Aerobar extension length vs grip position: the tube is not the hand point
Stock length, exposed length and a named grip coordinate have different endpoints. Keep bends, pad-to-grip projections and orientation visible without turning a length into a cutting or fit instruction.
Published 11 October 2026 · OpenBikeFit
Aero contact reference · not to scale
The tube is not the grip point.
Fictional P=(460,650) and G=(670,700) mm → local p=(210,50) mm; direct planar gap ≈215.9 mm.
Separate mathematical +10° rigid rotation about fixed P: p′≈(198.1,85.7) mm; G′≈(658.1,735.7) mm.
No actual hinge, missing lateral coordinate, bend geometry, cutting plan or physical adjustment is supplied.
On this page
- 01Separate stock, path and straight endpoint length
- 02Exposed length needs receiver and engagement references
- 03Locate a named grip point independently
- 04A different pad point changes the reported gap
- 05An angle does not specify a complete bent extension
- 06A rigid rotation requires a named pivot and included points
- 07Keep controls and physical checks outside the point model
- 08Complete the technical hand-off without field substitution
Free blank worksheet
Keep a technical paper reference
Use reference and question spaces for extra armrest fields. Fixed digital slots do not replace these distinct endpoints.
Open toolAn extension-length label describes a tube or a declared measurement between particular references. A grip position describes another point in the assembled cockpit. Equal lengths can produce different points when receiver location, insertion, bends or orientation differ. Conversely, an equal named grip coordinate does not document the stock tube, engagement or controls inside an assembly.
This guide records an existing technical reference and explains explicitly hypothetical point geometry. It does not calculate an ideal hand position, select an extension shape, authorise cutting, prescribe insertion or approve a cockpit change. A hand-contact point is not automatically the extension tip, shifter axis or centre of a visible bend. Name the intended endpoint before comparing anything.
Separate stock, path and straight endpoint length
A stock extension length may concern the component before it is installed. A centreline path length following a bent tube differs from a straight distance between its endpoints. Neither is automatically a horizontal projection. Preserve the manufacturer’s exact definition and drawing when available; do not apply a familiar straight-tube convention to a shaped component without evidence.
Profile Design lists extension length separately from armrest offset and stack for its named Subsonic assembly. The SRAM Vuka Clip manual likewise asks for a distinct existing extension-length record. Those sources establish separate records, not a universal stock-to-grip conversion. This article provides no cutting marks, removed-length calculation, tool sequence or fit claim based on a catalogue length.
Exposed length needs receiver and engagement references
Installed exposed length depends on a named receiver boundary, the chosen measurement direction and the extension reference. A length visible outside the receiver does not prove how much is supported inside it. A front tip can contain a control or plug that adds another endpoint, while the usable surface or intended grip station may stop elsewhere.
Keep receiver identity, extension identity, declared engagement conditions, observed exposed dimension and unresolved hidden checks as separate lines. Do not disassemble, slide or probe hardware to obtain the illustration’s numbers. An unknown engagement limit is not unlimited insertion permission. A nominal matching diameter cannot substitute for the exact support and hardware requirements described in the interface guide.
Locate a named grip point independently
Use the same declared BB-relative axes and observation condition as the pad record. In a fictional level side view let pad reference P=(460,650) mm and named technical grip reference G=(670,700) mm. The pad-to-grip vector is G−P=(210,50) mm. Here horizontal reach is 210 mm and vertical rise is 50 mm; neither number is the tube’s stock or path length.
These hypothetical points omit lateral differences on purpose. In the same sagittal plane their direct separation is √(210²+50²)≈215.9 mm. If the actual lateral difference is unknown, that planar length is not an established direct three-dimensional distance. Do not silently assume zero lateral separation simply because a side-view photograph overlaps the two references.
A different pad point changes the reported gap
Keep fictional G fixed at X670/Y700. Using the previous guide’s flat rear pad station R=(410,650) instead of its centre P=(460,650) changes horizontal pad-to-grip reach from 210 to 260 mm without moving any hardware. The vertical difference is still 50 mm only because that particular rear and centre were deliberately level.
A curved, rotated or loaded surface need not preserve that vertical relation. Carry the exact pad station, grip feature, load condition and sign convention beside the pair. If a hand-off says reach changed, first establish whether both records used the same endpoints and projection. A changed definition is not evidence of a mechanical change or a changed rider position.
An angle does not specify a complete bent extension
A product can use a bend or grip-angle label while leaving the full centreline and installed receiver relationship unresolved. A named angle in one plane cannot supply the lengths and positions of every bend, the grip station or a separate pad support. Different designs can share an angle label yet put their technical points elsewhere.
Do not multiply a stock length by sine or cosine and present the result as an installed grip coordinate unless the source explicitly gives the required straight-segment geometry and origin. A simple segment calculation explains its own model, not a complete shaped tube. Preserve the drawing and its dimensions or an actual named observation instead of inventing missing bend geometry.
A rigid rotation requires a named pivot and included points
For a separate fictional construction, hold P fixed as a mathematical pivot and rigidly rotate only the local vector p=(210,50) mm by +10° in the X/Y plane, with forward turning toward upward. Then x′=x cosθ−y sinθ≈198.1 mm and y′=x sinθ+y cosθ≈85.7 mm. The direct planar length remains about 215.9 mm. This is not an actual aerobar hinge or an instruction to rotate a part.
The resulting point would be P+p′≈(658.1,735.7) mm only under that explicit pivot and rigid-point assumption. A real support might rotate both pad and extension about another axis, or allow them to move separately; an extension adjustment does not automatically leave P fixed. No mounted-angle label establishes the linkage. If the pivot, support geometry or moving points are unknown, the modeled change stays unavailable.
Keep controls and physical checks outside the point model
A technical G is not a complete hand surface or a control-function check. Preserve shifter and brake identities, their distinct contact references and applicable routing or access questions separately. Point geometry cannot establish the ability to operate a control, steering clearance, support strength or riding suitability. An apparently matching tip position is not an assembled-system certificate.
The same boundary applies to any claimed aerodynamic, comfort, power or race-rule outcome: none is calculated here. The original schematic has no rider or pressure model. If the physical setup or applicable source is unresolved, retain the issue for its own qualified check rather than describing the hypothetical coordinate as an improvement.
Complete the technical hand-off without field substitution
Keep stock definition, any measured exposed dimension, exact receiver, named P and G, their independent coordinates and projections, plane or lateral state, support condition, source and raw readings together. Do not average a tube length and a pad-to-grip reach because they both use millimetres. Unknown stock or engagement data can coexist with recorded coordinates without being cleared by them.
Use the paper worksheet’s extra reference and question spaces for these aerobar-specific quantities. The fixed digital whole sheet and existing stem calculator are not an extension or armrest model. Return to the interface guide when the source or part identity changes, and preserve the separate pad and width records. The result is a clearer discussion note, not a cutting plan, installation permission or verified fit.
Practical questions
Frequently asked questions
Is a 340 mm extension a 340 mm pad-to-grip reach?
Not from that label. Stock length, exposed length, bend geometry and named pad/grip points have different references.
Is horizontal pad-to-grip reach the direct distance?
No. The fictional 210 horizontal and 50 vertical components give 215.9 mm in the declared plane; a real 3D distance also needs the lateral difference.
Does changing the extension angle leave the pad fixed?
Only if the actual mechanism establishes that relationship. The fixed-pad pivot in the example is an explicit mathematical assumption, not a universal aerobar linkage.
Can I use this guide to cut or install extensions?
No. Keep the exact model instructions, permitted engagement, controls and physical checks separate. No length or diagram approves physical work.