regear?

loosvelt · **Posted:** Thu Oct 25, 2007 10:35 pm

Should you regear if you put 30 or 31 inch tires on the KJ? I'm sure it would help the low end, but how does it affect the highway speeds

CATCRD · **Posted:** Thu Oct 25, 2007 10:41 pm

Not worth the expense for such a small change in tire diameter.

kj in a tight spot · **Posted:** Fri Oct 26, 2007 4:29 pm

CATCRD wrote:

Not worth the expense for such a small change in tire diameter.

x2 big ol waste...if you plan on gettin yourself a lift and 31"s and do some good crawlin out there, then go ahead and step youself up to 4.10s...

tjkj2002 · **Posted:** Fri Oct 26, 2007 4:51 pm

I would have to disagree,with the 3.7's torque curve and throwing on some heavy 31"+ MT's is not to friendly on the tranny and gas bill.Adding heavy armor(skids,bumbers,and such) will make it even worse,switching to 4.10's will get back some of the lost performence and MPG's.I really need 4.56's for my KJ with being 1500lbs over stock and running 32's,but 4.10's has helped a great deal over 3.73's.

Quote:

CATCRD

Not worth the expense for such a small change in tire diameter.

Going from a stock 29" tire to a 31" tire is a big jump.Just remember that increasing your tires size without regearing also increases your overall gear ratio.

Say you have the OEM 235/70R16's and 3.73 gears,switched to 31" tires your rear end gear ratio is now acting like 3.49:1 gears.If you aslo switched to 4.10 at the same time then the rear gears act like 3.84:1 gears.

kj in a tight spot · **Posted:** Fri Oct 26, 2007 5:00 pm

tjkj2002 wrote:

I would have to disagree

With what? If he stays stock whats the point?? If he jumps from a 29" to a 30" there aint a need...hell even a 31" mudder would be fine if he just wanted to chop stuff up and leave them on there without a lift...I do agree that 4.10s are necessary once the weight gets added, like I stated before in a previous post, with the lift and armor and all the goodies, but for the price of buyin and installin gears for such a small jump from a 29" to a 30" or 31" it aint worth it IMO...

nyrican52884 · **Posted:** Fri Nov 09, 2007 8:25 pm

Quote:

Going from a stock 29" tire to a 31" tire is a big jump.Just remember that increasing your tires size without regearing also increases your overall gear ratio.

Say you have the OEM 235/70R16's and 3.73 gears,switched to 31" tires your rear end gear ratio is now acting like 3.49:1 gears.If you aslo switched to 4.10 at the same time then the rear gears act like 3.84:1 gears.

How do you figure that out? I went to http://www.rocky-road.com/calculator.html and used the first calculator for gear ratio and I put the old tire size (28.69") and the new (30.47) and the gear ratio (3.73) but it gives me 3.96 for the new gear ratio. Isn't it supposed to go down?? Is it user error?

But when I change the old and new tire size I get the same numbers as tjkj2002

tommudd · **Posted:** Fri Nov 09, 2007 9:20 pm

user error I would say cause its just the way tjkj says. If those that say it doesnt make a diffrence could do a before and after just step out of one vehicle with say a 31 inch tire/3.73s and jump into one with same size tires but with 4.10s thay would see a huge difference if equipped with full armor etc. Doesnt seem like much but when you start getting fatter and bigger tires it does helps. Just like riding your old 10 speed :wink:

nyrican52884 · **Posted:** Sat Nov 10, 2007 12:42 am

So with 32" tires and 4.10 gears your almost back to stock gearing Would this make the speedometer back to normal? I think its worth it, because after just the tires and a lift you lose alot of power

tjkj2002 · **Posted:** Sat Nov 10, 2007 1:00 am

Here is a nice little chart to help with tire/gear ratio's,only good for 3rd gear in our KJ's(1:1 ratio) since it does not take into acount for overdrive(should go to the more power side to maintain OD).

http://www.4lo.com/calc/geartable.htm

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

I just went to 245/75R16 Silent Armors from 245/65R17 Destination ATs. The 4.10 gears seem about perfect with the 30.5" diameter tires I have now. Was geared a little low with the 29.5" diameter tires, but would really get off the line. To use the chart and figure out your rpm with overdrive, just multiply it by 0.69 if you have the 42rle, and 0.75 if you have the 45rfe. If you have the 545rfe, if it's in the first overdrive multiply by 0.75, and if in the second overdrive multiply by 0.67. In my opinion, if you go with a heavier tire and wheel combo, you'll want to move it a little towards the power side.

nyrican52884 · **Posted:** Sat Nov 10, 2007 9:53 pm

So how would I do this? I looked in the tech section and couldn't find a write up about doing this. It seems that if you are going to do a locker some don't require to measure and are almost plug and play, but what about new gears? Also would it be worth it just to install a limited slip while I'm in there. I don't think I would want to do a locker because I do all street driving.

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

Changing gears is something usually best left to a good transmission shop. I think there are 1 or 2 people here that have done it themselves, but it takes some specialized tools and is not something easy to get right.

regear?

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