Tire Size on JL Rubicon (8-speed automatic) without lift and re-gear.

isaaydin

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Hi Everyone. I just got my new JL 2dr Rubicon with Automatic 8-speed transmission. And I wonder how big can I go with tire size without lift and changing axle ratios.
My dealer also told me that your factory and 100k mi extended warranty will be voided if you do any changes to the car like re-gearing and lift. So, I am curius how everyone else deals with it and will just tire size void my warranty?
Any comment is helpful.

 

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Hi Everyone. I just got my new JL 2dr Rubicon with Automatic 8-speed transmission. And I wonder how big can I go with tire size without lift and changing axle ratios.
My dealer also told me that your factory and 100k mi extended warranty will be voided if you do any changes to the car like re-gearing and lift. So, I am curius how everyone else deals with it and will just tire size void my warranty?
Any comment is helpful.
I'd go with a true 35x12.50
Don't go metric (315/70/17) Metric tends to be a tad shorter depending on the manufacturer.
35" look great on a factory JL. Keep your factory wheels and tires. You can always just put them back on if a warranty is in question.
 

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Hi Everyone. I just got my new JL 2dr Rubicon with Automatic 8-speed transmission. And I wonder how big can I go with tire size without lift and changing axle ratios.
My dealer also told me that your factory and 100k mi extended warranty will be voided if you do any changes to the car like re-gearing and lift. So, I am curius how everyone else deals with it and will just tire size void my warranty?
Any comment is helpful.
Your dealer lied to you. There is a common misperception across the internet that certain changes made can void the warranty. This is not true and there is a federal law to protect consumers. The law is known as the Magnuson-Moss Act.

If modifications you make caused the problem they can deny warranty coverage in that specific instance. The legal responsibility is on them to show the changes you made caused the problem. That has no impact on your overall warranty. If you have a problem with your air conditioner or other unrelated component it would still be covered by the warranty.
 

hubbit

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My understanding from my dealer is that tire and wheel changes will not void the warranty. Neither will lift and certain performance mods.

IMHO, if you do not have a Rubi I’d stay away from 315’s or 35’s without a lift. To me it looks silly, like they are stuffed under the fenders. And it’s be rough off road tubing on the fenders when flexing. Without a lift, 33.5 is the biggest I’d go with a wheel that has 5” or more of bs. Otherwise the wheels will stick out way too far. A lift and bigger tires will correct that though.

If you have a Rubi, 35’s will be fine, even in stock wheels. That is what I was told by my dealer.
 

word302

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My understanding from my dealer is that tire and wheel changes will not void the warranty. Neither will lift and certain performance mods.

IMHO, if you do not have a Rubi I’d stay away from 315’s or 35’s without a lift. To me it looks silly, like they are stuffed under the fenders. And it’s be rough off road tubing on the fenders when flexing. Without a lift, 33.5 is the biggest I’d go with a wheel that has 5” or more of bs. Otherwise the wheels will stick out way too far. A lift and bigger tires will correct that though.

If you have a Rubi, 35’s will be fine, even in stock wheels. That is what I was told by my dealer.
35s fit just fine on a stock rubi with no rubbing. You actually need less backspacing as you get larger tires or you"ll have rubbing issues with the wheels turned. 4.5" is about max with 37s. 3.5" with 40s.
 


hubbit

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35s fit just fine on a stock rubi with no rubbing. You actually need less backspacing as you get larger tires or you"ll have rubbing issues with the wheels turned. 4.5" is about max with 37s. 3.5" with 40s.
Right. My understanding is the axles on the JL series, especially the rubicon, are wider and do not require the same backspacing as the JK. That’s a problem since a lot of aftermarket wheels have 4.5 backspacing and that may be too much for a mild build. My JKU had a 2” lift and 35’s with 5” backspacing. I also had flatties. It left plenty of room for flex and full turn flex. I think 4.5 may be too much for most mild upgrades on the JLU though. That being said, the dealers I visited never gave me a hard time with my JKU because of the upgrades, it didn’t effect the warranty coverage at all.
 

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Without lifting and without changing gear ratios?

It depends.

What can you live with?

We put 37s on our JLUR with no lift and I was fine with cutting the rock rails and removing the front bumper to clear the tires, as a very low CoG was my main objective before we even bought the Jeep....not everyone will be.

As for the power with that size tire and the stock gearing....it's subjective. Butt dynos don't mean much, but me personally....it didn't affect the power much.

Mileage is another issue entirely. I want to regear at some point to 4.88s or 5.13s to gain back the mileage we lost.

We're currently getting 13.6mpg in mixed driving on 37s.
Did you reprogram after putting the larger tires on?
 
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isaaydin

isaaydin

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Thanks everyone for detailed explanation.
I read a lot that some fellows had problems with automatic transmission which will not shift properly or at all after certain gear because they didn’t change axle ratios. Is that true? And will just reprogramming fix that problem or axle ratios have to be replaced?
 
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isaaydin

isaaydin

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Also what size are my tires in imperial? I have stock LT285/70R17C BSW tires?
 


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Thanks everyone for detailed explanation.
I read a lot that some fellows had problems with automatic transmission which will not shift properly or at all after certain gear because they didn’t change axle ratios. Is that true? And will just reprogramming fix that problem or axle ratios have to be replaced?
You read a lot? I would stop reading from those sources or really pay attention. If you go with too big a tire (like 40s) the car maybe will hardly ever shift to 8 gear because it has become simply too high a gear, but that is a completely different issue.
 

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Hi Everyone. I just got my new JL 2dr Rubicon with Automatic 8-speed transmission. And I wonder how big can I go with tire size without lift and changing axle ratios.
My dealer also told me that your factory and 100k mi extended warranty will be voided if you do any changes to the car like re-gearing and lift. So, I am curius how everyone else deals with it and will just tire size void my warranty?
Any comment is helpful.
I just upgraded to Cooper Discoverer STT Pro LT315 /70 R17 on my 2dr Rubicon. Stock wheels, no lift or re-gear. The only thing I did was buy a Superchips Flashcal to adjust the speedometer and tpms warning threshold for the new size/psi. I did pretty much lose 8th gear, but I didn't buy a Rubicon to race down the highway at 80... so, no worries there :)
 

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No. Was just driving it tonight and it still has very good power for 4.10s and 37s. I plan to get a programmer at some point, but I think 4.88s or maybe 5.13s would make this thing down right peppy.
This is why your MPG is showing so low. It is incorrect. Without reprogramming, the computer does not know how far you have traveled, it is still calculating with the smaller tire size. Between the stock 285/70 and 37/12.50 there is about a 13% difference. You are actually getting a few MPG more than it is showing. Your odometer is also showing less miles than actually traveled as well.
 

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I just gave the quick & dirty number off the computer....I work in rocket propulsion. I'm certainly capable of calculating the actual mileage...I simply don't care to.
FUNNY!

 

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