39" vs 37" tires and handling issues

[len919]

For the rev hang, I'm assuming you are on 4.10's still. The transmission rev hangs if you been on the gas and let up because it anticipates you nailing it again. For 39's you will want to regear, I ran 37's for nearly 20K miles on 4.10s and was moderately ok with it, but 39's on 4.10s the transmission just doesnt like it, the gears just arent deep enough to get the tires rolling and the transmission is basically always in 2nd/3rd when accelerating exacerbating the rev hang as it feels like you're asking for a lot of power.

With the steering a few things are potentially happening and there are a few things to check:

1) If this is your first jeep/gladiator its not IFS, it will bounce, it will wiggle, the steering wheel moves more because its a solid axle despite the jeep still just going straight, you'll have to just kind of get used to that aspect a bit. Its hard to not want to correct every little jiggle of the wheel at first. The truck will roll, sway, and just not feel as planted as a low to the ground IFS running small street tires.

2) Check your pressures, they should be around 30-32 cold maybe even a touch less, the higher you go the stiffer that ride is going to be. If you are getting bounce after hitting a dip, higher pressure is just going to make this worse.

3) Check your caster, toe, and retorque all the components especially the trackbar, draglink, and tie rod.

4) Check to make sure you have the steel steering box (you probably do), its black instead of gray. If you do have the steel box, dont bother with a sector shaft brace it wont make any appreciable difference.

1- Thanks! I'll keep this in mind.
2- I suspect this to be the outcome of my experiment - will keep you posted.
3- Will do
4-I do have the black/steel steering box. I was really torn on this one. Lots of ppl agree it isn't needed. The reviews on the SteerSmarts site are a mixed bag- some said it didn't help, but there are some who said it assisted w/ lurching/deflection issues over potholes and things. idk! I already ordered it from quadratec and will throw it on - if it doesn't help I guess I will have at leat beefed things up.

Thanks, great suggestions, esp on the rev hang. I am indeed running 4.10 still. Yes, the tires are like new - should be able to get $2k for them easily. I wanted 37's, the previous owner had 39s on it, so I rolled with those. They're like new and I may go to 37s. If I get the other issues remedied I can prob live w/ the rev hang, I rarely mash the gas anyways (and switching to manual takes care of this too)..

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[3VOLVE]

Lmk if you decide to sell the KM3s or a possibly trade down to 37s.

 

[KHam]

Suspension is everything. You really want a high quality suspension that addresses all the geometry changes associated with a lift. Unfortunately they're not cheap but they are worth their weight in gold. At a minimum, in my opinion, you should have adjustable upper and lower control arms so you can set your suspension up. You need different springs, and shocks that match the spring rates. Once you lift it, you've changed everything. You can throw away some of what Jeep says the alignment should be for the most part... that was for the stock suspension, not a lifted one.

Personally, I went with the Rock Krawler 3" Pro-X No Limits Stage 1 lift. It actually improves on the factory setup by getting rid of the rear track bar in favor of a triangulated four-link rear. Every time you go over a bump the track bar moves your axles left and right which is some of the instability you're feeling. This lift removes that cross talk between the front and the back.

The factory alignment calls for around +4.8 caster on my Rubi. I'm running about +6.75 caster. I also have the Fox Race Series 2.0 ATS adjustable steering stabilizer which allows me to run the steering a little bit on the "heavy" side. I don't like a light feel on the steering wheel.

I've traveled down some very rutted roads at high speeds and I have no issues at all. It feels solid and stable at all times. Of all the things you might skimp on with your Jeep, don't skimp on this one... go with a top well engineered suspension and you'll love your jeep both on and off road.

 

[Jglad15]

Can you post a pic of your truck with the 39s. I have the 37k02s and was questioning going to the 39s since they run smaller when mine wear down.

 

[len919]

All- for whatever reason, it feels a LOT better at 40psi. I guess it's this specific setup. ?‍

Going to add the Steer Smarts and will follow up in a few weeks or as soon as I get to it.

Can you post a pic of your truck with the 39s. I have the 37k02s and was questioning going to the 39s since they run smaller when mine wear down.

I am really happy with them other than the rev hang issue mentioned above (and it's rare I accelerate fast enough to cause the issue anyways). Everyone asks about them. I just did some mild trails for the first time this weekend and this went over all obstacles w/out bottoming out on anything. I just bought diff skid plates but tbh I don't even know if I need them. lol

 

[Mjolnir]

A lot to unpack here....

- Pressure is too high. DO NOT GO UP TO 50PSI. You should be around 30, but use the chalk test to figure out what pressure YOU need to be at.
- Check your ball joints along with EVERYTHING bleda2002 stated.
- Steering brace is not needed. Hell I am running 37's on the original silver steering box, 56k miles and it is fine.
- double and triple check your geometry
- Rev hanging: you have a cheap and expensive option here. Cheap is to get a taser and reprogram the truck to 38.5" tires. Expensive (and IMO correct option) is to regear which might also require you to get a taser anyway depending on if your dealer is willing to reprogram your truck for the new gears and tires.

Your tires could very well be cupped at this point from running too high of a pressure as well so check them all for any uneven wear.

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