// Free tuning tools
Performance,
dialed in.
Fast, ad-free calculators for people who actually turn the wrenches — then a build planner to spec your car and share it. No sign-up, no fluff, works on your phone in the garage.
// Calculators
Twenty-eight calculators, grouped by what you are working on. Every one shows its formula.
Wheels & tires
Tire sizing and speedo error, wheel offset and poke, bolt pattern, alignment units.
Engine builder
Displacement, compression ratio, cam timing and overlap, piston speed, airflow.
Forced induction
Compressor sizing in lb/min, pressure ratio, and what boost does to effective CR.
Fuel & tuning
Injector sizing, AFR and lambda per fuel, E85 blending, running costs.
Chassis & handling
Spring and wheel rate, ride frequency, brake bias, corner weights and cross-weight.
Performance & drag strip
Power-to-weight, 0–60 and quarter-mile, trap-speed horsepower, dyno correction.
Browse all 28 calculators in one list →
// Play
Tune It
Dial in the fuel curve, run the dyno and chase peak power — go too lean and it knocks.
GameReaction Time Test
Drag-strip Christmas tree — stage up, wait for green and launch. Beat your best, don't red-light.
GameDrag Race
Launch your My Build car down the ¼-mile — tree start, manual shifts, chase your best ET.
// Build planner
// Guides
How to read a tire size
Every number on the sidewall — width, aspect, load index & speed rating.
GuideWheel offset explained
ET, backspacing and poke — and whether a wheel will clear.
GuideCompression ratio explained
What it is, how it's calculated and what a good ratio is.
GuideAFR & lambda explained
Mixture, tuning targets and why lambda beats a bare AFR number.
GuidePower-to-weight explained
The number that really predicts pace, and how to compare fairly.
AllAll guides →
Plain-English explainers for the maths behind the mods.
Start with the tire size calculator
The most-used tool — diameter, gearing and speedo error in one screen.