SC300 Roll Center Adjusters
09-11-13, 12:11 PM
#1
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SC300 Roll Center Adjusters
I've been playing around with the idea of buying coil-overs for my 97 Black-on-Black SC (possibly MEGAN RACING Street LP Series)
My SC is still my A-to-B and as much as i love the stiff track feel .. I still desire a bit more luxury ride (I know i cant have both but I'm trying to find a happy medium)
My friend just recently bought a 97 Black-on-Black SC just like mine .. and it has Tein Super Street Coil-Overs on it with a 1 inch drop on 18's. The owner expresses that he has too much road feedback and what i can only diagnose as "bump steer" I've driven the car myself and fell in love with the handling and haven't experienced his "bump steer" issue yet (however he is WAY more mechanically knowledgeable then I so I have no reason to doubt his diagnoses) we are both a bit novices when it comes to aftermarket suspension systems and have had great difficulty tracking down Roll Center Adjusters or modified Tire Rod Ends to solve this issue .. I was hoping someone could drop some knowledge on me as to, where i should go? or what i should do?
... as you can tell, mine is the one with all the fender gap
My SC is still my A-to-B and as much as i love the stiff track feel .. I still desire a bit more luxury ride (I know i cant have both but I'm trying to find a happy medium)
My friend just recently bought a 97 Black-on-Black SC just like mine .. and it has Tein Super Street Coil-Overs on it with a 1 inch drop on 18's. The owner expresses that he has too much road feedback and what i can only diagnose as "bump steer" I've driven the car myself and fell in love with the handling and haven't experienced his "bump steer" issue yet (however he is WAY more mechanically knowledgeable then I so I have no reason to doubt his diagnoses) we are both a bit novices when it comes to aftermarket suspension systems and have had great difficulty tracking down Roll Center Adjusters or modified Tire Rod Ends to solve this issue .. I was hoping someone could drop some knowledge on me as to, where i should go? or what i should do?
... as you can tell, mine is the one with all the fender gap
09-11-13, 12:58 PM
#2
Moving to suspension forum.
once you lower the SC it changes the angle of the control arms where they are at rest, particularly the arms are more angled up as if you were hitting a bump on the stock ride height, only this is now your resting angle when lowered.
The issue is 2 arms attached to each other like that do not travel straight up and down, they travel in a very large arc, and the resting position is designed to be on the edge of the arc where the wheel is straight up and down meaning if the shocks compress or extend from that point it will change the wheel angle the same amount but positive or negative depending on if its compressing or extending. This is a small amount of angle really and since both extremes are balanced and centered around 0, you don't notice whats going on because everything averages out to 0.
when you lower it, you are moving the arms higher up on the arc of that circle, as if they were compressing and having some angle, and now this is your resting position. now imagine hitting a bump and you will hit a higher range of angle than you did since the control arms are already up some, and on extension it will actually become straight (like before it was dropped), and eventually come back to rest with some angle. So instead of having both extremes balanced, you have zeroed out one, and added it to the other one (compressing), so when you hit a bump and it compressing, you are hitting angles that it never hit before, and this increased and uncentered wheel angle is what you are feeling as bump steer as the larger value now makes it very noticeable.
and usually the more you drop it the worse it gets, the real remedy is custom control arms or setting the toe/camber properly after a drop so it is more back to normal. A good alignment can go along way, along with fresh lower control arm bushings and new poly rack bushings. I run the lance alignment and I do get a little bit on some of the bigger bumps but I think everyone with a lowered SC does, you will get used to it but if you lower your car and haven't done an alignment, that is the right place to start!
This site does a good job of explaining the circle thing.
http://www.mustangandfords.com/techa...d/viewall.html
once you lower the SC it changes the angle of the control arms where they are at rest, particularly the arms are more angled up as if you were hitting a bump on the stock ride height, only this is now your resting angle when lowered.
The issue is 2 arms attached to each other like that do not travel straight up and down, they travel in a very large arc, and the resting position is designed to be on the edge of the arc where the wheel is straight up and down meaning if the shocks compress or extend from that point it will change the wheel angle the same amount but positive or negative depending on if its compressing or extending. This is a small amount of angle really and since both extremes are balanced and centered around 0, you don't notice whats going on because everything averages out to 0.
when you lower it, you are moving the arms higher up on the arc of that circle, as if they were compressing and having some angle, and now this is your resting position. now imagine hitting a bump and you will hit a higher range of angle than you did since the control arms are already up some, and on extension it will actually become straight (like before it was dropped), and eventually come back to rest with some angle. So instead of having both extremes balanced, you have zeroed out one, and added it to the other one (compressing), so when you hit a bump and it compressing, you are hitting angles that it never hit before, and this increased and uncentered wheel angle is what you are feeling as bump steer as the larger value now makes it very noticeable.
and usually the more you drop it the worse it gets, the real remedy is custom control arms or setting the toe/camber properly after a drop so it is more back to normal. A good alignment can go along way, along with fresh lower control arm bushings and new poly rack bushings. I run the lance alignment and I do get a little bit on some of the bigger bumps but I think everyone with a lowered SC does, you will get used to it but if you lower your car and haven't done an alignment, that is the right place to start!
This site does a good job of explaining the circle thing.
http://www.mustangandfords.com/techa...d/viewall.html
Last edited by Ali SC3; 09-11-13 at 01:07 PM.
09-11-13, 02:39 PM
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the alignment has been done ... (lifetime alignment was been purchased and visited frequently)
like i said i drove the car before and didn't experience the bump steer ... ran the car at 70 mph and on a clean stretch of road and it felt perfect but from what the owner explained was that with Missouri being one of the worst road systems in the nation ( I've warped 17's on these roads ).. you cant help but hit breaks in the road .. constant pot holes and continuous road hazards (slamming on the breaks at 70 mph to crawl over a bump in the middle of the freeway is unacceptable) .. and if a simple pot hole is enough to make the steering wheel jump more then half a turn then that makes its unsafe .. and if your best advise is just deal with it ... that's not helping, no offence .. but i was hopping for a link for a purchasable item, other cars have a solution why not the SC ... thats why i started this post .. I tried to do my own research .. but Google and basic internet and E-bay searches come up short and all i can find are JDM Soarer parts that the seller wont ship here ..
Suck it up and Live with it is not suitable tech support no offence
so i am re-submitting my question because it wasnt answered
like i said i drove the car before and didn't experience the bump steer ... ran the car at 70 mph and on a clean stretch of road and it felt perfect but from what the owner explained was that with Missouri being one of the worst road systems in the nation ( I've warped 17's on these roads ).. you cant help but hit breaks in the road .. constant pot holes and continuous road hazards (slamming on the breaks at 70 mph to crawl over a bump in the middle of the freeway is unacceptable) .. and if a simple pot hole is enough to make the steering wheel jump more then half a turn then that makes its unsafe .. and if your best advise is just deal with it ... that's not helping, no offence .. but i was hopping for a link for a purchasable item, other cars have a solution why not the SC ... thats why i started this post .. I tried to do my own research .. but Google and basic internet and E-bay searches come up short and all i can find are JDM Soarer parts that the seller wont ship here ..
Suck it up and Live with it is not suitable tech support no offence
so i am re-submitting my question because it wasnt answered
09-12-13, 01:35 PM
#4
Lol, I am not tech support, Its my hobby and I take time out of my day to help people out.
I am pretty sure I recommended a very specific alignment, do you know what the lance alignment is?
If you are getting a regular alignment done that is not a "good alignment" and I assume its being done to regular specs cause most places that give lifetime alignments are the kind of shops that usually will not do a custom alignment on your car, and then you can expect it to handle as bad as it is.
I have not seen any roll centers used on our cars, some use custom tie rod ends but most do not.
I would not describe the bump steer I have felt as something that turns the steering wheel a half turn, I would venture to say there may be another issue like the rack bushings getting old. On mine I feel it a little on huge bump, but it doesn't feel dangerous like you are describing.
Most important things are lca bushings, rack bushings, and "proper" alignment after the drop.
also it took me about 5 seconds to find these
http://www.meganracing.com/product.a...d=957&catid=54
http://www.supraforums.com/forum/sho...-and-Trammling
I am pretty sure I recommended a very specific alignment, do you know what the lance alignment is?
If you are getting a regular alignment done that is not a "good alignment" and I assume its being done to regular specs cause most places that give lifetime alignments are the kind of shops that usually will not do a custom alignment on your car, and then you can expect it to handle as bad as it is.
I have not seen any roll centers used on our cars, some use custom tie rod ends but most do not.
I would not describe the bump steer I have felt as something that turns the steering wheel a half turn, I would venture to say there may be another issue like the rack bushings getting old. On mine I feel it a little on huge bump, but it doesn't feel dangerous like you are describing.
Most important things are lca bushings, rack bushings, and "proper" alignment after the drop.
also it took me about 5 seconds to find these
http://www.meganracing.com/product.a...d=957&catid=54
http://www.supraforums.com/forum/sho...-and-Trammling
Last edited by Ali SC3; 09-12-13 at 02:01 PM.
09-13-13, 02:29 AM
#6
The suspension design on the SC doesn't allow it to use a RCA like most other Lexus.
Looking at your friend's car he has stock 2IS rims. My question is what tires does he have? If it's the ER33's that normally come on those rims, then replace them and get better tires.
Looking at your friend's car he has stock 2IS rims. My question is what tires does he have? If it's the ER33's that normally come on those rims, then replace them and get better tires.
09-13-13, 11:31 AM
#7
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an inch should not give the car a noticeable amount of bumpsteer. even if it does, the issue can usually be resolved with an alignment and/or tie rod ends that're spaced down to accomodate the drop, which i believe battle version sells
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09-13-13, 11:10 PM
#9
I have stiffer swift springs on my cusco coilovers. Something like 18/22, (not sure at this moment in the night), and relatively low, maybe 1 finger gap on 275/40/17 front and rear. I've never had the steering wheel jerk, or even bottomed out, even with the bump lifting me out of the seat and stuff flying inside the car on the highway, lol.
I have stock control arms with prothane bushings and battle version steering rack bushings, stock tie-rods etc. 5 degrees castor, -3/-2 camber, and little toe. My car sees mostly track days and is extremely stiff. I slam the brakes, dodge pot holes, drive in the center of the road, etc, pretty much any time I drive on crappy city streets.
If you want to be able to go over bumps get a truck or suv. For a reference, my girlfriend's stock Camry bottoms out with normal driving on the streets here in Houston going 5mph over the speed limit. I slam the brakes on both, my dog flew into the dash earlier tonight while bottoming out the Camry.
I have stock control arms with prothane bushings and battle version steering rack bushings, stock tie-rods etc. 5 degrees castor, -3/-2 camber, and little toe. My car sees mostly track days and is extremely stiff. I slam the brakes, dodge pot holes, drive in the center of the road, etc, pretty much any time I drive on crappy city streets.
If you want to be able to go over bumps get a truck or suv. For a reference, my girlfriend's stock Camry bottoms out with normal driving on the streets here in Houston going 5mph over the speed limit. I slam the brakes on both, my dog flew into the dash earlier tonight while bottoming out the Camry.
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