Longer stem, flipped stem or moving spacers — how far does the handlebar really move? The calculator shows the change of the handlebar clamp in millimetres: horizontal (reach) and vertical (stack), taking the head tube angle into account.
The steerer is not vertical: it leans back by the head tube angle (typically 73°). The stem angle is measured from the perpendicular to that axis, so on a 73° head tube a −6° stem points 11° above horizontal, and a −17° stem is exactly level. Spacers raise the stem along the steerer axis — the bar ends up higher and slightly closer to the saddle. The calculator compares the centre of the handlebar clamp for both setups and assumes both stems have the same stack height.
| Change | Reach | Stack |
|---|---|---|
| Stem 10 mm longer (−6°) | +9.8 mm | +1.9 mm |
| 100 mm stem −6° → +6° (flipped) | −6.1 mm | +20.0 mm |
| 10 mm more spacers under the stem | −2.9 mm | +9.6 mm |
A few millimetres at the cockpit noticeably change your back angle and arm bend. As a guide, aim for a back angle of roughly 30–45° and a slight elbow bend of 15–25°. Whether your new stem gets you there is best judged from your real posture: our video analysis measures back, elbow, hip and knee angles and, in the report, estimates how a planned stem or spacer change affects your angles. More on target values in the cockpit guide to handlebar height and stem length.
Measure your posture by video now — free →