bb700092

I felt the same nose dive during braking when I purchased my 2016 GS. I changed all my tires with Michelin Pilot Sport A/S 3+ and there was a very noticeable reduction in the nose dive.

peteharvey

The 4GS is quite tall; probably the tallest car in its class, while the new E Class is lower slung.
Meanwhile the aging 4GS rides on the shortest wheelbase in its class, hence greater squatting under acceleration and nose dive under braking.

The firmer the coil springs and the lower the ride height [the shorter the suspension travel], the lesser the amount of squatting and nose dive, however the ride will also deteriorate.
OEM bushings are normally rubber-based for compliance and comfort, however you could use aftermarket polyurethane bushings that are both stiffer and last much longer, however the ride will be teeth shattering for most people.

Unlike softer sidewalled touring tires like Pirelli Cinturatos, Bridgestone Turanzas, and Michelin Primacies, sports tires like Dunlop SP Sport Maxx 050, Bridgestone Potenza RE050A, and Michelin Pilot Sports have more rigid side walls, and will reduce squatting and nose dive, but at the expense of ride quality and quietness.

It's all a compromize.

sarmyth

Here were my thoughts on it. I'm about half a year in on the swap and it's truly transformative on this vehicle.

https://www.clublexus.com/forums/sus...a-bushing.html

bb700092

Truly appreciate your sharing this mod and your experience at the Suspension forum. I have been looking for a suspension mod for better handling (as opposed to cosmetic looks) since I purchased my GS. There are a number of control arm bushings available in the market. Did you do any research on them and then choose the RR Racing one? If you did, which other ones did you consider?

I posted the above in your thread in the Suspension forum but it seems few people read and respond there, so posting it here again.

peteharvey

OEM bushings are normally made from rubber for ride comfort.
Aftermarket bushings are normally made from polyurethane for minimal flexing, hence sharper handling, but at an expense to the ride comfort.
Unlike rubber which is broken down by ozone in the atmosphere, polyurethane lasts longer.

Below is the OEM bushing for the GS, versus the red polyurethane bushings by RR Racing.
RR Racing also have polyurethane bushings for the compact 3IS to take the compact 3IS handling to another level.
Aftermarket polyurethane bushings will always sharpen up handling for any car, at the expense to the ride.
Theoretically, if polyurethane bushings could sharpen the handling with zero deterioration to the ride, then polyurethane bushings would be used OEM.
http://www.rr-racing.com/Lexus-Lower...isfxlca001.htm

bb700092

Pete, Thanks for your comments. While I would like to believe that polyurethane bushings lead to sharper handling, my independent research does not support that. For example, watch the following Youtube video on polyurethane bushings where the experimenters conclude that the difference between polyurethane and OEM bushings in everyday driving is minor (around 5% on the track). Further, not only are the polyurethane ones more costly, making one part of the suspension stiffer might create more wear and tear on other parts of the suspension.


IMHO, the following two points are important to keep in mind:
1. All suspension components work as a whole. Changing one small component of it will most probably not make much of a difference to the whole suspension. On the other hand, doing a major overhaul is probably not worth it due to cost, longevity and warranty issues.
2. The manufacturer of a vehicle knows more about its suspension than any of us. The manufacturer has certain goals in mind when it designs the suspension, including handling precision, comfort, longevity, cost, etc. If changing one small component could make a significant improvement to one of these goals without negatively affecting the others, they would have done that already.

peteharvey

I totally agree with you bb.
Overall, the handling improvements in upgrading tbe front bushing to polyurethane is small, but in the context of some one who is very "focused" on front bushings - to them, there is a "world" of difference.

sarmyth

Don't knock it before you try it, Google doesn't know everything =) Start from 9m53s to see the stock bushing dance.

sarmyth

In most positions in suspensions I completely agree with you and in the past, have had better results replacing poly bushings on cars with new *OEM* rubber to achieve better results. Usually the reason why it doesn't matter is these bushings aren't large enough to let the bolts deflect much, so while you may get better high-speed transient behavior, everywhere else you just get more roadfreel. The only universal place where I've seen poly bushings perform better is in swaybar applications on *thick* swaybars. Rubber bushings typically don't handle the load very well.

That being said, every suspension design is different, and if you look at how the GS is setup it's not typical with how they arranged the mounting points for the front arm and built compliance into an otherwise stiff setup. I've personally never seen a bushing on a front control arm as large as what's on the back of the lower control arm on the 4th gen GS. If you read the backstory on some of the changes, TMC intentionally made it larger and stiffer vs the 3GS to help sharpen the car's response but still maintain the same level of NVH due to the increased amount of material to absorb impacts.

Eliminating slop is the best way to make cars handle predictably and perform exactly what you ask of them; when you have that much deflection on a critical arm controlling tire placement, there's no way you're going to be happy if you drive your cars hard.

bb700092

I agree. But my question is, if it is as easy (and inexpensive) as replacing the OEM bushing with RR Racing ones to achieve better handling, why didn't Lexus do it already?

BTW, do you have the F-Sport model?

sarmyth

I do have the F-Sport model, and the answer is relatively simple; it increases NVH. If you read my comments from the thread I linked it takes a big car which soaks up potholes at speed but wiggles, flexes and shimmies and turns it into one which transmits those impacts instead but reacts better and is planted.

The mod is significant enough to not be for everyone; some may think it takes their luxury cruiser and turns it into a more pedestrian car. I can say I used to love the ability to blast through rough road and not care, I don't do that anymore. However the removal of understeer, the elimination of inner tire wear, and the added stability is just too good for me to ever return.

In my opinion this is how the car should have been from the factory. The NVH is not any harsher than your random german car... jetta/gti/3 series/c-class, but it's certainly not "Lexus" plushness.

bb700092

I do not have the F-Sport model or the Sport+ mode. A number of people in this forum have raved about the driving dynamics and throttle response in the Sport+ mode, however, adding that the ride might be a bit harsh in that mode in uneven roads. I was planning to replace all my suspension components (e.g. spring, sway bar, bushings) with OEM F-Sport suspension components to match the parameters in the Sport+ mode, hoping that my GS will always drive like a GS in Sport+ mode as far as suspension is concerned; the throttle response will depend on the mode I select (Eco, Normal, Sport). I am yet to locate all the OEM F-Sport suspension components in the 2016+ model though. Your post on making the driving dynamics sharper with a relatively simple and inexpensive mod is making me rethink my plans.

A few questions for you:
1. Didn't you feel the suspension to be adequate for your purposes in the stock Sport+ mode?
2. Now that you have done this mod, do you feel any difference in how the suspension works in the four modes (Eco, Normal, Sport, Sport+) in your GS?
3. If you have driven the 9th gen (2013-2017) Honda Accord, does your GS after the mod drive harsher than the Accord on uneven roads?

sarmyth

It was OK... I've always been one to modify the suspensions of my vehicles rather extensively and drive very aggressively so I'm the wrong person to ask in the general sense. What I liked about the GS was that it had the ability to shift between being somewhat sporty and back to very comfortable if you flipped it out of sport+. I always wanted more though as the thing washes out hard (understeers) under aggressive cornering regardless of the amount of throttle you dump in. I've been looking for a strategy to fix that since I bought the vehicle without affecting the softness being out of sport+. The bushing handled it where as my experiments with rim/tire widths and different tire compounds did not (though it was fun running with all seasons on the rear and S04s on the front! Not recommended unless you're trying to be a drift king =) ).

There's only 2 modes to the active dampers, sport+ and everything else. This mod changed things so that under normal cruising, there's little difference between sport+ and normal but in a good way... the body motions are much less even though the baseline damping is also less. For instance, side-to-side "wallowing" while cruising on the interstate in normal mode nearly disappears with this change. I attribute this to the fact that because the car is much more controlled in general, the AVS system doesn't need nearly the same amount of adjustment to keep things on an even keel so it effectively "defeats" the system resulting in little difference in a straight line between the two modes. ( Note that the system was effectively designed to limit the motions of the car, take away the motion, the system does less in both sport and normal modes ) The old bushing allowed so much play that it required the active damping to help keep things controlled. That's all wild speculation of course, I haven't plotted the before and after difference of the live damping adjustment to prove that is honestly occurring.

However, when driven aggressively, there's still a good amount of difference between the two modes in keeping the car flat which is what I was after. Read my posts in the thread I linked for more explanation of what I felt.

I have not, but I'm very surprised to hear the Accord is tuned that harshly! I can say it's a tad softer than a Focus ST or a smidge more supple than the non-avs IS350 but not by much. What I have right now is similar to a current or previous gen 335 but with more wheel travel. Not objectionable in my mind, but certainly a change from the original design of the car.

sarmyth

Another thing I'll add as an observation from someone who rode with me before and after... his comment after going through a couple high-speed sweepers:

Before, you didn't "control" the car, you guided it where you wanted and then let it do what it was going to do and corrected, but your input was secondary to what the car required in order to move at that pace. Now you tell the car what to do and it follows.