265-75-16s and why you need to swap to 4.10s

tommudd · **Posted:** Mon Oct 18, 2010 10:04 am

Why you need to swap gears if going to bigger tires
I will update after I get the gears broke in but for now here are the results
Short story
I knew from past experience that swapping gears was beneficial on performance and also gas mileage
I have had OHV-KJs front diff ( with 4.10s already installed) sitting in my garage since he did his SFA, yes that long! I also had bought the rears knowing I was going to do 265-75s sooner or later.
I had talked to sprsonic ( another LOST and KJC member here in Toledo) about installing the rears but our schedules never seemed to be good for the both of us.
I installed 265-75-16 Goodyear Duratracs last November and right away loved the tires but hated the way the KJ drove. On two lane roads at 55 there was no way I could just run it in overdrive, you kicked back and forth so often that it was annoying to say the least. Only time overdrive could be used at all was to keep the speed at 75-77 at least. Then it was only turning in the 1900/2000 range.
Up here in the great Northwest part of Ohio it's flat so at the 75-77 range I could get 20-20.5 pretty easy even lifted and the 265-75s but get on two lanes and mileage dropped a bunch, the KJ was simply not running in its sweet spot.
This past Saturday, the stars aligned and sprsonic was able to install my gears for me, ( he even threw the front diff in as well since it was up on the rack) so yesterday I took it out to break in the gears and also see the difference in drivability. I put about 120 miles on with a mixture of interstate and two lane. Driving taking a break to let the gears cool down, drive again etc.
Before at 60 mph with the OD on I was at 1650-1680, with it off at 60 I was at 2475-2500
Now with the 4.10s with the OD on I am at 1950-2000, with it off at 2775-2800. Its now running in more of the sweet spot where the engine was designed to run.
With the OD on I can actually drive down the road at 55 or 60 and its not trying to find a gear to stay in, it drives like it did stock almost. ( Speedo is still off by 4 MPH , was 8 off )
Another benefit, cruising at 70 ( OD on) I used to see 20-20.5 average, now I am seeing 22 -22.5 on the same road. Back roads ( two lane) at 50-55 I was seeing a lot of 23-24 according to the scan gauge yesterday and that was with the OD on even, before it would of been 15-17.
I still want to break them in more before any long trips but so far its well worth the $$$
( or should say the money I have in mine)
NOTE: All RPMs and MPG's/speed taken from the Scan gauge and GPS before and after
So for anyone even thinking "I want to run a 32 inch tire do I need to swap gears" , the answer is "Heck yes!!!!!"

long_tall_texan · **Posted:** Mon Oct 18, 2010 10:22 am

I noticed 4.10ls in your sig last night. Wondered when that happened. That is the next thing I am saving for...

tommudd · **Posted:** Mon Oct 18, 2010 10:30 am

long_tall_texan wrote:

I noticed 4.10ls in your sig last night. Wondered when that happened. That is the next thing I am saving for...

It makes a huge difference for sure
And I'm using parts from some of those doing SFA's
front diff with 4.10s-was from OHV-KJ
Yukon axles-were from ARBSeth's by way of JJsKJ
RL Rockrails-from tjkj2002's

tjkj2002 · **Posted:** Mon Oct 18, 2010 10:56 am

Yep been saying it for a long time Tom,many don't want to listen.I gained 6-8mpg's on the highway after my 4.10 swap and 265/75's over the stock 3.73's and 265/75's.

tommudd · **Posted:** Mon Oct 18, 2010 11:05 am

Well Troy its like everything else, we can suggest but only a few will listen and do it the right way. :-)r

I just wish I could of gotten it done a lot sooner!

2006 KJ · **Posted:** Mon Oct 18, 2010 12:23 pm

i know i really should change to 4.10's .. but dont want to shell out the cash yet. my 6 speed makes it tolorable but.. i know 4.10's would be a world of a difference!

DirtyKK · **Posted:** Mon Oct 18, 2010 1:08 pm

Wish I could get my 4.10s and ARB installed but something always seems to go wrong with my Jeep before I can get it into the shop, it needs to be fully functional before spending money on mods.

LibertyGuy · **Posted:** Mon Oct 18, 2010 6:03 pm

Do you need to upgrade gears if you install 245/70/16 or 255/65/16?

tommudd · **Posted:** Mon Oct 18, 2010 6:43 pm

245-70s would be the same as stock, I never noticed any difference at all with that size. You'll be fine
Didn't really notice a difference until I went to the 265-75s.

LibertyCRD · **Posted:** Mon Oct 18, 2010 8:18 pm

If you guys were going from 3.55 to 4.10, I could believe this. But 3.73 to 4.10 is barely going to even be noticeable to the average person. In fact, that small of a ratio change is a total waste of money, considering what it costs...unless you get a REALLY good deal on the gears and do the install yourself. I usually go 3.55s to 4.11s, or 4.11s to 4.88s. If I'm going to change the gears, I'm going to make it worth it.

tjkj2002 · **Posted:** Mon Oct 18, 2010 8:23 pm

LibertyCRD wrote:

If you guys were going from 3.55 to 4.10, I could believe this. But 3.73 to 4.10 is barely going to even be noticeable to the average person. In fact, that small of a ratio change is a total waste of money, considering what it costs...unless you get a REALLY good deal on the gears and do the install yourself. I usually go 3.55s to 4.11s, or 4.11s to 4.88s. If I'm going to change the gears, I'm going to make it worth it.

That .37 lower ratio makes a world of difference.Just remember that the 265/75's are only about 2" taller then OEM so you do not that much difference bewteen the gears to see a drastic difference in power and such.

Not that I was really concerned but my gear swap,including the DTT and ARB cost,was paid for by gas savings in about 6-9 months for me at the time as I did four 1500mile trips right after the gear swap.I bought a brand new front diff($1400) so that added alot of cost to the swap.

Yes 4.56's would be better but not possible on a KJ without spending some big $$$$.I personally wanted lower then what JBA's steel front diff can hold so I SFA'd so I could have my 5.13's.

tommudd · **Posted:** Mon Oct 18, 2010 9:40 pm

LibertyCRD wrote:

If you guys were going from 3.55 to 4.10, I could believe this. But 3.73 to 4.10 is barely going to even be noticeable to the average person. In fact, that small of a ratio change is a total waste of money, considering what it costs...unless you get a REALLY good deal on the gears and do the install yourself. I usually go 3.55s to 4.11s, or 4.11s to 4.88s. If I'm going to change the gears, I'm going to make it worth it.

It is a big difference trust me, lot of it has to do with the engine we have, yes agree that I have in the past went from say 3.55 to 4.56s or lower but this is the best we can do and it works GREAT
but then you see no advantage to doing anything to upgrade and no matter what works better than stock, you have to always disagree with whatever it is.
So I'm happy with results as I know most others will be when they do theirs.
:JEEPIN:

2006 KJ · **Posted:** Mon Oct 18, 2010 9:58 pm

tommudd wrote:

LibertyCRD wrote:

If you guys were going from 3.55 to 4.10, I could believe this. But 3.73 to 4.10 is barely going to even be noticeable to the average person. In fact, that small of a ratio change is a total waste of money, considering what it costs...unless you get a REALLY good deal on the gears and do the install yourself. I usually go 3.55s to 4.11s, or 4.11s to 4.88s. If I'm going to change the gears, I'm going to make it worth it.

It is a big difference trust me, lot of it has to do with the engine we have, yes agree that I have in the past went from say 3.55 to 4.56s or lower but this is the best we can do and it works GREAT
but then you see no advantage to doing anything to upgrade and no matter what works better than stock, you have to always disagree with whatever it is.
So I'm happy with results as I know most others will be when they do theirs.
:JEEPIN:

ive never heard anyone that was 'disappointed' that they went to 4.10's. everyone always praises them!

LibertyCRD · **Posted:** Mon Oct 18, 2010 10:09 pm

Well if you're happy with them that's all that matters. :mrgreen:

That little of a change isn't worth it to me, but to each their own. We can all rejoice that Jeep didn't put the 3.07s in these KJs like they did the WKs and XKs. We had a XK with the 3.7L and 3.07 gears...and that thing was miserable to drive. :banghead:

tjkj2002 · **Posted:** Mon Oct 18, 2010 10:18 pm

LibertyCRD wrote:

Well if you're happy with them that's all that matters. :mrgreen:

That little of a change isn't worth it to me, but to each their own. We can all rejoice that Jeep didn't put the 3.07s in these KJs like they did the WKs and XKs. We had a XK with the 3.7L and 3.07 gears...and that thing was miserable to drive. :banghead:

Yeah but having a 5-speed auto trans makes a big difference for what rear gears are needed.

265-75-16s and why you need to swap to 4.10s

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