JK-Fam

Hey everyone,

I am currently running 255/80r17 BFG KM2's on factory 17" wheels. I want to change setups to a taller/wider setup without sacrificing the current drivability.

The setup I am running now weighs 83lbs:
255/80r17 KM2: 57lbs
Factory 17": 26lbs
33.3" x 10": roughly 31.75-32" tall mounted

The setup I am considering weighs 80lbs:
35x12.5r15 KM2: 60lbs
15" Level 8 Bully Pro: 20lbs
34.8" ish x 12.50": roughly 33.5-33.75" tall mounted

Here is my question and I would appreciate the help in figuring out if my reasoning here makes sense. Would changing to the 35" KM2 really be that much more of a strain on the Jeep than what I currently run? The height and width go up, of course, so a little more leverage on the axle and a little more friction on the road. The weight drops, and more of the weight is actually going to be towards the center of the wheel than before. Just wondering if running this "lightweight" 35 vs my "heavy" 33 would change much in the drivability and/or strain on the drivetrain? I was considering doing a larger tire on a 17" rim but the weights of the tires are much higher and the cost of a "large 33" or a 35" is much higher than the equivalent on a 15" rim. I'm basically thinking that this is as close as "having your cake and eating it too" can be when upsizing tires. My hope is that I can do this and not see a drastic change in performance while commuting and MPG as this is my DD. Any thoughts on this? Am I missing that the extra inch and a half (ish) of height stresses the axle that much more as to require reinforcement and would make the drivability in road that much worse?

I have a 2013 2 Door Sport Auto with 3.73 gears and the 5AT. The front has a Aussie locker and the rear is the factory LSD, both axles have a corresponding PSC diff cover if it matters. I only get to off road 5-6 times a year at the most and when I do it's usually at Windrock OHV and consists of diverse trails with gravel roads, dirt roads, heavy mud, water crossings, rocky hill climbs and creek beds etc.

Thank you for your help
Andrew

Dutchman82

There a few additional things to consider aside from the weight. To maintain stock performance weight and dire diameter go hand in hand. If you think of the tire diameter in relation to a gear to gear ratio, smaller tire turns faster bigger tire turns slower, lower weight assists the larger tire to turn easier but doesn't really affect the speed of it. A larger tire will always turn slower, that being said your jeep will more easily turn a lighter bigger tire than a heavier one. Wheel size doesn't affect the overall tire diameter, but does have drastic price differences in overall diameter vs. wheel size. Even though a 15'' wheel and tire may be similar weight and more affordable you also have to keep in consideration that there are brake caliper and rotor clearance issues with smaller wheels. Contact with the inside of your wheel to the brake assembly is no good, bigger wheels are often the solution, or can be overcome by wheel backspacing (essentially buying wheels where the inner lip is pushed farther out) or using wheels spacers, that bolt onto the hub, and you bolt your wheel onto the hub spacer. All this aside I run 35/12.5/17 Goodyear duratracs on factory gearing (3.73 for the sport), and have a little lag on take off but they drive incredibly well anywhere I go. Be sure to remember as soon as you change your tire size your speedometer is no longer accurate!

Saharaunlmtd

I went the 15" route to cut some weight and get 35s for a $100 cheaper than the same size tire for a 17". You will notice the handling diminish some from the extra sidewall but mine drives fine with 3.73s power-wise.

JK-Fam

Thank you for the feedback, I appreciate it. I use a Diablosport Trinity with the 93 octane tune and have used it to calibrate the speedo already. I have used discount tires approved list of aluminum 15" wheels to find one that clears the calipers without issue as well. I really am also considering those 305/70r17 Duratracs you have but they are considerably more expensive per tire than a 15". I have a "lightweight" build 2 door (minimal light stubby bumpers front and rear, no back seat etc.) I average anywhere from 14-22 MPG depending on if I'm all city or all highway on my current 33" setup that weighs similar to your 35" setup so I would anticipate the economy won't change too much from these tires.

Thank you

JK-Fam

Thank you, that's the route I think I want to go as well. A bigger tire setup that weighs less than the smaller one I run now. I already run a KM2 and have taken a hit in MPG already, 14-22 according to the dash readout as stated above. I would think it won't change too much since I havnt run the stock tires since I bought it lol.

kspano

JK-Fam, I'm in the same boat as you. I have a Sahara but I picked up a set of 17" wheels from a sport, thinking that I would like to run the 255/80's, but I also like the idea of the 15" 35x12.50 KM2s being that they are lighter and load range C. Mine is an '08 with a 4 speed, and it lacks power with stock wheels and tires. I use the SuperChips FlashPac, and it helps, but it's still no torque monster. I understand that gearing would help, but in the end I am still dealing with a 200hp, low torque mill.

If you do pull the trigger on the 35's I will be very interested to here your experience in the difference between the 255/80s and the 35s.

Keep us in the loop! Thanks,