Most of us pay little thought to our fork offset. Buried deep in the geometry table, it’s easily overlooked by riders and even manufacturers. Yet, as we've been been finding out, it can have a dramatic and surprising effect on a bike’s handling.
Given its relative obscurity, you might be wondering what fork offset is. Simply put, fork offset, or fork rake, is the distance between the front axle and the steering axis – the imaginary line running straight through the midpoint of the steerer tube. Fork offset is linked to another important measurement: trail.
What is ‘trail’, you ask? Trail is the horizontal distance between the steering axis and the contact patch of the front tyre. Higher trail means greater stability and lazier, slower steering. Shorter offset or a slacker head angle results in more trail (slower steering); longer offset or a steeper head angle reduces trail, quickening the steering response. Finally, into the mix comes wheel size. Bigger wheels imply more trail, as the axle is higher and so the gap between the steering axis and contact patch increases proportionally. However, 29ers use steeper head angles and increased offset to compensate for this.
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Fox uses 40mm offset for 26in forks, 44mm for 27.5in and 51mm for 29in. RockShox uses similar offsets, but offers the 29in Pike in 46mm offset, as well as 51mm. In the case of my Specialized Enduro 29, the 67.5-degree head angle and 51mm offset results in a trail figure of 105mm. For comparison, let’s look at the 650b version of the Enduro – a contrast often made to establish the differences between wheel sizes.
The three fork crowns used in our experiment – giving 51mm, 44mm an 37mm offset respectively
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