What do the angles do?

Stack and reach decide how you sit. The angles decide how the bike rides. The exception is the seat angle: it moves the saddle forward or back.

The starting point is a typical race bike in size 58. Calculated for a person 178 cm tall with an 84 cm inseam. With your bike and your measurements: enter them in the calculator. Stack, reach, saddle height and the seatpost setback stay fixed.

Saddle to grip 668 mm · Trail 59 mm · Wheelbase 1011 mm

as it started changed Steering axis and trail

Seat angle 73.2°

Steeper puts the saddle further forward, closer to the bar. Of the five sliders the only one that noticeably changes your position.

Head angle 73.0°

How steep the fork stands. Slacker brings more trail and a longer wheelbase: the bike runs calmer in a straight line and turns in more slowly.

Fork offset 45 mm

How far the fork puts the axle ahead of the steering axis. More offset takes trail away: the bike turns in more eagerly.

Bottom bracket drop 70 mm

How far the bottom bracket sits below the axles. More drop brings it closer to the ground: the bike feels more planted, and in a corner the pedal touches down sooner.

Chainstay 409 mm

Bottom bracket to rear axle. Longer makes the wheelbase longer and the bike calmer, shorter makes it nimbler and leaves less room for wide tyres.

For you

You sit as long as before: saddle to hoods stays the same.

Saddle to grip: 668 mm Horizontally from the saddle nose to the hoods: that is how long you sit.
Effective reach: 406 mm The reach, converted to a 73.5° seat angle. That is how you compare bikes with different seat angles.
Back angle: 42.6° Against the horizontal. It follows from saddle and hoods.

For riding

Trail: 59 mm How far behind the steering axis the tyre touches the ground. More trail: calmer in a straight line, slower to turn in.
Wheelbase: 1011 mm Axle to axle. Longer runs calmer, shorter is nimbler.
Bottom bracket to front axle: 612 mm How much bike lies ahead of you. More leaves your foot more room and takes a little weight off the front wheel.
Bottom bracket height: 276 mm Above the ground, with a 346 mm tyre radius. Lower feels more planted, higher gives the pedal more room in a corner.
Toe and front wheel: 3 mm clearance Gap between the toe of the shoe and the tyre with the crank level, with shoe size 43. The shoe size is estimated from your height.

What seat tube, head tube, fork offset and trail are exactly, where they run and what you can swap: The bike, part by part

Whether that makes your bike calm or agile, next to real bikes: Calm or agile

Reset the sliders

Where the numbers come from

How you sit on the changed frame is calculated by the same part of the app as the comparison of two bikes.

Trail = (tyre radius · cos head angle − offset) / sin head angle, with a 346 mm tyre radius. On race and endurance bikes that is the tyre the makers themselves quote their trail with (worked back from 5 charts); so the numbers here and there are within a few millimetres.