Source: https://guthlabs.ai/docs/instruments/tire-size-comparator/implementation/

instrument implementation / implementation-contract

# Tire Size Comparator implementation

A source-bound implementation contract for Tire Size Comparator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t4-127

**Effect**: Computation or source lookup only

## Input and validation requirements

The formulas produce an undefined percentage when the old tire's computed diameter is zero, and they also accept physically invalid zero aspect ratios unless input validation rejects them. The speedometer-error label is convention-sensitive because the specification's ratio differs from the usual indicated-versus-true-speed interpretation.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "old_tire": "225/45R17",
    "new_tire": "235/40R18"
  },
  "expected_outputs": {
    "old_diameter_mm": 634.3,
    "new_diameter_mm": 645.2,
    "diameter_delta_mm": 10.9,
    "percent_difference": 1.71843,
    "speedometer_error_percent_same_ratio": 1.71843,
    "ground_clearance_change_mm": 5.45
  },
  "working": "Old sidewall = 225 × (45/100) = 101.25 mm. Old rim = 17 × 25.4 = 431.8 mm. Old diameter = 431.8 + 2 × 101.25 = 634.3 mm. New sidewall = 235 × (40/100) = 94 mm. New rim = 18 × 25.4 = 457.2 mm. New diameter = 457.2 + 2 × 94 = 645.2 mm. Diameter delta = 645.2 − 634.3 = 10.9 mm. Percent difference = 10.9 ÷ 634.3 × 100 = 1.71843%. Ground-clearance change = 10.9 ÷ 2 = 5.45 mm. Speedometer same-ratio value = 1.71843%."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/tire-size-comparator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/tire-size-comparator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/tire-size-comparator/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`