Calculation to correct my gears after bigger tires?

BustedPinion · Mar 6, 2011

i forgot what to use to figure out whar gears i need to get to stock gearing or just a slight bit better for towing but dont want too low for freeway. i know 33's are not big but this came stock with 235/75/15 so its a big jump.

91 sub k1500, stock 5.7 and stock drivetrain 3 steed + OD, has 33" tires and currently 3:73 gears

Boonie Buster · Mar 6, 2011

http://www.grimmjeeper.com/gears.html

Using that calculator. I figured, to get you back to stock, you need somewhere between 4.10s and 4.56s.

And 4.30s (if they offer them for your diffs), would almost be perfectly stock.

leadfoot067 · Mar 6, 2011

i just got rid of my 3.73s and 33s for 4.56s and 35s,89 burb with 700r4...and my speedo is now 3mph fast as per my gps...so its pretty close..i think 4.10s and 33s(that actually measure out closer to 32) should put you in the very closee range

BustedPinion · Mar 11, 2011

i was thinking that too shane then realized 235/75/15 is stock tire size, so going up essentially 8 tire sizes (33=315 i think) i doubt jumping one gear size will do it, i was think 4:30 would be good too. tired of no torque pulling my cargo trailer around, and also dont wanna lose freeway MPG any worse then i have to.

anyone selling a 430 axle :haha: :haha:

GaryTJ · Mar 16, 2011

You will never get back to stock fuel economy and remember you have to go beyond factory gearing to get the power back as you are now driving a lifted brick that has to move a lot more air around it to keep speed, and has a lot more rolling resistance. Go 4.56

junkyard jim · Mar 17, 2011

BustedPinion said:
i was thinking that too shane then realized 235/75/15 is stock tire size, so going up essentially 8 tire sizes (33=315 i think) i doubt jumping one gear size will do it, i was think 4:30 would be good too. tired of no torque pulling my cargo trailer around, and also dont wanna lose freeway MPG any worse then i have to.

anyone selling a 430 axle :haha: :haha:

315/75/15 is 33.6

255/85/16 is 33"

235/75/15 is 28.9"

At the speedo reading of 100 mph you will really be doing 114 or 14% higher with 33" tires

Your truck currently feels like you have 3.27 gearing

Like they said, 4.26 is the match, but 4.10 will keep some highway economy
http://4lo.com/calc/geartire.htm