Understanding Suspension Numbers: Fork Travel, Rear Travel & Shock Stroke

Three numbers, three different things

A full-suspension bike's spec sheet throws several travel-adjacent numbers at you at once: fork travel, rear (wheel) travel, and — if you're looking at the shock itself — its eye-to-eye length and stroke. It's an easy trap to assume these all describe the same kind of thing on the same scale, especially when a shock's stroke number and a bike's rear-travel number appear in different places for the same build. They don't share a scale, and mixing them up is one of the more common points of confusion when reading a spec sheet.

Fork travel: the straightforward one

Fork travel is the simplest of the three — it's how far the fork itself compresses, measured directly on the fork, and it's the same number whichever bike the fork is bolted to. See the Choosing Fork Travel for Your Frame guide for how this interacts with a frame's rated maximum and design intent.

Rear travel: the frame's number, not the shock's

A bike's rear (wheel) travel figure is a fact about the frame's rear-suspension linkage, not a fact you can read directly off the shock. The shock itself only moves through its own shaft stroke — a much smaller number — and the frame's linkage converts that stroke into rear-wheel movement through its leverage ratio. Two real examples from this catalog show how differently that plays out: a Trek Top Fuel Gen 4 frame runs a shock with just 50mm of stroke, but produces 120mm of rear-wheel travel — roughly a 2.4:1 leverage ratio. A Santa Cruz Bronson 5 frame runs a shock with 57.5mm of stroke and produces 150mm of rear-wheel travel — roughly a 2.6:1 ratio. Two different frames, two different leverage ratios, two different relationships between the same kind of shock spec and the resulting wheel travel. Neither number is more "correct" than the other; they're just two different linkage designs doing their job differently.

Why you can't just do the math yourself

It's tempting to think you could estimate a frame's leverage ratio once and use it to predict what a different-stroke shock would do in that same frame, but on most modern frames the leverage ratio isn't constant through the stroke — it's progressive, changing as the suspension compresses. That's exactly why, elsewhere on this site, a shorter-than-spec shock stroke is flagged as a warning that points you to the frame maker's own published list of supported strokes rather than a computed "you'll lose X mm of travel" number (see the Rear Shock Sizing guide) — a simple ratio would produce a precise-looking number that's often wrong.

Reading a spec sheet without getting them confused

• A bike's rear travel figure is the frame's job — it describes what the whole rear end does, and it's the number to compare between bikes.
• A shock's own eye-to-eye and stroke only matter if you're buying a replacement shock for a specific frame — they're a parts-fit spec, not a bike-comparison spec.
• A bike's fork travel is a completely separate, independent number from either of the above — it describes only the front end.

Practical takeaways

• If a shock's stroke number looks tiny next to a bike's advertised rear travel, that's expected — it's the frame's leverage ratio at work, not an error.
• Don't try to compare two bikes' suspension by their shocks' stroke numbers — compare their published rear-travel figures instead, since that's the number that accounts for each frame's own leverage design.
• Fork travel and rear travel are unrelated numbers on the same bike — a longer fork doesn't imply a longer rear travel, or vice versa.