At first glance, a gravel bike looks a lot like a mix between a road bike and a cyclocross bike. The shapes are similar, plus they both have drop bars. But road bikes have narrower tires and don’t always come with disc brakes. Mountain bikes look significantly different, but they actually have a lot in common with the best gravel bikes. In this article, we’re going to look at the specific geometry of a gravel bike, and how it compares to road, CX, and mountain bikes.
Designed for all things off-road
Before we get into the math and measurements associated with gravel bike frames, we first need to consider what is a gravel bike and what they are designed for. Gravel bikes are designed for all kinds of off-road riding, with the only exclusion being hardcore mountain bike trails with jumps, steep drops, and heavy rock gardens. Other than that, a gravel bike can handle just about anything.
Gravel bikes are also designed to be comfortable for the long haul, and many include space and mounts for accessories such as light, bikepacking bags, and extra water bottles. Due to the tough nature of gravel and trail riding, gravel bikes are also designed to be lightweight and agile so that they won’t hold you back on steep climbs. Built for everything from gravel racing to bikepacking, gravel bikes are designed to be more comfortable than road bikes, but faster and more efficient than mountain bikes. Now, let’s dive into the details.
Fits like a road bike
Looking at it from the side, a gravel bike looks awfully similar to a road bike, apart from the wider tires. Both frames have similar overall shapes, drop bars, and disc brakes (on most road bikes). Compared to CX and mountain bikes, the fit of a gravel bike is closest to that of a road bike.
In terms of specific sizing, most road bikes are listed in centimeter increments (e.g. 52cm, 54cm) whereas most gravel bikes are listed in a broader range of sizing (e.g. Small, Medium, and Large) – you can find conversions on most manufacturers’ websites.
If you're between sizes you will need to consider the bike's geometry to determine which size bikes stack and reach numbers will best suit you. The choice between two different sizes is going to change the ride quality of the bike. Smaller frames will offer better agility and performance however lower front stack height (the height of the top of the head tube in relation to the bottom bracket) may require more compromises to get the right fit.
Ultimately if you are unsure on what size of bike to get talk to the shop or test ride a few bikes if possible. While it will add extra cost, the best option is to consult a qualified bike fitter as they will provide the most comprehensive advice on size and fit.
Wheelbase and head tube angle
One of the defining features of gravel bike geometry is a longer wheelbase and slacker head tube angle. The longer wheelbase helps ‘stretch out’ the frame, which improves handling and stability on rough terrain. This differs from CX bikes and some road bikes which have much shorter wheelbases for quick handling in tight corners.
The head tube angle is the angle between the horizontal plane and a straight line running down the center of the steerer tube – making this angle “slacker” means lengthening the wheelbase and pushing the front wheel further in front of the bottom bracket. Thus a slacker head tube angle has similar effects on handling as lengthening the wheelbase – they both improve overall handling, especially on technical terrain and at slow speeds. The slacker head tube angle also reduces the chance of toe overlap, which is an important factor for riders on smaller frames.
Many gravel bikes feature unique frame tubing that includes curved and flattened sections of material, especially in the rear triangle where they are meant to increase flexibility and comfort. These features are designed to absorb vibrations and improve comfort over all-terrain, since gravel bikes are expected to experience punishing conditions on gravel, sand, mud, and pavement. Some bikes even include vibration absorption elastomers, or a short travel suspension design.
Gravel bike frames are heavier than most road and CX frames because they are designed to be more comfortable and durable. Road and CX frames are lighter, but they are also much less comfortable, especially on rides lasting more than a few hours. Gravel bikes are designed to be comfortable all day – which we’ll get to more when we talk about riding position – while many also include extra mounts and accessories for mudguards, lights, luggage, and more.
Gravel bikes have a shorter reach than most road bikes which helps keep the rider’s center of gravity in the middle of the bike as opposed to stretched out over the front wheel. Road bikes are known for having long stems and longer reaches, which puts riders in a simultaneously powerful and aerodynamic position. While this is great for straight-line speed, it is terrible for bike handling and limits a rider's ability to use their body weight to control the bike on off-road terrain.
The stems of gravel bikes are much shorter than stems on road bikes which, coupled with wide handlebars, helps improve handling and overall control, similar to how a mountain bike uses wide flat bars to improve leverage for steep descents and tight corners.
A defining feature of gravel bikes is their use of drop bars, contrary to mountain bikes which use flat bars. Both bikes are designed for off-road riding, but the differing style of handlebars makes them distinctly unique. The best gravel handlebars offer a better balance of comfort and speed due to reduced aerodynamic drag and a narrower shoulder stance. They are also more comfortable for all-day bikepacking and offer a few different grip options on the drops, hoods, and tops.
Most gravel bikes have drop bars that include a wide flare, which means that the drops are bent outwards. This creates ‘the best of both worlds’ where you can have a faster overall set-up, while also having the wide grip option for technical terrain and steep descents. Gravel bike drop bars are offered in all the same sizes as road bike drop bars, while the gravel market includes even wider options – some styles are offered in bar widths up to 52cm wide.
You may have gleaned thus far that gravel bikes have a more upright riding position than road bikes. It’s true – due to the unique frame geometry and slacker angles of gravel bikes, you’ll be sitting at a higher angle and taking more wind compared to a more aerodynamic road bike position. And while you won’t be as fast in a straight line, a more upright position will help increase handling, stability, and control on bumpy terrain.
While many CX bikes are designed for relatively upright positions, they are still very different from gravel bikes due to their shorter wheelbases and shallower angles. They handle well in tight corners, but will be inferior to the gravel bike on everything from technical trails and rough tracks, to steep descents and the classic gravel road.
Gravel bike geometry can accommodate wider tires
Another defining feature of the gravel bike is its extra room built-in for wide tires. While a handful of road bikes can fit wide, off-road-ready tires, few can match gravel bikes which offer clearance for tires up to 50mm wide. The frames and forks themselves are designed around the space for the tire, making them a truly unique gravel bike feature.
Different styles of gravel bikes
Most gravel bikes have drop bars, disc brakes, relaxed geometry, and 40mm tires – but not all gravel bikes are the same. Some are meant to be gravel racing machines, with a full carbon set-up that is lightweight, fast, and durable. Other gravel bikes are designed for long-haul epics and even overnight bikepacking trips. These frames are heavy-duty, built to withstand the roughest roads, and with room for accessories to help aid your adventure.
As with all bike designs, there is a wide range of price points from high-end to cheap gravel bikes. The frame, components, and features are what separate one bike from another, and how much you ride it should tell you which kind of bike you need.
For beginner-gravel riders, look for a gravel bike with relaxed geometry and comfortable fit, with capable disc brakes but no unnecessary accessories. As you ride more and more, look to add mounts and accessories before upgrading your gravel frame. The best-of-the-best come with built-in mounts for lights, luggage, and mudguards, powerful disc brakes, flared drop bars, comfortable frame geometry, and room for wide tires to help you tackle the toughest off-road terrain.