Don't expect anything from a tuner they really don't do much.
You're not going to be happy without re-gearing. Not sure why you're so opposed to getting the correct r&p in those axles, but be warned... you're not going to dig 33's if you already hate it with the stock tires/ gearing. Re-gearing for 33's will make driving so much less frustrating... well worth the expense if set-up correctly by a qualified shop.
Originally Posted by Chicagojeepgirl
I know this topic has been discussed before but not exactly to my situation. I'm having a really hard time deciding between 285/70r17 or 315/70r17 for my JKU. It's a 2008 with 265/70r17 currently and has the crap 3.8L...it's already a nightmare going up hills and merging on the highway, etc. I found an absolute steal of a deal on the 35's and would love to get them. I've read a lot that this will make the jeep even weaker and even less fun to drive on the highway. I don't do much off-roading- basically just some light trail riding on hiking trips so offroad performance is NO concern to me at all. I want to know how my highway driving and every day driving will actually be affected. I plan to purchase a tuner. The 35s are falken Rocky Mountain tires and I believe I have 3.73 gearing. I also have a 2.5" TF BB. What should I do?
From your OP, it doesn't sound like you "need" tires right now, just found "an absolute steal" on some 35s that would look really "BA" on your rig. Looks won't be very satisfying when you hate to drive it because it's a dog (worse than it already is). And those looks won't pay for the repairs you're going to have to do down the road because you overworked/overstressed your drivetrain from trying to turn those really "BA" 35s with improper gearing. Think transmission repair or replacement; not pretty.
IMO, a better approach is to create a long term plan and work toward that plan in steps you can afford and that meet your current needs. If you don't "need" the tires yet, then do the gearing now then replace the tires when yours wear out. I'd be surprised if even your "absolute steal" is much less than the cost of a gear swap at a competent shop. Tell them what you want to accomplish and let them advise you on gearing; they're the pros and they're in your area. All of us on here could give you our opinions, but they don't come from the same place and so may be totally invalid.
Or, you could do what so many of us find so difficult -- you could do NOTHING right now and SAVE that money you'd be spending on the 35s, add some more to it while you're wearing out those awful looking tires that are on it now, and then when the need arises go for those "BA" 35s and the PROPER gears to make "the love of your life" more fun than you've ever known it to be.
For comparison, I ran 37s on 4:10s for about a year, but that was on a 3.6 Unlimited so it's already inherently more peppy than the 3.8. It was just barely workable and I was constantly concerned for my auto trans. In the hills and mountains here in California, it would "search" for the right gear too much. So to make it more fun to drive, but more importantly, to save my transmission, I bit the bullet and regeared. The 3.6 gear chart shows 4.56:1 to be the "good" daily driver gear for 37s, with 4.88s and 5.13s being "performance" gears. I went with 5.13s for a handful of reasons. 1) I intended to do most of my wheeling in the Sierras and I drive to the trails -- no trailer queen. 2) I pull a relatively heavy trailer, often on those wheeling trips into the Sierras, and the lower gears will more easily pull that load. 3) At the recommendation of my gear shop, who brought up the real situation that those 37s create a greater flywheel effect than 35s or 33s, and so have a bigger impact on drivability than a person might first think. The 5.13s definitely cost me some top end on the freeway, but I can still get above legal speeds pretty easily, so it's kind of a moot point. I'm running 200-300 rpm higher at 70 MPH now than I was with the factory 4.10s and stock rubicon tires (whatever size those were -- can't remember).
Your area and your goals may require a different approach, but I would suggest that with your 3.8, your drivability with 35s and 4.10s might compare to mine with 37s and 4.10s. So it will be even worse if you leave your 3.73s in place. Bottom line to what I understand is a long post, is that I would urge you to re-think your plan and not make a spur-of-the-moment decision that you may regret later on. And the worst case scenario would be that you regret it and don't know why it happened so you dismiss your Jeep as "a piece of junk," when a better-thought-out plan could have REALLY made it the love of your life.
My .02. Take it or leave it.