bigger tires = axle gear change?

[LibertyFever]

I'm curious, do you fellows ever consider changing the gearing in your axles when you upgrade to larger tires?

My calculations put the OEM tire at about 29" in diameter and an upgrade to 31" tires isn't much bigger so would I be right in guessing it wouldn't be worth it to regear?

 

[jsc7002]

if you go with a 32" its best to regear I dont know about a 31" you prolly would see some benefits from it especially if you have a heavy Jeep from bumpers winch tools etc.

 

[J-Thompson]

Depends on what you want from your Jeep
We have 245/75 MTR's on our '03
gets about 15 MPG city and 19-20 highway ,not bad
does what we want off road so that is good enough

Now when I put the Locker ,LSD combo in then I will regear as it will only be the cost of gears but I dont see the value in regearing for the tire size we have just for fuel savings or the minimal power loss
it will NEVER pay for it self in fuel savings

 

[tommudd]

In the hills that I run in I think they will pay for themselves in extra power and also since I drag a trailer around quite a bit would help with that. Now if I lived somewhere that is fairly flat , then I would not care but most of my driving is in Southeastern Ohio and WV / Kentucky so I need them!

 

[J-Thompson]

What about remapping the ECU instead?

So you get a bit more power from the engine to compensate the bigger tires.


Not good for MPG though...

nothing you can ever do to the engine will make up what you can do with gears

Heck guys with 4 bangers on rock buggies turn 40"+ tall tires with ease
I want to put 4.56 gears in my TJ but with no OD I would break 4K rpm at 70 mph and that would really suck
I would put the same 4.56 gears in the KJ if they made them for the front
I think that if you drive it carefully you could get 20 MPG in the city with this set up ,now it would be the same ,or worse, on the highway cranking out 3K rpm at 70 mph but it would kick butt out on the trails

 

[tjkj2002]

I'm curious, do you fellows ever consider changing the gearing in your axles when you upgrade to larger tires?

My calculations put the OEM tire at about 29" in diameter and an upgrade to 31" tires isn't much bigger so would I be right in guessing it wouldn't be worth it to regear?

You live in the mountains like I do,I'm at 6000' and wheel at 10,000'+,31's and 3.73 gears = sucking wind.Heck I'm sucking major wind with 4.10's and 32" tires right now.31" tires and 4.10's for the KJ's powerband is perfect,32" tires really need 4.56's(which we can't use).I'll be gearing all the way to 5.13's when I shoehorn 35" tires under my KJ.

 

[icarl]

One other thing that i think makes a difference is not just the diameter of the tire but the tire/wheel weight. The difference in the diameter of a 30" and a 32" tire is only 6.25% This means your engine has a 6.25% less mechanical advantage using a 32" tire over a 30" tire. For example, this equates to a difference from 20 to 18.75 mpg on the hwy. Not too big of a difference. I think the other mpg loss that people experience is from the weight of new tires and wheels. Some are reporting an extra 50 ibs of weight per tire from using steel wheels with mud tires. This is one reason that i am planning to go with 235/85R16's on stock wheels. Using the stock lightweight wheels will save a lot of weight. The 235 also generally weighs less than the 265.

 

[JeepJeepster]

I agree icarl. That and how soft/aggressive the tire is. I had some 255/70/16 Grabbers and could hardly get up a hill at hw speeds. I went down to a less aggressive A/T tire and down to 245/70/16 and I can hardly tell a difference if any at all over the stock tires.