Automatic Car Transmission

So I’m calling for anyone who knows a little bit about vehicle transmissions…

I’m currently using vector forces for my vehicle but I want to simulate an automatic transmission to my chassis.

How will I go about doing this?

What I’m currently doing is calculating the engine RPM through the wheel RPM as so:

local wheelRPM = 60 * (zVelocity/(2 * math.pi * wheelRadius))
local engineRPM = wheelRPM * gearRatio

if engineRPM < 1000 then
engineRPM = 1000
end

Then I would look up the engineTorque on my torque graph:

Keep in mind that the x axis is x1000 RPM.

The issue I’m having is that car never passes 1000 RPM. It reaches constant velocity before. Keep in mind that I do have drag and friction simulated on the cars. I’m not even sure which RPM I should be up shifting gears up at.

How would I do about solving this issue?