# Tuning4U

> Free, ad-free car tuning calculators, a build planner and tuning games for car enthusiasts. No sign-up, no tracking beyond privacy-safe analytics, works on mobile. All tools run in the browser and show the underlying formulas.

Tuning4U (https://tuning4u.info) is a static reference site. Every calculator explains how the result is derived, so the content doubles as a learning resource for car tuning, engine building and wheel/tire fitment.

## Calculators
- [Tire Size Calculator](https://tuning4u.info/tire-size-calculator/): Compare two tire sizes — diameter change, sidewall, circumference and speedometer error.
- [Wheel Offset & Fitment](https://tuning4u.info/wheel-offset-calculator/): ET/offset, backspacing and poke; check whether a wheel clears.
- [Bolt Pattern (PCD)](https://tuning4u.info/bolt-pattern-calculator/): mm ↔ inch stud spacing and common-pattern matching.
- [Spring Rate](https://tuning4u.info/spring-rate-calculator/): Wheel rate via motion ratio, ride frequency and N/mm ↔ lb/in.
- [Gear Ratio & Speed](https://tuning4u.info/gear-ratio-calculator/): Speed per RPM in every gear, final-drive swaps and rev-drop.
- [Power-to-Weight](https://tuning4u.info/power-to-weight-calculator/): hp/ton, kg/hp and how a build compares.
- [HP ↔ kW Converter](https://tuning4u.info/hp-kw-converter/): Horsepower, kilowatts and PS.
- [0–60 & Quarter-Mile](https://tuning4u.info/0-60-calculator/): Estimate acceleration from power and weight.
- [Trap Speed Horsepower](https://tuning4u.info/trap-speed-calculator/): Estimate flywheel power from quarter-mile trap speed or ET.
- [Top Speed](https://tuning4u.info/top-speed-calculator/): Drag-limited vmax from power, Cd and frontal area.
- [Boost & Compression](https://tuning4u.info/boost-compression-calculator/): Effective compression, pressure ratio and density.
- [Fuel Cost & Economy](https://tuning4u.info/fuel-cost-calculator/): Cost per trip, L/100km ↔ MPG and running costs.
- [Compression Ratio](https://tuning4u.info/compression-ratio-calculator/): Static CR from bore, stroke, chamber, gasket and deck.
- [Engine Displacement](https://tuning4u.info/engine-displacement-calculator/): cc, litres and cubic inches from bore, stroke and cylinders.
- [Mean Piston Speed](https://tuning4u.info/piston-speed-calculator/): m/s and ft/min from stroke and RPM.
- [Engine Airflow (CFM)](https://tuning4u.info/engine-airflow-calculator/): Intake airflow from displacement, RPM and VE.
- [Turbo Size](https://tuning4u.info/turbo-size-calculator/): Required compressor airflow and pressure ratio for a power target.
- [Injector Size](https://tuning4u.info/injector-calculator/): Required cc/min and lb/hr plus fuel-pump LPH from target hp.
- [AFR ↔ Lambda](https://tuning4u.info/afr-lambda-calculator/): Air-fuel ratio ↔ lambda per fuel, with tuning targets.
- [E85 Mix](https://tuning4u.info/e85-mix-calculator/): Blend two fuels to a target ethanol percentage.
- [Dyno Correction](https://tuning4u.info/dyno-correction-calculator/): SAE J1349 correction factor from temp, pressure and humidity.
- [Density Altitude](https://tuning4u.info/density-altitude-calculator/): Air density, density altitude and naturally-aspirated power loss.
- [Brake Bias](https://tuning4u.info/brake-bias-calculator/): Ideal front-to-rear brake split from weight transfer.
- [Corner Balance](https://tuning4u.info/corner-balance-calculator/): Front/rear, left/right and cross-weight from four corner scales.
- [Gearbox Designer](https://tuning4u.info/gearbox-calculator/): Sawtooth speed/RPM chart, top speed per gear and shift rev-drops.
- [Camshaft Specs](https://tuning4u.info/camshaft-calculator/): Overlap, valve events and net lift from duration, LSA and centerline.
- [Carb CFM](https://tuning4u.info/carb-cfm-calculator/): Carburetor airflow requirement from displacement, RPM and VE, with common sizes.
- [Alignment Converter](https://tuning4u.info/alignment-converter/): Toe mm/inches/degrees (via tire diameter) and camber decimal/degrees-minutes/mm-m.
- [OBD-II Code Lookup](https://tuning4u.info/obd2-code-lookup/): Search 1,100+ generic powertrain codes with symptoms and common causes.

## Browse
- [All calculators](https://tuning4u.info/tools/): Every tool, what it works out and what it needs.
- [Glossary](https://tuning4u.info/glossary/): 58 tuning terms defined, each linked to its calculator or guide.
- [Cheat sheets](https://tuning4u.info/cheat-sheets/): 7 printable reference cards covering fuel, fitment, air, suspension and gearing.
- [Wheels & tires](https://tuning4u.info/tools/wheels-tires/)
- [Engine builder](https://tuning4u.info/tools/engine/)
- [Forced induction](https://tuning4u.info/tools/forced-induction/)
- [Fuel & tuning](https://tuning4u.info/tools/fuel-tuning/)
- [Chassis & handling](https://tuning4u.info/tools/chassis/)
- [Performance & drag strip](https://tuning4u.info/tools/performance/)

## Guides
- [Guides index](https://tuning4u.info/guides/): Plain-English explainers for the calculators.
- [How to read a tire size](https://tuning4u.info/guides/how-to-read-a-tire-size/)
- [Wheel offset explained](https://tuning4u.info/guides/wheel-offset-explained/)
- [Compression ratio explained](https://tuning4u.info/guides/compression-ratio-explained/)
- [AFR and lambda explained](https://tuning4u.info/guides/afr-and-lambda-explained/)
- [Power-to-weight ratio explained](https://tuning4u.info/guides/power-to-weight-ratio-explained/)
- [How to size a turbo](https://tuning4u.info/guides/how-to-size-a-turbo/)
- [Brake bias explained](https://tuning4u.info/guides/brake-bias-explained/)
- [Corner balancing explained](https://tuning4u.info/guides/corner-balancing-explained/)
- [Trap speed vs ET explained](https://tuning4u.info/guides/trap-speed-and-et-explained/)
- [Injector sizing explained](https://tuning4u.info/guides/injector-sizing-explained/)
- [Dyno correction & density altitude explained](https://tuning4u.info/guides/dyno-correction-explained/)
- [E85 explained](https://tuning4u.info/guides/e85-explained/)
- [Gear ratios explained](https://tuning4u.info/guides/gear-ratios-explained/)
- [Camber, toe & caster explained](https://tuning4u.info/guides/camber-toe-caster-explained/)
- [Camshaft specs explained](https://tuning4u.info/guides/camshaft-specs-explained/)
- [How to read OBD-II codes](https://tuning4u.info/guides/how-to-read-obd2-codes/)
- [Bolt pattern (PCD) explained](https://tuning4u.info/guides/bolt-pattern-explained/)
- [Spring rate & ride frequency explained](https://tuning4u.info/guides/spring-rate-and-ride-frequency-explained/)
- [Engine airflow & VE explained](https://tuning4u.info/guides/engine-airflow-and-ve-explained/)
- [Boost & effective compression explained](https://tuning4u.info/guides/boost-and-effective-compression-explained/)
- [Top speed: aero, power & gearing](https://tuning4u.info/guides/top-speed-aero-power-and-gearing/)
- [Mean piston speed & RPM limits](https://tuning4u.info/guides/piston-speed-and-rpm-limits/)

## Tools & games
- [My Build](https://tuning4u.info/my-build/): Spec a car, save mods and generate a shareable build sheet. Saved in-browser, no sign-up.
- [Tune It](https://tuning4u.info/tune-it/): Dial in a fuel curve, run the dyno and chase peak power.
- [Reaction Time Test](https://tuning4u.info/reaction-time-test/): Drag-strip Christmas-tree reaction game.
- [Drag Race](https://tuning4u.info/drag-race/): Launch your My Build car down the quarter-mile.

## OBD-II code ranges covered
- P0xxx generic powertrain (1,171 rows, legacy import, unverified against SAE J2012)
- P2xxx selected generic (18 curated)
- U0xxx network / communication (49, standard wordings, marked recalled-standard)
- Not covered: P1xxx and P30xx-P33xx (manufacturer-specific), P34xx-P39xx, B and C ranges

## Diagnose
- [Will these wheels fit?](https://tuning4u.info/diagnose/will-these-wheels-fit/): Fitment fails in four places, and only one of them is the bolt pattern everybody checks first. Work through these and you will know which number is about to bite you.
- [Why is my AFR off?](https://tuning4u.info/diagnose/why-is-my-afr-off/): A mixture that reads wrong is either genuinely wrong or being reported wrong, and the two need opposite fixes. Start with which way it is off.
- [Where is my quarter-mile time going?](https://tuning4u.info/diagnose/where-is-my-quarter-mile-going/): Estimate your ET from power and weight first, then bring your time slip here. The gap between them tells you exactly which part of the run is costing you.
- [Which final-drive ratio do I need?](https://tuning4u.info/diagnose/which-final-drive-ratio-do-i-need/): A higher-number final drive multiplies torque and RPM; a lower-number one stretches every gear. Start with the behaviour you want to change and end with the calculation that proves the direction.

## Policies
- [Accessibility](https://tuning4u.info/accessibility/): WCAG 2.2 AA statement — what is supported, how it is tested, known gaps.
- [Privacy & Cookies](https://tuning4u.info/privacy/)