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CalculatorsStem Length and Angle Calculator

Stem Length and Angle Calculator

A stem is a hypotenuse, but its angle is quoted square to the steerer, not to the ground. On a 73° head tube a −17° stem sits level and a −6° stem still climbs 11°. Length and that real tilt split into horizontal reach and vertical rise.

Inputs

Units
Measured square to the steerer. −6 and −17 are common; −17 is level on a 73° head tube.
Road and gravel frames sit near 71–74°, trail MTBs near 64–66°.

Results

Stem horizontal
3.9 in
Stem rise
0.8 in
Reach plus stem
19.2 in

The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.

How the number is made

Tilt above level = stem angle + (90° − head tube angle). Horizontal = length × cos(tilt). Rise = length × sin(tilt), negative when the bar sits below the stem clamp. Reach plus stem = frame reach + horizontal. Spacers and the headset cap under the stem are not included.

Stem angles are quoted square to the steerer, so the same stem sits differently on a slack MTB and a steep road bike. Each 10 mm of spacers under the stem moves the bar about 9.6 mm up and 3 mm back on a 73° head tube. Bar reach (the drop-bar extension) adds more horizontal millimetres than the stem alone.

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Questions

Does −17° shorten reach?

Not on a typical 73° head tube. A −17° stem sits level, so its whole length points forward: 100 mm against about 98 mm for a −6° stem. What changes is height: the bar ends up about 19 mm lower.

Where do spacers go?

Above or below the stem. This calculator stops at the stem itself.

Does a positive stem angle drop the bars?

No, it raises them. On a 73° head tube a 100 mm +6° stem climbs 23° and lifts the bar about 39 mm above the clamp, against about 19 mm for the same stem flipped to −6°.

Does a negative stem angle always lower the bar?

No. The angle is measured square to the steerer, so on a 73° head tube a 100 mm −6° stem still lifts the bar about 19 mm above the clamp. Only angles past −17°, such as −20° or −25°, put the bar below it.

Example products

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