I've got a 91 pickup and I think the gears have been changed from original and I'm not sure what the new gear ratio is

How do I tell what gearing is my truck without taking it out and counting the teeth?
I was thinking I could jack up one wheel, turn it 360degrees by hand and count how many degrees the driveshaft turns or something.

Is there some kind of chart that will give me a rough idea on the gear ratio based on this? ie 360deg on the driveshaft = 45deg on the wheel = x.xx gearing or something?

 

Yes there is. Look HERE .

 

Thanks!