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Old 10-20-2012, 06:10 AM   #1
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Location: Ottawa, CAN
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Question Power Train Issues With Larger Tires?

Myself and another buddy recently bought Jeeps and naturally, we immediately began planning mods for them. One of them was to mount them on bigger tires than stock. Then, while looking into it, my buddy was told that there could be issues with the power train if going up more than 3% bigger than stock. I believe he said anything over a 255 could cause problems. My question is, has anyone had issues due to mounting tires bigger than this, or have heard of any issues? I can't believe the good people at Jeep would not factor in buyers upgrading their tires, considering this is one of the most common mods any Jeeper does.

For the record, I think my buddy is running 225s on his stock 2012 JK sport and I have the stock 255s on my 2012 JK Sahara UL.

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Old 10-20-2012, 06:17 AM   #2

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While just slapping bigger tires on is fairly easy to do, there is a little more to it than that. the short answers is it depends. On the old tired question, "what are you going to do with your Jeep?" How much bigger of a tire? What gearing do you have? Will it ever be off-road? At some point there comes a time when wheels gearing and axles and suspension MAY need to be addressed. Bottom line you can probably go up to a 33" tire and maybe even a 35" and not have to change much but wheels and install pucks on the springs after that it is gonna get $$$$$$$$$$$$$$$

I have a '12 also it will stay on the stock tires for a while...the TJ is for the MUD!!!

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Old 10-20-2012, 06:50 AM   #3
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I can only speak for myself in terms of what I will be doing with my Jeep. It would serve mainly as a daily driver but I will certainly be taking it offroad. I don't plan on mudding but trailriding is definitely something I want to do. I know the stock Bridgestone Duelers are more than capable of serving for now on and offroad, but I would like to go up to 275s with a little more bite on the tread. I'm not planning on going nuts with the idea. 33' would probably be the biggest I'd go anyway.
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Old 10-20-2012, 11:13 AM   #4
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Location: SoCal High Desert and IE
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I'm not sure about the 3% increase part...never thought about it in those terms. However, the larger the tires, the lower the gearing needed to keep the drivetrain happy. That being said, there's a sort of buffer zone you can play with depending on what you're using it for. So usually, 33" tires go well with a 4.10 gear ratio and keep things in the driveline about what stock would be like. There are several gear ratio calculators out there but I like the one on GrimJeeper.com the best. Take a look at that and play around a bit. That should get ya started on gears and tire combos.

Another thing to think about is the increase in rotational inertia from larger tires. Obviously, bigger tires weigh more. So when it comes to stopping, we might require more force to stop than stock brakes can handle. On a 2012, you won't have that issue as much. Older models like my CJ-7, that really needed an upgrade.

Another thing with the added weight to consider is the impact damage created when you're out wheelin. The axle shafts are not indestructible. A few hard smacks while out doin hard rock crawling and you might snap an axle. It happens. A lot of guys tend to either reinforce the axle housing by having it "sleeved" and then also reinforcing the C bushing (bushing? Is that what it's called? Can't remember...haven't had coffee yet) or they replace the stock shaft with chromoly shafts or they do both. This way, when you get the bigger tires that let you play on tougher trails, you're not slamming away at the steering/driveline system and getting stuck when you break something in the middle of nowhere.

Hope all that helped!
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Old 10-22-2012, 08:43 AM   #5
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Thanks for all the help! Might just stay with the stock size but just go with a more aggressive tread for now until I find out exactly what I have to do to go any bigger. Like I said before, i'll just be doing some beginner trail riding for now until I get a little more experience anyway, so there's no rush. I plan on keeping this Jeep for a while so there's plenty of time to upgrade as I need it. Thanks again!
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