speedometer correction confusion

[smoke81]

gotta 94 ranger 2.3/auto with stock axles far as i know.i changed tire size from 225/70/14 to 235/75/15. from what i can tell speedo is 6-7mph slow.took the gear outta trans tail and counted 18 teeth(recounted many times)ford dealer told me the stock gear is 21tooth and by his calculations i need a 19 tooth(which i thought WAS stock)this makes no sense to me.parts guy gave up & gave me the "its special order/no returns?(and i never heard this)"u gotta buy 2 cuz there's 2 to a bag)by my calculations i need a 16tooth but not sure.i get paid for mileage so every day gone by costs a little more. im even tryin' to nudge it up alittle.

 

[trail B2]

Sounds like your on course to me, smaller gear faster speed reading you just let the parts man derail your program. you need to figure percentage wise if its one tooth or two.He knows what it's supposed to be but you know what it is.

 

[Downey]

pick a higher speed to check your it at. then recalculate