility issues to worry about. Riders may want this for increased simplicity and for the extra low gearing for big hill climbs. The other way you could go would be a more traditional double chainring setup with the option of going bigger on the chainrings for a more road-specific setup with a bigger gear for spinning on faster rides. The great news is that Shimano have road clutch derailleur options in either GRX or Ultegra RX to suit. Either way, there are options for every type of rider and every type of terrain.
How are Gravel bikes different to CX?
I hear what you're probably thinking - gravel bikes and CX bikes are essentially the same thing, right? Drop bars, knobby tires and disc brakes. Well, yes and no. CX bikes are typically designed for short, high intensity efforts. As such, they're very light with low rotating weight for quick acceleration, and short, aggressive geometry. This means though they're knobbly, CX tires are often quite narrow, around 33c, and often tubular. Gearing on CX bikes is also typically much higher as there is little need for an easy gear for sitting and spinning up a big hill. CX races are usually flat out sprints and the gearing is harder to reflect this.
Gravel bikes typically are designed for longer rides at a slower pace. As such, they have more relaxed, comfortable geometry. They'll have clearance for the bigger 42c tires, fender and rack mounts. Gear range will be wider, and they're overall much more comfortable to ride over longer distances and time periods. Even race-specific gravel bikes such as the Cervelo Aspero are designed to be raced over a much longer day where comfort and a wider gear range is important.
Gravel riding is a little more of a slow-paced pastime to compared to CX racing!
All of the above technologies combined have allowed modern frame builders to build bikes that are both lighter, more capable and more robust than ever, somewhere between a road and mountain bike. The problem is that these bikes need some kind of label, and this is where "gravel" comes in. It's an easy way to describe this new category of drop-bar bike, and it's exciting because they're improving all the time.
People have been squeezing wider and wider tires into cyclocross bikes for a long time now, converting them to 1x and using them as gravel bikes, the modern gravel bike is simply a more purpose-built instrument. Similar to the way mountain bikes evolved from klunkers in the early repack days - the bikes changed and became more purpose-built, but they were still being ridden in the same places. We all know that "gravel riding" itself has been around since the dawn of time and, it's simply what most of us would call just riding a bike, and that hasn't changed. It's just that we're now lucky enough to have a wider choice of more suitable tools for however you want to get the job done.