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Old 08-24-2013, 01:14 PM   #1
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35-37s DD?

For my next tire size I'm debating between 35s and 36x13.5s. Anyone have them for a DD? And i will upgrade my axles. 4:10s are as low as I'll go. I don't care about low end performance lacking. I want highway mpg.

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Old 08-24-2013, 01:19 PM   #2
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You will get worse mpg by gearing to a ratio like 4.10 with that big of a tire, not better. It's never a good idea to gear axles to such an inappropriate ratio like that which just causes the engine to lug.

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Old 08-24-2013, 01:37 PM   #3
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I have stock gears and 33s right now and im perfectly fine with the way it performes, straight 6 and a 5 speed... and fyi this engine is only temporary... im gonna put in a double disk clutch later and either bore and stroke the engine or put a cummins 4bt in it
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Old 08-24-2013, 01:39 PM   #4
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And wouldn't i get better highway mpg? Lower rpms because of the bigger tire. It will just lag on hills like it does now wont it?
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Old 08-24-2013, 01:44 PM   #5
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NO, lower RPMs don't necessarily create better mpg... the RPMs have to be high enough so the engine is not lugging. If that wasn't the case, we'd all be running 2.73 axle gearing, and is why there are multiple axle ratios available. If getting better mpg was simply a matter of running a high axle ratio without it causing other problems, it'd be easy for us all to get better mpg.
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Old 08-24-2013, 01:45 PM   #6
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Being new here, I first thought something else after reading the title of your post....I'm sure this is a family oriented site!

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Old 08-24-2013, 01:47 PM   #7
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Old 08-24-2013, 01:50 PM   #8
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Old 08-24-2013, 01:56 PM   #9
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NO, lower RPMs don't necessarily create better mpg... the RPMs have to be high enough so the engine is not lugging. If that wasn't the case, we'd all be running 2.73 axle gearing, and is why there are multiple axle ratios available. If getting better mpg was simply a matter of running a high axle ratio without it causing other problems, it'd be easy for us all to get better mpg.
Then what gears should i run? And what tire size would ya'll recommend? And what mileage would i be looking at?
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Old 08-24-2013, 01:58 PM   #10
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What axle ratio would be best depends on the tire size (35" vs. 37") and what engine and especially which transmission you have.

And the cost in the lower mpg you'll see after you're done with all this will be insignificant when compared to the cost of everything involved in buying & getting everything set up properly for that big of a tire. Even when geared to the best possible/most efficient axle ratio, your mpg will be lower with bigger tires... it simply takes more power to turn bigger tires which costs mpg.
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Old 08-24-2013, 02:12 PM   #11
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I average 16 mpg with 33s and 4.88. I'd expect a 1-2 mpg hit moving up to 35s.
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Old 08-24-2013, 02:17 PM   #12
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I get 12 now with my 33s...
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Old 08-24-2013, 03:34 PM   #13
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If you are so concerned about mileage why would you consider DD'ing a TJ on 35-37" tires?

With a lightweight TJ with 4.88 gears and 37" MTR's, I average 14-15 mpg no matter how I drive. I could DD it if I want but I'm not a fan of filling up my fuel cell every other day. But in terms of drive quality, it's fantastic. If the mileage wasn't so bad and the tires weren't so expensive, I'd drive it every day.
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Old 08-24-2013, 03:55 PM   #14
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Im happy with 12, that's my goal. So if i can do that with bigger tires then great
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Old 08-24-2013, 04:05 PM   #15
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I get 16-17 with 4.10 and 33's same motor and transmission. It did great until all the added weight. When I go to 35's I will regear to 4.88.

I find myself staying in 4th around town (35-45 mph) and 5th when I hit 50 or above. Doing this increased my mileage by 2mpg because with 4.10 I was about 1500 rpms or so at 45-50. Driving was not a problem it handled it fine, just the higher rpm's are better.

oh and if you have not calibrated your speedometer to your tires your mpg is off.
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Old 08-24-2013, 04:14 PM   #16
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Quote:
Originally Posted by Jerry Bransford View Post
You will get worse mpg by gearing to a ratio like 4.10 with that big of a tire, not better. It's never a good idea to gear axles to such an inappropriate ratio like that which just causes the engine to lug.
what would you suggest for a gear ratio for 33-35s I currently have 3:21s?
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Old 08-24-2013, 04:19 PM   #17
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I DD 35's...currently have 4.88's as well with 5spd

also, as you'll find out, you'll need to upgrade a few more things than just axles going that big of a tire.
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Old 08-24-2013, 04:34 PM   #18
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Quote:
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For my next tire size I'm debating between 35s and 36x13.5s. Anyone have them for a DD?
Engine Revs:
I am still running 4.10 gears with a 5-sp with 35x12.5r15s. This took some getting used to, and in order to get the Jeep up to speed, I find myself revving the engine higher than I had to with 33s - something you'll notice right away.

Suggestion: Why not bolt on a friends 35s and see what your drive will feel like?

Braking:
I also noticed that stopping distance has increased, requiring an immediate brake job. New pads, and lately, a new rear brake caliper. The brakes can lock up, if necessary, but I equate locked up brakes with partial loss of control. To compensate for increased stopping distance, I drive more carefully, watching my speed on the street. I plan on upgrading my brakes to better handle the additional rotational forces I'm exerting on the braking system.

Steering:
I had a long-running issue with my steering - when running 33s. Having to replace my Tie rod ends, Track bar, control arm bushings, shocks, and drag link in 2009 - while running 33s, driving my Jeep daily. After bolting on a set of 35s in Feb. 2013, I noticed that my steering componentry was in shambles. The Tie Rod ends needed replacement, the Moog Track bar that replaced the OEM Track bar could not handle the additional rotational forces I exerted on the steering system, causing the front end to exhibit Death Wobble. I had 3 weeks to trace down the cause of this Death Wobble just to get the Jeep ready for TDS and the Baja Pole Line Road - Just Empty Every Pocket. I have a spare brand-new Rancho steering stabilizer on reserve, just in case I need it. A new Rubicon Express Adjustable Tie Rod has helped. My next area will be to look at new ball joints.

Suspension:
The Control Arm bushings have had to be watched carefully. The swaybar link hardware has to be watched regularly for becoming stripped. The draglink worked itself loose on the trail (no thanks, Goodyear alignment guy), and I watch the draglink hardware closely. My set of shocks that I purchased in '09 are due for a complete new set.

Wheels:
I was running a 1/2" wheel spacer for greater clearance, but I was told that these spacers could be contributing to Wheel Shimmy - I pulled them off.

Tires:
I am running a (newer) used set of 35" BFG AT/KOs. One of the tires requires 3 lead weights, possibly adding to my current shimmy issues.

I plan on pouring through the front-end this afternoon in order that I can drive the Jeep down the 91 Fwy.
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Old 08-24-2013, 04:40 PM   #19
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4.88's I have 35's and 5.13's and I'm geared a little tall but i plan on going 37's next. I still get abt 13-14 with mine 6sp manual
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Old 08-24-2013, 04:43 PM   #20
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Mileage definetly increased 1 or 2 mpg with 5.13's over 4.10's with 35" tire. It was such a dog on 35's with 4.10's but now it has some power again
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Old 08-24-2013, 04:46 PM   #21
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I get 12 now with my 33s...
If you'd re-gear to 4.56s your mileage would jump up to around 15-16 with the 33's. You have to get the engine in the rpm range that it's most efficient in 4.0's love the 2800-3200 rpm range.

Once you get into 35s and above the tires are heavy, have a huge rolling resistance and raise your brick even higher in the air....forget gas mileage.

Balancing, tire wear and stress on your driveline also factor into running that big of tire on a DD.

Big ass tires may look cool but a DD is better off with 33's.
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Old 08-24-2013, 05:17 PM   #22
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what would you suggest for a gear ratio for 33-35s I currently have 3:21s?
What transmission do you have, and which of those two tire sizes would you like a ratio suggestion for? There is no single ratio that would be optimal for both 33" and 35" tire sizes.
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Old 08-25-2013, 08:51 AM   #23
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So what gears should i use for 35s? 4:88s? Or at least that's what it sounds like. And I'd get around 14mpg?
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Old 08-25-2013, 08:56 AM   #24
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If you have the 4.0 and 5 speed then yes 4.88
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Old 08-25-2013, 11:05 AM   #25
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X2 on the 4.88 recommendation for 35" tires, 4.0L engine, and 5-speed transmission. I ran that combination for years & it was superb. I can sometimes get 14 mpg if I can keep my foot out of it/keep my speed down on long trips.
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Old 10-04-2013, 11:55 AM   #26
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So what do you guys recommend for a DD on 35's? Its a 2006 LJ 4.0 automatic 4 speed. I currently have 285's and I'm moving to 315's. What gear should I use?
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Old 10-04-2013, 12:42 PM   #27
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5:13's if the tire measures out to 35"
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Old 10-04-2013, 12:59 PM   #28
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But...I believe 4.88 is the lowest gearing that will fit in a D30 due to the Ring size.
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Old 10-04-2013, 01:06 PM   #29
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5.13's will fit assuming he has the right carrier

I take that back... mine was a cj
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Old 10-04-2013, 06:17 PM   #30
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I run 4.88 and 35s on my LJ and I average 11-13 around town and 14-16 on highway.

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