[Jeffy45]

What's the deal with Yukon gears 3.92 for the front 3.90 for the rear?

 

[Elwenil]

Same deal as Dodge selling trucks with 3.21 and 3.23 gears or 3.54 and 3.55 gears.  It makes no difference.

 

[Jeffy45]

So i would have 3.21 in the front and 3.23 in the rear stock? My under hood tag just says 3.2

 

[dodge82273]

the 3rd digit there is usually a tad faster speed in the front .

 

[Jeffy45]

Ok, is 3000 rpm at 65mph for an hour and a half while towing about 2000lbs ,on the highway ok for these motors.

 

[Jeffy45]

I believe I'm going to go with 3.90 gears with a true 31" Tire if I can find it. I think I'm making the right decision, this vehicle doesn't see any off-road only Street driven and highways towing a small boat and trailer roughly 2000 pounds + 700 pounds of gear , including me and my fishing buddy . am I making the right decision here??

 

[dodge82273]

321's won't do it ? 354/5 is what dodge uses in the later 1/2 tons , and that is with over drive , Personally , 3 grand is more than I like to run for hours on the highway . Newer 3/4 tons with 4.10's have over drive , which is what mine is in when towing a ton ( 2klbs ) on the highway .  6 out of 10 fellas will tell ya its fine , 4 of us will say why wear it out faster ? (mostly older guys I'm bettin )

 

[Jeffy45]

Well shit I already ordered the gears and a whole bunch of other stuff got a really good deal on them. I'll punch a true 32in Tire into the calculator and see what I come up with. I'm roughly at 2700 RPMs right now with the 3.21 s at 65 miles per hour with 235 70 15 when i get to a pretty good grade it dogs down and I have to kick it down.  should I be measuring my RPMs with my foot on the throttle or off at 65 miles per hour??🤔

 

[Elwenil]

32s with 3.90s is about 2,800 RPM which is pretty good.  There is nothing wrong with running an engine at higher RPMs, it can use more fuel if you have to keep your foot in it, but with the better mechanical advantage of the lower axle gears you mileage may actually improve a slight amount.  I don't think you would notice any extra wear.  Years ago most trucks had 4.10s, or 3.55s at the most and they ran 70 MPH as well without causing any real harm.  Now if this were a commuter vehicle, I wouldn't necessarily want to put 25k miles a year on it like that, but then I would probably be buying a little shitbox car for mileage.  Either way, you should be fine with 3.90s and it will probably feel like you added a cam and 4BBL to it.

 

[Jeffy45]

yeah I think I'll be fine, I punch some more info into the Grimm Jeepers calculator and with a true 31 it should give me 2903 RPMs at 65 with the 3.90s I just went out and measured my tires they appear to be exactly 27 in, with the 3.21 gears that comes out to 2743rpm at 65 miles per hour pretty much right where I'm at right now by my tach. if I punch in 27.5 in it gives me 2693 RPM so it's fairly accurate. once she's going on the flats at 65 it's effortless to keep speed and I can actually get the speedometer needle down to where it says Drive without the boat on the back of course but once she gets to the hills she bogs down. I figured I'd put the money into the old girl because a deal fell through on a 75 Plymouth Scamp that I was trying to buy for 5 years, it's a shame it was an high option vehicle and the earth started to take it back sitting in the dirt, funny the unibody was still perfect. enough of my rambling I appreciate you guys it's just a big chunk of change for me and I didn't want to make a bad decision .it's done now though they're on the way.I have to punch myself in the face every now and then and tell myself it's not a fucking race car .😎

 

[abranz]

Of all the bs I’ve done to my dodge re-gearing to 4.10’s was the best for my situation.  It’s primarily used on county or dirt roads and plows snow all winter.  Sometimes I’ll take it down the freeway @65 and it doesn’t seem to mind it a bit.

 

[Jeffy45]

so I guess getting a 32 inch tire will bring me closer to an actual 31 probably more like 30 and a half. I know all manufacturers are different but usually they're 2 inch smaller than stated on the sidewall🤔??🤔

 

[Elwenil]

It varies a lot depending on the tire and the rim the tire is mounted on.  I remember my old BFG 32s were a little over 32" when new, but not by much.  Almost every other tire and size I have seen tends to be slightly under the stated size except for Interco/Super Swampers which tend ot be an inch or more less than the stated size.  Most of the "good" tire manufacturers will list the actual diameter on their website if you look up the specific tire specs.

 

[Jeffy45]

Yeah thanks E. I think I'm going to go with a Cooper Discoverer AT3 the 32 x11.50 x15 states its 31.4" on a 9 inch rim. put it on an 8-inch rim it'll probably be 32" subtract 1 inch for it being on the vehicle and the weight of the vehicle we're back to 31. Although the tires I have on now measured 28 1/2 off the vehicle, on the vehicle they measure exactly 27.I like deep dished rims with a crazy negative offset. Bare in mind  my suspension is new  and stock height maybe a half inch to an inch higher than stock but my Springs are extra capacity the suspension doesn't move at all it's very stiff. Can I fit 10 inch wide rims on?

 

[Jeffy45]

I look at some of the Jeep sites a lot these guys measure  the shit out of everything😎 I do have a good friend that's been in the tire business for many many years but I usually end up being down there hours on end because he's always extremely busy

 

[dodge82273]

it's an auto , not a Swiss watch , try not to get your self confuzed by too many numbers . Install your new gears , drive it , see how it does , adjust tire diameter to change Final Gear Ratio to suit you needs .
when you select rims , realize that real wide ones require fender flairs or sling mud , road spray onto door windows till you can't see outta them , AND throw the steering off , where you needed X to Y  amount of toe in , now that number becomes very critical... because of the change in distance from the steering axis  ( ball joints) 

 

[Jeffy45]

yeah I do tend to overthink things a lot.

 

[dodge82273]

its ok as long as it don't cause you to " freeze up"  and "DO NOTHING "  ,  like some of us....... 

 

[Jeffy45]

man I ain't freezing up it's been the feel of like a 105 degrees, with crazy humidity for the past 4 days. My thermometer in my driveway reads over 130😎 ,obviously it's in the Sun. After the gears wheels and tires it'll be on to next thing.