Gear Ratio Calculators!

A long while ago I created a gear ratio calculator for my Evo 8 to help figure out how I wanted to gear the car as finding a good compromise can be a challenge when you drive both large and small tracks; getting the spacing proper so you're not caught between gears too often, making sure you have enough speed in each gear, and keeping the engine from fall out of its powerband after a shift are all things that need to be considered and making sense of these numbers without a visual aid can be very tough. The engine RPM redline, tire size and final drive are all variables as well so I wanted something that could take all of these inputs in and spit out a fairly easy to interpret graph and that's what this is.

Using The Calculator

To use it all you need to do is fill in the cells highlighted in blue with your respective information. The X axis on the graph is vehicle speed and the Y axis is engine RPM. Changing the Engine Speed cell will only update the numbers in the table above the graph as it's doesn't impact the graph calculations. Tire diameter is calculated (hence why it's not blue) from the three inputs below for width, aspect ratio and wheel diameter. Final drive is the final drive you're using for your transmission. Engine Redline is the redline for your car, changing this will move the horizontal red line on the graph up or down and the gear lines will adjust accordingly. For the table numbers to match the graph Engine Speed and Engine Redline need to be the same value. For the 1-6 gear cells you just need to input the name of the gear you're using as it is written below the graph. The graph will automatically update as well as the table above the graph for those that want easily digestible numbers to look at.

Note: For the Evo 8/9 calculator (and maybe others in the future) there are sequential transmission options, they are highlighted in yellow and many of them have multiple gear ratio options so be sure to use the drop down options in each corresponding cell to select your ratios. Sequentials also only use the final drives they're offered with so check the note for each one to see what options it has.

Interpreting Results

There are 6-7 lines total. The horizontal red line represents your engine redline as mentioned earlier, and the other 5-6 lines are for each gear in chronological order. The steeper the slope of the line, the shorter the ratio is and every line stops when engine redline is achieved, where the next line starts is the RPM your engine will drop to if you were to shift at redline.

Moving to the graph, column G (Speed) represents the vehicle speed your car will be going for the value you have entered in the Engine Speed cell, if this value matches the value for Engine Redline this is your speed at redline for each gear. Column H (MPH increase over last) is how much MPH vehicle speed each gear has compared to the one before it. Column I (increase %) is column H shown as a percentage, so how much speed was gained as a percent of the previous gear.