In the world of mountain biking, the choice between a coil shock and an air shock can greatly impact your ride. Both serve the purpose of absorbing trail impacts, storing the energy in the damper, and prepping for the next hit. However, the true distinction lies in their unique traits, benefits, and limitations, making them suitable for different riding styles or even simply rider size.
A coil shock operates on a linear spring rate, indicating a proportional increase in compression force as the spring is compressed. In contrast, an air shock exhibits a progressive pattern with an exponentially increasing force required to compress the air spring throughout its stroke. This difference makes an air shock more adaptable for varied terrains, while a coil shock could exhaust its travel swiftly if used in the same context. Certain mountain bikes do offer the flexibility to switch between these shocks to cater to varying terrains and riding styles.
A progressive suspension component or bike design will better resist bottom out by becoming more firm towards the bottom of the stroke. A linear rate will create an equal amount of force throughout the travel. Every bike has a different progression which is tied to its suspension design. If a bike manufacturer says their bike is “Coil Compatible” that means generally that the bike is Progressive enough to offset the linear nature of a coil shock.
There are however ways to get coil shocks that are more progressive in nature. Those are called Progressive coil springs and have a “Range” of progression. For example, it might take 300 lbs of force to move through the first inch of the bike's rear travel, but 350 for the second inch, 400 for the third and so on. These CAN makeup for a bike frame's lack of suspension progression if you really want to run a coil.
Suitable for trail riding due to its diverse and adjustable features, air shocks are a favorite for most riders. The primary advantage of an air shock is its high tunability. For instance, you can modify the shock's progression by adding or subtracting volume spacers. It's also a great solution for riders looking to reduce weight as the sag can be conveniently adjusted to compensate for weight fluctuations. Furthermore, its lightweight design is perfect for climbing, making it popular among cross-country riders. Air shocks offer bikes a lively feel, although they might not be as fast as coil shocks.
Coil shocks are a good fit for riders who frequent bike parks or downhill rides due to their excellent heat management capabilities during extended descents. The absence of seals makes them more responsive on small bumps, providing a more grounded ride. However, for riders who enjoy jumping or popping over features, a coil shock could feel restrictive. If you crave a smoother ride on rocky terrains covered in roots, a coil shock is a standout choice with its superior shock absorption. Plus, it requires minimum maintenance, making it a hassle-free option.
Here is where I have a strong preference, especially for kids who were seeking to RACE. And when it comes to riders who are lightweight this factor is perhaps the one which most greatly affects the performance of the bike.
Lightweight riders have all sorts of challenges when it comes to optimizing mountain bike components that work for them, but the biggest silent killer is Stiction. Stiction is what happens when there is friction created between the seals and the stanchions of your fork or shock. This friction is firmest at the very top of the shock’s stroke … the first movement of the fork or shock requires that it overdoses that stiction which requires it to “Break Away”. When you weigh 150lbs … the break away force required is small relative to the energy the rider can output … but when you kid weighs 90 lbs .. that Break Away force can really impact the performance of the shock and fork.
That is why in my opinion a coil is the ONLY choice for riders who are under that 100 lbs mark, especially if they are race focused. A coil shock does not have any stiction which means an amazing, smooth and high performance ride quality.
As outlined, both shocks come with their unique set of pros and cons. Your choice should primarily depend on your preferred terrain and riding style.
Carefully considering these factors will help you achieve the ideal suspension setup for your bike.
If you are considering a coil for your Grom, the hardest part is finding a brand which also supports a coil spring weight light enough for them. The most flexible brand Ive found so far is Fox .. They make springs down to 250 lbs which is about right for a normal trail bike around 85lbs rider.
Use this calculator to verify the coil spring weight you need for your kids bike. Spring Calculator - TF Tuned
**A dad’ Bod Take: Simple, I prefer riding tech vs hucking my body aimlessly through the air, so I much prefer a coil shock. :-)**