Privacy Policy

This page describes what happens to information you give this site, and what happens without you giving it anything. It is written against what the code actually does, and it is re-read whenever that changes.

The short version

You can read every page here without an account, without logging in, and without giving an email address. The calculators run entirely in your browser: the sizes you type are never sent anywhere. They appear in the address bar so the result is a link you can share, and that is the only place they go.

What is collected, and when

Server logs and traffic measurement, by default. The site is hosted on Vercel, which records standard request information — the requested address, an approximate location derived from the network, the browser's user-agent string and a timestamp — for the purposes of serving the page and defending against abuse. One cookieless measurement service also runs on every page, and a second is present in the code but switched off; both are described under Measurement and advertising below, and that section is written against the code rather than around it.

Calculator inputs are not collected. They are computed in your browser and written into the address bar. No calculation is sent to a server.

Your email address, if you subscribe. The newsletter is operated through Brevo. If you enter an address, it is stored by Brevo along with the fact that you subscribed from this site, and used to send the occasional email described on the form. Every message carries an unsubscribe link, and using it removes you.

Your name, email address and message, if you use the contact form. The form is operated through Formspree, which forwards the message to a mailbox and retains a copy so it can be re-sent. The email address published on the contact page reaches the same mailbox directly if you would rather not use a form.

Payment details, if you buy something or contribute. Payments are processed by Stripe on Stripe's own pages. Card numbers are never entered on this site and are never seen by it. Stripe returns confirmation that a payment succeeded and the email address you gave it, so an order can be fulfilled.

Measurement and advertising

Traffic measurement and advertising are handled by third parties, and this section describes what the code on this site actually loads rather than what a policy of this kind usually claims.

Traffic measurement. One service runs here today. Vercel Web Analytics counts page views without setting a cookie and without an identifier that follows you between sites, which is why there is nothing to switch off: it stores nothing on your device.

Google Analytics 4 is not running at the time of this review. The code for it is present and carries no measurement identifier, so the component renders nothing at all and no page on this site loads anything from Google's tag server. This paragraph is written now, before that changes, for the same reason the advertising one below is: a disclosure that arrives after the first cookie is a disclosure that arrived late. When the tag is switched on it will set first-party cookies — one named _ga, one named after the measurement identifier — which tell one browser from another for about two years, so that it is possible to see which pages people arrive on and which searches brought them. Those cookies would carry no name, no email address and nothing typed into a calculator.

When it is switched on, it will not sit behind a cookie dialog. That is a decision rather than an oversight, and it is why this section is written as plainly as it is: an interstitial that most people dismiss unread is not consent, and telling you straight is worth more than a button. If you would rather not be counted then, block cookies for this address, turn on your browser's tracking protection, or install Google's own Analytics opt-out add-on, which stops the tag reporting from every site you visit.

Advertising. Advertisements are not being served on this site at the time of this review. When they are, they will be served by Google AdSense, and this paragraph is here so that the disclosure exists before the first one appears rather than after. Google and its partners use cookies to serve advertisements and to personalise them based on your previous visits to this and other sites. You can control personalisation at Google My Ad Center and opt out of personalised advertising from participating vendors at aboutads.info. If and when advertising runs for visitors in the European Economic Area and the United Kingdom, Google's certified consent message is configured for this site before it does, because Google requires it.

Advertising never influences what a page says. No advertiser, affiliate or sponsor has any input into a figure, a comparison or the order anything appears in, and there is no mechanism by which one could: the numbers are arithmetic, and arithmetic is not for sale. Nor is there a recommendation to buy — the site declines to say that any tire suits any vehicle, which removes the thing an advertiser would most want to influence. How these numbers are calculated sets out where every one of them comes from.

Cookies

This site sets no cookie of its own, and as of this review no page here sets any cookie at all: Vercel Web Analytics stores nothing, Google Analytics is not switched on, and no advertising is being served. Every cookie that ever appears will come from a service named above — the Google Analytics cookies described in the previous section, and advertising cookies set by Google once advertising runs. Stripe, Brevo and Formspree set cookies on their own pages, not on this one. Clearing cookies in your browser removes any of them, and blocking them for this address stops the analytics ones being set at all.

Retention, and how to be removed

Newsletter subscriptions are kept until you unsubscribe. Contact messages are kept while they are useful to answer and then deleted. Payment records are kept by Stripe for as long as its own obligations require. Server logs are short-lived and are held by the host, not by this site.

To be removed from the mailing list, use the unsubscribe link in any message. For anything else, email the address on the contact page and say what you want deleted.

Children

This site is not directed at children and does not knowingly collect information from them.

Changes

When the services above change, this page is re-read line by line against the code and updated in the same pass. The date at the top is when that last happened.