Setup Calculators

Three numbers, worked out in the pits.

Gearing against tire diameter, weight transfer off the line, and what a boost target does to your fuel requirement. Everything is calculated in the browser as you type — nothing is logged and nothing leaves the phone.

A.1 · Gear ratio vs tire diameter

Tire

Enter the rolling diameter, or build it from the sidewall markings.

Tire diameter (in)

Section width (mm)

Aspect ratio (%)

Rim diameter (in)

From the sidewall--

Rollout, one revolution--

Driveline

Leave unused gears blank.

Rear-end ratio

1st

2nd

3rd

4th

5th

6th

Report rpm at this speed (mph)

Report speed at this rpm

Gear	Ratio	Effective	RPM	MPH

What-if: two setups side by side

Setup A uses the tire and rear-end above. Setup B is whatever you are thinking about.

A · gear ratio

B · gear ratio

B · rear-end ratio

B · tire diameter (in)

	Setup A	Setup B	Change

A.2 · Weight transfer estimator

Vehicle

Total weight (lb)

Wheelbase (in)

CG height (in) Estimate — roughly crank-centreline height on a door car.

Static rear (%)

Launch

Use a measured g figure if you have one, or let a 60-ft time stand in for it.

60-ft time (s)

Acceleration used--
Weight transferred to the rear--
Static front / rear--
Under launch, front--
Under launch, rear--

Estimate only. This is rigid-body math — weight × g × CG height ÷ wheelbase. It ignores suspension geometry, instant centre, tire growth, chassis flex and aero, all of which matter on a real launch. A 60-ft time gives an average acceleration over the first sixty feet, assuming constant acceleration from a standstill; the peak off the line is higher. Use this to compare changes, never to certify anything.

A.3 · Boost vs fuel demand

Engine

Displacement (ci)

Boost target (psi)

Peak-power rpm

Volumetric efficiency (%)

Target AFR at full load

Injectors

Injector size (lb/hr) --

How many

Max duty cycle (%)

Pressure ratio--
Air flow--
Air mass--
Fuel flow required--
Per injector at target duty--
Duty cycle with yours--
Spare capacity--
Rough crank hp at 0.55 BSFC--

Sizing aid only, gasoline assumed. It treats the charge as cooled back to roughly ambient and ignores intake air temperature, fuel pressure at the rail, pump and line capacity, and injector non-linearity at short pulse widths. It is a starting point for choosing injectors, not a tune.