Editing Gear ratio check

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==Rotating the tires method==

With a standard open (non posi traction) differential raise one wheel off of the ground, mark the tire at the 6:00 position, mark the drive shaft. Turn the tire exactly 2 full turns. Count the number of times that the drive shaft turns. 

2 3/4 turns of the drive shaft = 2.73, just past 3 turns = 3.08, 3 1/3 = 3.23 or 3.31, almost 3 1/2 = 3.42, just past 3 1/2 = 3.55, 3 3/4 = 3.73, just past 4 = 4.10 or 4.11.

With a good solid limited slip differential (posi) raise both wheels off of the ground and turn both wheels exactly 1 full turn. Everything else is the same as above. You can also do this with a standard differential as long as both wheels turn exactly 1 full turn.

This is much easier with 2 or 3 people.

==Optional Methods==

If there is a removable cover on the differential you can count the teeth on the ring and pinion gears.

Count the teeth on the pinion and ring gears. Then divide the number of teeth on the pinion into the number of teeth into the ring gear and you have the ratio.


For example:

41 divided by 10 = a 4.10 ratio

40 divided by 13 = 3.08 


'''Another Method'''
An easy way to estimate the final drive is to use a calculator like the last one, "Determine Ratio" http://ctny.audiworld.com/mark/s4/gears/gear_calc.html .

Drive the vehicle at 50 MPH (as an example), note and enter the speed (55 mph), the RPM (what ever you noted), and for the final drive, enter 1. When you hit calculate, the rear gear ratio estimate will come up.

'''Another Method'''
1. Drive the vehicle at a steady speed. Note the RPM.
For example, if the vehicle is driven at 50 mph, and at that speed the tachometer reads 2,000 RPM, record that the engine speed was 2,000 RPM at 50 mph.

2. Measure a drive tire’s diameter in inches.

3. Multiply the RPM by the diameter of the tire.
For example, if the diameter of the tire was 30 inches, 30 multiplied by 2,000 equals 60,000.

4. Multiply the speed at which the vehicle was driven by 336.
In this example, the vehicle was driven at 50 mph. So, 50 is multiplied by 336 to equal 16,800.

Divide the figure produced in Step 3 by the number produced in Step 4 to determine the rear end gear ratio. In this example, 60,000 is divided by 16,800 to equal 3.57. Therefore, the rear end gear ratio is 3.57:1.
60,000 / 16,800= 3.57 or 3.57:1 gear ratio.

'''Determining Transmission Ratio'''
A way you can get a ballpark figure for what the '''transmission ratio''' is - if the car is driveable, and has an accurate tachometer and speedometer- is to drive the car at 1000 RPM (you can use a different RPM and convert it easily) in whatever gear is 1:1. Note the speedometer reading. Put it in whatever gear that you want to know the ratio of and drive at the exact same speed. Note the tach reading. If you move the decimal point three places to the left, that's your low gear ratio. 

Example: If the tach says 3200 RPM, your ratio is 3.2:1.



[[Category:Rearend]]
[[Category:Good articles]]