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Old 03-25-2008, 03:21 PM   #1
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Stock TJ with 31x10.5

I recently put 31x10.5 tires on my stock jeep ( 2004 X ) which upgraded from 30x9.5's.

I have had two issues with this

1. a huge vibration coming from the front end some where?

2. My wrangler is know sucking gas as well


Should i switch my gears from 3.07 to 3.73 to improve mpg?

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Old 03-25-2008, 03:50 PM   #2
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Definitely not nessessary to change gearing after going from 30's to 31's, thats way to much money that you dont need to spend. If you went from 30's to 35's that would be a different story, but going from 30's to 31's is not a big deal at all.

A couple things come to mind here with your issues...

1. Did you mount these tires yourself or did you get it done at a tire shop? The vibes could be from a poorly or unbalanced wheel after the new tires were put on.

2. Check the lug nuts to see of any of them are loose, the wheel could be wobbling around cause the vibe.

3. You will notice a small drop in gas mileage going from 30's to 31's but it shouldn't be a huge drop. If you changed from highway tires to mud tires this will impact mileage as well. Also check your tire pressure cause low tire pressure will drop gas mileage as well.

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Old 03-25-2008, 03:57 PM   #3
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Definitely not nessessary to change gearing after going from 30's to 31's, thats way to much money that you dont need to spend. If you went from 30's to 35's that would be a different story, but going from 30's to 31's is not a big deal at all.

A couple things come to mind here with your issues...

1. Did you mount these tires yourself or did you get it done at a tire shop? The vibes could be from a poorly or unbalanced wheel after the new tires were put on.

2. Check the lug nuts to see of any of them are loose, the wheel could be wobbling around cause the vibe.

3. You will notice a small drop in gas mileage going from 30's to 31's but it shouldn't be a huge drop. If you changed from highway tires to mud tires this will impact mileage as well. Also check your tire pressure cause low tire pressure will drop gas mileage as well.
x2, what speed is vibe. around 55-65 or so is usually tire balance.
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Old 03-25-2008, 04:10 PM   #4
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definitely check tire pressure. you shouldn't have a huge change in MPG just because of 1" bigger tires
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Old 03-25-2008, 04:52 PM   #5
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Seems like a balance issue to me.
Any pick of Your jeep with the new tires??
I'm planning on doing that since I only can make one expense on my jeep right know, and I'm more inclined on 31's M/T since I really dont need a lift here for FL muddy trails.
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Old 03-25-2008, 06:52 PM   #6
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One other item on your gas mileage is the difference in how far the tire travels for one rotation. Larger tires will travel a greater distance. If you use the odometer/trip, it will be slightly off since the tires are larger.
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Old 03-26-2008, 07:42 AM   #7
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Thanks for all the great replies!

The tires were just mounted by my shop that I’ve been using for 11 years, never had a problem but I will certainly double check everything.

I was more inclined to see about the wheel alignment rather than the wheel balancing.

As far as the vibe goes, it seems to be a side to side vibe at around 62-70 mph, it smoothes out after that but it’s still present.

We just checked the front end after a recent clutch job and found no problems.

Would increasing the tire size, reveal a minor problem that I might have not been previously noticed in my front end? Do front end parts wear out around 95K miles?

What does everyone think about the programmers you can get for the jeeps that will help with hp or mpg?
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Old 03-26-2008, 07:50 AM   #8
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Ill try and take a newer picture this weekend
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Old 03-26-2008, 09:40 AM   #9
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that description has tire balance written all over it. it isn't impossible even for a good shop to not balance a tire well, or a weight falls off. it is almost impossible for alginment to cause a vibration. if it did, you'd be able to see how off the alignment is by looking at the jeep. and you'd notice it before those speeds.
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Old 03-26-2008, 12:07 PM   #10
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that description has tire balance written all over it. it isn't impossible even for a good shop to not balance a tire well, or a weight falls off. it is almost impossible for alignment to cause a vibration. if it did, you'd be able to see how off the alignment is by looking at the jeep. and you'd notice it before those speeds.

x2 bring it back to the shops and have them rebalanced...even good mechanics can make mistakes every once in a while


Also about chips, unless you're going to spend the cash to get a good one i wouldn't even bother, even then the amount of money you save on gas will not offset the cost of a good chip.
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Old 03-26-2008, 01:06 PM   #11
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I know I'm piggybacking her, but at the moment I can't afford to get a lift kit for a my Jeep, but I was still looking at getting bigger tires, (I gotta replace the old ones anyway) does anyone know of any problems with this combination?

Tire: 30/9.50r15 BFG All Terrain KO
Wheel: 15x8 US Steel Rock Crawler

The jeep is entirely stock right now, and I wouldn't be able to afford making major changes yet, but this seems like as good a place to start as any, right?

Thanks
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Old 03-26-2008, 01:10 PM   #12
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that should work, and look good
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Old 03-26-2008, 01:16 PM   #13
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I ran that combo for about 3 yrs and it worked well with the bigger tires.


I just noticed after a review in the parking lot that my drivers side tire does not have any weights on ether side.

Already made the phone call and it should be redone this afternoon.
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Old 03-26-2008, 01:25 PM   #14
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Also be aware that some tire shops only balance tires "good enough". And the bigger the tire on a TJ, the more important it becomes that the tires be perfectly balanced. Imperfectly balanced tires on the front are one possible source of Death Wobble, something you definitely do not want.
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Old 03-26-2008, 01:26 PM   #15
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I ran that combo for about 3 yrs and it worked well with the bigger tires.


I just noticed after a review in the parking lot that my drivers side tire does not have any weights on ether side.

Already made the phone call and it should be redone this afternoon.
let us know if that does the trick
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Old 03-26-2008, 01:48 PM   #16
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Originally Posted by Sailor2017 View Post
I know I'm piggybacking her, but at the moment I can't afford to get a lift kit for a my Jeep, but I was still looking at getting bigger tires, (I gotta replace the old ones anyway) does anyone know of any problems with this combination?

Tire: 30/9.50r15 BFG All Terrain KO
Wheel: 15x8 US Steel Rock Crawler

The jeep is entirely stock right now, and I wouldn't be able to afford making major changes yet, but this seems like as good a place to start as any, right?

Thanks

Sounds good but i'd go 31x10.5 instead. If you're gonna pay the money for bigger tires you might as well put on the biggest (reasonable) tire size you can and it wont cost you much more to do so.
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Old 03-26-2008, 02:32 PM   #17
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x2^^ the price difference from 30s to 31s isnt much but it may help you just enough on trails to have a little bigger tire. let us know how it goes
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Old 03-26-2008, 08:29 PM   #18
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most of your MPG drop would be balanced by the larger tire size. I am running 31-10.50's on a stock 04 and I have noticed that the distance that I cover is about 10% more than my odometer is reading. So take that into account when figuring your MPG if you haven't regeared.
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Old 03-27-2008, 10:54 AM   #19
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Someone recommended the 30 x 9.5, because I want to use my Jeep for trails, but also as my commuter, I'm only able to get one vehicle. Plus as it is, for work (I'll only have to do it once, but everytime I look at it, it's a lot of miles) I have to relocate from NY to Texas, so I'll have to drive the old girl down to Tx. Which leads into another question, the Jeep I am buying is a '98 with 152,000 miles on her, is that too many miles? or do these really last that long? all of those miles were done by one owner, and it was all highway (he drove to Ohio from NY alot), he takes great care of the Jeep, but still....

-Thanks
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Old 03-27-2008, 11:09 AM   #20
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152K miles wouldn't scare me if the vehicle history is known and if you know the owner changed the lubricants regularly. My '97 TJ has 174K miles on it and I've not had any drivetrain problems, plus the engine runs as smooth as the day I bought it brand-new. Zero oil consumption I might add.
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Old 03-28-2008, 08:43 AM   #21
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I went to my shop yesterday and discovered that the tires are fine. the balancing is fine and the alignment is fine.

My next step is to look into a heavy duty steering damper, proably a nice dual one like skyjacker makes. im told this will help reduce the vibration.

I replaced the OEM last year with a monoe but im told its not good enough to handle highway use with these tires. front end checked out ok as well.

any suggestions?
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Old 03-28-2008, 11:19 AM   #22
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A "heavy duty steering dampener"... especialy the dual-dampener made by Skyjacker... is not the answer. First, Skyjacker's dual-shock setup just makes the power steering system work much harder. So much so that on a hot day on a tight twisty offroad trail it could make the difference of your PS fluid boiling and your steering getting even stiffer, and not boiling and your steering remaining usable.

Whoever told you that Monroe stabilizer was not enough for such a small tire is full of it, we use such stabilizers including the monroe for even 37" tires so it's plenty strong enough. A steering stabilizer is nothing more than a small band-aid that can help mask minor problems.

You really need to find the true source of that vibration, not just try to hold it down with a bigger steering stabilzer. A "huge vibration" is anything BUT a steering dampener problem.
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Old 03-28-2008, 12:39 PM   #23
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Thats really odd...so you didnt have vibes before the new tires but right after they were installed you got vibes? That leads me to believe the shop screwed something up...simply changing tire size will not give you vibes. Also a steering stabilizer, like jerry said, isnt the answer. At best doing that will just mask the problem temporarily.

Do you have steel wheels? If so one could be bent and causing a vibe. Maybe double check the lug nuts.

The fact that you got vibes right after you got new tires put on makes me believe that it has to be something that happened during the installation that's causing the vibe.
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Old 03-28-2008, 04:41 PM   #24
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Quote:
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x2, what speed is vibe. around 55-65 or so is usually tire balance.
My vibe is around 40-45, still balance?
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Old 03-28-2008, 04:45 PM   #25
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My vibe is around 40-45, still balance?
It's not guaranteed but very (!) likely nothing more than a tire balance problem. As anal as my local tire shop knows I am about them getting my tires balanced perfectly, since out of balance 35" tires are VERY noticeable, it often takes them two "we're done" events before they're truly done and gotten them balanced perfectly.
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Old 03-28-2008, 05:10 PM   #26
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Switch your tires front to back and see if it changes. As far as mileage goes, what speed is your engine turning at hiway speeds ? If it's loping along at 2,000 rpm it's going to suck gas. The 4.0 runs best at around 2400rpm. I know my XJ with LT235's at hiway speeds gets 16-18mpg in 5th gear at 60-65, in 4th gear at 65 it get 22, thats from leaving a scanner plugged in while driving and looking at it. At 75 in 5th it gets 22-24 depending on hills. This by the way is with the corrected speedometer gear and the chrysler scan tool.
If you have an auto tranny the correct speedometer gear is important.
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Old 03-28-2008, 09:36 PM   #27
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It's not guaranteed but very (!) likely nothing more than a tire balance problem. As anal as my local tire shop knows I am about them getting my tires balanced perfectly, since out of balance 35" tires are VERY noticeable, it often takes them two "we're done" events before they're truly done and gotten them balanced perfectly.
i agree, still most likely balance
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Old 03-31-2008, 09:06 AM   #28
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I'm taking it to the shop to get rebalanced and have the front end and u joints checked out on saturday.


Does anyone know what speed gear i need to show the right mph for what I am running?
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Old 03-31-2008, 11:40 AM   #29
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Switch your tires front to back and see if it changes.
I agree. Additionally, do you stall have your old tires? If so, try reinstalling and checking if in fact the culprit is the new shoes. Else check a fellow Jeeper if you could temporarily swap to see if different tires do not vibe.

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Old 04-04-2008, 03:59 AM   #30
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Quote:
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It's not guaranteed but very (!) likely nothing more than a tire balance problem. As anal as my local tire shop knows I am about them getting my tires balanced perfectly, since out of balance 35" tires are VERY noticeable, it often takes them two "we're done" events before they're truly done and gotten them balanced perfectly.
Thanks alot Jerry.

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