35" tires with spacers and springs -- front end wobble in 4WD

[nate.co]

After doing a lift and adding 35" tires (315/70R17 K03), I've got a pretty bad wobble on the front end when accelerating in 4A or 4H. If I switch to 2H it goes away. It doesn't happen every time I accelerate but is there maybe 4 out of 5 times or so. I am assuming this is from too much drive shaft angle.

I am using the 2"/1" spacers from GOAT and have Eibach springs as well. I went with the combo after measuring droop from added weight (Rival bumper and winch up front, Decked drawer full of junk in the back) and working through the lifting guide. The amount of droop I have is less than the added height from the springs, so in the front including the droop correction, I'm at 2.6" above stock, and in back I'm at 1.2" above stock (measured droop of 1" front and 1.4" rear, springs are +1.5 front and +1.6 rear)

I looked around at front diff drop kits but there don't seem to be any for the Ranger Raptor. There's quite a few for the 2019-2023 (5G) Ranger, but I don't find any for the RR. Also looking under the diff, the back side of the diff is very close to the frame crossmember and the bottom of the diff is close to the skid plate so I'm not sure there's room to move it anyway.

Anybody have similar issues? I had the lift on for a few days before doing the tires (which are about 11 lbs heavier on each corner) and the wobble is worse with the bigger tires, but was there with the stock wheels/tires as well. I assume the added tire weight is just exacerbating the wobble and isn't the cause.


Trying to brainstorm options, here's what I came up with:

1. Go back to stock springs and keep the spacers -- problem here is the added droop up front especially with the winch hanging out there in front of the axle.

2. Slice the front spacer in half. I'm assuming the issue is too much angle since the springs are correcting more than the weight droop by about 0.6" up front, which seems to be causing the wobble. Obviously not a huge fan of this option as machining that spacer is not going to get done with a sawzall.

3. Remove the spacers, keep the springs. I do really like the springs as the front end doesn't dive as much with the winch etc, and my worry with option #1 with the stock springs is that they will still be "divey" up front. With this option I would probably go back to either the stock tire size or something slightly bigger than stock, like a 295/70R17 (about 1/2" bigger than stock, vs 1.6" bigger with the 315)


Thanks all -- I spend about 99% of my time in 4A so this wobble is driving me crazy.

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[embedded rock]

Maybe an alignment shop could increase the castor as your trucks sits now. That would improve stability.

 

[nate.co]

Yeah I was thinking the same thing, so I put in a Foutz UCA. It aligned better with the new UCA and is definitely more stable (that fixed a 50mph straight-line wobble), but that had no affect on the wobble under acceleration in 4A or 4H.

 

[embedded rock]

What do you think about moving the castor outside of the factory range? Increase castor a few degrees and see how that feels. Won't hurt high-speed, but maybe you notice a little more effort steering at parking lot speeds.

 

[nate.co]

Not great honestly. Leaning towards #3 or #1.

 

[Arsenall11]

Since it is only doing it 4WD, I would look more towards the drive shafts and CV joints.

 

[embedded rock]

This definitely a wobble and not driveline vibration, right? My assumption is the tires are balanced and this is not driveline vib.

 

[nate.co]

Correct, tires are balanced, was just aligned.

 

[E40]

@nate.co how much castor did you get with OEM UCA vs Foutz UCA?

 

[nate.co]

After the lift, caster on the OEM UCA was 3.3° left and 3.0° right. After the Foutz UCA it was 3.0° left and 2.9° right

 

[embedded rock]

Coming from a '23 Tacoma and a '24 Wrangler, those were around 6 degrees. The Tacoma needed this for driveline vib and the Wrangler for the death wobble preventions.


Edit. It's been a minute or two since my Tacoma days and that may not be quite right.

 

[nate.co]

You might be on to something, found this spec sheet listing preferred caster as 3.45.

I don't understand how that would affect the drive shaft angle though?

 

[embedded rock]

Let's take the easy one first--straight axles. Caster there is dependent on rotating the axle forward/aft which also changes the driveshaft to pinion angle. This castor is adjusted with the upper and lower control arms for the axle. Btw, look at your rear axle and control arms for you RR. Same basis arrangement for a front straight axle.

With IFS, the pumpkin has to be rotated to change the driveshaft to pinion angle. The cross shafts don't care. This is more for vibration reduction.

With IFS the castor is set by location of the upper and lower ball joints. More caster, more stability. Also, the steering tends to self-center better with more caster. Pretty much need an alignment machine to measure.

 

[embedded rock]

Also driveline vibrations due to excess angles and traditional u-joints are more temperamental. Now, we have CV joints on driveshafts that pretty-much don't care about angles.

 

[embedded rock]

Anything new @nate.co?

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