Gravel has been the hot button topic over the past couple of years with everybody and their cousin talking about wheel sizes, flared drop bars, tyre width and tread pattern, but for the uninitiated, the road bike vs gravel bike question might seem strange at first, as they may not look all that different on the surface; they both have drop bars, two triangles, and roll on 700c wheels and tyres (at least some of the time).
In the same way that a cross-country mountain bike differs from a trail or enduro bike, a gravel bike and a road bike exhibit a wide variety of design elements which allow the bike to excel in a specific arena.
Road bike vs gravel bike: What are they supposed to do?
As you can probably work out from the name, road bikes are designed to be ridden on routes with a tarmac bias, while gravel bikes can be taken off-road, on gravel paths, dirt roads, fire trails, and even singletrack.
That’s not to say that road bikes can’t be used for some gravel riding — heck, every year, the pro racers take the world's best road bikes onto the white gravel roads around Siena, Italy. Road bikes are considerably more capable than we often give them credit for, but they do have a well-defined limit, one which you will quickly establish once you venture onto loose gravel roads.
Road bikes ultimately fall into two camps, race bikes, and endurance bikes. Race bikes are what you see the pros pushing to the absolute limit and feature aggressive angles, low weights, and tube shapes and components designed to reduce aerodynamic drag. Endurance bikes are a bit more upright, feature more stable handling, put a premium on comfort, and may have built-in storage and mounts for racks and fenders.
Gravel bikes, on the other hand, are designed to be more capable and tackle a wider variety of terrain. They can happily plod along on the tarmac or jump onto the back of a group ride, but if you plan to pin on a number for a Tuesday night crit, you will find yourself under-gunned on even the best gravel bikes. We don’t officially have the same race and endurance categories of gravel bikes (yet), but some are designed more for racing, like the Allied Able, while others are built with more of an adventure focus, as we found out in our Merida Silex review. They will usually have mounts galore for bottles, luggage, and fenders and will usually be a bit heavier than their tarmac faring relatives.
This weight is higher, too, because the frame will be reinforced to deflect airborne debris and withstand the rough and tumble terrain found once you leave the tarmac, but the additional grammage also helps with stability. Ultra-lightweight bikes can get bound around when the terrain gets spicy, while something slightly heavier will remain more composed.
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Wheels and tyres
The most visually striking difference between a road and gravel bike will be the wheels and tyres. Road bikes will usually have an absolute max tyre clearance around 33-35mm depending on the category, with most erring on the side of slightly narrower rubber. These days, most race bikes will come stock with 25mm tyres, with room for 28mm, while endurance bikes will have wider rubber. Wider tyres allow for lower pressures, which creates a wider contact patch for more grip and comfort. Lab testing has established that fatter tyres make for less rolling resistance.
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However, wider tyres are heavier, and depending on the rim, may mess with the aero mojo of your wheelset — today's best road bike wheels are designed to spread a 25c or 28c casing to sit flush with the rim, too wide, and the tyre will balloon out over the side.
On the other hand, gravel bikes will have clearance for 33mm tyres all the way up to casings that are measured in inches, and gravel frames may even be compatible with both 700c smaller 650b (27.5in) wheels and tyres. Like with road tyres, the broader contact patch, lower tyre pressures make for improved comfort and grip, and the additional width will also make negotiating uneven surfaces a bit less technical.
The tread pattern is a much bigger consideration on gravel bikes than it is on road bikes. Unless rolling over a surface it can dig into, tread on road tyres doesn't add much in the way of grip, hence why road bike tyres are more or less smooth.
Gravel bikes are designed to venture onto softer surfaces, and as such, they feature tread and knobs that can dig into offroad surfaces. There is a massive range of tread patterns available for gravel tyres, and which is right for you depends on the weather, where you plan to ride and what the terrain looks like.
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Many gravel bikes will also have the ability to be used with a 650b (27.5in) wheel and tyre combo. This smaller wheel allows for a wider tyre, in the ballpark of two inches, allowing for lower tyre pressure and more comfort and grip. This is possible because a 700x28-30mm tyre is approximately the same diameter as a 27.5x1.6in-1.8in tyre, which means that it won’t change the head angle or trail figure, and should not have a drastic effect on handling characteristics. To maximise clearances for such wide tyres, and the mud and debris that will eventually build up on the frame, gravel bikes will often feature a dropped driveside chainstay or machined yoke behind the bottom bracket — these same features are also used to improve chainring clearance.
The other thing to note about gravel and road tyres is the proliferation of tubeless. As the best tubeless road tyres continue to get better with each iteration, the technology is becoming more and more prevalent on the road, however, off-road where punctures are much more commonplace, pretty much all of the best gravel tyres are tubeless by default.
You likely won’t be able to spot the geometry differences between a road bike and a gravel bike unless you have one of each right next to one another; the nuanced differences and a few millimetres here or half a degree there will have a drastic effect on the way a bike behaves.
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Road bikes will typically have a short wheelbase and steeper angles for nimble ride quality and lively handling. Gravel bikes have a longer wheelbase and slacker head angle to add stability and slow down the handling for negotiating technical obstacles and loose descents.
For example, a Specialized Roubaix endurance road bike has a head-angle of 72.75-degrees and a wheelbase of 988mm in size 54; meanwhile, a Specialized Diverge gravel bike has a slacker 71.75-degree head-angle and 1032mm wheelbase in the same size.
Road bikes will also have a longer reach, and shorter frame stack and head tube to facilitate a longer, lower, more aero position, while gravel bikes are shorter and more upright.
If we compare Trek’s new Emonda race bike and Checkpoint gravel bike; the Emonda has a frame reach of 386mm, a fame stack of 541mm, and a 121mm head tube in size 54, while the Checkpoint sees a 383mm reach, 547mm stack, and 125mm headtube.
Suspension has been a mainstay of mountain biking for quite some time; however, various forms of suspension are available across both road and gravel bikes — the breadth of which across both categories is surprising.
Specialized uses a damped coil shock, dubbed the Future Shock, on the front end of both the Roubaix endurance road bike and the Diverge, as shown in more detail in our Specialized Diverge review. Trek and Cannondale both have their own take on pivot based flex suspension for the rear; the IsoSpeed decoupler found on the Domane endurance road bike, Madone aero race bike, and Checkpoint gravel bike, and the Kingpin thru-axle pivot on the Topstone Carbon gravel bike.
Gravel bikes, however, are the only lot to see air-sprung forks, with Cannondale offering its 30mm Lefty Oliver on specific models of the Topstone - shown in our recent Cannondale Topstone Lefty 3 review - and Fox offering its 32 AX (Adventure Cross) gravel fork.
Technically, both road and gravel bikes come in ‘full suspension’ varieties, albeit in very different forms. Trek’s Domane has IsoSpeed decouplers front and rear, which technically qualifies as suspension. It's a far cry from Niner’s Magic Carpet Ride (MCR), which comes complete with the Fox 23 AX fork and rear linkage that offers 50mm of travel, thanks to the X-fusion Microlite shock.
Most of the components found on a gravel bike will be compatible with a road bike and visa-versa; however, there are key differences that prevent a gravel bike from falling to pieces in the flint hills of Kansas, while other components still will help a road bike to dance up the slopes of Mont Ventoux.
Road bikes are still hit and miss with disc brakes (though things are trending into the direction of rotors and hydraulic calipers); every gravel bike will come equipped with discs. Rim brakes are lighter and work just fine riding on tarmac, but discs provide superior power, modulation, and control, and consistently perform across all weather conditions. You will appreciate this added control when you are picking your way down a technical descent on your gravel bike, especially in the wet.
Both road and gravel bikes will sport 1x and 2x drivetrains. Road bikes trend towards two front chainrings, as the jumps between gears are smaller, meaning it’s easier to find a comfortable cadence at any speed.
Gravel bikes have both 1x and 2x drivetrains with a slight bias towards 1x. With only a single front chainring, 1x drivetrains are still capable of achieving the same gear range as 2x, though to do this in 11 or 12 gears instead of 22 or 24 means the gaps between each ratio will be more significant. Eliminating the need to shift at the front has allowed drivetrain manufacturers to employ narrow-wide chainrings, which feature alternating teeth profiles that grip the inner and outer chain links to prevent it from bouncing off over rough terrain.
Gravel bikes typically feature a rear derailleur with some definition of a clutch. Whether it’s of the roller bearing or fluid damper variety, the primary function is to pull the chain taut to prevent chain slap or it bouncing off the front chainring(s). These are usually a few grams heavier than their non-clutched compatriots and require a bit more gusto to push the chain up the cassette, but the difference in chain retention is night and day.
Cockpit and seat post
Many gravel bikes will have flared drop bars, and some times shorter stems than cockpits you'll find on road bikes.
Drop bars on road bikes will typically have a deeper drop and a slightly longer reach than those usually found on gravel bikes.
Flared drop bars place your hands in a broader position, allowing clearance for your wrists and added control when navigating your way through loose corners or up and over obstacles. The flare also makes it easier to reach the brake levers from the drops.
The last and most controversial component difference you’ll find on gravel bikes is a dropper post. These are seen as a must-have for mountain bikers, and have even made an appearance on Mavic neutral support bikes to help riders dial in their saddle height on the fly, but that’s not their intended purpose. The idea behind a dropper post is to move the saddle out of the way on steep descents so you can get your weight back to prevent being ejected over the handlebars.
On a paved road, you’re unlikely to come across a gradient steep enough or a road surface so broken that you will need to get behind the saddle, but it’s not uncommon to find fire roads that are plenty steep and rough enough to warrant dropping your saddle out of the way.