Nice tidbit from the boys next door
How To Select The Right Rear End Gears
#1
Shift Point x Tire Height
336 x Trap Speed
*Multiply your shift point by your tire height
*Multiply your trap speed by 336
*Divide top number by bottom number
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#2
5500 x 30 = 165,000
336 x 130 = 43,680
*In this example, your shift point is 5500
*Your tires are 30 inches
*Your trap speed is 130 mph
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#3
165,000
43,680
Result is 3.78
*Multipling 5500 RPM by 30 inches gives you 165,000
*Multipling 130 MPH by 336 gives you 43,680
*Dividing 165,000 by 43,680 gives you 3.78
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#4
Gears available for 9.75"/8.8" rear:
3.08
3.27
3.55
3.73
4.10
4.30
4.56
*From here, you simply select the closest gear available to 3.78 = 3.73