Ford Mustang Forum - View Single Post - 3.73 or 4.10 for auto transmission
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post #2 of (permalink) Old 01-21-2014
SHELBY GT 350 Member
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JBert's Avatar
Joined: Jan 2011
Location: Central Massachusetts
Posts: 9,165
For highway driving the taller gears (3.73) will be "better" meaning keep the RPM's down for less noise, smoother drive, better MPG. Since you have an automatic, it will downshift almost instantly when you want to accelerate so that is not an issue.

You can do the math yourself on the RPM's, if you know what rear gear ratio you have now.

new gear ratio / old gear ratio X RPM at speed = new RPM at speed

For example if your old gears are 3.31 and you are turning 2000 RPM at 70 MPH, and you want to look at 4.10 new gears:

4.10/3.31 = 1.24 X 2,000 RPM = 2,477 RPM at 70 mph with the 4.10's

Or you can use one of the on line calculators, but you have to know your tire size and transmission gear ratio

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