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Old 11-19-2011, 04:17 PM   #1
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increasing tire size on 09 JK

Here's another tire question that I haven't exactly found an answer to in the forum. I currently run a 285/70/17 A/T tire on my 09 wrangler X.
I want to move up to a 315/70/17 duratrac, but the jeep is already such a dog on the highway, I'm afraid that if I zap any more power out of it, I'll never get it to stay in overdrive or be able to pass a motor scooter. Changing the gearing along with the cost at this time is not an option. I do have a highway commute to work and I do on occasion do some offroading.
I was curious to know if anyone has upsized that much from stock to a 315/70/17 which equates to roughly a 34.5 inch tire or a size close to that and what if any negative impact it had.
I had little no change in performance upsizing to the 285/70/17. Any real world experience, advice or profound statements from anyone that's done a similar upgrade would be appreciated.

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Old 11-20-2011, 07:28 AM   #2
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We put 315's on the Rubi and around town it's fine, but it does kinda lack some "umph" on the highway if you get into hills. Still has it's stock 4:10 gears.

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Old 11-20-2011, 07:43 AM   #3
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We put 315's on the Rubi and around town it's fine, but it does kinda lack some "umph" on the highway if you get into hills. Still has it's stock 4:10 gears.
I run 305/70/17s and my JK is about the same with 3:73 gears. I believe the Duratrac tires are a little lighter than the Goodyear MTRs i'm running so maybe they would be an improvement...not sure
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Old 11-20-2011, 09:21 AM   #4
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I would go the 305/70/17 it would only be about an inch taller than what I'm running now and I'd chance it. But unfortunatly they don't make the 305/70/17 in the duratrac.You're right they are lighter than your MTRs, I think they're less plys. I just hate to make a $1200 mistake trying to have the best of both worlds.
Thanks!
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Old 11-20-2011, 09:27 AM   #5
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I run 305/70/17s and my JK is about the same with 3:73 gears. I believe the Duratrac tires are a little lighter than the Goodyear MTRs i'm running so maybe they would be an improvement...not sure
5 lb difference between the 17" MTR and Duratrac. Duratrac is lighter and I'm putting 315/70/17's on next week. I'll let you know how they are on an 09 JKU Automatic w/3.73.
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Old 11-21-2011, 08:05 AM   #6
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Awesome. Yes, please keep me posted.
Thanks.
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Old 11-21-2011, 08:23 AM   #7
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The tire weight will account for less than 5% of your applied power-

Haven't you guys read anything about the requirement for REGEARing, when you raise the rotating diameter (height) of tires-

There are only three ways to correct power after the increase in tire size, ESPECIALLY FOR AN AUTO TRANNY !

1)--regear

2)--superchip (maybe)

3) buy a 2012 jeep

Forget tire weight--it means NOTHING (relatively)

Did I mention REGEAR ?

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Old 11-21-2011, 09:49 AM   #8
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2)--superchip (maybe)

JIMBO
Got that covered. My main concern on weight is the stress put on my girly dana 30 until such time I can gusset and upgrade the shafts or replace it with a 44.
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Old 11-21-2011, 10:02 AM   #9
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Gotit-


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Got that covered. My main concern on weight is the stress put on my girly dana 30 until such time I can gusset and upgrade the shafts or replace it with a 44.
There are a lotta guys that have run 35/38" tires on dana 30s and doso, by being VERY GENTLE, or regearing-lotta 5.13s around them thar hills

The throttle, tranny and rotational mass, is what bends/breaks/ruins the D30 axles/diffs--

So just mind your Ps and Qs--

Good luck

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Old 11-21-2011, 10:08 AM   #10
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Just remeber you have to run diagnostics for the bigger tires, or you could get a low tire pressure signal
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Old 11-21-2011, 02:11 PM   #11
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Yes JimboX, regearing is the holy grail but it's a bit expensive and I thought it'd be a better option to wait to change the gearing until I can afford to upgrade the front Diff to a 44 and I would like to add lockers front and rear. Research says about 600 to 800 bucks just to regear each axel.
I'm just looking to have my (cheap) cake and eat it too. So until some family member croaks and leaves me about 6 grand to do the upgrades i want, I'll be waiting 2 yrs until it's payed off.
I have heard that a superchip does help a bit.
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Old 11-21-2011, 03:10 PM   #12
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If you cant afford to regear to cant afford 35's, they go together. Either that or be prepared to ride the clutch lots at take off and forget about 6th gear, even in 5th you will still be under 2000 rpms at 100km/hr (60mph).
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Old 11-21-2011, 03:21 PM   #13
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If you cant afford to regear to cant afford 35's, they go together.
^This, especially for damndirtyog's auto transmission. If you're concerned about the power drop, you're going to hate it without a regear.

For me, a regearing would be a mandatory part of owning a pre-2012 auto transmission JK. Even on stock tires.

Why not spend your tire money on a regear? I know it messes with your plan, but over two or three years you could regear-->35s-->D44 front (probably don't need) or a front/rear locker. I know there'd be some duplicative spending involved in separating the locker from the regear, but it'll give you a much more enjoyable performance from your Jeep and wouldn't delay your 35s for much longer.

If you do 35s first--and you already think your Jeep is a dog--you'll be permanently unhappy. JMHO.
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Old 11-21-2011, 06:41 PM   #14
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All makes good sense. I do believe I'll get another set of 33s until I can do it right down the road a bit. It seems that you guys don't believe that a front axle upgrade is needed from the stock 30 for moderate rock and offroading? I was looking at the new Teraflex Dana 44 front housing that uses the guts from your 30, but gives you a stronger housing for gears and shafts for about 2 grand? i was consitering that route.
Any opinion on that option while we're kind of on the subject of differentials?
Thanks for all the good advice.
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Old 11-22-2011, 05:57 AM   #15
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With spinning larger wheels, the most damage seems to be twisted or snapped axles. Running the same axles in a stronger housing then would seem a rather expensive and pretty pointless excercise to me.
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Old 11-22-2011, 08:19 AM   #16
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Well, thats obviously kinda true, except-


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With spinning larger wheels, the most damage seems to be twisted or snapped axles. Running the same axles in a stronger housing then would seem a rather expensive and pretty pointless excercise to me.
If you apply the SAME torque, to the SAME axles/fat tires, but using a better diff. ratio (Mechanical Advantage), the torque is rationed in a more gentler/acceptable way and the abrupt shock to the axles, can ultimately be the same, but in a more gradual application !

Something will give, maybe---depends on the drivers right foot !

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Old 12-05-2011, 09:54 PM   #17
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I went with the 35's first with my stock 2011 automatic and 3.73's. It won't even shift into overdrive @ 75 mpg. Plus my mpg went from around 19 avg to around 10. I'm waiting so much money now. I get about 200 miles per tank. I'm going with 5.13's and chrome molly axles with a locker asap.
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Old 12-19-2011, 06:22 PM   #18
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Yea that's what I figured would happen. I'm planning to put on 285/75/17 duratracs.
Not much rock crawling here in florida so I plan to upgrade axles with lockers in the next 2 yrs when I move out to Utah. Should have the Duratracs burned up by then and move up in size. Thanks "Myfurous" for the input.

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