I have an old Halibrand rear in a vintage sprint car. The gears I have are both the same diameter. Anything I've ever worked with before always had a small gear and a larger one, and knowing the ring and pinion with a gear chart, it was easy to determine the ratio. I've determined this ring and pinion to be a 4:11. One of the gears has 28 teeth and the other 27 teeth. Looking at a chart, I'm assuming with the 28 on top is gives me a 4:26 and reversing the two gives me a 3:96. By both being the same diameter and only going by the number of teeth, it's got me wondering. Am I correct???

You only use the number of teeth to figure your final gear ratio. The outside diamater of the gears in a since is really not important( yes the more number of teeth the O.D. has to get larger)
Hope this helps.
Bobby Layne

I'd say you are spot on, with no way to adjust the centerline spacing on the 2 shafts, some very interesting tooth designs come into play, there are also "combo gears" that with one large gear, and 2 smaller gears, but with a different tooth count, but cut so they mesh, you can have 2 ratio's, and only 3 gears, the smaller gear for instance, will be some times be marked 13/14 or something like that, and it will mesh correctly with a larger one, giving 2 ratios. Bob

Dave
The formula straight off of Winters gear chart
# teeth top gear divided by # teeth bottom gear X ring & pinion ratio = final drive
Jeff

Thanks guys, looks as if my assumptions were correct.

It justs amazes me how smart people like Ted Halibrand, Jim Calvert(C.A.E.) Taylor Pappy Weld and my dad Elmer Layne were. They figured out all of the different racing parts we have today without computers or CNC machines. TQ29m and DAD can tell all of you there isn't any other things than electronics that is new it's all just warmed over.
Bobby Layne