Tire Compare

{
  "actualKmh": 99.3,
  "actualMph": 61.7,
  "asOf": "2026-10-11T14:38:38.436Z",
  "current": {
    "aspectRatioPercent": 45,
    "circumferenceInches": 78.45,
    "diameterInches": 24.97,
    "diameterMm": 634.3,
    "revolutionsPerKm": 501.8,
    "revolutionsPerMile": 807.6,
    "rimInches": 17,
    "sidewallMm": 101.25,
    "size": "225/45R17",
    "widthMm": 225
  },
  "degraded": false,
  "diameterDifferenceMm": 18,
  "diameterDifferencePercent": 2.838,
  "disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
  "effectiveGearingChangePercent": -2.759,
  "indicatedMph": 60,
  "notChecked": [
    "tire wear and pressure: a worn tire is up to about 2% smaller in diameter, and a loaded tire runs slightly smaller than its nominal size",
    "manufacturer measured diameters, which differ from the calculated nominal by up to 1 to 2%",
    "…2 more"
  ],
  "odometerErrorPercent": -2.759,
  "reasons": [
    "A larger tire covers more ground per turn, so the speedometer reads low and the odometer under-counts; a smaller tire does the reverse.",
    "A change within about 3% of the original diameter is the commonly used limit for keeping the speedometer, ABS and gearing within tolerance.",
    "…1 more"
  ],
  "replacement": {
    "aspectRatioPercent": 45,
    "circumferenceInches": 80.68,
    "diameterInches": 25.68,
    "diameterMm": 652.3,
    "revolutionsPerKm": 488,
    "revolutionsPerMile": 785.3,
    "rimInches": 17,
    "sidewallMm": 110.25,
    "size": "245/45R17",
    "widthMm": 245
  },
  "source": "computed locally",
  "speedErrorMph": 1.7,
  "speedTable": [
    {
      "actualMph": 30.9,
      "indicatedMph": 30
    },
    {
      "actualMph": 51.4,
      "indicatedMph": 50
    }
  ],
  "speedometerFactor": 1.02838,
  "summary": "245/45R17 is 25.68 in against 24.97 in for 225/45R17: +2.84% diameter. With the new tires a speedometer showing 60 mph means 61.7 mph actual (99.3 km/h); the odometer under-counts distance by 2.76%.",
  "verdict": "WITHIN_3_PERCENT"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://automotive-calc.x402tookit.com/tire-compare?currentSize=225%2F45R17&indicatedMph=60&newSize=245%2F45R17'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://automotive-calc.x402tookit.com/tire-compare?currentSize=225%2F45R17&indicatedMph=60&newSize=245%2F45R17' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fautomotive-calc.x402tookit.com%2Ftire-compare
const res = await pay("https://automotive-calc.x402tookit.com/tire-compare?currentSize=225%2F45R17&indicatedMph=60&newSize=245%2F45R17");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://automotive-calc.x402tookit.com/tire-compare?currentSize=225%2F45R17&indicatedMph=60&newSize=245%2F45R17")
    print(res.status_code, res.text)