Coil vs. Air Rear Shocks

Two ways to store the same energy

Every rear shock stores and releases energy through some kind of spring, and there are two fundamentally different ways to build that spring: a solid metal coil, or a sealed air chamber acting as the spring instead. Both do the same basic job — resisting compression and pushing the shock back to full extension — but they get there with different mechanics, and that difference shows up clearly on the trail.

Coil: linear, consistent, heavier

A coil shock's spring rate — how much force it takes to compress it a given distance — stays essentially constant through the stroke (a linear spring curve), and coil springs are largely unaffected by heat buildup on long descents the way an air spring's internal pressure can be. That consistency is why coil shocks are popular for aggressive enduro and downhill riding: predictable, plush small-bump sensitivity and performance that doesn't fade as the shock heats up on a long, rough descent. The trade-offs are weight (a solid metal spring is heavier than a sealed air chamber) and a fixed spring rate — changing how firm or soft the shock feels means physically swapping to a different spring weight, not just adjusting air pressure with a shock pump.

Air: adjustable, lighter, progressive

An air shock uses a sealed, pressurized air chamber as its spring, which makes it meaningfully lighter than an equivalent coil shock. Air springs are also naturally progressive — they get proportionally harder to compress the deeper into the stroke you go — which many riders like for resisting harsh bottom-outs, and that progression can often be tuned further with volume-reducing spacers. The trade-off is a spring curve that's inherently less linear than a coil's, along with more moving seals that need periodic service, and (on lower-end air shocks especially) some sensitivity to heat buildup on sustained descents.

The one thing that's a real compatibility question: coil approval

Neither spring type is a physical fit issue in the way, say, eye-to-eye length is — a coil and an air shock built to the same eye-to-eye, stroke, and mount type will both bolt onto the same frame. But that doesn't mean every frame is a good candidate for a coil shock. A frame's rear-suspension linkage is engineered around a specific leverage curve (how much the rear wheel's travel changes relative to how much the shock itself compresses), and some frame designs lean on a naturally progressive leverage curve to do work that a coil's flat, linear spring rate doesn't help with — running a coil on a leverage curve that was designed assuming an air spring's built-in progression can leave the suspension feeling harsh to bottom out or too soft in the early stroke, depending on the specific design. Where a frame maker has explicitly published that their frame isn't coil-compatible, that's a real, maker-stated fact worth respecting rather than a matter of taste.

How BuildMyMTB checks this

The spring type itself (coil vs. air) is recorded on every shock, but it isn't compared against every frame — only where a frame maker has explicitly published that the frame is not coil-shock compatible does the tool raise anything, and in that case it's a warning, not an outright block, since the shock will still physically bolt on; it's the leverage-curve behavior that suffers. Frames that haven't published a coil-compatibility statement stay silent on this dimension rather than guess at how a given leverage curve handles a linear spring rate — that's a call that needs real engineering data from the frame's designer, not an assumption from a general rule about progressive vs. linear curves.

Everything else about matching a shock to a frame — eye-to-eye length, stroke, and mount hardware style — works identically regardless of whether the shock is coil or air; those checks are covered in the rear shock sizing guide and apply the same way to both spring types.

Practical takeaways

• Coil shocks favor consistent, plush performance on long or repeated rough descents at a weight and tunability cost; air shocks favor lower weight and on-the-fly pressure tuning with more built-in bottom-out resistance.
• Changing a coil shock's firmness means swapping the physical spring for a different rate — budget for that if you're dialing in a coil setup.
• Before buying a coil shock, check whether your specific frame's maker has published anything about coil compatibility — some progressive-leverage designs are explicitly not recommended for a coil spring.
• Where no coil-compatibility statement exists for a frame, that's not a guarantee either way — it just means the tool has nothing published to check against yet.