Cheap Gravel Bikes

About Gravel Bikes

Gravel Bike Geometry

Reach, Stack Height, Wheelbase, Head Angle, Fork Rake & BB Drop on a Gravel Bike.

A gravel bike has many of the same features as a road bike; at first glance you may struggle to tell them apart. However, upon a closer look you'll notice a few subtle differences designed to improve handling when riding off-road.

Stack and reach are two of the more important measurements of a gravel bike frame.

Stack is the vertical distance between the heights of the bottom bracket and top of the head tube.

Reach is the horizontal distance between the same two points.

On a gravel bike, the reach is shorter and the stack is greater than that of a road bike. Essentially this means that the front end of the gravel bike is higher up and closer to the saddle, and so less aerodynamic, but more relaxed and comfortable to ride.

The wheelbase of a gravel bike is longer than that of a road bike, and the head angle is slacker.

The wheelbase is the distance between the wheels, and the head angle is the angle of the head tube / fork steerer in relation to the ground.

The increased wheelbase adds stability when travelling over rough ground.

Similarly, the slack head angle enables the bike to handle rocks, bumps and roots easier, as your weight is positioned further back from the front wheel. This is exaggerated yet further by the fork rake - essentially how far the fork travels forward from where it leaves the frame to where it meets the wheel axle.

Decreased Toe overlap

Both the head and rake angle reduce the possibility of toe overlap, which again reduce the chance of your foot touching the front wheel whilst pedalling.

Increased Tyre Clearance

Tyre clearance is a lot larger than a road bike, often allowing you to run tyres up to 38c, which are required due to the gravel bike's intended use on varied terrain.

Bottom Bracket Drop

Bottom bracket drop is the vertical distance between the bottom bracket and the hub height of both wheels. The greater this distance, the lower the bottom bracket. A bike with a greater bottom bracket drop gives more stability as your centre of gravity is positioned lower.

However a low bottom bracket also results in your cranks and pedals being closer to the ground, which increases the chances of them hitting rocks, roots and other obstacles.

To sum up Gravel Geometry

All of these measurements leave a gravel bike somewhere inbetween a road bike and a modern mountain bike, which underlines it's purpose as a versatile all-rounder.

Gravel Bike Frame Options

As with most bike frames, you have a few main options when it comes to a gravel bike's frame material. These choices are largely defined by your budget.

Alloy: a popular choice, very cheap, can be repaired, lightweight and strong.

The cheapest gravel bikes will almost certainly feature an alloy (aluminium) frame, often using a 6061-T6 alloy. This is a cost effective material, being resilient to corrosion, lightweight and strong. It's heavier than carbon, and has a better strength to weight ratio than steel.

Alloy easier to repair than carbon, and far cheaper to produce. Generally speaking, the majority of gravel bikes under £1500 will feature an aluminium frame.

In terms of riding, alloy frames are slightly less forgiving than carbon and steel, but are one of the most popular choices of frame material due to it's low cost and durability. It won't suffer oxidation damage to the same extent as steel, and so requires less maintenance.

Aluminium frames will typically be a pound heavier than an equivalent carbon frame, but will cost considerably less.

Steel: nice to ride, traditional and strong, easy to fix, can rust, and has a weight penalty.

Steel gravel frames are seen as a traditional choice of material for a new genre of riding. Steel can be used to create strong and forgiving gravel bikes, with steel being both sturdy yet still flexible enough to remove the buzz of the trails. For this reason, steel is a popular choice with those who ride long distances. You won't feel as "beaten up" after a day in the saddle on a well designed steel gravel bike as you would on many other frame tyres.

The main disadvantage of steel is it's weight penalty; it will weigh an additional pound or two over a carbon frame, and if not maintained and checked can also be prone to oxidation (rusting).

Steel does have it's advantages however: it's easier to mend than all other materials, requiring less specialist equipment, and is far less likely to be written off in a crash than it's carbon counterparts. If travelling in a remote area, it will be far easier to find someone to fix a steel frame compared to a carbon or alloy framed bike.

In terms of price, steel gravel bikes start at around £800, all the way up to made-to-order boutique steel framesets costing several thousand.

Carbon: great to ride, lightweight but expensive and difficult (but getting easier) to get them repaired.

Carbon frames are constructed by weaving together carbon fibre strands and setting them within resin. The end result is a very lightweight, stiff and strong bike frame, which would typically weigh a pound less than an alloy gravel frame. The material itself has vibration damping properties which reduce any buzz from the wheels for a smoother ride. Many alloy framed gravel bikes utilise carbon forks for this very reason.

Carbon can be easier to damage; dropping or crashing your bike is more likely to result in a broken frame than alloy or steel. Essentially carbon frames are exceptionally strong at their intended purpose, but a random sideways impact to a frame's tube when dropped can easily cause major structural damage rather than a small dent. Similarly, it is easy to damage a carbon frame by over tightening bolts or clamps, so more care is required when building or maintaining the bike.

Other downsides of carbon are the cost, and the difficulty of repairs. As carbon bikes become more popular, the latter is becoming more common, although it is a more skilled job than mending an alloy or steel frame.

Titanium: very expensive, lighter than alloy and steel, a unique, forgiving ride that stands out from the crowd.

Finally, there are a few posh titanium models on the market, usually produced in small quantities by non mainstream boutique brands. Often seen as works of art, titanium gravel frames are sought after but very pricey. As a material, titanium is stronger than aluminium and considerably lighter than steel, as well as being very robust.

Titanium frames are rarely painted, typically being left with the natural ti finish.

In terms of weight, Titanium is slightly heavier than carbon, but lighter than alloy and steel.