# Automotive Calculators – Tire Size Comparison & Speedometer Error

> Automotive Calculators – Tire Size Comparison & Speedometer Error is a paid API for AI agents from automotive-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-30).

Calculates physical dimensions for a tire size code and computes speedometer/odometer error when switching to a different tire size

## Facts

- Endpoint: GET https://automotive-calc.x402tookit.com/tire-compare?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/automotive-calculators-tire-size-comparison-speedometer-error-1b9f2e02
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_cabrmkWDjV9y5lznscx9F

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 automotive-calculators-tire-size-comparison-speedometer-error-1b9f2e02
```

Example prompt: I'm upgrading from 225/45R17 to 235/40R18 tires — can you compare those two sizes and tell me what my actual speed will be when my speedometer reads 65 mph?

## When to prefer this

Use this endpoint when you need precise tire dimension calculations from standard metric (225/45R17) or flotation (31x10.5R15) size codes, or when comparing two tire sizes to quantify speedometer and odometer error. Prefer this over generic search when you need structured numeric outputs (diameter, revolutions per mile, actual speed) that can be used programmatically downstream.

## Known failure modes

- Invalid or unrecognized tire size format returns an error or null dimensions
- Missing required currentSize parameter returns a 400-level error
- Malformed size code (e.g. missing aspect ratio) may yield null fields
- indicatedMph outside 5–200 range may be rejected or clamped
- Network timeout or upstream service unavailability returns 5xx

## How this service works

Tire dimensions from size codes like 225/45R17, and speedometer and odometer error when you change to a different size.

## Output

Returns parsed physical dimensions for the current tire size (width in mm, sidewall in mm, rim diameter in inches, overall diameter in mm and inches, circumference in inches, revolutions per mile and per km), and if a replacement size is provided: the same dimensions for the new size, the percentage difference in diameter, actual vs indicated speed at the given mph, a speed correction table across a range of indicated speeds, a verdict on compatibility, and any warnings or disclaimers.

## 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": [
      "currentSize"
     ],
     "properties": {
      "newSize": {
       "type": "string",
       "description": "Replacement size to compare"
      },
      "currentSize": {
       "type": "string",
       "description": "Tire size now, for example 225/45R17 or 31x10.5R15"
      },
      "indicatedMph": {
       "type": "number",
       "description": "Speed shown on your speedometer in mph, 5 to 200 (default 60)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "current": {
       "type": [
        "null",
        "object"
       ],
       "properties": {
        "size": {
         "type": [
          "null",
          "string"
         ]
        },
        "widthMm": {
         "type": [
          "null",
          "number"
         ]
        },
        "rimInches": {
         "type": [
          "null",
          "number"
         ]
        },
        "diameterMm": {
         "type": [
          "null",
          "number"
         ]
        },
        "sidewallMm": {
         "type": [
          "null",
          "number"
         ]
        },
        "diameterInches": {
         "type": [
          "null",
          "number"
         ]
        },
        "revolutionsPerKm": {
         "type": [
          "null",
          "number"
         ]
        },
        "aspectRatioPercent": {
         "type": [
          "null",
          "number"
         ]
        },
        "revolutionsPerMile": {
         "type": [
          "null",
          "number"
         ]
        },
        "circumferenceInches": {
         "type": [
          "null",
          "number"
         ]
        }
       }
      },
      "reasons": {
       "type": [
        "array",
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/automotive-calculators-tire-size-comparison-speedometer-error-1b9f2e02/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from automotive-calc.x402tookit.com](https://www.zero.xyz/host/automotive-calc.x402tookit.com/llms.txt)