Which Mods Needed to Switch non-XR 392 to 35 inch KO2s?

CBH

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I’m contemplating putting 35” KO2s on the OEM wheels of my non-XR 392 (with the OEM Hinged-Gate Reinforcement); however, after pouring through the 392 forums, I am still a bit confused about what I need to do to make the 35s work properly and safely.

Here’s what I’ve learned:

-- 35” KO2s on OEM 17” x 7.5” Wheels OK? Is it Safe?
-- Install Oversized Spare Tire Carrier Bracket Kit?
-- Install Wheel Flare Extensions?
-- Install Rear Tail Light Extensions?
-- Change Rear Axle Gearing?
-- Re-Calibrate Speedometer?
-- Adjust Shift Points?

Five Questions:

1) Which of the above mods are “must-dos” vs. “nice-to-haves”?
2) Could any of the mods impact the Basic Warranty?
3) Could there be issues with the Rear Bumper Motion Sensors?
4) Could there be Tire Clearance issues?

Have I overlooked anything? I welcome your comments.
 
-- 35” KO2s on OEM 17” x 7.5” Wheels OK? Is it Safe?
Probably ok, but 8.0" would be best

-- Install Oversized Spare Tire Carrier Bracket Kit?
Mandatory to reinforce the tailgate, especially if you wheel it.

-- Install Wheel Flare Extensions?
Nah, just more mud on the doors. I think these were widened for Jeep to pass DOT regulations.

-- Install Rear Tail Light Extensions?
Same as the wheel flare extensions.

-- Change Rear Axle Gearing?
470 HP / 470 LB/FT. I doubt you're going to feel sluggish going to 35" from 33"

-- Re-Calibrate Speedometer?
Not mandatory, but your speedo will be off. Can you live with that?

-- Adjust Shift Points?
Is the transmission tuned between the non-XR and the XR?
 
1) I’d say since you have the hinge reinforcement, none are “must do’s”. The long term excess weight would’ve probably eventually become stressed
2)No, a single size up will not impact warranty. You could always get “that guy” who tries to tell you “it’s your fault” in the shop, but I’ve never known a single case with a size up to be an issue, even if “that guy” tries.
3) Most likely not… from 33 KO’s to 35 KO’s that’s only a 1.6” addition in diameter, which translates to just 8/10ths of an inch radius from mount and about 7/10th inch thicker. Camera might see slight edge? But should safely be out of sensors sight line.
3) See #2 dimension changes.

*edit: missed you mentioned spare tire bracket… if you stick with stock you may need a spacer to bump it out about a quarter inch from the tailgate….

however, KO2’s have a higher rim width range, but still acceptable (8.5 on 33’s and 8-11 on 35’s)

Your speedo will be off about 1.5 mph at 60 as well, but a Tazer can adjust for this.
 
Last edited:
-- 35” KO2s on OEM 17” x 7.5” Wheels OK? Is it Safe?
Probably ok, but 8.0" would be best

-- Install Oversized Spare Tire Carrier Bracket Kit?
Mandatory to reinforce the tailgate, especially if you wheel it.

-- Install Wheel Flare Extensions?
Nah, just more mud on the doors. I think these were widened for Jeep to pass DOT regulations.

-- Install Rear Tail Light Extensions?
Same as the wheel flare extensions.

-- Change Rear Axle Gearing?
470 HP / 470 LB/FT. I doubt you're going to feel sluggish going to 35" from 33"

-- Re-Calibrate Speedometer?
Not mandatory, but your speedo will be off. Can you live with that?

-- Adjust Shift Points?
Is the transmission tuned between the non-XR and the XR?
Thanks for the detailed response. I’m not clear on your answer regarding the shift points. I read on some forum about needing to change the shift points to adjust for the larger diameter tires?
 
1) I’d say since you have the hinge reinforcement, none are “must do’s”. The long term excess weight would’ve probably eventually become stressed
2)No, a single size up will not impact warranty. You could always get “that guy” who tries to tell you “it’s your fault” in the shop, but I’ve never known a single case with a size up to be an issue, even if “that guy” tries.
3) Most likely not… from 33 KO’s to 35 KO’s that’s only a 1.6” addition in diameter, which translates to just 8/10ths of an inch radius from mount and about 7/10th inch thicker. Camera might see slight edge? But should safely be out of sensors sight line.
3) See #2 dimension changes.

*edit: missed you mentioned spare tire bracket… if you stick with stock you may need a spacer to bump it out about a quarter inch from the tailgate….

however, KO2’s have a higher rim width range, but still acceptable (8.5 on 33’s and 8-11 on 35’s)

Your speedo will be off about 1.5 mph at 60 as well, but a Tazer can adjust for this.
Regarding the warranty...I was thinking mods to the gearing or altering the shift points could be used against you during a warranty dispute.
 
Gotcha… if you do opt for gearing (which would be a nice to do not a must do) you could pay to play and go the MOPAR route, but be prepared for a long wait on parts through Jeep… and twice the bill $$$
 
Thanks for the detailed response. I’m not clear on your answer regarding the shift points. I read on some forum about needing to change the shift points to adjust for the larger diameter tires

this isn’t necessary. The transmission on these 392s is stellar as it is and you have gobs of torque regardless of axle ratio.
 
this isn’t necessary. The transmission on these 392s is stellar as it is and you have gobs of torque regardless of axle ratio.
I’ve changed my non XR to 35” tires and have tailgate reinforcement and spare tire and camera images are good. I do recommend re calibrating speedometer, it helped with transmission shift points for sure. I used Tazor and you will notice little or no power loss with tire change and calibration from my experience. . Hope that helps.
 
Couple things for you. I changed my non XR to 35s right away because my Falken m/t we’re not snow service rated which causes issues with traction laws here in CO.

I went with toyo at3 in 35x11.5x17. They fit on the stock 7.5” rims within manufacturer Spec. They are <1 pound heavier than the Falkens. They don’t stick out more than stock. They fit on the carrier without a bracket. They are C rated. 3.73 gearing seems great with them. Mounted speedo calibration actual size is 34” With GPS distance measured for 5 miles. Shift points are learned so no adjustment needed.

Last item is something not popular, KO2s are not quality tires. They take more weight to balance. I had 2 tires totally disintegrate with a panic stop a few years back. They were a few weeks old and the treads pulled to pieces, replaced them with Toyos much higher quality.
 
I have 35 inch Nitto Ridge Grappler which by manufactures specs are about 0.5 inches larger than the KO2 in 315/70 R17. The spare was close but did not fit so I used the Teraflex bracket and very happy with all of it. Tazer will adjust the speedometer and therefore will fix any transmission shift points needed. Dont worry about re-gearing you are only going up 7% in rotations per mile, and that will be what your speedometer is off without adjustment, 7%. The Teraflex bracket also moves the camera out farther to get a better view past the tire. All backup, cross traffic, blind spot sensors work perfectly. I firmly believe the XR gearing is not really meant for 35's but larger tires.
 
All the above @CBH! I put 37x12.50R17's on my stock non-XR wheels (which are 17x7.5). Purchased a Tazer Mini and adjusted accordingly. Speedo is right on the money, and I have not noticed any gear shifting issues. I will probably go with 4:10 diff's at some point, but I'm in no hurry. I purchased (still waiting on it) the spare tire reinforcement (Teraflex) for the tailgate. Have fun!
 
I purchased (still waiting on it) the spare tire reinforcement (Teraflex) for the tailgate. Have fun!

The Teraflex bracket I ordered from Northridge 4x4 was shipped same day and arrived in two days. They also offer military discount @RugbyRef . I see your avatar pic, pretty impressive. I have two pins also, both Naval Aviation.
 
I used the JScan app for speedo and importantly, tpms warning set at 30psi. Simple setup and a lot cheaper than Tazer if you only want to change tire size and psi.
 
Couple things for you. I changed my non XR to 35s right away because my Falken m/t we’re not snow service rated which causes issues with traction laws here in CO.

I went with toyo at3 in 35x11.5x17. They fit on the stock 7.5” rims within manufacturer Spec. They are <1 pound heavier than the Falkens. They don’t stick out more than stock. They fit on the carrier without a bracket. They are C rated. 3.73 gearing seems great with them. Mounted speedo calibration actual size is 34” With GPS distance measured for 5 miles. Shift points are learned so no adjustment needed.

Last item is something not popular, KO2s are not quality tires. They take more weight to balance. I had 2 tires totally disintegrate with a panic stop a few years back. They were a few weeks old and the treads pulled to pieces, replaced them with Toyos much higher quality.
I used the JScan app for speedo and importantly, tpms warning set at 30psi. Simple setup and a lot cheaper than Tazer if you only want to change tire size and psi.
I almost went with the Toyo AT3 but I would have gotten the 12.5 or 315 wide. Sounds like you are happy with them. Care to post some pics?
 
I had the dealer swap my 33's for 35's before I even picked it up. No additional accessories or mods are necessary, at all. The spare still fits. The 3rd brake light is still visible. You will need to adjust the tire size (Tazer) to make the transmission shift correctly.
 
I almost went with the Toyo AT3 but I would have gotten the 12.5 or 315 wide. Sounds like you are happy with them. Care to post some pics?
2nd pic is 295/70/17 toyo r/t, toyo at3 35/11.5/17, falken 285/70/17(mounted).
3rd pic is comparison of stock and new
B37AE650-2CD5-4948-8862-839B22422247.jpeg
EDA09EEE-15B5-492B-A0F5-4294D130F956.jpeg
0D400F70-6490-41F0-B55F-CA2EB3164F69.jpeg
 
I responded to your question in my post about this, and others have stated you will want the reinforcement hinge. I threw a spacer on so I could mount the spare until my hinge shows up (hopefully today). After a week of driving it there are no real noticeable differences in acceleration, no differences in how it drives on the top end and if the speedo is off its probably a mph or two. If you want to fix that the Tazer will do the trick. Good luck to you.

Mike
 
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