What the site does
Every tool here turns numbers you enter into numbers you can use: a tire size into its real diameter, a new tire into a new gear ratio, a bore and stroke into a compression ratio, a trailer into the share of each of your truck's ratings it uses. Everything is calculated in your browser. There is no sign-up and nothing is locked.
How we keep the numbers right
- Every page shows its formula and a worked example, so you can check the result by hand.
- The calculations are tested. Each formula is checked against hand-worked values before a page goes up.
- Standards come from their source. Tire markings follow the published load index and speed symbol tables and the US federal rules for the DOT code (49 CFR 574.5) and quality grades (49 CFR 575.104). Bicycle rim sizes follow the ISO bead seat diameters as listed by Sheldon Brown.
- Assumptions are labelled. Where a result depends on a value that differs between vehicles, such as drivetrain loss, road grip or a battery's usable capacity, the field is yours to change and the page says it is an assumption.
What the site does not do
It does not know your vehicle. It never says that a tire, wheel or trailer will fit, or that a setup is safe or legal: those depend on your vehicle, its labels and your local rules. It does not hold any vehicle's specifications or ratings. Check your owner's manual, the labels on the door jamb and hitch, and the parts maker's data.
Found a mistake?
If a result looks wrong, the formula on the page is the place to start. If the formula or the example is wrong, we want to fix it.
Contact
Questions, a mistake in a formula, or an idea for a calculator: write to hello@rpmkit.com.