MTB frames are built for riding at speed off-road but there is a huge variety on the market, with types to suit every possible riding discipline and riding style – from lightweight carbon racing whippets to burly bruisers that can take on the toughest terrain.
In the first instance, MTB frames fall under two main categories: hardtail and suspension frames.
• Hardtails: As the name suggest, hardtail (HT) MTBs forego rear suspension in favour of a fully-rigid frame. They are generally lighter and less expensive than their full-suspension cousins so are commonly used as the basis for entry- or mid-level bikes, or else for lightweight top-end racers. Some people, however, just prefer to ride a hardtail.
• Suspension: Suspension MTB frames feature a design that incorporates a shock absorber, allowing the rear end to independently move and soak up trail bumps. Suspension MTB frames may feature varying amounts of rear ‘travel’ (the amount the rear end can move). Lightweight race frames may have 100mm travel, for example, while ‘big-hit’ gravity frames may have up to 200mm.
Both hardtail and suspenson MTB frames are available in ‘women-specific’ iterations to reflect the different ergonomic needs of female cyclists, such as greater standover, shorter top tubes and narrower handlebars.
Hardtail or full suss? That is the question. For years the choice was simple – if you wanted light weight and efficient power transfer for racing and speed you holstered a hardtail, but if you wanted big-hit ability and didn’t mind the weight payoff, you armed yourself with a full-suss.
However nowadays things are a little different, as technologically advances have eroded the performance advantages of the hardtail. The latest generation of full-suss frames use materials (carbon fibre) that erode the hardtail’s weight advantage, and technologies (suspension design, platform-damped shocks) that maximise power transfer for a firm feel under load. Meanwhile the inherent advantages of suspension – better traction when climbing, better stability at speed when descending – may result in better overall speed, efficiency and comfort over the course of long hours in the saddle.
On the flipside, hardtails are simple, durable and buckets of fun – and under the right rider every inch the equal of a full-susser.
The choice between hardtail and suspension frame is a personal one. For some it can come down to their local terrain and preferred riding style (suspension MTBs being generally able to cope with rougher stuff than hardtails, assuming ‘normal’ riding skills), while for others it can be a question of budget (a quality hardtail frame is generally less expensive, meaning more money for quality components!).
Meanwhile some riders just prefer the ride ‘feel’ of one over the other and many may indeed have both in their arsenal – a winter hardtail for long, pedal-heavy days in the hills and a five-inch bouncer for big descents, fun in the woods or whatever you’re having yourself.
There are many different types of hardtail frames, some designed as all-rounders and others to cater for specific disciplines. Geometry will vary according to what type of riding the bike is intended for, while different frame materials suit rider preferences or the particular demands of a branch of the sport. Most budget and mid-range hardtail MTBs will feature a lightweight aluminium frame. Top-end bikes typically use lightweight carbon fibre, while many bike makers also offer steel or titanium frames that appeal to a wide range of rangers.
From superlight short-travel cross-country (XC) race rigs to rough, tough dirt and street machines, from beginner-friendly budget bikes to the latest generation of long-travel trail machines: there’s a hardtail frame to suit every riding style and every budget.
Some of the most common categories of hardtail frames are race, trail and dirt/street/4X.
Race: These frames are aimed at cross-country (XC) racers, long-distance marathon-style events; less technically challenging trail centre runs and just generally covering plenty of off-road miles. They typically feature relatively steep head and seat angles (a seat angle of around 73 degrees and a head angle of around 71 degrees being considered ‘classic’ XC geometry), placing the rider in the optimum position for seated pedalling, especially uphill. Top tubes will meanwhile be on the long side, allowing for the ‘stretched’ riding position that enables riders and racers get plenty of air into their lungs.
Race frames are typically made from aluminium allow (for low- to mid-level offerings) or carbon fibre (for high-end models). They are designed for 80-100mm travel forks and 26”, 27.5” or 29” wheels, with the latter being increasingly common.
Trail: More and more hardtail frames have departed from the ‘classic’ XC design above (steep angles, 80-100mm travel) in favour of slacker angles and longer-travel forks. These modern trail hardtails of 120-140mm front travel offer many riders the perfect balance between lightweight pedalling efficiency and rough-and-tumble high-speed fun.
Seat and head angles are a little slacker (head angles of 69 degrees or less being characteristic of the modern trail hardtail) so that riders can get their bodyweight well back on the bike on steep, technical downhill trails. Top tubes are generally shorter, giving a more upright riding position which is not optimum for all-day pedalling but gives much greater rider control on difficult terrain.
Frame materials are typically aluminium or steel, the lively and supple ride feel of the latter having made it increasingly popular among modern trail hardtail riders not overly concerned with the slight weight penalty involved, with 26” or 27.5” wheels.
Street, dirt and 4X: Hardtails frames built for the demanding disciplines of dirt jumping (DJ), street riding and four-cross racing (4X) are designed less with pedalling efficiency in mind than with the ability to take serious and sustained punishment, and live to tell the tale.
DJ and street bikes generally feature overbuilt aluminium or steel frames which are tougher and heavier than those found on their xc and trail counterparts, with smaller sizes providing increased agility in the air and ‘chuckability’.
The frames are married to 26” wheels and around 100mm of suspension travel courtesy of stiffly-sprung front forks.
As with hardtails, there is a huge range of MTB suspension frames on the market. Some ‘full-sussers’ are designed as trail-ready all-rounders; others are more specifically tailored to competitive disciplines such as cross-country (XC), Enduro and downhill (DH) racing; while still more are built to take the monster hits of freeride (FR) or bike park riding.
Advances in suspension technology mean the latest full-bounce frames are lighter, more efficient, more reliable and better value for money than ever before – but with infinite variations in travel length, intended use and suspension design, our short guide will help you negotiate the full-suss frame maze.
While the amount of suspension travel is not the be-all-and-end-all when it comes to determining how a frame will ride and what kind of riding it is suited for – with geometry equally as important, if not more so – it provides a useful way to group together full-suss frames into various categories. Here are some of the most widely used:
80-100mm travel: Frames with 100mm or less rear travel are typically fast and lightweight mile-munchers designed for climbing and long-distance efficiency over the ability to take on challenging technical terrain. Aimed at competitive xc racers and marathon riders whose priority is cross-country speed rather than downhill thrills, these frames feature steeper XC geometry for optimum pedaling efficiency and are designed for use with 27.5” or 29” wheels. Frame materials are typically lightweight aluminium or carbon fibre in the case of top-of-the-range models aimed at serious racers. Race and marathon frames will normally feature a lightweight air shock.
120-140mm travel: Typically a little bit beefier than shorter-travel race frames, these trail frames are built with fun in mind, rather than a competitive edge. They are often designed with slightly slacker frame angles for downhill confidence. While older design/budget trail bikes are often found with 26” or 29”wheels, the 27.5” standard has become typical on new models. Frame materials are stiff and lightweight aluminium or carbon fibre.
140-160mm travel: Frames with suspension travel of more than 140mm are built with the emphasis on downhill punishment, featuring slack frame angles and 26” or 27.5” wheels. These bikes are intended for riders who push the limits on very demanding terrain, but as they can still be pedaled uphill are popular with the latest generation of Enduro riders.
160mm and more: Full-suspension frames with more than 160mm of travel are built for the specific demands of downhill (DH) racing and freeride (FR), featuring super-slack angles, a low-slung bottom brake, long wheelbase, 26” wheels and aluminium or carbon construction.
Why rear suspension?
The full-suspension frame has some obvious advantages over the hardtail.
Because the extra suspension absorbs more of trail obstacles encountered when riding over typical off-road terrain, the bike can typically go faster, with the back end smoothly sucking up the hits rather than being kicked around.
The extra cushioning of rear suspension can also offer increased comfort on long-cross country rides, especially helping to minimise lower back and knee pain.
However suspension frames can be heavier than similarly-equipped hardtails, due to the shock, pivots and linkages that the frame must carry. This may be detrimental if much of your riding is done on smooth trails or even on tarmac, where the advantages of having rear bounce are outweighed by the smooth and energy-efficient power delivery of the hardtail.
While hardtails may usually be the lighter option, the advantages of an active rear end make it sometimes worth a weight penalty on more challenging trails. Rear suspension can offer more speed through the rougher downhill sections and more confidence when tackling ‘bigger’ terrain including the drops, jumps and rock gardens found on most trail centre black runs, but will also work hard to provide extra traction on technical climbs where many a hardtail would ‘spin out’, losing essential rear-wheel grip.
Today there are almost as many different suspension systems as there are manufacturers, with new and improved designs appearing to great fanfare every year as engineers chase the holy grail of the perfect suspension system.
The principles of suspension dynamics are complex – and too detailed to go into here, but nonetheless the different types of suspension design fall under two main categories: single pivot and four-bar.
• Single-pivot suspension: As the name suggests, this features a single pivot on the front triangle. The rear wheel is attached to one end of a swingarm, the other end of the swingarm pivots on the aforementioned pivot, and a shock unit between the swingarm and the frame absorbs and rebounds. Some suspension designs further develop the single pivot concept, using additional rockers or linkages to affect shock compression rate (these are sometimes known as faux-bar or complex single pivot designs).
• Four-bar suspension: With this design the rear end is made up of four bars with connecting linkages and pivots, the main ones being on the front triangle and chainstays. Different iterations of the four-bar design exist, characterised by different pivot positions.
The main problems associated with earlier generations of suspension design – an over-active suspension absorbing rider energy when power is applied during the pedal stroke (‘pedal bob’) and a suspension system that stiffens under braking (‘brake jack’) – have been largely overcome by a new generation of suspension innovations.
Different manufacturers have found new ways to isolate pedaling forces from the suspension and to ensure that the rear shock remains active under braking, while classic suspension designs have been given a new lease of life by advances in the development of platform-damped shocks which effectively ignore pedal feedback to counteract pedal bob.