4.56 or 4.88 gears

[grumpygy]

I must be lucky cause with 31.5 I can hit 80 on flat ground.  Now it does take me a while But I can.  since the Highest speed here in Oregon is 65 Most times I run 70.  Takes a steep hill to slow it down and most times I still do not need to down shift before I reach the top.  And I'm running stock 4.10.

[Jeffy]

I must be lucky cause with 31.5 I can hit 80 on flat ground.  Now it does take me a while But I can.  since the Highest speed here in Oregon is 65 Most times I run 70.  Takes a steep hill to slow it down and most times I still do not need to down shift before I reach the top.  And I'm running stock 4.10.

That's still pretty close to stock tires.   31's are rarely 31" tall.  Most AT's are well under.  Around 30.3-5".  MT's are usualyl 30.5-7".

If there's no wind and it's flat, I can probably get up to 80mph but it would take a long runup.  Once the gears kick in, I can usually hold 80 as long as I don't have to slow down.  Slow down and if there is a heavy wind and or small hills and I can't get back to 80.  Long run down hills is a lot easier but like I said, it gets sketchy with a tall Jeep.

[Torch_Ind]

I must be lucky cause with 31.5 I can hit 80 on flat ground.  Now it does take me a while But I can.  since the Highest speed here in Oregon is 65 Most times I run 70.  Takes a steep hill to slow it down and most times I still do not need to down shift before I reach the top.  And I'm running stock 4.10.

my jeep would be a rocket on 31's with 4.88's

[jfrabat]

my jeep would be a rocket on 31's with 4.88's

When I ran that combo, I could hold 80mph on the FL turnpike no problem (5th gear with cruise control on holdingn the speed steady)

[4banged]

When I ran that combo, I could hold 80mph on the FL turnpike no problem (5th gear with cruise control on holdingn the speed steady)

Wow, you guys don't know good you have it.  My 3rd gear is 1 to 1 then od is .69 ... Might as well shift it into reverse! 

[jfrabat]

Wow, you guys don't know good you have it. 

Well, me being a Jeeper, I could not leave well enough alone, so I went to 33's and lost that..  Of course, i gained more offroadability, but I had to sacrifice this.

[KenF]

I picked a D44 rear out of a rubicon to put my 95 YJ. It has 5.13s .
Need to decide what to do up front. Been told 5.13s an D30 is a bad idea. Pinion way too small (weak).
I plan on running 32" TSL radials.
Should I swap out the front axel and keep the 5.13s.
Our build up the D30 with4.88s and change to D44 to match ?

[neale_rs]

With 32s, 4.88 should work very well.  But if you plan to go to 35's, a front D44 and 5.13s would be a great setup.

[sharpxmen]

If there's no wind and it's flat, I can probably get up to 80mph but it would take a long runup.  Once the gears kick in, I can usually hold 80 as long as I don't have to slow down.  Slow down and if there is a heavy wind and or small hills and I can't get back to 80.  Long run down hills is a lot easier but like I said, it gets sketchy with a tall Jeep.

reading all these posts went for it this morning on the hwy, got up to 85mph and it seemed to be able to go more, had to let off as there was traffic ahead of me and also my tires are way out of balance, once i get over 110kph (65mph) you can really feel them so need to take care of that first. I want 35s but I am really concerned to lose whatever pep she's got now.

EDIT: not sure if there was wind or not but (didn't feel there was) but to be honest a realistic test would be to go both ways and average the result, even a 5 mph wind makes a difference with the wide/tall tires and jeep lifted 5 inches.

[chardrc]

x2. after the 50mm tb swap my jeep  (4:10 31's tbi) can do 80 all day on the freeway if its fairly flat. it does hit a aerodynamic wall at about 88mph though.. but no need to go that fast in a jeep anyways. I wonder if some people aren't factoring in the amount the speedometer is off with bigger tires without changing the speedo gear.

[sharpxmen]

I wonder if some people aren't factoring in the amount the speedometer is off with bigger tires without changing the speedo gear.

some people don't but it's been repeated here lots of times so eventually they figure it out.

did my gas mileage, first 200 km (120 mi) i got 18L/100km which is 13.1mpg, did it again today and got 16.34L/100km or 14.5mpg - I could probably get 15 but i doubt i can get any better than that, possibly in the summer since will get to temp quicker but not sure how much difference that would be (with 4.88 seems a bit better than with 4.10 as i was always in the 13mpg range before swapping the gears)

[jfrabat]

with 4.88 seems a bit better than with 4.10 as i was always in the 13mpg range before swapping the gears

When I swapped from 4.10 to 4.88, I also gained about 1 mpg...  But then I lost about 1.5 when I went from 31's to 33's! 

[neale_rs]

With the jumps between gears in a manual tranny it is hard to say what gearing in the diffs will be better.  For highway use, you might hit a sweet spot dead on with 4.56 diff gears in 4th gear and you might end up with neither 4th nor 5th being as good with 4.88 in the diffs.  To really optimize your setup, you would need to do some real world testing and some math.

[dwtaylorpdx]

I used my GPS for getting the speed...  I never have trusted the speedometer on the jeep ... :)

dave