so i just broke some teeth off my rear axle gears. im runnin 40" tires with factory gear ratio. so should i change the ratio? if so to what? and wouldnt i have to get the front axle changed too? i obviously dont tow or anything i just want power.

 

with that big of tires you probably need 410 or lower, and yes if its a 4dig your guna have to change gears in the front to

 

i'd leave it alone. diesels have enough torque that the oversize tires dont bother them too bad

 

ya but it needs new gears cus i just shredded the old ones. so if im doing it anyway then why not change the ratio up? and my front driveline is broken so i never drive with it in. so then if i never use 4wd then couldnt i just change the rear gears then do the front when i get my driveline fixed?

 

yeah. what gears r in your truck.

 

stock 3.54

 

if you drive alot of freeway id go with 4.10's. if you only driver city and never do highway id go with like a 4.56. i got 4.10's on my 35's it still gets up and goes but on the freeway at 65mph im only at 1700 rpm

 

keep you 3.54 like haymafia stated the diesel has plenty of torque to push the tires and pull a load, with diesel going up do the 3.54's again

 

With 40's and 3.54's you do not have a very good mix at all.
Yes,the torque of the Cummins will move the big tires but using torque instead of HP can and will break parts,as you have already found out.I'd say 4.56's with 40's would give you a nice highway driver but for all out brute force power displays you going to have to step up to at least 5.38's.

Below os a link to a chart I ALWAYS use when looking at new tires for my ride and what to consider with diameter changes......Hope this helps you out with your decision.....Andy

http://www.4wheelparts.com/aux_incl/gear_ratio.html

 

I agree w/Hammer. That big of tire, 4.56 minimum. Even 4.10s will be relatively sluggish.