SatiricalHen

I would suggest using gps speeds for the calculations. I suggested using the jeepers creepers gear ratio calculator which has worked for me and quite a few of my friends. Most tires aren't true to size and sometimes even with a "corrected" speedo it can be off. Mine was corrected with the speedo gear that charts and websites and other people said worked. It was still slightly off. I would put 4.56 gears in the vehicle for a nice power/fuel mileage balance with 32s. I was trying to suggest an axle upgrade at the same time as gear as to avoid further expenses. It was merely a suggestion. When you stated that a properly built dana 35 was just as strong I provided a comparison between the sizes of the components and the fact that they are indeed not capable of being built the same without some how modifying the axle to fit an 8.25" ring gear.

riskywhiskey

I did state within acceptable parameters my speedo is off by less then a mph If I was to give an estimate I would state probably .2-.6mph off and when installed the 32s measured in at 32inches from tread peak to tread peak sidewall before tread came in at 31 3/4 inches

SatiricalHen

At what speed are you getting .2-.6 off? Because it's is a percentage not a set amount. Since I never re corrected it when I went from 31s to 35s I know that when I'm doing 50 it's really more like 60 and when I'm doing 60 it's more like 72 according to gps and speedometer readings.

Dumajones

Outlaw showed me this way to do the math for gears.

its OTD / NTD x CGR = EGR
OTD: Old Tire Diameter (stock size in inches)
NTD: New Tire Diameter (in inches)
CGR: Current Gear Ratio (what gears you have now)
EGR: Effective Gear Ratio (again, what your vehicle acts like it has)

Now, majority of our rigs came with roughly a 28" tire, this is the OTD.
A majority of Automatics have 3.55's for gears. This is our CGR.
Now let's say you want to add those 31" tires, this will be your NTD.

Now the fun part. 28 / 31 x 3.55 = 3.20:1
3.20:1 is what you vehicle acts like it has now that larger tires have been added.

"But what gears should I regear to?..."

Simple, start plugging in available gear ratios for your axle into the CGR slot until the EGR number comes as close to the stock ratio as possible. (3.55:1 for Automatic & 3.07 for Standard. Yes, the numbers won't be exact as stock but as close as possible)

By doing this, your vehicles powerband will be as close to factory as possible causing less strain on your engine and transmission. Basically, your vehicle will think and act like it still has stock tires even with the larger tires.


Here is a vid I did,,with my 4.56 and 32" HWY speeds. Im now 35" tires.. The jeep is more back to stock with 35"
With 4.56 32" it was fine and doable.

riskywhiskey

Everyone is making so much harder then it has to be I'm not worried about the 30/35 danas as it's a pavement princess I'm not looking for math because though the math may be close every rig is different depending on wear and tear and usage I'm not talking about 31s or 33s or 35s I'm looking for a friggin average graph of what people got with 373 and 410 gears with 32s I stay at 32s because they are stamped 32s and are 31 3/4 inches which makes them not a 31 I feel like I'm conversing with the squirrel from Hoodwinked y'all talk a mile a minute only one person understands what your saying and you not even on the topic at hand which is 373 or 410 with 32s and average mpg that your getting

00t444e

Overdrive ratio on the 42RE is .69 not .96.

riskywhiskey

i pulled a dyslexic moment i cant remember if i was tired or getting around for work but ive decided that 3:73.1 is what im going with mostly because i dont need something as aggressive as 4:10:1 in a street vehicle that doesnt require the torque that i would need in an offroad vehicle i know its a brick and even if i get 2-3 mpg more out of it then fine this is my DD that goes on a 794 mile highway trip once a month i see people saying that with 4:10 gears it down shifts alot going up hills but with 3:55 gears and 32s mine doesnt kick out of overdrive going up hills it drops down into 2nd and tachs 2600-3000 rpms which isnt very fuel efficient so if i can get it to stop doing that id be happy im sticking with the 30/35 axles unless something happens then id find a set of 40/44 danas and throw under it and will be going to my daughter in 4 years when she turns 17 and has her license l because im looking into getting a jku with a 6speed

00t444e

If you have 3.55s now going with 3.73s would be a waste of money, you wouldn't notice much difference. It would be less likely to downshift with 4.10 gears than 3.55s.

SatiricalHen

Also if you're going to get 3.73 you couple probably find another stock axle with 3.73 in the junkyard and swap it in for cheaper than gears and set up.

GreaseMonkey17

mwritter

32s and 4.10s and I'm around 11.5-12mpg.

riskywhiskey

it seems that 4:10 is not something i would be interested in then if im loosing 7-8 mpg i got 23-24 stock before 3.5 inch lift and 32s im trying to get alteast 21-23 out of it again i think its possible with 373s since they bring me closer to stock gearing

00t444e

Your not going to loose 7-8 mpg with 4.10 gears, you mpg numbers are far above average, is that hand calculated or going off of the lie-ometer? With a 3.5" lift and 32s you looking at a realistic 15-16 mpg tops, regardless of gearing, unless you drive 50 mph on flat land or downhill all of the time.

SatiricalHen

If you're going to regear I recommend 4.10 since you are more concerned about mileage than power. If you wanted power I would say 4.56. 3.73 will not make a big difference. Other things like a good tune up, better injectors and fluid changes all around would be a better place to put money. The price of 3.73 vs the money saved in gas is not worth it.

riskywhiskey

i dont know here the hell it went but i posted it the motor just had a head swap with alot done to it harlandsharp roller rockers ( saved them from my 89 before i sold it ) new pushrods and lifters 350 valves shaved to fit bored channels port and polished exhaust ports polished intake ports polished intake swirl bored tb apr race header has new ngk coppers oil was changed 400 miles ago new radiator new fluid clutch fan installed new waterpump new thermostat new o2 sensors new cps/kps/tps/aic/map sensors new 2 1/2 inch exhaust flowmaster 44 muffler flowmaster high performance cat.. its probably getting stroked come next march because i think its got piston slap because with the hs rockers new rods and lifters it still taps until its ran for quite some time and @ 0tt44e i get 17-18 hand calculated highway 14-16 in town im not a lead foot and typically do 55-60 on the highway mostly because the low drone at 65 drives me nuts