How 2006 F-150 4.10 Axles Affect Gas Mileage

The gear ratio in the 2006 Ford F-150 determines how many driveshaft revolutions are needed to make the wheels turn one revolution. The F-150 was available with several different gear ratios. Rear axle gear ratio has a direct effect on acceleration, pulling power and gas mileage. There are advantages and disadvantages to different ratios. It really depends on what you use your F-150 for.

4.10-to-1

The 4.10-to-1 gear ratio in the F-150 means that it takes 4.1 revolutions of the driveshaft to make the rear wheels turn one revolution. The number of teeth on the ring and pinion gear set determines the gear ratio. A Ford 4.10-to-1 gear set has 41 teeth on the ring gear and 10 teeth on the pinion gear. Dividing the number of teeth on the ring gear by the teeth on the pinion gear, gives the ratio. This would be expressed as 41 / 10 = 4.10.

Other Ratios

Other common ratios for the F-150 are 3.55-to-1 and 3.73-to-1. With the 3.55-to-1 gear ratio, the driveshaft turns 3.55 times for every one revolution of the wheel a difference of 0.56, or about one half of a revolution. It may not sound like much but when the driveshaft is turning at 2,000 rpm, it adds up.

Overdrive

The four-speed automatic and five-speed manual transmissions on the F-150 have an overdrive gear. This means that in fourth or fifth gear, the driveshaft is turning faster than the engine. For the automatic transmission, third gear has a 1-to-1 engine to transmission output shaft and driveshaft gear ratio. Fourth gear is 0.70-to-1, meaning the engine only turns 0.70 revolutions for each driveshaft revolution. Overdrive lowers engine rpm in top gear for fuel economy. It effectively lowers the axle's gear ratio and can make running 4.10-to-1 gears acceptable in terms of gas mileage.

Math Class

Using the formula (mph x gear ratio x 336) / tire diameter = rpm, you can calculate and compare differences between rear axle gear ratios. This formula is written for a 1-to-1 transmission gear. To calculate for overdrive or one of the lower gears, multiply the answer by the transmission gear ratio. To see the difference between 4.10-to-1 and 3.55-to-1 gears, you need to know the diameter of your tires. The original equipment 235/70R17 tire has a diameter of 30 inches. A common highway speed is 65 mph. With these numbers you get (65 x 4.10 x 336) / 30 = 2,985 rpm, which is a bit high. With the transmission in overdrive and a 0.70 gear ratio, 2,985 becomes 2,985 x 0.70 = 2,090. The values for 3.55-to-1 gears would be 2,585 and 1,809, respectively.

Power and Gas Mileage

A 4.10-to-1 gear ratio will provide better acceleration and pulling power than the 3.55- or 3.73-to-1 ratio, because more driveshaft revolutions and therefore more engine revolutions are being used to turn the wheels at any given time. That is the advantage. The disadvantage is that more revolutions means more fuel burned and a lower speed in mph at the same rpm. If you carry a lot of weight or pull a trailer, 4.10-to-1 gears would probably be the better choice because it will be easier to get the F-150 moving. For the best gas mileage 3.55-to-1 gears would fit the bill.