how much gear for 30" tires?

[winkosmosis]

Don't bother. Put on 32" or 33" which AFAIK fit fine with a BB and a lot of cutting, and go to 4.10 or 4.56

The gear for 33" to return to stock is 4.10

 

[HaleYes]

The gear for 33" to return to stock is 4.10

Wrong.

That's the combo I run and it is not the equivalent to stock. 4.56's would be more realistic for a stock comparison.

 

[XJBlackPDX]

So you're currently on 31"s and 3.55s, and your mileage went in the tank? Many people run that combination with little to no real change in power or mileage, but I also noticed a drop in both just going to 30"s with the stock 3.55s. If it's a huge deal, switch back to stock-ish size tires until you're ready to lift, re-gear and throw bigger tires on. That's what I'd do if I knew I wasn't going to address it for 4 years. Sell the 31"s, chalk it up to a lesson learned.

What I meant was that I would be keeping the 31's through the life of the tires, about 4 more years. I am thinking 4.10's for the 31's and am hoping to gain back 2-3 mpg and some power, is that realistic?

 

[winkosmosis]

Wrong.

That's the combo I run and it is not the equivalent to stock. 4.56's would be more realistic for a stock comparison.

Do the math. Aerodynamics will affect how it feels at higher speed but that's the exact ratio if you want to keep the same rpm at a given speed.

 

[HaleYes]

Do the math. Aerodynamics will affect how it feels at higher speed but that's the exact ratio if you want to keep the same rpm at a given speed.

I'm not doing the math. I could care less what the numbers tell me.
I've "tested" real world conditions. I can tell you 4.10's, 33's and an AW4 sucks. That's all he needs to know. Lots of things look good on paper but, when it actually comes down to it working, it's not worth a poop.

 

[winkosmosis]

I don't think you would get same gas mileage as stock with 4.10 and 31", because that gear will be shorter than stock.

 

[winkosmosis]

I'm not doing the math. I could care less what the numbers tell me.
I've "tested" real world conditions. I can tell you 4.10's, 33's and an AW4 sucks. That's all he needs to know. Lots of things look good on paper but, when it actually comes down to it working, it's not worth a poop.

I"m just saying that at some fixed speed, you get the same RPM with 4.10 gears and 33" tires as you do with 3.55 gears and 28" tires. If you're happy with 2200rpm at 70mph, use 4.10 and 33". If you're happy with 2400ish rpm at 70mph, use 4.10 and 31". If for some reason you want 2700 rpm at 70, the buzzing, and crappy gas mileage, then pair 4.56 with 31".

 

[XJBlackPDX]

I"m just saying that at some fixed speed, you get the same RPM with 4.10 gears and 33" tires as you do with 3.55 gears and 28" tires. If you're happy with 2200rpm at 70mph, use 4.10 and 33". If you're happy with 2400ish rpm at 70mph, use 4.10 and 31". If for some reason you want 2700 rpm at 70, the buzzing, and crappy gas mileage, then pair 4.56 with 31".

Actually, with 4.56 and 31" tires going 75, you are at about 3500 rpm, which I would say is worse. It seems to me that you lose OD with the AW4 in that combo.

 

[HaleYes]

I've drove 31's and 4.56's. Loved it.

I ran 30's and 4.10's.....loved it too.


You guys are hung up on crunching numbers. Like I said, real world is what counts.

 

[XJBlackPDX]

I've drove 31's and 4.56's. Loved it.

I ran 30's and 4.10's.....loved it too.


You guys are hung up on crunching numbers. Like I said, real world is what counts.

Those are real world numbers on a 98. What year/axle setup were you running and what kind of fuel numbers were you getting?

 

[HaleYes]

Those are real world numbers on a 98. What year/axle setup were you running and what kind of fuel numbers were you getting?

All XJ's I've drove were 96's.

Not sure on MPG's of past.

Right now, with my current setup, I'm getting 12 best case, mostly in town driving.
~5", 33's, 4.10's, D30, 8.8, AW4

 

[blondejoncherokee]

i was getting around 17mpg with 33's and 3.55s on the freeway since my rpms were so low... but in town it wasnt too good

 

[Ivan]

Fuel mileage and XJ's should not even be used in the same sentence. Accept the XJ to be fuel pig it is, an move on. If you're worried about gas mileage, get an econobox...

You state you currently have 3.55's. When I ran 30's with my 5 spd with 3.07's, it really sucked to the point where 5th gear was almost useless, except going down hill...

I've now got 32's and 4.56's and love it. At 65 mph, I'm about at 2750 rpms. Perhaps a weee bit to low of gear ratio for freeway driving, but my low end power is awesome where in Jeep it means the most, despite the relatively minor hit in gas mileage. That a small trade off I can live with...

If I didn't feel like hacking up my fenders, I'd run 33's and it would be perfect. I was able to get 32's to clear with NO trimming and stock flairs, so that extra half inch of clearance between 32's and 33's was not worth the hack job on my fenders to me....

....all this real life experience.

 

[winkosmosis]

Come on, it's not a fuel pig. A stock one gets similar gas mileage to a sedan.

Looks like a lot of people get ridiculous gears so they can crawl in overdrive, put on roof racks, etc... then get 12mpg and say "XJ is a fuel pig anyway, buy an econobox!"

Sounds like stuff Hummer owners would say!!

 

[HaleYes]

I'm not complaing about milage at all. I did a while back though. I swapped out a few sensors now I'm back up to 12. I'm not super concerned with milage. On average I drive 12 miles a day, not much for me to complain about. Now, if I were commuting 30-40 miles daily, I'd find a ricebox and the XJ would be a trail toy.

 

[rifle6]

i get near 20. after tune up, 2 inch lift and 30's
thats dam good MPG for what it is.

 

[pyrotyro]

I'm not doing the math. I could care less what the numbers tell me.
I've "tested" real world conditions. I can tell you 4.10's, 33's and an AW4 sucks. That's all he needs to know. Lots of things look good on paper but, when it actually comes down to it working, it's not worth a poop.

i guess this all depends on opinion... i drove 33s with the stock 3.55s just fine, gas milage wasnt great, but it was always above 15, and powerwise it was no issue

 

[vegas_baja]

I'm not doing the math. I could care less what the numbers tell me.
I've "tested" real world conditions. I can tell you 4.10's, 33's and an AW4 sucks. That's all he needs to know. Lots of things look good on paper but, when it actually comes down to it working, it's not worth a poop.

X2......

I've done the math and also tested real world conditions w/ an AW4. 4.10's w/ 33's suck balls.
4.88's w/ 33's kick ass for wheeling, in town driving and even short trip highway (100 miles or less).
If you do alot of highway driving 4.56's are the way to go.
I actually saw a 2mpg increase when I changed from 4.10's to 4.88's.
All with corrected speedo......

 

[vegas_baja]

Do the math. Aerodynamics will affect how it feels at higher speed but that's the exact ratio if you want to keep the same rpm at a given speed.

Most people understand the math.
Its the inexperienced that dont factor in the rotating mass of larger tires and the stress it adds to a drivetrain.
You dont actually run the same rpm at a given speed due to extra load from the taller heavier tires.
My rig w/ 33's and 4.88's actually runs quieter on the highway due to less load on the motor.
I'll run 2800 rpm all day w/o noticing any engine whine and get better fuel milage than running 4.10's at the same speed w/ lower rpm.
This is w/ an AW4 tranny, so I cant speak for manual tran's people.

 

[moparjim1987]

if i were to swap in an axle from a four cyl. xj with the 4.10's, could i use my big-joint axles? i know the older xj's had smaller u-joints, and my 97 ha the bigger ones....