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Major stability issue at highway speeds

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I have a 2021 JT Sport with 37”x12.5” ko2s on 17” rims



When I’m on the highway and hit a bump in the road the entire cab starts rocking back and forth so hard that the traction control turns on and I have to slam on the breaks to get it to calm down. It feels like the truck is going to flip over.

I have the 2.5” skyjacker spacer kit installed on it, but it only started doing this after I put 37s on. It drove fine with 33s on the same rims and lift.

Any idea what else could cause this excessive body sway/cab shaking?
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Tire pressure, out of balance tire, caster could be off, track bar or other suspension components could be loose and you may have not noticed it as much on the 33's but the added weight of the 37's could of triggered it. That's a good starting point
 
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CoreyOringderff
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The rims are 17 x 9.

I had my tires re-balanced and rotated last week and it didn’t seem to make a difference. The tire shop put them to 40psi so I’m going to reduce it to 35 to see if that helps.
 

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The rims are 17 x 9.

I had my tires re-balanced and rotated last week and it didn’t seem to make a difference. The tire shop put them to 40psi so I’m going to reduce it to 35 to see if that helps.
I run my 37's at 33psi on stock wheels and I got no issues. 40 is to high IMO.
 

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2.5 spacers and nothing else suspension wise?
 
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CoreyOringderff
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2.5 spacers and nothing else suspension wise?
Nothing yet. I put this lift on as a place holder until I can put a beefier lift on.

it’s just spacers in the front and back, shock relocating mounts on the front and longer sway bar end links
 

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Sounds to me like a suspension issue that is showing up due to the added weight of the wheels. Improving the suspension should do the trick.
That's what I was thinking. I personally would not add anything spacer wise over 1", with that much of a spacer and no control arms, that caster has to be wack as fuck.
 
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CoreyOringderff
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I have seen some other threads on here with people running the same lift and 37s with no issues. I do plan on doing a full lift with adjustable lower control arms and an adjustable track bar, though. The lift I have on it is the G250MSB.

I’m assuming the stock shocks and springs from the sport model are fairly soft and my have trouble holdimg the body steady so a new lift kit with springs and shocks is on the list of to-dos.
 

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Sounds like the rest of your suspension needs help with the extra weight.

"People are running the same lift with no issues" isn't a feasible excuse. And I mean no disrespect by that by the way. They'll have issues eventually. All comes down to driving habits. Yours just happened to pop up faster than theirs.

Best of luck.
 

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The rims are 17 x 9.

I had my tires re-balanced and rotated last week and it didn’t seem to make a difference. The tire shop put them to 40psi so I’m going to reduce it to 35 to see if that helps.
Wow 40 is way high on tires that big.

You also say "on the highway" but don't say how fast you are going. Big tires, big lift, yes, it won't be as stable if you try to drive 85, just as an example.
If you set the tires way out, you've impacted the scrub radius which can lead to problems with stability, bump steer, brake steer and so on.
Offset, backset, you give size but not much other detail.
 

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I missed a part of the conversation - you lifted 2.5" but have the stock lower control arms and stock track bar?

My bet - caster is way low, and the axle is offset to the side - which throws off geometry. Sounds like you are already thinking ahead to some potential fixes. Get the axle back to center with a quality adjustable track bar (by quality, I mean a stiff one that can handle the extra stress and not flex at all) and get your caster back to where it should be - you may find a big difference! (and we're hoping so)
 
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I took some air out on my lunch break and it helped the ride quality but not the side to side bouncing.

when I got back to work I put a wrench on my sway bar end links and noticed the front driver side was really loose. The bolt would spin with just the weight of the wrench.

I’m going to check the rest of the bolts that came off to install the lift but hopefully that makes it safe to drive 70mph again.
 

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I took some air out on my lunch break and it helped the ride quality but not the side to side bouncing.

when I got back to work I put a wrench on my sway bar end links and noticed the front driver side was really loose. The bolt would spin with just the weight of the wrench.

I’m going to check the rest of the bolts that came off to install the lift but hopefully that makes it safe to drive 70mph again.
You probably already know - tighten, then torque, those bolts and nuts with the wheels on the ground and the weight of the truck on the springs. Never with it's feet dangling in the air.
(*just a reminder for others who may be looking in)
GREAT idea checking all of those critical areas for being tight/torqued. Some of those suspension and steering bolts/nuts have some pretty high torque specs.
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