When it comes to optimizing the performance of your electric mountain bike, the suspension system is one of the most critical components to consider. It not only absorbs impacts from the trail, making your ride smoother and more comfortable, but it also plays a crucial role in traction and control. For e-MTB riders, the choice often comes down to two primary types of suspension: air suspension and coil suspension. Each has its own set of advantages and disadvantages, and the right choice for you will depend on a variety of factors, including your riding style, the terrain you frequent, and your budget. In this article, we will delve into the details of both air and coil suspension systems to help you make an informed decision.
How Do They Work?
At a fundamental level, both air and coil suspension systems are designed to do the same thing: absorb bumps and keep your tires in contact with the ground. However, they achieve this in very different ways.
Air Suspension
As the name suggests, air suspension utilizes a pressurized air chamber to act as a spring. When you hit a bump, the suspension compresses, and the air inside the chamber is squeezed into a smaller volume. This creates a progressive spring rate, which means that the suspension becomes stiffer as it moves further into its travel. This "ramping up" effect provides excellent bottom-out resistance, preventing the suspension from fully compressing on large impacts [1].
Coil Suspension
Coil suspension, on the other hand, uses a more traditional approach with a steel spring to absorb impacts. The spring rate of a coil shock is linear, meaning that the amount of force required to compress the spring remains consistent throughout its travel. This results in a very supple and predictable feel, especially over small bumps and chatter [1].
Comparison Table: Air vs. Coil Suspension
To give you a quick overview of the key differences between these two suspension systems, here is a comparison table:
| Feature | Air Suspension | Coil Suspension |
|---|---|---|
| Weight | Lighter | Heavier |
| Adjustability | Highly adjustable | Less adjustable |
| Performance | Progressive, poppy, and lively | Linear, plush, and planted |
| Maintenance | More frequent maintenance | Less frequent maintenance |
| Cost | Generally lower initial cost | Can be more expensive initially |
Weight Differences
One of the most significant differences between air and coil suspension is weight. Air shocks are considerably lighter than their coil counterparts, often by as much as 500 grams or more [1]. This weight saving can be a significant factor for riders who are looking to build a lightweight e-MTB for climbing or racing. However, for many e-MTB riders, especially those who prioritize downhill performance, the extra weight of a coil shock is a worthwhile trade-off for the improved suspension performance.
Adjustability and Tuning
When it comes to adjustability, air suspension is the clear winner. The spring rate of an air shock can be easily and infinitely adjusted by simply adding or removing air with a shock pump. This allows riders to fine-tune the suspension to their specific weight and riding style. Additionally, many air shocks allow for further tuning with the use of volume spacers. These small plastic tokens can be added to the air chamber to reduce its volume, which in turn increases the progressivity of the spring rate and provides more bottom-out resistance [2].
Coil suspension, on the other hand, is less adjustable. The spring rate is determined by the physical coil spring itself, so adjusting it requires swapping out the spring for a different one. While this is a relatively simple process, it does mean that you will need to purchase different springs to find the perfect one for your weight and riding style. Preload can also be adjusted on a coil shock to fine-tune the sag, but this does not change the spring rate [1].
Performance on Different Terrains
The different characteristics of air and coil suspension lead to distinct performance differences on the trail.
Air Suspension
Air suspension is known for its "poppy" and "lively" feel. The progressive spring rate provides a supportive platform that is great for pumping through rollers and berms, and for getting airborne off of jumps. This makes air suspension a great choice for flowy trails and for riders who have a more playful and active riding style [2].
Coil Suspension
Coil suspension offers a "plush" and "planted" feel that excels on rough and technical terrain. The linear spring rate allows the suspension to move freely and absorb small bumps and chatter, which provides excellent traction and control. This makes coil suspension the preferred choice for many downhill and enduro racers, as well as for riders who frequent rough and rocky trails [2].
Maintenance Requirements
In terms of maintenance, coil suspension generally has the upper hand. Coil shocks have fewer seals than air shocks, which means there are fewer parts that can wear out or fail. As a result, they typically require less frequent maintenance, with service intervals often being longer than those for air shocks. The main maintenance task for a coil shock is servicing the damper [1].
Air suspension, on the other hand, requires more frequent maintenance to keep it running smoothly. The seals in the air chamber need to be cleaned and lubricated regularly, and the damper also needs to be serviced. Heat can also be an issue with air shocks on long descents, as the friction from the seals can cause the oil in the damper to heat up and lose its effectiveness [2].
Cost Considerations
The cost of air and coil suspension can vary widely depending on the brand and model. In general, air shocks tend to have a lower initial cost than coil shocks. However, the long-term cost of a coil shock can be higher if you need to purchase multiple springs to find the right one for your weight. It is also worth noting that high-end air and coil shocks can both be very expensive.
Which is Better for You?
So, after all of that, which type of suspension is better for you? The answer, as you may have guessed, is that it depends.
Rider Weight
For heavier riders, a coil shock can be a better option. The linear spring rate provides consistent support throughout the travel, which can help to prevent the suspension from feeling harsh or overwhelmed. Air shocks can be more difficult to set up for heavier riders, as they may require very high air pressures to achieve the proper sag.
Riding Style
If you have a playful and active riding style and enjoy popping off of jumps and pumping through rollers, then an air shock is likely a good choice for you. If you prefer to keep your wheels on the ground and plow through rough terrain, then a coil shock will provide the planted and controlled feel that you are looking for.
FAQs
Can I put a coil shock on any e-MTB?
Not all e-MTB frames are designed to be used with a coil shock. Some frames have a suspension linkage that is not progressive enough to work well with a linear coil spring, which can lead to harsh bottom-outs. It is always best to check with the manufacturer of your bike to see if it is compatible with a coil shock.
How often should I service my suspension?
The recommended service intervals for your suspension will vary depending on the brand and model, as well as how much you ride. As a general rule, it is a good idea to have your suspension serviced at least once a year, or more frequently if you ride a lot.
Is one type of suspension faster than the other?
While some riders may feel faster on one type of suspension over the other, there is no definitive answer as to which is faster. The best suspension for you is the one that gives you the most confidence and control on the trail.
What is "stiction" and why is it important?
"Stiction" is a term used to describe the initial friction that needs to be overcome to get the suspension to start moving. Coil shocks generally have less stiction than air shocks, which is one of the reasons why they feel more supple and sensitive over small bumps [2].
References
[1] Coil vs Air Shocks: Selecting Mountain Bike Suspension | CANYON US [2] The Great Debate: Air Shock vs Coil Shock | The Loam Wolf
