Help and contact for the GearRatio app.

Contact

Questions, bug reports, or feedback — email shop@skunkriverresto.com and we’ll get back to you.

Frequently Asked Questions

How do I measure my rear axle ratio?

Enter your tire size, then drive in a steady gear and hold your tachometer on a round number — say 3,000 RPM. Tap Capture at that instant and GearRatio records your GPS speed, pairing it with the RPM and tire size to compute the ratio. Take a few readings and the app averages them. For the truest axle ratio, run the test in your direct 1:1 gear (top gear on a non-overdrive 4-speed) and leave the transmission ratio at 1.000; to test in another gear, enter that gear’s ratio.

What tire size should I enter?

You can enter a printed metric size (for example 205/55R16), an overall diameter in inches, or — most accurate — a measured roll-out: mark the tire and the ground, roll the car forward exactly one revolution, and measure the distance travelled. The app shows the diameter and circumference it derives.

What is the DynoJet mode?

Switch to DynoJet mode and GearRatio computes the “gear ratio” value you enter in DynoJet’s Power Core software so the dyno can derive engine RPM from road speed. It is referenced to the DynoJet 224xLC’s fixed 24-inch drum, so it needs no tire size and no transmission ratio — just run the test in the same gear you’ll use for the dyno pull, hold the target RPM, and tap Capture. This value is not the same as your axle ratio, and only the 224xLC (24-inch drum) is supported.

My GPS speed seems off.

GPS speed needs a clear view of the sky and a few seconds to settle. The status row shows whether the app has a fix — if it says “Acquiring GPS,” give it a moment or move out from under heavy tree cover or a steel roof.

Does the app work offline?

Yes. GearRatio makes no network requests of any kind. GPS works without a cellular signal.

How do I switch between MPH and KM/H?

Open Setup and choose your speed unit. It applies to the live readout and the recorded readings.

Is it safe to use while driving?

Please don’t operate the app while driving. Have a passenger hold the phone and tap Capture, or use cruise control to hold a steady speed and mount the phone where you can glance at it the way you would a dash gauge.