Boozshey

So I found a calculator for the speedometer difference with a gear swap. Is a 20% difference about right going up to 4.10 with the 05 GT's stock gears? Basically the speedo at 100 i'd really be going 80? Also does it have an effect on the Tach?

Professor Wizard

It has NO effect on the Tach... that is driven off of the ignition and simply displays the RPM of your engine.

However, having different gears, your shift points WILL change.

If you have a tuner - SCT or Preditor, read your book, it will tell you how to reprogram your car so the speedo will display the correct speed when you change tire sizes or gear ratios.

2oo5stang

that's sounds right also, showing 100mph but really going 80mph