my 87 f350 4x4 dually has a 429, c6 and 4.10's on the factory 235/85/16 tires...needless to say its winding up tight at 60mph...an overdrive tranny would be wonderful but stand alone computers for the e40d's plus the cost of the transmission or a zf 5 swap would be more expensive than i really want to get in to...so the only other options are to regear which im sure im looking at $1500 plus or to keep the 4.10's and go up to a bigger tire size which im changing tires anyway to mud grips....my goal is to be able to cruise down the road at 70mph and not be turning crazy rpm's....what do you guys think? going with bigger tires would probably be cheaper and id have to buy a spacer for the rear duals...so what tire size could i go up to that would make the 4.10's cruise like having 3.55's?

 

70 mph, 4.10 gears, 1:1 high, 32" tire = 3014 rpms
70 mph, 3.55 gears, 1:1 high, 32" tire = 2610 rpms
70 mph, 4.10 gears, 1:1 high, 37" tire = 2606 rpms

37s? My guess is the extra weight would cancel out most of the savings.

I used the calculators here:

Novak Conversions - Gearing & Gearing Math for Jeeps

 

wow 37's huh? i could probably regear and get new factory sized mud grip tires for less than the cost of the 37's lol....ya know i thought going to 3.55's would bring my rpm's more than that...maybe i should go higher? or numerically lower...maybe a 331? i rarely pull anything and this truck is just a toy and something to get to work in...do you think 3.55's would be enough or should i go even higher?

 

ive found that baumann makes a stand alone computer for the e4od and ive just got off the phone with them and i can do this as cheap as a regear...a local reputable transmission shop will sell me a rebuilt e4od for around
$900 so im looking at roughly $1600 to $1700 for a regear or e4od swap.....next question is drive line lengths...if i regear i dont have to mess with that and if i go e4od im sure i will