Shock sizing: eye-to-eye and stroke
A rear shock is sized by eye-to-eye (distance between the centres of the two mounts) and stroke (shaft travel); for example 210x55 or 230x60 mm. It must match the frame EXACTLY: the wrong eye-to-eye changes the geometry and the leverage ratio, and a longer stroke can make the wheel hit the seat tube. It's given in metric (210x55) or imperial (8.5x2.5"). If your frame uses a special mount, also check metric vs trunnion; and if you're reviewing the whole suspension, start with what fork fits your bike.
It's not an approximate size: it's two numbers the frame fixes. Getting it wrong isn't "a bit different", it's geometry and clearance compromised.
The two figures
Eye-to-eye. It's the distance between the centres of the shock's two mounting eyes, with the suspension extended. It defines where it fits in the frame; if it's not right, it won't even mount properly and alters the geometry.
Stroke. It's the shaft travel: how far the shock compresses between extended and bottomed out. The frame is designed for a specific stroke; a longer one can drive the wheel into the seat tube as it compresses.
Why each number matters
The wrong eye-to-eye moves the pivot points and changes the suspension's leverage ratio, as well as the bike's geometry. The wrong stroke, especially if longer, can bring the wheel close to the seat tube until it hits it under compression. That's why both figures must match exactly what your frame requires.
Key facts
What it pairs with
This sizing is a sibling of how the shock mounts: check metric vs trunnion so you don't confuse the mounting type. And if you're reviewing the whole suspension, start with what fork fits your bike so front and rear stay in tune.
Send us your frame model and we'll confirm the eye-to-eye and stroke it requires. Message us on WhatsApp
Frequently asked questions
How is a shock measured?
By eye-to-eye (between mount centres) and stroke (shaft travel), e.g. 210x55 or 230x60 mm. Both must match the frame exactly.
What if the size doesn't match?
The wrong eye-to-eye changes the geometry and leverage ratio; a longer stroke can make the wheel hit the seat tube.
Metric or imperial?
It's the same measurement in another unit: metric in mm (210x55), imperial in inches (8.5x2.5"). Know which one your frame uses.
Related
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