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Old 02-19-2020, 03:19 PM #16
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The primary error in a lot of what I've read in comments above is that the sway bars do not ever become disconnected or act as though they're disconnected. There are two independent hydraulic circuits between the two cylinders - one front one rear. Each circuit has a gas charged small expansion chamber called an accumulator. Each circuit also has a valve that opens or closes the expansion chamber from the rest of the circuit. The fluid transfer between the cylinders is 1:1 in either circuit. The result is that in "closed" position there is no dampening and it's a very rigid connection front/rear, but the two cylinders can and do still move - they do so with a very rigid master/slave function.

When the valves are in the "open" position the two circuits are dampened by the accumulators. So the master/slave movement is not fully rigid. It is not fully free either. And that's the main point I'm trying to correct. They act as a softer master/slave, not really like a disconnected sway bar. And they only have a limited range of travel. Combined with the accumulator having a gas compression spring rate (highly progressive) the result is that they have relatively soft feel near the neutral position in the travel range of the cylinders and become progressively more rigid near the ends of the piston travel, and then very rigid beyond the max travel of the cylinders. There is also a significant force applied to the body to retain it's position balanced between the front and rear axle angles. So there's a body stabilization function occurring along with a forced articulation function (the two are really the opposing reactions of the same forces).

The accumulators start with IRC 500psi charge. They're not really disconnected or fully connected. It's somewhere in between. I've often been curious how the ride quality would be with a sway bar spring rate similar to an SR5 but mounted in the KDSS system. I think that could offer a feel much closer to a true disconnected sway bar.

The 12mph is taken from this diagram I believe. I'm not sure if it's totally correct though. My reading of the diagram is that over 12mph it will close the valves if the steering rate of change exceeds the limit (you turn the wheel fast) or if the lateral acceleration exceeds a certain amount - you go around a corner fast. I'm not sure if they otherwise remain open or not - for example going 40mph in a straight section of road.

I am also unaware of anyone having played with the gas pressure to see how it might work with 100psi for example.


Last edited by Jetboy; 02-19-2020 at 03:32 PM.
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Old 02-19-2020, 03:57 PM #17
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Quote:
Originally Posted by enyce View Post
Reading this thread and I don't own a KDSS 4runner... Grabbing my coffee and cookies for this one.
I have the popcorn popping.
I have KDSS...that is all
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Old 02-20-2020, 06:39 PM #18
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Quote:
Originally Posted by vicar View Post
This is probably discussed somewhere but here goes....

I know KDSS is supposed to decrease body roll on road. But is it possible for KDSS to actually increase body roll at low speeds?

I have a 19 TRD ORP with KDSS. I liked it when I test drove it (mostly on the interstate) - it seemed firmer and more controlled than the non-KDSS 4runners I have driven. But now that I own the car I’m experiencing it under different conditions. I’ve got a couple places in my work commute where I have to take a left turn at very low speeds, one of them coming off a bit of a hill. On both turns I notice very excessive body roll. I know various sensors, including speed sensors, are involved in engaging KDSS. Is it possible the system is just giving extra articulation in those instances since I’m going slow? The body roll is far greater than other trucks and SUVs I’ve driven on this same route. Since I’m new to KDSS I wanted to see if anyone else had similar experiences making low speed on-road turns. Is it something I need to get used or something I should check into?

I’m on the stock Bridgestone tires, which I realize are pretty squishy. But I do have them at 35 psi. I look forward to replacing these tires with better ones eventually...

Thanks.
So, to add a nice bow on this whole thread: YES, you can perceive your KDSS equipped 4Runner to have more body-roll at low speed. Since the anti-sway bars are not doing their job, you can feel more body-roll because there likely is more body-roll.


Last edited by DigitalVex; 02-20-2020 at 06:41 PM.
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Old 02-20-2020, 06:49 PM #19
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That's not really how it works, jetboy has a great explanation above
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Old 02-21-2020, 04:41 PM #20
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That's really how it works, jetboy has a great explanation above.
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Old 02-21-2020, 06:01 PM #21
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Quote:
Originally Posted by DigitalVex View Post
That's really how it works, jetboy has a great explanation above.
Just let it go man. At this rate, this time next week you'll be explaining to us the difference between tq and hp, or how VTEC works...
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Old 02-21-2020, 07:39 PM #22
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Originally Posted by Space King View Post
Just let it go man. At this rate, this time next week you'll be explaining to us the difference between tq and hp, or how VTEC works...
How does VTEC work?











P.S. This question is asked in jest. I know how it works, and don't need it explained.
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Old 02-21-2020, 08:19 PM #23
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Old 02-22-2020, 12:05 AM #24
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how about the initiator of this thread performs a test and posts the results back. the test is to go around the same two corners at a bit higher speed if possible to do so safely (say more than the acclaimed 12mph) and see if the body roll he experiences is less or not there at all. what i have gathered so far from the posts is that the low speed cornering with KDSS gives a different experience than higher speed cornering in a KDSS equipped 4R. the low speed comparatively has more body roll (some folks are calling this 'KDSS is designed to add body roll ... but its just a matter of explaining !!!?)
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Old 02-24-2020, 03:16 PM #25
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We don't really need the initiator of this thread to perform the test. I have a KDSS equipped 4Runner.

At lower speeds, the body rolls more on the suspension. This is because the anti-sway bars are not actively adding pressure (read: opposite side force) to the opposite side wheel. Like what others have said, it sort of feels like not having sway bars at lower speed.

Opposite to this, because the KDSS anti-sway bars are thicker than standard bars, body roll and sway is more controlled at higher speeds. Some people have said the handling of KDSS vehicles at higher speeds is noticeably different than standard anti-sway bar 4Runners.

I noticed a difference on test drives.

The one area I actually do not like KDSS is between 15-30 MPH. Because of the added stiffness of the anti-sway bars, it seems to "bounce" and "jounce" more when going over crappy roads. Basically, a harsher ride in the cab.

I think it would be pretty cool (as jetboy alluded to above) if you could "dial-in" the pressure in the system, effectively softening up the anti-sway feedback manually. Basically letting a user choose a Firm, Soft, Super-soft, or Off version of KDSS.

Something along those lines, at least.

Last edited by DigitalVex; 02-24-2020 at 03:18 PM.
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Old 02-26-2020, 01:23 AM #26
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Great discussion. Thanks everyone.
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Old 02-26-2020, 03:48 PM #27
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Originally Posted by vicar View Post
Great discussion. Thanks everyone.

Well, it was A discussion.

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Old 02-26-2020, 04:22 PM #28
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Since we're discussing - BMW has had a system it's used for a while that does a very similar function. The problem with the BWM version is that the range is small and it can't withstand offroad type use (too much movement too fast overheats it). It uses pressure from the power steering pump IIRC to actively balance body roll, not front/rear connection.

But the idea is kind great IMO.


What would be fun in an experimental world would be to just use one of the center sections with a very light weight fluid and no front/rear connection. Just a circular routing so the fluid goes in one side and through a valve and back to the other side. The result - using a solenoid valve - would be a push button sway bar disconnect that doesn't flop around or have the other issues of the dog clutch mechanism like on the FCA/Jeep versions. And - bonus is that they're really cheap from junker BMWs.

Last edited by Jetboy; 02-26-2020 at 04:25 PM.
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Old 02-26-2020, 05:32 PM #29
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Quote:
Originally Posted by Jetboy View Post
Since we're discussing - BMW has had a system it's used for a while that does a very similar function. The problem with the BWM version is that the range is small and it can't withstand offroad type use (too much movement too fast overheats it). It uses pressure from the power steering pump IIRC to actively balance body roll, not front/rear connection.

But the idea is kind great IMO.


What would be fun in an experimental world would be to just use one of the center sections with a very light weight fluid and no front/rear connection. Just a circular routing so the fluid goes in one side and through a valve and back to the other side. The result - using a solenoid valve - would be a push button sway bar disconnect that doesn't flop around or have the other issues of the dog clutch mechanism like on the FCA/Jeep versions. And - bonus is that they're really cheap from junker BMWs.
I had this on my BMW and it was absolutely amazing how flat such a heavy sedan cornered at speed. Checkout the initialization procedure:
https://youtu.be/tktOJMzIJog

Paired with active steering that thing was a dream when it came to eating up highway miles
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