Twist/roll under acceleration and braking after adjusting springs.

I'm getting a bit of chassis twist on moderate braking and acceleration after upgrading to 650 lb/in coils along with a stubby bumper and 10K winch.

Previous Setup:

• Bilstein 6112s with 600# coils set at clip 6/8
• ¼" thick top hat spacer
• OEM rear leafs + AAL

Current Setup:

• Swapped in Ironman medium-duty leafs (~2.5" of rear lift)
• Installed 650# Bilstein coils, set at clip 7/9
• Upgraded to a ⅜" thick top hat spacer
• Added stubby bumper + 10K winch

I currently have around 0.80" of positive rake, but I've noticed the passenger side sits ~⅛" higher than the driver’s side.

Dynamic Behavior:

• Under acceleration, the driver’s side lifts first, then the passenger side follows.
• Under braking, the passenger side dives more noticeably before the driver’s.

Feels like the vehicle is twisting rather than pitching straight—likely due to preload imbalance and the stiffer driver's coil being more compressed at ride height.

My Plan:

• Leave passenger side at clip 7
• Drop driver’s side from clip 9 to 8
• Swap current ⅜" spacer for a ½" thick spacer

This should reduce preload on the driver’s side while maintaining overall ride height and rake. Hoping it'll help balance out the dynamic response under load.

Would love to hear if anyone's dealt with a similar pitch-roll twist and what worked for you.

 

Why wouldn't you set both fronts at the same clip and let the spacer deal with the Taco Lean?

Seems when you have different spring preloads you're going to get the type imbalance you describe. Due to one spring being 'shorter' than the other.

 

I went with what billstein reccomended in this but am thinking that the heavier duty springs and moving 1 notch higher on each side are attributing to this

I was using a spacer on both sides so I didn't have to crank the preload so high and lose travel, but in this case I'm thinking I need to go down one or two notches probably one notch and use a 1/8" thicker spacer on the driver's side to reduce the behavior (
Moving from 3/8 to 1/2)

 

I figured I would give the new leafs in the rear a month to settle and likely slap in a steel rear bumper before messing with the front ride height again.

 

Be careful with putting spacers on top of 6112’s if you drive off-road at all. 6112’s are technically extended travel — they are just as long at full extension as most extended travel shocks.

For instance, I found that putting a 3/8” spacer on 6112’s caused my upper control arms to contact the coil springs at full droop. (There was also contact of some sort with the CV boot while drooped and fully turned to one direction, but it’s been awhile now and I can’t remember the specifics.) You’ll need to check for yourself by jacking the front of the truck up and looking for points of contact.

Additionally, when you lift much beyond 2” you will find that the fins on your CV boots will rub, causing them to tear prematurely.

Finally, it is completely natural for the truck to twist during acceleration in the opposite direction that your drivetrain turns. It’s like recoil on a firearm. This will be more pronounced as your suspension becomes softer relative to the suspended weight of the truck. When you add a bumper and a winch, you are adding close to 200 lbs., which is cantilevered perhaps two feet in front of your coilovers, so it is equivalent to more than 200 lbs. Your new springs are 50 lbs. stiffer per inch of compression than the old ones, but, (aside from not requiring as much preload to maintain a given ride height with the additional weight), they only begin to help handling of the additional weight upon compression below ride height.

On top of that, the valving of your shocks has not changed, so they do not resist the unloading of a 650 lb spring as efficiently as they would a 600 lb spring when you accelerate. So, without custom tuning your shocks (you can’t with 6112’s), you are going to notice more tilt and squat on acceleration, and more nose dive on braking, when you add weight to the front. There’s no way around it.

The nose dive when braking is also due in part to your rear shocks unloading, and they may not resist the unloading of the new leaf packs as efficiently as they did the old ones. (Edit: In fact, you can be fairly confident that is the case. Aftermarket leaf packs allow for more droop. That is, they compress to ride height over a longer range, meaning their spring force also falls off more slowly — along a longer length of the shock shaft — as the shock extends during braking.)

Regarding the *asymmetrical* nose dive, I don’t know what that might be about, but I’d check my tire pressures, my brakes, my alignment, and the condition of all my shocks, before starting to introduce asymmetries to the spring rates.

 

Thanks, I'll carefully check my droop and compression again when I adjust a few things this weekend, I do have jba UCAs which will help with the uca to coil contact as well as a 1" front diff drop bracket installed to help reduce the angle of the CVS and potential binding full droop.

I saw that ready lift sells a kit with 6112s and what appear to be either 1/2" or 1" thick spacer tophat so assumed I should be fairly safe with 3/8" thick spacer.

 

My UCA contact was with SPC’s, but YMMV.

The CV boot contact was at the outer boot, at full steering lock and full droop — it might have been contacting the LCA, but I can’t remember. A diff drop wouldn’t do anything to help it though.

 

Thank you , I'll check that out later today when I replace my A arm skid fasteners.

Assuming there's no rubbing, what I'm planning to do is give the rear leafs a few hundred miles and a month to settle, add a steel bumper (for protection, recovery points and to help balance the weight distribution of the truck) , see where it rests and then readjust the front to maintain a .5 to 1" rake.

What I may end up doing depending where the rear comes out is either run 7PS+ 3/8 spacer , 8 DS + 1/2 spacer or 6 PS+ 3/8 spacer , 7 DS + 1/2 spacer to minimize the handling differences between the sides.

ill reduce the spacer size if I am rubbing or close to rubbing full droop. E.g. if I'm close I'll probably drop passenger side to 1/4 and keep 3/8 on DS

I also have the bolts for my RCI A arm skid to be cautious of at full droop.

 

Surprisingly I have a little bit of wiggle room, the clearance between the fins and the strut mount and skid bolts is a bit close but I couldn't get them to touch. I did however add another washer to the bottom side of the skid bolt and a neoprene washer to the top since taking the photos so that there's only a sliver of exposed thread. I have about 1/4 clearance from it full droop.

 

Closer shot of the UCA and bucket
I could probably get away with a 1/2 spacer but that would be the absolute limit before things start touching and the lines begin getting strained.

 

That’s close!

 

stop with the spacers, you dont need them and are just making things more complicated. The spacers mess up your compressed length and you run the risk of bottoming out the shock. The recommended clip settings should account for the lean. If they dont, then shift the clip position to accommodate.

There are no handling differences with running different spring preload left vs right. All production trucks do this.

 

You can put up to a 3/8” (and maybe even 1/2”) spacer on 6112’s without bottoming out the shock before you hit the bump stops, *as long as* you aren’t creating interference issues at full droop. The advantage of this is you get almost an inch more droop at the tire. It also keeps 33” tires from rubbing the tops of the wheel wells.

Regarding the preload, you are generally correct — preload does not affect ride quality until you crank it to crazy amounts — but that applies to evenly preloading both coilovers so that the truck sits level.

On the other hand, if he preloads one side a half inch more than the other side (which would equate to nearly a full inch of lean), *but then he corrects the opposing side with a 1/2 spacer*, he has given the more heavily preloaded spring a 325 lb. head start in stiffness while the truck sits level. A driver will almost certainly feel that difference.

(I personally would be hesitant to set up my front coilovers so asymmetrically.)