What Gears Should I Choose?

A Common topic for discussion on most of the Mustang performance related newsgroups and message boards, here are my thoughts on the matter.

First of all a brief explanation of gears in layman's terms. When people talk about changing their gears, they are not referring to the transmission, but the rear axle gear ratio. By going to a numerically higher gear (for example, you replace the factory 2.73's with 3.73's) you will have a lower overall gear ratio, and the car will go through the gears quicker. The main advantage is that you get into the powerband a lot quicker than with the higher gear ratio, and you will feel a real seat of the pants pull from your 5.0 liter Mustang. The main disadvantage is higher RPM's at highway speeds.

Mustangs come from the factory with either a 2.73 or a 3.08 (the performance option) gear ratio. To optimize performance a gear ratio of 3.55, 3.73 or 4.10 is desirable. The first consideration is how you drive the car. If you spend a lot of time on the highway, keep in mind that if you choose the "low" gear ratio, you will be running about 2000 RPM at 60 MPH. The "high" gear option will result in about 1900 RPM at 60 MPH. Of course if you drive at higher speeds, 80 MPH or so, the high gear will rev the engine a little higher than I like to run it for extended periods of time. Most people report about the same or even a little better gas mileage after making the change.

If you have an AOD transmission (Automatic) you will want 4.10 gears if you want the "low" gear option as described above, or 3.73 gears for the "high" gear option. If you have a T-5 Transmission (5 Speed Manual), you will want 3.73 gears for the "low" option and 3.55 for the "high" gear option. The difference has to do mainly with the final gear ratio of the highest gear in the transmission.

In my opinion, this is the single most cost effective modification you can make on your Mustang. You can get a good Motorsport ring & pinion set for about $200, and a good speed shop should be able to perform the labor for $150-$250 depending on where you live. Do it...you won't be disappointed with the results

If you are interested I wrote a little spreadsheet to calculate the effects of a gear ratio change. You are more than welcome to use it.

Craig Kiddoo