Metric Shocks

Everything You wanted to know about Metric Shocks

Starting in 2017, several of the industry’s leading suspension manufacturers (RockShox, Cane Creek, SR Suntour, X-Fusion, DVO, and Manitou) announced via a joint press release that their new models would start using metric sizing to “…allow both suspension and frame manufacturers to significantly simply rear shock sizing and fitment, while also providing performance benefits to both suspension and frame designs.”

The simpler sizing makes perfect sense due to everything metric being divisible by 10…but what other advantages do metric shocks offer? Are there any disadvantages? What else should you know?

What is a Metric Shock?

A metric shock is a new mountain bike rear shock innovation agreed upon by many suspension manufaturers that includes standardized sizing to simplify shock fitment that is measured in the metric vs imperial system with millimeters (mm) versus inches (in).

Why the Switch is Being Made

As we mentioned above, the best part about the metric system is everything is divisible by 10…EVERYTHING. That makes on the fly calculations quite a bit simpler, and it also greatly reduced the rather insane amount of options when it comes to shock sizes. Between standard and trunnion mounts, there are well over 80 different shock options and sizes. How did it come to this?

Primarily, because shock manufacturers were trying to create products based on rider demands. People would test ride new trails, have specific demands in mind for shocks based on a wide variety of frame sizes, and companies would roll out a new shock. This might seem like great customers service but being reactive instead of proactive isn’t without its faults, and the resulting confusion for rear shock sizing and fitment was the biggest one.

Metric Shock Sizing Overview

If you have ever upgraded the rear shock on your mountain bike and been overwhelmed at trying to determine what size you need, don’t worry – you’re not alone. As previously mentioned, going metric will simplify things a bit, but there are still some important things you need to be aware of to find the right shock.

The two most important terms when determining your shock size is the eye-to-eye measurement and the stroke. Eye-to-eye refers to the total length of your shock when measured from the center of each mounting bolt hole, also known as the eyelet (hence, “eye” to eye). Simple, right? We think so.

The stroke refers to the total distance the shock can travel in its fully compressed to when it’s fully extended. Also sounds simple, right? Well, yes and no. If your shock features a simple coil, yes – you can simply measure the exposed part of the shaft (the smaller portion), but you’ll likely need to remove the coil to get the best measurement. For air or gas-based compression shocks, it’s just a tad bit trickier. The air canister sits over the piston, but many models employ internal spacers to have full control over the stroke, so removing the canister and measuring the internal piston is your best bet.

So…now you have two measurements, an eye-to-eye distance and the length of the shock’s stroke. That’s how shocks are sized, and while traditionally it has been in inches (e.g. 8.5” x 2.5”), you’re going to start seeing more and more in millimeters (e.g. 210mm x 55mm).

(Speaking of – 1 inch is equal to 25.4 millimeters and you should commit that to memory. You never know when you might need to bust out some quick conversion map on the trail, and for the foreseeable future you’re going to see shocks with both units of measurement out there.)

Benefits of Going Metric

As metric shocks are a relatively recent introduction to the world of mountain biking, reports of upticks in performance or rideability are still only trickling in. We can examine some of the benefits right up font though.

One of the most anticipated changes among riders that the new metrics shocks allow is the increased bushing overlap. In the shock, bushings lie between the external housing of the shaft and shaft itself. The main job of these tube-like objects is to keep the shaft centered as it glides through the bushings, and bushing overlap is simply the distance between the two bushings. The smaller that distance, the greater the odds you’ll experience binding under lateral frame flexion. By increasing the bushing overlap and thus the distance between them, you’ll reduce binding which reduces wear and tear on the shock components and lessens the likelihood of oil leaks.

Another is increased air volumes in air springs. The metric sizing on the Deluxe and Super Deluxe from RockShox gives the internal components of the suspension more room to breathe (pun indented). Larger shocks can fit more air (duh) which creates a smoother flow of air in the chamber, allows for better gas compression, and softens the ride.  

The last benefit we’ll mention (but believe us, there are lot more) is simplicity, We know, we’ve mentioned it already in this piece several times but it really does bear repeating, especially when considering the benefits of going metric. Finding replacement parts or upgrading the internals on your shock will be dramatically less confusing with fewer sizing options to wade through.

Possible Disadvantages of Metric

Nothing’s perfect in this world, unfortunately, so there are some possible drawbacks.

First and foremost will be cost. The well-reviewed RockShox Super Deluxe we mentioned earlier will set you back a bit, and that isn’t just because it’s a new product and slightly larger than previous shocks – it’s also because for any new manufactured product, companies have to invest in new molds, new production methods, and a lot of R&D before you ever can get your hands on it. This investment must be recouped somehow.

Another is size – bigger can be better for a lot of reasons, but when it comes to mountain biking, increased weight is rarely desirable. In an activity where every gram (we could have said ounce but we figured staying metric was more apropos) matters, adding even a small amount of weight can impact how easy it is for you to pack in and out of the trail and can have small yet noticeable effects on your ride.

The last one worth mentioning is adoption. America’s rich tradition of metric opposition is not to be trifled with, which could have a significant damping effect on how popular these new metric shocks become. While all the industry heavy hitters have pledged support to making the move to metric, they also said in the initial press release that they would commit to “…supporting imperial shock sizes as long as market demand is relevant.” This is critical to note, especially if you live in a rural or small market area – investing in an expensive new frame designed for metric shocks, it might be challenging to quickly find replacement parts locally, especially if the metric thing never catches on.