Who runs Gear Toolbox
Gear Toolbox is founded and edited by Fernando Margareto, who designs and builds online tools from Yátova, a small town in the province of Valencia, Spain. He is not a mechanic, an engine builder or a professional tuner, and he does not live in the United States. That is exactly why the site is built the way it is: every number comes from a stated formula or a cited source, and every result is presented as an estimate rather than as professional advice.
His job on Gear Toolbox is to take the calculations that car builders already rely on, write them down correctly, make them easy to use on a phone in the garage as well as on a desktop, and keep them accurate when someone points out a problem.
Why the site exists
Most performance calculators online are scattered. A parts maker offers one or two calculators for its own products, a long-running hobby site has another that no longer works on a phone, and a general calculator site has a third that does not speak the language of people who build cars. Each one asks for the same numbers again: bore, stroke, gear ratios, tire size, weight.
Gear Toolbox puts the whole set in one place and links the calculators to each other. My Garage keeps the specs of your builds in your browser, so every calculator fills itself in, and the Build Sheet puts your numbers on one printable page to take to the shop. US units come first, with a metric switch on every calculator.
How the results are worked out
The calculators fall into three groups, and each page tells you which kind of result you are looking at.
- Exact relationships. Displacement, gear ratios, engine speed at a road speed, tire dimensions, compression ratio and unit conversions follow directly from geometry and definitions. For the numbers you enter, the result is exact; the uncertainty is in the measurements themselves.
- Empirical estimates. Formulas such as the classic quarter-mile, eighth-mile and 0-60 estimates were fitted to real results. Their pages say where the formula comes from, what it assumes and how far real cars usually land from it.
- Typical values. Figures such as fuel consumption per horsepower, drivetrain loss or volumetric efficiency vary from engine to engine. They are shown as ranges from technical references, the page explains the range, and the calculator lets you change the value.
Behind the pages, every formula lives in its own small piece of code with automated tests: cases worked out by hand, extreme values that must give a clear message instead of a wrong number, and checks that the same case gives the same answer in US and metric units. The worked example on each page is produced by that same code, so the text cannot drift away from what the calculator does.
Where the formulas and values come from
Every constant the site uses, from the stoichiometric ratio of each fuel to the exact length of an inch, is kept in a single list together with its source. The sources are engineering references such as John B. Heywood’s Internal Combustion Engine Fundamentals and the Bosch Automotive Handbook, published standards (SAE, ASTM), US government data (NIST unit definitions, the Department of Energy and fueleconomy.gov), the Tire and Rim Association’s tire size nomenclature, and technical documentation from component manufacturers. A value without a reliable source is not published.
When sources disagree, the page gives a typical range instead of pretending there is one right number, and the input stays editable so you can use the figure that matches your engine.
How AI tools are used
AI tools help prepare and review the content and the code of this site, including a separate review pass over every formula, typical value and worked example. The decisions about what is published, and the responsibility for it, are Fernando’s. The results are not certified by a professional mechanic or engineer, which is one more reason they are always presented as estimates.
Your data
There are no accounts. The builds you save in My Garage stay in your own browser and are never sent to this site; you can export them to a file and import them on another device. The privacy notice covers the details, including the contact form.
Corrections and contact
If a result looks wrong, please say so. Tell us which calculator, the numbers you entered and what you expected, using the contact page. Reports are checked against the formula and its sources, and confirmed mistakes are fixed and the page’s date updated. For the limits of what the calculators can tell you, see the disclaimer.