Gearing for Oversized Tires

[RonT]

Only had my Liberty for a few weeks. Had a 2.5 inch lift kit installed, and put on new wheels & tires. Stock tires were 29", new ones are 31". I haven't noticed any big change in drivability, but I know the math doesn't lie. I understand I can have gearing changed (in the differentials, correct?) to make the drivetrain get back to stock specs. What exactly does that entail? In the meantime (because I'm sure it will cost more money), anything I can do to minimize damage to the current drive train? Drive gentle? What part of the drivetrain is most prone to damage? Issue same/better/worse in 2 or 4 wheel drive? Lot's to learn, thanks for any guidance!

 

[rjkj2005]

Your not going to cause any damage. You'll find yourself staying out of overdrive more in town to keep the Trans from shifting up and down so much. As far as re gearing. Most go to 4.10s. They find the diffs out of a 4 cylinder liberty and swap the whole axle out front and back. Some do some dont. There are some out there running 275/75r16s. That are still running the stock gears (3.73) and are happy with the set up. Gear calculator doesn't even show a 4.10 change until 265/75r16s

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[TwoBobsKJ]

I'm running 265/70's and I regeared to 4.10's and am very happy - basically back to stock ratios.

If you don't regear you should turn your overdrive off when driving around town to keep your transmission from constantly shifting into and out of overdrive. When running 55mph consistently then use the overdrive. Without regearing you'll notice a drop in gas mileage and power.

Regearing to 4.10s is going to run you a nice chunk of money since you'll need an experienced mechanic do it for you - it isn't just a swap - plus the cost of the gears and installation kits. There are specific tools and measurement devices used to set the gears up properly.

The "easier" way is to do as rjkj2005 indicated - find a KJ with a 4 cylinder engine. It's differentials come with 4.10s and you swap out the entire front differential and rear axle. Not a technically difficult job but one you'll want experienced help with if you haven't tackled something like it before.

Bob

 

[tommudd]

Your not going to cause any damage. You'll find yourself staying out of overdrive more in town to keep the Trans from shifting up and down so much. As far as re gearing. Most go to 4.10s. They find the diffs out of a 4 cylinder liberty and swap the whole axle out front and back. Some do some dont. There are some out there running 275/75r16s. That are still running the stock gears (3.73) and are happy with the set up. Gear calculator doesn't even show a 4.10 change until 265/75r16s

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You will cause damage to the transmission and motor due to running larger tires / more weight etc. Transmission works harder , engine doesn't run at a good RPM, keeps lugging down etc
Have heard of only a handful over the last 12 plus years that went bigger tires and stayed stock gearing and say they were happy, well they did when they finally regeared ! :icon_lol:
Gear calculators are not even close to being right for the KJs , but with a 32 inch tall tire it would work out to a 4.25/4.27 or so to be in the right range. So with say 245-75-16s or 265-70-16s ( same height ) 4.10 is perfect for the KJ

I ran for a week with 265-75-16s and 3.73s couldn't even use OD until 70-75 and then still kept shifting back and forth
BEST thing you can do is regear

 

[Jim McClain]

What model years did the 4-bangers come with 4:10 gears? My long-term plan for my 05 KJ is to do a lift and use larger tires, so I should be on the lookout for these used diffs.

 

[tjkj2002]

what model years did the 4-bangers come with 4:10 gears? My long-term plan for my 05 kj is to do a lift and use larger tires, so i should be on the lookout for these used diffs.

'02-'05

 

[TwoBobsKJ]

What model years did the 4-bangers come with 4:10 gears? My long-term plan for my 05 KJ is to do a lift and use larger tires, so I should be on the lookout for these used diffs.

'02-'05

Mine came out of an '05.


Bob

 

[tommudd]

I think Johns was an earlier model and the last one of mine was from an 04

 

[RenKJ]

Do 05s still have the dual brake line and abs? This is the next step for me

 

[tjkj2002]

Do 05s still have the dual brake line and abs? This is the next step for me

Nope the 4 channel ABS did not appear till '06 and the demise of the 2.4 gas engine and 4.10 gears.

 

[u2slow]

In the meantime (because I'm sure it will cost more money), anything I can do to minimize damage to the current drive train? Drive gentle? What part of the drivetrain is most prone to damage? Issue same/better/worse in 2 or 4 wheel drive? Lot's to learn, thanks for any guidance!

Auto or stick? The manual trans won't be hurt by the larger tires.

 

[tommudd]

Auto or stick? The manual trans won't be hurt by the larger tires.

BUT still should regear manual or automatic
Most find that 5 or 6th gear is useless when running larger tires, just like with the automatics, regearing brings the engine back into the right torque range

 

[u2slow]

Funny thing is Mopar 'degeared' the KK manuals to 3.21. KJ's 3.54 was too deep I guess. :shrug:

 

[tommudd]

Funny thing is Mopar 'degeared' the KK manuals to 3.21. KJ's 3.54 was too deep I guess. :shrug:

NO the funny thing is they were just trying to get an extra .0111111 MPG:happy175:
Driven manuals/ automatics etc over the past 40 plus years that have been lifted and with UP TO 44s and no matter which transmission or motor, they all benefited from a regear when larger/ heavier tires and wheels were added.

 

[jharrisliberty]

Nope the 4 channel ABS did not appear till '06 and the demise of the 2.4 gas engine and 4.10 gears.

I was planning to regear at some point and possibly go this route. Would this still be possible with my '06 or at that point would it just make more sense to just take the 4.10 gears out and swap them.

 

[tjkj2002]

Auto or stick? The manual trans won't be hurt by the larger tires.

The actual trans will not but the clutch will be effected alot.