fattypros

Hey Folks,

I could use some help. I made the switch from 37 inch Super Swamper MT's to 38 inch Goodyear Wrangler MTRs. I am stationed on Guam so my options for tires are limited. They did not have 37 inch MTRs in stock and I thought my JKU could handle the inch size increase, being sleeved and gusseted with the D44 in the front but now I am second guessing it.

I had them mounted and saw that with the increase I needed to move my axle back to recenter the tires because I could not trim the pinch seal any further. I was unable to do this because my lower control arms were seized and needed to be replaced.

I drove around on these 38's for some time, they affected the characteristics of the JKU significantly where it took a lot more effort to get the jeep moving compared to the old 37's. I couldn't off road for fear of hitting my rock rails so I was on the street until I could get replacement lower control arms.

Then 2 months later, my auto trans went into limp mode. I took it to the stealership and they said it smelled like burned clutches and they would have to rebuild the transmission. With labor and parts it came out to 3k with a 90 day warranty. I said thanks but no thanks and found the ATS Diesel Remanufactured transmission for 1000 less and a 5 year warranty.

It was installed, plus I got new lower control arms and everything seemed pretty good, but the JKU still took more pedal than normal to get moving.

Today I was attempting to make a turn at an intersection when my traction control activated and robbed me of all my power. The road was dry, I came off the gas, came back on, still just flashing in my face, eventually it worked it's way through it and I got going. I decided to keep it light on the skinny pedal.

Things were going alright but then later in the day I went to make another turn up an incline and once again, my traction control activates, the vehicle is lurching and being starved of fuel. I came off the gas and gave it less pedal but still for the duration of the incline I was stuck, traction control just flashing. It was still dry and I had not had any issues at that intersection before.

For the duration of the ride home, I turned traction control off to see what that would do, besides an alert from my hill assist and a momentary loss of traction and abs light, nothing else happened.

I never had any issues with my old 37s and although I've made a few mods in the jump to 38s (big brake kit, replaced u joints) I don't know what the problem could be.

I feel like this is too much tire for my drive train, I need to look up the weight difference but I think I will be going back to 37s and selling the 38s second hand. They only saw 4 months of on road use.

But I am interested to hear thoughts from my fellow jeepers. Has anyone else seen something like this before? Would increasing tire diameter by an inch and tire width really slow the vehicle down that much or should I be looking elsewhere?

Thanks for any help or advice.

fattypros

Here's the 37s, sorry for pic quality.

fattypros

And the 38s

sa29560

Sounds like deeper gear set would help.

The steering issues seem characteristic of alignment issues. You have a rack printout on hand or could you get one?

tasi

what are your current gears? By the way "hafa adai"

Joe_B

That's a very wide tire (14.5") and as you've noticed will affect drive ability. That's a lot of rolling resistance you have. The general rule is running 38s requires the same preparations as 40s.

Are your tires rubbing when cornering causing the esp to kick on?

jedg

The other consideration is, I believe, that MTRs are usually truer to size, so a 38 in MTR pretty close to a 38" diameter. Not sure about the 37s you run. (example, a 37 BFG usually comes in about 35 1/4 true diameter). Perhaps you've got a similar situation where you've effectively increased the measured diameter by 2 or more inches. Maybe?

larry0071

I would hope that 5.13 gears would be good enough? I have the newer 3.6L engine (extra 100HP or so) and run 4.88 gears and find the gearing to be about right, so I his 5.13 gears should be around the same level of satisfaction with his 3.8L?

His build in his profile is:
Year:2011Model:Rubicon Unlimited
Color:Black
Transmission:Automatic
Suspension:Teraflex 6" LCG Longarm W/ Speedbumps, ELKA shocks, Teraflex Sleeve and Gusset kit
Wheels & Tires:37" Super Swampers on 17" Pro Comp Rims, skyjacker dual stabilizer
Bumpers:Smittybuilt stubby stinger with rancho rear
Armor:Body Armor Tube Doors
Drivetrain:5.13 synergy gears, teraflex driveshafts
Winch:warn VR10000
Performance:Banks CAI, MBRP Offroad exhaust

Smudgeontheglass

Those are giant tires for the stock drivetrain. The traction control issue is very common with the bigger sized tires if they weren't programmed in. Make sure you're programming for the correct size because if it is too small the transmission will constantly be looking for the right gear. The wheel speed sensors are pretty sensitive on these vehicles, make sure none of the cables are taught and there is enough slack. Also make sure your steering wheel is centered.

TheDirtman

Yes you are putting more wear and tear on everything from the drivetrain to ball joint to unit bearings to the steering box and so on. I agree you likely have alignment issues and not enough in the gears. Thats not a tire that I would want to run on the road.