haha ok last post from me. Even in your example the KDSS did not cause, and could not cure the lean. KDSS can effect the tilt of the truck, but don't start using it to try and cure lean caused by a lift kit. It can't. It would be like trying to fix it with fuel level, it would only work right now, its a bandaid.

The lift kit caused the lean. We are at least in agreement that adjusting the ride height is the way to fix it. That is because the ride height is the cause of it. I'm trying to crush this myth, and save people a lot of time and money.

YOU CAN ONLY FIX YOUR RIDE HEIGHT BY FIXING YOUR RIDE HEIGHT.
No one would suggest fixing lean by changing your sway bar link length. That is what messing with your KDSS does. My only guess is that the accumulators are not always at the same pressure when you shut the truck off, and that it does actually vary on a stock truck as well.

Don't worry though, my lift is still sitting in my garage. When I finally get time to install it, I may come crawling back to this thread.

Ha ha, yep you might be. KDSS can and does affect the balance of the vehicle. It is difficult to know what is causing the issue once you modify the truck. There are solutions, it just takes some trial and error over time. I recommend trying the tilt calibration procedure before adjusting springs...

FWIW - KDSS, if set to zero properly, seems to have no effect whatsoever on lean in my 4runner.

I have air suspension and adjust my ride height all the time. I never notice any lean whether I'm at oem hight or +5 inches. (I can lift the rear until I max the shocks out). I don't totally understand why some people are having issues with KDSS and lean. It's something I'm struggling to understand the physics of as to why it happens. I can understand that if it's setup wrong initially it would lean, but if it's set level once, it should always be level regardless of lift. There must be something I'm missing. Like the leverage on the front piston is different than the rear due to geometry changes in the front control arm and over time it pulls the left side down or something? Or the rear without an adjusted trac bar is off center and causes some imbalance?

I took several measurements before and after my lift install.
I too had about a 3/4 inch lean on the rear passenger side and 1/2 in the front.
(full tank)

I remeasured six months later and it had reduced to about a 1/4 inch even on the passenger side.
I've checked it a couple more times and have noticed slight variations but never more than 1/2 inch which i can live with. Not really noticable to the naked eye.

I've never attributed this to the KDSS all be it possible.
Installing any suspention kit will alter the geometry. This is why it is important IMO to have someone you know has off road suspention experience do your install and alignments.

They're easy to do if your mechanicaly inclined ( I am) but just as easy to screw up. I gladly paid an old freind in the business and another friend for the alignment. I haven't had any issues and it rides like a dream.

if most ppl w kdss have a lower, passenger side lean, why do my cornfed rear spacers have less lift on the passenger side and more on the driver side? should i reverse the orientation for the rears?

The other day I drove the 4R with an empty tank for the first time in a while. The lean was obviously much more dramatic. It bothered me so much I went home and ordered front and rear Toytec spacers for the pass side.

Hey guys, I'm a 3rd gen owner considering upgrading to a 2014-2015 TE with KDSS and an ICON Stage 5 lift. It occurred to me reading here that the lean may have a simple explanation. Has anyone measured the lengths of all 4 OEM coils before doing a lift? And then measuring all 4 new lift coils before they go on to note the differences?

On the 3rd gens, the OEM driver side front coil is longer/taller than the passenger side to compensate for the drivers weight. Stock springs are pretty soft, much softer than after market lift coils so different lengths makes sense. I'd bet the KDSS system is tuned accordingly and I'd also bet most lift coils are the exact same length between left and right, which would make perfect sense why spacers would be needed on the passenger side.

I'd love to hear from anyone that's done an ICON stage 5 lift on a KDSS Trail about the experience and if it's doable by oneself in the home garage with jacks and stands.

SO... I've been tracking this a bit more lately. Something is happening with the KDSS. I've noticed that over time I have been adding more air to the passenger side airbag to balance out the system and sit level. At first I was balancing pressure side to side, but it developed an inch plus lean over time. I did adjust my front coilovers during this time up about 1.5 inches for a trip to moab. I need to drop them back down and see what happens. I count the rotations of the collars and I assume that moving each the same amount should give equal lift to both front corners. I'll keep updating this as I learn more. There's obviously an asymmetry in KDSS, but it doesn't make sense to me why it would cause a lean or develop a lean at a different ride height. I actually don't understand how it can develop a lean without some internal issue with the valves or something like that.

i have an adjustable trac bar and that didn't fix it just helping your theories by ruling that out

Interesting. Everyone is talking about mostly passenger side being low. My front drivers side is about 1" lower than the right.

I haven't read this for a while, but I've had some PM conversations regarding it. As of now my working opinion is that you must either spacer or have different springs side/side to balance KDSS lift. I haven't had time to calculate the difference yet or exact measurements to get a better calculation of spring rates. But this is a copy/paste from a conversation I've had about the front to give an idea of what I think is the issue and how to solve it.

Also note that the rear is more complex because of the suspension is "dependent" side to side, so it's a more complicated calculation to get it right.


The downsides are the complexity and one design flaw. The problem with using two pistons in this way is that the piston rod that extends has volume. And as a result as the piston moves the volume of fluid in the combined chambers changes. The excess volume from the piston rod has to go somewhere. To account for this the system uses a pair of accumulators. They are basically just small tanks that act as reservoirs for the extra fluid. But then how do you have a closed system and still allow for expansion without mixing air in the oil? The small accumulator tanks have a rubber diaphragm inside them that is pressurized on one side. - Like a little balloon inside them. As more oil comes in, the balloon full of air gets compressed. No big deal. That's actually exactly the same thing that happens inside of a shock absorber.

Where this becomes an issue is that both pistons are cross linked to make them act as reverse master/slave - when one compresses the other extends. The piston rod area is deducted from the surface area that the hydraulic force of the fluid pushes on. So the top of the piston without the rod has at he full area of the piston, the bottom has the area of the piston minus the rod diameter. Why does that matter? - the answer is that the accumulators are pressurized to about 500psi. And as a result the entire hydraulic circuit set is also pressurized to 500psi. That pressure in the system along with the slight mismatch in the top and bottom of the pistons due to the piston rod means that both KDSS cylinders has a constant pressure pushing down on it of somewhere around 1-300 lbs of force. It's a complex calculation to do without any exact measurements. I can probably do it whenever I get some actual measurements. But my guess is that it results in somewhere around a net force of 100ish lbs of force on the front and rear sway bars pushing down on the driver's side and up on passenger. By that I mean it wants to tilt the vehicle to the passenger side by around 100lbs on each axle. That doesn't sound like a lot -but it results in a slight lean.

If the normal spring rates are around 600lbs/in on the front coils - but they have a 2:1 leverage ratio, that means effectively they are 300lb/in and the same is roughly correct for the rear. If you have 100lbs of extra lift on the front and rear on one side, you would expect approximately 1/6" of lean. It could easily be as high as 300lbs though. I just don't know. If you had 300lbs of effective difference you'd expect a full 1/2 inch of height difference left to right if all else were equal.

For this reason Toyota balances the KDSS lean with slightly longer springs on the passenger side of KDSS 4runners. (Ideally you want a longer spring not a stiffer one - it's a long explanation, just trust me.)

Most aftermarket lift springs will not have a different spring length or spring rate side to side. The result is that you often end up with a "KDSS lean" when you lift them. It's not necessarily a result of the lift, rather it's a result of the spring changes from two different springs to matching ones.

With a 600lb spring and a goal of counteracting the KDSS lean effect, I think you would be pretty darn close by adding somewhere in the range of 3/16 and 1/4" spring spacer to the passenger side front coilover.

Great explanation. I think you've got the theory down pretty good, will be interesting when/if you measure and prove it. To note, dobinsons sells longer springs for kdss trucks to correct lean.

I have lean after my dobinsons spring install. Front driver side is about an inch lower

Did you mix up the front springs? It's the passenger side lean that people are seeing with kdss.

I haven't installed mine yet so I can't say what I'm going to deal with.

I don't think so. The springs were only marked with stickers that said left and right, which drives me nuts since perspective can change what that means. I went with right being passenger side (right side when sitting in vehicle)