Final gear ratio

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Slantsix64

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So I know originally my 64 dart came with 13 inch rims and 3.23 gear ratio, but now I have a 255 60 15 rear tire 27inches tall I have the first year ball and trunion a833.

my question is what would my final gear ratio be? Engine is a 225 slant six!
 
The only time the transmission changes final ratio is if a newer overdrive, either stick or auto is installed. All older 3/ 4 speed or automatics are 1:1 in high gear, so your only concern is the rear gear and so far as cruise/ per speed RPM, the tire diameter
 
Your 13s "should" have been about 24". Using that on the effective gear ratio calculator, you now have an effective gear ratio of 2.87 with the 24" tires.

But of course, as Del eluded to, that does not change the ring and pinion ratio, only the effective final ratio.
 
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