Bicycle Fit & Cockpit Comparison / no guesswork hidden

A new frame. A familiar position.

Compare two cockpits in millimeters, then see the stem and spacer changes needed to reproduce your reference handlebar position.

No sign-inLocal calculationsEditable assumptionsSource-linked methodology

Illustrative starting inputs. Replace them with your own measurements and evidence.

Your working plan

Match the contact point, not the size label.

Computed locally

A geometric match is possible within the modeled range

A 91.3 mm stem at -8.4° reproduces the reference clamp coordinates at the entered candidate spacer height. This is geometry, not a parts recommendation.

Handlebar clamp reach change+7.9 mmPositive means farther forward

Clamp height change+5.4 mmPositive means higher

Matching stem length91.3 mmContinuous solution; available sizes may differ

Matching stem angle-8.4°Angle relative to perpendicular to the steerer

Frame geometry comparison

Reference stack560

560

Candidate stack575

575

Reference reach385

385

Candidate reach390

390

Before you act

Spacer limits, steerer engagement, stem orientation, cable routing, and torque requirements must be verified with the manufacturer.
This model assumes the same bars, hood position, headset bearing reference, and stem clamp convention. It does not solve saddle position or guarantee fit.

Clamp coordinates


Forward from bottom bracket	477.3	485.2	7.9
Above bottom bracket	598.2	603.6	5.4

Calculation notes & limitations

Clamp X = frame reach − spacer height × cos(head angle) + stem length × cos(90° − head angle + stem angle).

Clamp Y = frame stack + spacer height × sin(head angle) + stem length × sin(90° − head angle + stem angle).

The inverse solution uses the vector from the candidate steerer clamp reference to the target handlebar clamp. Manufacturer stack/reach definitions and headset top-cap heights must be reconciled first.

Plan name

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02 / Look under the hood

The method is part of the tool.

Use manufacturer stack and reach for the exact model year and size. Add headset top-cap height consistently to the spacer-stack input.

Convert the stem and spacer arrangement into handlebar-clamp coordinates relative to the bottom bracket. Compare those coordinates instead of nominal frame size.

Solve the inverse stem geometry while holding the candidate spacer height fixed. Check real component sizes and every manufacturer limit before making a change.

Read the full methodology

03 / Know the boundaries

Evidence before certainty.

A cockpit calculation cannot guarantee fit, comfort, safe component installation, or handling. Validate the setup with a qualified fitter or mechanic.

These are reference sources, not evidence that example records have been verified. Imported records retain the source links you provide.

Trek bicycle sizing and fit guidance

Field notes / Position Match