What rear axle ratio do I have

I think my brain is getting tired. I can't remember how to calculate rear end ratio. If i spin the wheel 10 times, the yoke turns 17 times, if I turn the yoke 10 times, the wheel rotates 5.5 times. Someone help me out.

 

While turning, count the number of drive shaft revolutions required for one revolution of the tire. If the drive shaft turns approximately 3-3/4 times, you have a 3.73 ratio, etc. It may help to use a piece of chalk mark a reference point on both the tire and drive shaft. For increased accuracy it is recommended to rotate the wheels two times and divide the result by two. You may have different gearing front to rear (but the difference is typically very slight) so be sure to check the other axle too.

 

If there is any play in axles, etc may not be truly accurate. Also, rim diameter makes a difference.

 

So that means I have a 170 rear??? Also, how can the diamater change the ratio? the same turns of the yoke for a 13in tire would be the same to rotate a 15in tire, no??? Now I am confused........

 

No,rim diameter does not make a difference.One revolution of the axle will make one revolution of the wheel,whether is 28" od or 48"od.Gear slop will affect it slightly.BBT.

 

Go to search: "REAR END RATIO" 20 pages to really confuse you!

 

Wheel Diameter has nothing to do with your ratio..
tboich does it the way ive been taught

 

just make sure both tires are turned the same direction at the same speed or it may not be correct. You are better off putting a chaulk mark on the tire and with the car on the ground roll it one full turn of the tire and count how many times the driveshaft turns 3 1/2 turns+3:50 gears and so on.

 

If I yurn my tire 1 revolution, with the other blocked, the yoke rotates 1.7 times. I can't have a 1:70 rear can I ???????

 

you likely have an open rear end. when that is the case, with the rear end in the air, the yoke will only turn half as much per wheel revolution. You have a diff. with a ratio of approximately 3.40/1

 

that is the case with 1 wheel blocked also? That is the ratio I was thinking.

 

winner!!:d

 

Open diff.
stop one wheel from turning.
Mark the other wheel and rotate it 2 complete turns exactly while counting the revolutions of your pinion exactly.
The number of turns of the pinion is your gear ratio.
(If you only spin the wheel once you double the turns the pinion made to get the gear ratio.)

 

or to be exact you could count the teeth on the gears. # of teeth on the ring gear (?) divided by the number of teeth on the (pinon gear?)- something like that