SCV8

Yeah, it's more of a geometry thing, not a loose parts thing, not to say new parts can't help certain problems, but....
The lower control arms are mounted where they are for a reason, if you could re-locate the arms, like I have done before, you can go on without any compromises.
Of course the lowered situation will work better with extremely stiff springs, like over three times as firm as the cars came with, but then you're not really using the suspension, more the tires.

The body roll is different on a lowered car; the point from which the car rolls, or rotates in turns is determined by the control arm angles. So when the car is up around stock height, the car will rotate around an imaginary point right around ground level, maybe a tad higher, but when the car is lowered and the control arms begin to point upward from the centerline of the car, the roll center goes far below the road surface. What used to be just pure roll has now become more of a pitching action for the mass of the car, towards the outside of the corner as well; not good.

lighthalo

what year is everyone's lexus here? i went from a 92 to a 97and the steering feels diff, both are stock except for temporary wheels (235/45/18) on both, i just wish it had a tighter turning radius, btw my 92 has a lot of body roll

azian21485

I don't post here much (as i don't own a sc300, my brother does) so i'll be brief...or try to be but there's some things I would like to clear up :

basic overview:

Roll center = a geometric point. It's an intersection made by drawing imaginary lines from the upper and lower control arm angles along with the centerline of the tire. So, as the control arms move, roll center moves constantly, in all directions. It is measured from ground to roll center.

There are very few factory cars that have a roll center at ground level. Most of the time, they are quite high. Lowering the car will lower the roll center. But SLAMMING the car will put the roll center BELOW the ground which causes weird handling. Some non production race cars like F1 actually do this on purpose. But to prevent my head from exploding, I don't look into it further.

Maybe the sc300 is a special car. But i doubt it. Measure them yourself and let us know =) Roll center plays a roll in the jacking forces of the car. Jacking is sorta explained by the inside jacking up as the body rolls. Jacking force is reduced as the roll center is lowered.


Center of gravity = a point based on the mass of the car. 99.9% will be higher than the roll center. The center of gravity will play a roll on lateral and longitudinal load transfer. The lower the center of gravity, the lower the load transfer.



roll moment = distance between the roll center and center of gravity.

As the roll moment increases, roll increases. I've yet to measure the change in roll moment as you lower a car, however it isn't as big a deal as people make it out to be. You reduce roll with stiffer springs. Pretty simple.

Notice: If you use a larger swaybar to control body roll, you will increase lateral load transfer. Springs do not effect lateral or longitudinal load transfer. Please keep that in mind when tuning your car.


Bumpsteer = changes in toe as the car dives, squats, rolls, etc. It does not have anything to do with bumps in the road, nor does it have to do with the car wandering.

Basically, for those who have lowered their cars, you had to get an allignment because your front and rear had toe OUT (sc300's might be different that cars i'm used to, but in either case you should get the idea).

Generally:
Car lowers = toe moves out
Car raises = toe moves in

Situation:
If you brake, your front squats (bump) and the front wheels toe out. The rear lifts (rebound) and the rear wheels toe in.

If you turn, your outside front goes into BUMP and toes OUT. As you can see, this causes the OUTSIDE wheel to be pointed AWAY from the way you actually turn the wheel causing you to turn the wheel MORE. This effects slip angle which effects many ther things but you should get the picture of what's happening here.

Unfortunately, on production cars, bumpsteer isn't tunable without custom parts and relocating suspension components. Is it worth the effort? no. Unless you're building a dedicated race car where the rules allow it. But, if you're knowledgable enough to be building a race car, you wouldn't be listening to me in the first place =)


NOTE: You might be confused with load transfer. But I won't get into it. It's a long long subject and I really don't want to type it out. There are many people who are WAY more qualified to talk about it. Google Mark Ortiz should help. But there's TONS of articles on load transfer.

Suggestions:
Don't get too caught up with the nitty gritty aspects of tuning. It really doesn't lead anywhere on the amature level. There's enough headaches figuring out spring rates, tire pressures, swaybar sizes, allignment, etc. to be worried about things you really can't and shouldn't be changing

Anyways, 99.9% of the drivers out there won't even be able to take advantage of subtle changes to squeeze out those 1/10ths gained from hours of tuning. INCLUDING ME AND YOU who are reading this unfortunately. Work on the driver before the car.

And to end it off, go hit the books =)

PS: Wandering can be caused by: allignment, worn ball joints, worn bushings, worn steering components, uni-directional tires. Good luck.

PSS: I typed this in a hurry and it's past my bedtime. So it's probably sloppy. Might edit tomorrow

drnkcarlos

Those of you running coilovers on your SC's what spring rates do you run? (please in kilograms if you would.) I'm using 20K front and 16K rear still feels a little soft sometimes, but I'm hoping the sways help correct that in the corners. But that was what was recommended to me by Ueno ... think Ueno runs 16/14 but his is superlightened too.

chitwnsazn

iTrader: (3)

Then GTFO!!! Just kidding. So how is that Tuning to Win book treating you?

azian21485

your a ***. =)

Lars619

I voted no...

I just went from a 99 GSX Eclipse with front upper, front lower, and rear RRE strut bars, and front and rear sway bars.... just picked up a stock 95 sc with 125k miles on it and let me tell you, the handling is like night and day! The gsx under steered like CRAZY. I'm in love with the sc after driving it for a week. I haven't driven many other cars but the sc's handling is amazing compared to the awd dsm.

Before I get comments about putting the front sway bar on.... I shouldn't have done that because of the under steer problem but I didn't know better when I put it on. Wish I hadn't but I did.

Just my .02

poser714

I vote no also.. My SC stock handled good, could have been better but after overhauling the suspension, its night and day. The only complaint I have is that I do get some tramlining/wandering on certain roads but other than that it handles great. And by overhauling I replaced my front LCA's with supra's, replaced all my bushings front, rear upper and lower with poly urethane bushings, steering rack bushings, otto-r front strut bar,Tien CS coilovers and Largus swaybars.The only thing else I plan to do with the suspension is probably get the camber kits for our cars. Hopefully that will get rid of the tramlining/wandering.
Oh BTW Im riding on Supra TT wheels 235/45/17 up front and 275/40/17 in the rears.

lighthalo

where did u get the largus bars? the website is in japanese....

92 SC400

You think some of the problems could be subjective? Maybe you're comparing to a previous or another car you own that handles (feels) better? I'm not saying you're wrong for saying the SC doesn't handle well because I will admit it doesn't handle well at all. And possibly there really is something wrong, especially if you're having to keep the wheel turned 20% to keep the car straight...Try driving another SC and see if handling is similar...I thought mine just sucked too, but having driven two others I realize that is just how the car feels (or maybe they were crapp too...? hahah). I might say this in comparsion to my modded S14 and G35 coupe...Maybe some of you are doing the same...?

poser714

I got the Largus Bars from one of my friends that has a local shop in NYC. He does a lot of business with over seas and JDM companies. If your interested I could give you his # or some way of contacting him. just pm me. But im not sure if he can order just 1 set of bars, because i had to jump on with his order, when he ordered like 5-10 sets

And as for the car handling crappy. i dont think the car handles crappy at all, maybe compaired to a 350z or g35 it does. Those cars handle like go-carts straight from the factory. but considering the cars body style and suspension hasnt change in 10 years i think its great.

SC400-V8

iTrader: (1)

Mine handles ok-good, but Im also due for new front LCAs and a nice new set of Dunlop Sp9000s.

When those are in there, I guarantee my handling will be at "excellent"

dejacky

iTrader: (2)

Got any pics of your ride? I've been considering a setup exactly like yours .

poser714

i do.. but i dont have any really good or clear pics.. but as soon as i do, i'll post them

poser714

heres one more.