Well you learn something new every day. It makes sense that there would be a formula for optimum gearing I just never knew that one existed.

My tires are 215/75 R15's and a quick measurement shows them to be 27" diameter.



Pete

That overall ratio should be 9 to 12  Example: 3.00 1st gear X 3.50 rear=10.50

With tall ie 29" tires i'd shoot for 12.

Goodluck,

Ron.

I would do the math, because we really don't know what your rear tires are. If you can shoot for an over all ratio in low of between 6.5 and roughly 8.0 I think you'll be in the ball park. Racing (drag ) would want more.    

Frank/Rebop

Bristol, In ( by Elkhart) 

I was thinking about it on the way to work today. Again, I was jumbling cars and trucks. Cars tend to use smaller diameter tires so taller ratios will work better with them.


Lawrenceville, GA

I second Petes opinion about 1st gear being useless w/a 4+ rear gear. Your not thru the intersection and the engine is screaming. I dropped mine back down to 3.55 and its much more streetable.

Dan      Kingman Az.      86409

First gear is nearly useless with the 4.09's but the car is to heavy to start out in 2nd. Having done this 5 speed conversion in other cars I have learned that a 3.30 - 3.50 rear gear makes better use of the gearing in the tranny and gives you longer legs on top.



Pete

Then do you really need a taller gear? I'll be running a 4.something with my overdrive. It's 3.70 now.


Lawrenceville, GA

Thanks to both of you for the reply. The 3.15's may be a little to low numerically. The car has been converted from the original 3 speed od to a T-5 5 speed which would make those 3.15's about a 2.22 in 5th.



Pete

Pete  I sent you a PM about the gears you need.  Carl

The merc is a different animal. I do have a good 3.15 gear set up for a 56 mercury which is a spare I can sell. The gear selection is small for the mercury unlike a 9" which has a lot to choose from. PH: 828-298-2197 if interested.

-Gary Burnette-