My 69 442 has 27" rear tires and a 3.23 rear end.Got excellent cruising and mileage but not much speed out of the hole. Joe P. on a recent thread on tire size stated that the writer's large{30"] tires reduced his rear end ratio by 13%. Is there a formula that one can use to establish a "true" rear end ratio? eg. ...a tire this size reduces your rear from 4.18 to 3.42? I want to keep my rim/tire combo and end up with a 3.42.Thanks....Derek

 

Try this, I'm not sure if it is what you are after but it may help.

http://www.richmondgear.com/streetcalculators.html

https://classicoldsmobile.com/forums...ifference.html