# Bicycle Wheel Size Calculator

> Bicycle Wheel Size Calculator is a paid API for AI agents from bike-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Returns rolling circumference, diameter, and revolutions per km for a given tyre size, either from a preset tyre label or from rim bead seat diameter and tyre width.

## Facts

- Endpoint: GET https://bike-calc.x402tookit.com/wheel-size?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/bicycle-wheel-size-calculator-50763d8c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_d55_0SqYyKIdBpqIDI9c-

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability bicycle-wheel-size-calculator-50763d8c
```

Example prompt: What's the rolling circumference and diameter of a 700x28c tyre in millimetres, and how many revolutions would it make per kilometre?

## When to prefer this

Use this endpoint when you need accurate wheel circumference or diameter figures — for calibrating GPS cycling computers, computing gear development distances, or feeding into cadence/speed calculations. It covers both common ISO tyre presets and custom rim+width combinations, making it more flexible than a static lookup table. Pair with the sibling gear-ratio endpoint when building complete drivetrain calculators.

## Known failure modes

- Missing both 'tyre' preset and 'bsdMm'/'tyreWidthMm' parameters — endpoint cannot compute without at least one valid input
- Unrecognised tyre preset string — no matching entry for the given label
- Partial custom inputs — providing bsdMm without tyreWidthMm or vice versa may return a degraded or null result
- Values outside plausible ranges (e.g. bsdMm of 0 or extremely large width) may produce nonsensical estimates

## How this service works

Rolling circumference and diameter for common tyre sizes, or an estimate from rim bead diameter and tyre width in mm.

## Output

Returns the wheel's outer diameter in mm and inches, rolling circumference in mm, meters per revolution, and revolutions per kilometre. Also includes the basis of the calculation (preset lookup or estimate), an optional disclaimer about estimated values, and metadata such as timestamp and source.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [],
     "properties": {
      "tyre": {
       "type": "string",
       "description": "A preset: 700x23c, 700x25c, 700x28c, 700x32c, 700x35c, 700x38c, 26x2.0"
      },
      "bsdMm": {
       "type": "number",
       "description": "Rim bead seat diameter in mm (622 for 700c/29er, 584 for 650b/27.5, 559 for 26 inch MTB, 406 for 20 inch BMX)"
      },
      "tyreWidthMm": {
       "type": "number",
       "description": "Tyre width in mm, with bsdMm, for an estimate"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "basis": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "diameterMm": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "diameterInches": {
       "type": [
        "null",
        "number"
       ]
      },
      "circumferenceMm": {
       "type": [
        "null",
        "number"
       ]
      },
      "revolutionsPerKm": {
       "type": [
        "null",
        "number"
       ]
      },
      "metersPerRevolution": {
       "type": [
        "null",
        
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/bicycle-wheel-size-calculator-50763d8c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from bike-calc.x402tookit.com](https://www.zero.xyz/host/bike-calc.x402tookit.com/llms.txt)