Jack McNeal

Here's a question for all of you suspension gurus out there. My 1999 GS 400 has Bilstein Sport shocks, stock springs and Daizen bars with the rear set to full soft. The wheels and tires are stock 17" with 235/45-ZR17 Bridgestones (soon to be replaced with Goodyear Eagle F-1 GS-D3's), and the predominant handling characteristic is oversteer. I made a decision to keep the stock ride height when the shocks were installed because this car is my daily driver, and I didn't want the inconvenience of a lowered car. I've owned many lowered cars in the past. I'm having second thoughts about the ride height decision, and would like your input on how Eibach springs will affect the ride and handling. The ride now is firm but compliant. Thanks in advance for your recommendations.

FutureGS400

Welcome to CL, Jack!
A couple of suggestions to consider:

~Definitely go to the Goodyears-fantastic tire! You could go to the 245/45 size for a bit more tire. Still within acceptable outside diameter parameters compared to stock. Also go with about 40-42 psi instead of the typical 32-36 psi most places put in. The tires alone will vastly improve the handling!

~Consider a good set of coilovers. Yes, they're expensive but you can dial in the ride height you need (within limits) and still have a huge performance increase. For example, the Tein CS still gives a very nice ride with the dampers set more toward the soft end of the adjustment range. Then you could easily lower the car a bit if you want to try it, or keep it near or at stock height.

~Oversteer is more prominent on these cars (depending on the suspension setup, tires etc.) if you are used to FWD cars like I was! With my car modded the way it is now, the balance is excellent and it still has a very decent ride quality. Also, some of the various chassis braces can improve the handling of the car quite a bit, although this is somewhat subjective.
These cars can be made to handle REALLY well for a fairly large, heavy 4 door luxury/sport sedan! Have fun with it!

Jack McNeal

I forgot to mention that I have the TRD STB, which made a huge difference in feel, but did not affect the handling much. I need to stay with the Bilstein Sports for budget considerations, so if any of you have the Bilsteins, Daizen bars and Eibach springs, I would love to hear from you.

BA_GS400

iTrader: (1)

this may help, I wrote my impressions of the Eibach, and there are some other links here too:
PS. I have 245/45/17" tires.

clicky!!

lexforlife

iTrader: (7)

you asked and now is answered

i have the setup you just mentioned

Ltuned springs(rebadged eibachs) bilstein sport shocks ,daizen sways,toms 6piece links ,front and upper strut bars , trd lower brace, ltuned steering ecu and 19in staggered setup with the goodyear f1 tires

this a real complete pkge for those not looking to slam their cars, the ride is very firm very bmw m series feel, very precise cornering virtually no roll unless pushed very very very hard, turn in response instant, lane changes immediate , no float whatsoever... many who have driven with me have stated ,man this feels like a tuned bmw or amg benz.. in fact their was a thread started by reggiek about how he felt riding in my car he compared it to space mountain (i drive real aggressive all the time).. make no mistake 99% of the smooth floaty bouncy lexus feel is gone , its firm german style feel now, in fact prior to the addition of the bilstein sports i had the ltuned (rebadged kyb junk) and they were the single most detrimental thing to the handling just not up to the task , the bilsteins although much firmer are completely up to keeping everything under control... my daizens are set on most aggresive so the rear whips around to follow the front in cornering ( should be set that way when running stagg setup )

to get this feel all of the components are necessary and do work in harmony ... although i am going to be changing to bilstein pss coilovers soon to get the right height i am looking for and even tighter feel and next week willbe swapping out my front lower control brace to the toms piece for better stress resis..

hope some of this helps

Jack McNeal

To be much more specific, with my current setup, will the addition of Eibach springs make the ride firmer (harsher) (the Daizen bars are pretty hefty), and reduce the tendency to oversteer? My guess it that the answers are yes to the ride and no to the oversteer, but I'm hoping that the lowered CG will help the latter.

RON430

You want to explain a little more about your oversteer? GS is far more prone to understeer than oversteer. Even trailing throttle oversteer isn't much of a problem with a stock engine/transmission due to the electronics.

Jack McNeal

In a decreasing radius turn with no increase in throttle, the rear comes out about a foot before the skid control catches it. Maybe I'm overly sensitive, but I just like neutral handling.

bitkahuna

iTrader: (20)

I don't know, but maybe it's the setting you have the adjustable rear Daizen sway set to that affects this?

You want neutral handling? Get a mid engine car!

Jack McNeal

I thought about the setting on the rear bar, and I set it in the middle hole when I first put them on, then went to the outer hole to theoretically induce understeer. Didn't happen. So, this gets back to my original question. Will lowering the car 1" help? I'm also trying to avoid making it ride like a Z06, since this is the car I use to transport my family around. I know that lowering it will make it look "right", but I'm more concerned with ride and handling.

RON430

I have stock springs with bilstein sports and have used TRD Sportivo, Daizen, and TRD blues. Of course, a decreasing radius turn can describe a lot of turns depending on the radius. And they can be nasty, or not, depending on your speed. I have spent time with all three sways and all the settings on the Daizen and in most instances, the GS will stay solidly with understeer. TM claims to have done the engineering on the Daizens so you may want to contact them to find out what is going on, the middle setting on the rear is about as good as it gets with them. If you notice that this is happening more on a turn in one direction than the other, take the rear bar off and look at it carefully. I go back and forth between the Sportivos and the Blues with the blues currently on the car and the back end doesn't really do anything unusual.

If the back end is stepping out that much, once again depending on a lot of other things on the road and vehicle speed, it might just simply be lack of grip. I have 245/50 - 16 Pirelli P Zero Nero and the back definitely does not want to step out without a lot of provocation, more than the roads and engine/transmission are able to induce on the street around here.

If your driving style and roads are such that you are regularly getting the rear going out by a foot, and that has to be very annoying, more grip in the back (larger section or softer compound) might be a simpler way to solve it. Of course, the softer, grippier tire is going to wear faster but the rear end of higher powered, heavy cars have always benefitted from more rubber. Size of the spare is not much of an issue with modern tires but if you watch the overall circumference, the spare should be fine for short periods. For a quicky you might want to play around with tire pressures. A little lower pressure in the rear might help. But I keep coming back to a lack of grip in the back rather than suspension. Bilstein Sports are pretty good all by themselves at making a fairly neutral handling GS. All the bars and braces in the world won't make up for a tire that is giving up early. Lowering might help things by lowering the roll center but if you do it without adjustable coilovers, it is a pain to experiment with.

Good luck.

FutureGS400

Sounds to me like Ron is on the right track-the most effective thing at this point for your car would be to increase traction with some really good tires (like the Goodyears! ) I was completely unimpressed with the traction of the stock tires on my car!
What you described would be trailing throttle oversteer as opposed to power on oversteer (which can be fun in moderate doses especially on a track). Here are some other typical solutions to correct oversteer depending on the cause of the problem on your particular car:

increase front tire pressure
decrease rear tire pressure
smaller front tire section
larger rear tire section
more positive front wheel camber
more negative rear wheel camber
more front wheel toe in
more rear wheel toe out
more negative front wheel caster
stiffer front springs
softer rear springs
stiffer (heavier) front sway bar
softer (lighter) rear sway bar
more forward weight distribution

BTW, where are you in California? You might be able to ride/drive some CL members cars with different suspension and tire set ups to check out your options.

bitkahuna

iTrader: (20)

Get coilovers! You can have the best of both worlds.

My wife is very impressed with the comfort of the Tein Flex at a soft setting (14/16 with the EDFC electronic control module), and I'm very impressed with the variety of settings and the 'Flex'ibility from comfy to stiff and very capable, and this is with *19s* and the coilovers are threaded so the car is pretty slammed.

I was skeptical about coilovers before I got them, but now I 'get it'.

FutureGS400

I agree coilovers are the way to go except Jack mentioned "budget considerations".
Jack-you won't have the Z06 ride you are concerned about with the Tein coilovers if you can swing the cost on them. You might be surprised by the excellent ride/handling balance with them. You could always sell your Bilsteins to offset the cost of the coilovers...
As an alternative, check other springs (search here on CL) there are past threads that have the spring rates and drop of the different springs that are available. You might find some that are even more appropriate for you than the Eibachs.
If you are in So. Cal, you are more than welcome to meet up with me and drive my car to see what you think. I'm sure others would be willing to help out that way too...

RON430

Real problem is trying to do a suspension setup for a decreasing radius turn. Variable radius turns were made to make sure drivers don't think they are passengers. An increasing radius turn is a lot less of a problem as you set the car for whatever apex seems appropriate initially and then feed in power and let it drift out. Cars that are not very good at putting power down, like the GS, can make a pretty reasonable exit from an increasing radius turn. A decreasing radius is a lot more fun and the reason why you check your gauges on the straight, not the turns. The initial, larger radius can take a higher speed, demands it if you are racing. Depending on the transition to the shorter radius, you may have to pick a second apex but in any event you end up yanking on the wheel to tighten the turn up. If you are carrying all the speed you can in the initial portion of the turn, you definitely have too much when you crank on the wheel.

If the car is understeering, you start to scrub out and need to lower speed even more to follow around. If you have a car that is oversteering, which I personally prefer, when you tighten up for the decreasing radius, you need to be pretty sharp to catch it. This is the biggest reason why understeering is inherently safer than oversteer which is what most every volume produced car is set up for. There is no question about feeding in more throttle in a decreasing radius turn if you are carrying all the speed you can in the initial portion of the turn. This is also the reason why you don't encounter very many decreasing radius turns. The people who layout roads avoid them at all costs. Most decreasing radius turns in the real world are mistakes that were made by some reconfiguration rather than being laid out that way. A lot of freeway off ramps are increasing radius turns that make it easier to get up to speed to merge.

So you can play with setup but a driving course might be a better investment than any bar, brace, or spring. Then again, oversteer can require someone to be on their game most of the time. And if you let your wife or gf drive the car. Oh, you know how that goes. If the oversteer is due to poor grip in the rear, better fixed sooner rather than later.