How we check facts

These are the rules every Sidewall Math page follows.

1. Show the working

Each calculator page explains the formula it uses, gives a worked example you can check by hand, and says where the numbers come from. If a result depends on an assumption, the page says so.

2. Official and reputable sources first

We check facts against primary sources wherever they exist: government agencies, university extension services, standards bodies and manufacturers' published specifications. Each page lists its sources and the date we last checked them. When sources disagree, we say so rather than pick one silently. When we cannot confirm something, we leave it out.

3. Written in our own words

We write every page ourselves. We do not copy text, tables or images from other websites.

4. No made-up details

We do not invent reviews, test results, ratings, prices, experts or personal stories. Examples that use made-up numbers are labeled as examples.

Sources we use

Sidewall codes, tire aging, tread and pressure guidance come from the U.S. National Highway Traffic Safety Administration (NHTSA). Load index and speed symbol tables come from tire manufacturers' published charts. Plus-sizing guidance comes from tire manufacturer technical bulletins. Dimensions are calculated from the size code; actual measured sizes vary slightly by tire model, which we say on every page.

Dates and updates

Every page shows when it was last updated and when its facts were last checked, plus a short "What changed" list. We re-check pages when the underlying rules or sources change.

Corrections

If you find an error, please tell us through the contact page. We fix confirmed mistakes promptly and note the change on the page.

Advertising and affiliate links

Advertisers and retailers do not see or approve our pages before they are published, and they do not influence our calculations. Affiliate links are limited to a few genuinely useful items, never placed inside a calculator, and always disclosed at the top of the page.