Mountain bike frames are the heart of the machine, and their geometry significantly affects your riding experience. Companies design them according to the performance probabilities of the type of bike and its expected use. The differences in frame geometry make every mountain bike’s ride attributes the only one of its kind; it depends on what the maker is going for.
Descending/ascending abilities, pedaling efficiency, and cornering stability are just a few affected areas. As a result of the many possible variations, it’s essential to know what cycling characteristics you are looking for when searching for the right bike. Here are some examples:
- A shorter wheelbase will allow tighter turns, while a longer wheelbase allows more high-speed stability.
- A “steep” head tube angle moves your weight forward for superior climbing performance and makes ascending trickier.
- A lower bottom strut will make the bike feel more “sunk in” and balanced on the turns and enhance the pedals’ chance of hitting obstacles.
Mountain Bike Frames Sizes
Having a frame size that best fits your body type is extremely important. If too small, you will feel crunched up and low, and if it’s too large, you will feel stretched out and high. Mountain bike frames sizes directly affect how comfortable you feel and how the bike handles.
An ill-fitted bike is also a safety hazard and can contribute to accidents. The length of the seat tube is a fundamental measurement for determining the size of the frame. However, different companies vary in how to take this measurement, which allows for misleading numerical sizing of the bike. It does not account for the length of the top tube, which is an essential dimension because it determines your arm’s reach.
Since most frames are created with proportional seat and top tubes, companies usually use the more common designations of small, medium, large, extra-large, and XXL. The following table is a chart of adult sizes and is just an estimate:
| Bike Size | Rider Height | Seat Tube Length |
| Small | 5’2″ – 5’6″ | 15” – 16” |
| Medium | 5’6” – 5’’10” | 17” – 18” |
| Large | 5’10” – 6’-1” | 19” – 20” |
| Extra-Large | 6’1” – 6’4” | 21” – 22” |
| XXL | 6’5” – 6’7” | 23” – 24” |
Because of the many variations in the torso and leg lengths of different people and the differences in frame geometry between the other models and companies, those at a borderline height will need a little testing with each bicycle being considered.
One of the best ways of determining the correct size is by physically checking how you fit. The saddle’s height and the saddle setback will need to be adjusted. If one or more adjustments have reached the end of their limit, you have the wrong size frame. For example:
- You probably would require a much larger frame if you have the saddle adjusted equally to the handlebars in height, but the seat post is stretched past its limit line.
- If you adjust the saddle setback forward, but your reach to the handlebar still doesn’t provide a good bend at the elbows, you probably need a more petite frame.
Women Specific Bike Frames
Though both women and men can utilize mountain bikes, most women will require a different frame geometry than men to get the best fit. Average-sized women mostly have a more diminutive stature than men with proportionally longer legs, narrower shoulders, and a shorter torso.
Many mountain bike companies have models designed especially for women to accommodate the differences. Certain factors and the geometry of these bicycles are a better fit for the physique of a female. They are taller (in proportion to the rest of the frame) for much longer legs, have slightly shorter top tubes for shorter torsos, and narrower handlebars for narrow shoulders.
Considering the average height of a female, companies also design these bikes with a lower standover and shorter crank lengths and height.
To decide if this is the particular bike you will need, make sure to test the fit of both women-specific and regular to see which is best for your needs. Depending on the dimensions of your body, you may or may not require a women-specific mountain bike. The chart below is just an estimate of their sizes:
| Bike Size | Rider Height | Seat Tube Length |
| Extra Small | 4’10” – 5’2” | 13” – 14” |
| Small | 5’2” – 5’6” | 15” – 16” |
| Medium | 5’6” – 5’10” | 17” – 18” |
| Large | 5’10” – 6’1” | 19” – 20” |
Frame Material
When it comes to frame material, it is an essential factor because it affects the flexibility, durability, price, and weight of the mountain bike. While carbon and aluminum fiber are the most popular by far, titanium and steel are also described for comparison. Each has its own set of unique properties and prices that should be considered when deciding.
Aluminum
Mountain bike frames made of aluminum alloy are trendy because they are lightweight and not that pricey. Most cyclists consider them excellent for first-time and mid-level bikes. Though aluminum is not as strong as steel, extra material is required to make the difference, so the tubing is much broader.
The tubes that are much larger in diameter can cause them to ride stiffer than mountain bikes with steel alloy frames, which is a characteristic that allows them livelier handling in tight riding situations. Many riders enjoy this quality, but the stiffness can also transfer trail chatter and vibration throughout the bicycle, which can cause a rougher ride.
Another great trait of aluminum is its ability to resist corrosion, which is perfect for more damp climates. A well-made aluminum frame can provide years of reliable use. Strong and lightweight, it is the best value for your dollar.
Carbon Fiber
Carbon fiber, a non-metallic material, has become the typical material for higher-end bikes. It’s more expensive than aluminum and steel but rugged, lightweight, and does not corrode. In fact, it is one of the most robust materials engineered in the world.
The advancement in the manufacturing technology of carbon fiber has come a long way over the years. Entire fuselages of some of the latest military and commercial aircraft are currently being designed using this material.
This ultra-lightweight material is an exceptional choice for mountain bike frames and has become extremely popular with bicyclists. It provides an advantage in weight and strength over frames that are metal. Its flexibility and stiffness create an excellent balance between steel and aluminum. Riders that want the lightest mountain bike frames will find that this material is well worth the money.
For riders that compete and push the limit of the sport, a carbon fiber bike frame can be the difference between losing and winning. Thanks to increased sales volume, prices are decreasing; however, they are still on the pricey side and will most likely remain so. This is a result of the cost of the raw carbon fiber material, the price of the unique molds needed for each frame, and the amount of hand labor that goes into each mountain bike frame.
The more expensive and higher-end mountain bike frames are usually made with a carbon fiber material designed with labor-intensive layup processes. The frames are lighter, stronger, and allow for less flex in specific areas.
In comparison, cheaper carbon fiber mountain bike frames can be rough riding and run the risk of cracking during high impacts. Always purchase from a reputable company to receive a reasonable quality frame.
Steel
Steel alloy mountain bike frames are the cheapest frame materials and the heaviest. Steel is very strong and provides durability, making it less likely to dent or crack during accidents. Unfortunately, the extra weight will increase the effort required to climb hills and make the bike less agile.
Companies usually design the tubes with a smaller diameter to help offset the heavier weight. However, this tends to make them more flexible, which will result in a springier ride. The upside of this flexing is reduced fatigue resulting from the vibrations of trails.
Another thing to consider with mountain bike frames made of steel is their tendency to rust over time in damp climates. If you are going to expose your bike to water, a steel frame may not be the best option. If you choose a steel frame, make sure that it is the more popular Chromoly blend of durable and stronger steel.
Titanium
Mountain bike frames made of titanium alloy are a less common material used in bicycle frames, even though it is the 4th most common metallic element globally. Because of its high price, usage is low because of the enormous amount of energy needed to extract it from the earth.
The low usage can be attributed to the fabrication process, which tends to be troublesome because of the many difficulties involved with manipulating the welding joints and tubing. However, titanium offers some positive advantages over other materials, and it possesses the highest weight to strength ratio.
This allows companies to make the tubing thinner in certain places, which increases the flexibility for absorbing trail vibrations while shaping the tubing wider in other areas where greater stiffness is required. The fatigue life of titanium, which measures the number of times a material can be stressed without being damaged, is almost infinite. Its ability to resist corrosion means it will not rust, another highly desirable quality.
Because of these factors, titanium mountain bike frames will most likely outlast all others. It will always remain a high-priced frame material; however, if you cannot afford the high-priced tag, it will provide excellent flexibility, durability, and strength in a lightweight frame that can last a lifetime.
Rear Suspension Systems
Rear suspension systems play an intricate role in the performance and handling of the bike. This fantastic system consists of the rear shock absorber, and the frame’s pivoting rear triangle activates. There are many variations of this, each with its unique features designed to match with forks and frames so that all parts work in unison to give the bicycle its riding characteristics.
Mountain bike manufacturers have made considerable improvements since about 2003 to rear suspension by lowering pedal bob, the tendency of the rear shock to compress with each pedal stroke, resulting in a loss of pedaling efficiency. They have overcome this inherent efficiency problem with an anti-squat force working closely with the shock absorber companies.
Through the years, improvements in rear shock technology and rear linkage arrangements, most can now handle it somewhat well. For instance, the pedaling platforms of some XC models are so amazing that they closely rival the performance of a hardtail mountain bike while maintaining excellent shock absorption.
When it comes to the price of a mountain bike, the degree of complexity of the suspension system can have an impact. Different mountain bike companies utilize one of the several different types of suspension designs, with new variations not far behind. The many other jargons used in the cycling industry for these systems can complicate understanding the designs.
Though it is not crucial to be overly familiar with all the different variations, you should at least familiarize yourself with two basic designs that the variations are based on, such as the four-bar linkage and the single-pivot. The best system depends on what feels right to you; there is no best overall choice. The easiest way to find the best one you will love is to test ride bikes at your local shops that sell mountain bikes.
Single Pivot
This suspension design is the simplest but the least popular. It has a swing arm that pivots at the frame just ahead of the bottom bracket. The main advantage of this system is its ease of maintenance, lower price, and lightweight. However, the disadvantage of this design is that it creates a certain degree of brake interference, which is a compression of the shock during braking. Some companies that have used this system on some of their bikes are Diamondback, Orange Santa Cruz, Trek, Cannondale, and Devinci.
Four Bar Linkage
This design consists of four pivot points needed to complete the suspension. These pivots join the linkages at specific locations that depend on the configuration. Many patented designs have derived from this basic concept, each with a different appearance and performance. The shock may be connected to the tube on the bottom and others connected to the tube on the top, but they are all part of the same four-bar family. These include the Horst Link (Specialized, Scott, Norco, Cube); the Active Braking Pivot (Trek, Kona); The virtual pivot Point (Santa Cruz, Intense); as well as the DW Link (Ibis, Turner, Pivot, Independent Fabrications, Iron Horse).
