Bicycle Trail
Calculator.
Enter your head tube angle, fork offset (rake) and wheel and tyre size to get fork trail in mm and inches, plus mechanical trail, wheel flop and a plain-English read on how it will steer.
Results update as you type. Trail is a handling preference, not a target to hit exactly, and it works alongside your frame, load and tyre choice. Use it to compare setups, not to declare one right.
How the calculator works
Trail comes from three numbers: your head tube angle, your fork offset and your wheel radius. The formula is trail = wheel radius ÷ tan(head angle) − fork offset ÷ sin(head angle).
We also show mechanical trail, the same lever measured square to the steering axis, and wheel flop, which is how much the front end drops as you turn the bars and makes slow steering feel heavy. Both fall out of your trail and head angle. Read them together: two bikes with the same trail can still steer differently if their head angles and offsets get there by different routes.
Bicycle trail FAQ
Trail is the horizontal distance between where the steering axis meets the ground and where the tyre actually touches down, a little further back. That gap is what makes the front wheel want to straighten out and self-centre, like the castor on a shopping trolley. More trail feels stable and planted, less trail feels quick and darty.
For drop-bar bikes, roughly 55 to 63 mm is the neutral, all-round road range. Racier, quicker-steering bikes sit nearer 50 to 57 mm, while endurance, gravel and touring bikes run 60 to 75 mm or more for calm, stable handling. Mountain bikes with slack head angles naturally produce much higher trail figures. There is no single correct number: it is a handling preference, and it works alongside your frame, load and tyres.
Trail = wheel radius ÷ tan(head angle) − fork offset ÷ sin(head angle), with the head angle measured from the ground. So a bigger wheel or a slacker head angle increases trail, while more fork offset (rake) reduces it. That is exactly what this calculator does once you enter your three numbers.
More fork offset reduces trail. Offset moves the front axle forward of the steering axis, which shortens the trail distance. This is why endurance and gravel forks often add rake: it quickens and calms the steering back to a sensible figure without having to steepen the head angle. Less offset, or none, increases trail and adds stability.
Mechanical trail is the trail measured square to the steering axis rather than along the ground, so it is a truer measure of the self-centring lever, and it is always a touch smaller than ground trail. Wheel flop describes how much the front of the bike drops as you turn the bars, which makes low-speed steering feel heavy or floppy. Both are derived from your trail and head angle, and the calculator shows them alongside the main figure.
Yes, a little. A larger overall tyre diameter raises the wheel radius, which increases trail and makes the same frame feel slightly more stable and slower to turn. Going from a 25 mm to a 32 mm road tyre, or fitting a taller gravel tyre, nudges trail up by a couple of millimetres. It is a small effect next to head angle and offset, but it is real, so set the tyre you actually ride.