Fork Rake

Definition

Fork offset is the perpendicular distance from the steering axis to the center of the front hub. It is built into the fork and is one of the two variables (with head tube angle) that determine trail.

Analysis

Fork offset displaces the front axle forward of the steering axis. Combined with head tube angle and tire radius, it sets trail, which determines steering feel.

Context

Fork offset is reported in millimeters from the steering axis to the front hub center, measured perpendicular to the steering axis. Manufacturers spec offset on the fork; some forks offer multiple offset options.

Function

Increasing offset reduces trail, making steering quicker and lighter at low speeds. Decreasing offset increases trail, making steering heavier and more stable at speed. Offset works in concert with head tube angle to fine-tune handling.

Variation

Fork offset varies by discipline. Road forks tend toward 43 to 50 mm offset. Mountain bike forks have shifted toward shorter offsets to compensate for slacker head angles, since longer offset would otherwise create excessive trail.

Common Ranges/Values

Road bike forks typically run 43 to 50 mm offset. 27.5-inch mountain bike forks run 37 to 46 mm. 29-inch mountain bike forks run 42 to 51 mm, with reduced-offset variants at 37 to 44 mm. Touring forks may run 50 to 55 mm.

Common Practices & Evolution

The mountain bike industry adopted 'short offset' or 'reduced offset' forks around 2017 to 2019 to balance the transition to slacker head angles, especially on 29-inch wheels. Road has remained largely consistent over decades.

Specifics

Offset must be considered together with tire radius and head angle to evaluate trail. Two forks with identical offset can produce very different handling on different frames or wheel sizes.

Impact

Fork offset is the fine-tuning knob for steering feel. It is one of the few geometry variables that can be changed by swapping a fork without altering the frame.

Pros & Cons

More offset gives lighter, quicker steering and better low-speed maneuverability but reduces high-speed stability. Less offset gives heavier, more stable steering at speed and improved straight-line composure but can feel sluggish in tight turns and at trackstands.

Relations

Fork offset combines with head tube angle and tire radius to set trail. It also affects front center and wheelbase.