Every rear shock is defined by two numbers: eye-to-eye length and stroke, both in millimetres. Get either one wrong and the shock won't fit your frame, full stop. This is the reference chart and measuring method we use in the shop when a customer isn't sure what size they're running.
How Shock Sizing Actually Works
The first number is eye-to-eye, the distance between the centres of the two mounting bolts at full extension. The second number is stroke, how far the shaft travels when the shock fully compresses. A shock labelled 210x55 has a 210mm eye-to-eye length and 55mm of stroke.
Your frame's linkage is designed around one specific eye-to-eye and stroke combination. A longer eye-to-eye won't fit in the mount. A different stroke changes your travel and can throw off the leverage curve entirely. This isn't a part where "close enough" works.
Common MTB Rear Shock Sizes
This covers the sizes we see most often come through the shop. Always confirm against your frame's spec before ordering; this list isn't exhaustive.
| Eye-to-Eye | Stroke | Common On |
| 165mm | 45mm | Shorter-travel trail bikes |
| 185mm | 55mm | Trail bikes, some enduro frames |
| 190mm | 45mm | Trail and downcountry bikes |
| 200mm | 50mm–57mm | Trail and enduro bikes |
| 205mm | 60mm–65mm | Enduro bikes, often trunnion mount |
| 210mm | 50mm–55mm | Enduro and long-travel trail bikes |
| 225mm | 75mm | Long-travel enduro and freeride bikes |
| 230mm | 60mm–65mm | Enduro and DH bikes |
Older bikes, particularly pre-2018 models, may use imperial sizing instead (measured in inches, like 8.5x2.5). If your bike predates metric shock sizing, measure in inches rather than assuming a metric conversion, and bring it in if you're not sure which standard applies.
Trunnion vs Standard Mount: Why It Matters
Beyond eye-to-eye and stroke, shocks mount to your frame one of two ways, and they aren't interchangeable.
Standard mount uses a bushing at each end of the shock body, with the eye-to-eye measured between the outer edges of those bushings.
Trunnion mount attaches directly to the frame via a stub on the shock body itself, rather than a bushing. Trunnion shocks are shorter for the same stroke length, which is why you'll often see trunnion-specific sizes like 205x65 that don't exist in standard mounts.
Check your frame's spec sheet or the shock currently installed. Buying the wrong mount type means the shock physically won't sit in the frame, even if the eye-to-eye number matches.
How to Measure Your Current Shock
If you don't have your frame's spec sheet handy, you can measure the shock directly:
- Measure eye-to-eye first, centre of bolt to centre of bolt, with the shock at full extension (uncompressed).
- Attach a shock pump and fully release the air pressure (skip this step on a coil shock).
- Compress the shock by hand to fully bottom it out and measure eye-to-eye again.
- Subtract the compressed measurement from the extended measurement. That difference is your stroke length.
If you're not comfortable releasing air pressure yourself, bring the bike in and we'll measure it for you in a few minutes.
Getting the Size Wrong: What Actually Happens
A shock that's too long in eye-to-eye won't fit between the mounts at all. A shock with the wrong stroke will either bottom out prematurely or never reach full travel, and it can put unwanted stress on your frame's linkage since the whole system was tuned around a specific stroke length. Neither situation is a simple fix after the fact. Confirm sizing before you buy, not after.
Once You've Confirmed Your Size
Sizing only gets you to the mounting point. Choosing between air and coil, dialling in spring rate, and setting up damper adjustment are separate decisions, all covered in our rear shock buying guide.
FAQ
Can I fit a longer stroke shock than my frame came with?
Almost never. Your frame's linkage is designed around a specific stroke length, and increasing it can cause the shock to bind, over-extend the linkage, or bottom out incorrectly. Match your frame's spec.
Are trunnion and standard shocks the same price?
Generally yes, pricing is driven by the damper and brand rather than mount type. Availability can vary more than price.
What if my bike uses an imperial-sized shock?
Pre-2018 (roughly) frames often use imperial sizing (inches, like 8.5x2.5). These are less common to find in stock and may need to be special ordered. Bring your bike in and we'll confirm what you need.
Shop MTB Rear Shocks at Dunbar Cycles & Corsa Cycles
We stock a full range of MTB rear shocks, shock springs, and shock pumps from Fox, RockShox, Ohlins, and more. Not sure what size you're running? Bring your bike into either Dunbar Cycles in Vancouver or Corsa Cycles in Squamish, and we'll measure it for you on the spot.
