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Discussion Starter · #1 ·
Somebody PM'd me for information regarding TRD springs, rear antisway and strut tower tie bar; I wrote a really long-winded answer to their question and I don't feel like having to go through it again so I figured I'd post it here and just maybe get it stickied. Also, could all the forum gearheads please double-check that my information is correct before we sticky this?

Thanks!

The TRD sport springs do several things for you. First is that what you mentioned; by lowering the car (between 1.25 to two inches depending on how they settle), the car's center of gravity becomes lower. This naturally has the effect of reducing lean when turning and also diving when braking and sagging backward when accelerating (drive a tall vehicle like an SUV or minivan and you'll see just how prone to this taller vehicles are).

Additionally, the TRD sport springs are firmer than the stock springs, which further contribute to reduction in lateral and longitudinal roll/leaning--this is called increased wheel rate (firmer springs results in more resistance to individual wheel compliancy). The primary reason for lower center of gravity and increased spring rate and their resulting decrease in lateral and longitudinal roll is superior control over the vehicle when turning, accelerating and braking, particularly in transitional situations (for example, the cone slalom or in the real world, emergency lane changes).

It's important to note that an increase in wheel rate provides superior control in transitions and also allows the car's grip to break away much more smoothly and controllably, but it also actually can reduce grip at the limit, depending on suspension geometry. The optimal suspension tuning is such that the wheels are at the best angle to get maximum contact patch to the ground, particularly at the outside wheels in a turn.

Most suspension come from the factory to work best closer to stock height with soft springs, so springs designed to lower the car without becoming much firmer will not help handling--Trades springs are fine because they are calibrated to settle the car's suspension geometry at the correct point even with the car lower (the firmer settings come into play).

The bad thing about lowering/sport springs is that first of all they reduce maximum suspension travel, making it easier to bottom-out the suspension and cutting down on the size of the bumps and dips the car can handle, particularly at speed. The other bad thing is that with increased wheel rate, your ride becomes harsher.

Finally, particular to the TRD springs, the rear wheel rate increases more than the front wheel rate, indicating two things; first of all, that the geometry of the car's suspension from the factory is such that camber more at the rear than at the front during transitions (so the increased wheel rate helps prevent excessive change from stock geometry) and that TRD springs also help reduce overall understeer compared to stock (understeer is where the front of the car does not follow the intended arc of the turn as well as the rear wheels do, or what I call, bobsledding a turn, which is extremely common in front wheel drive cars, particularly with excessive throttle application in a turn).

Antisway bars are designed to further reduce lateral body roll in turns without increasing wheel rate. Basically, they tie together the left and right sides of the suspension system in independent suspension cars so that the wheel on one side is more resistant to move without the wheel on the other side, resulting in less roll. In situations where both wheels can move together, wheel rate does not change, so the ride is not affected (like in speed bumps, dips and other sorts of bumps that cross the whole lane). Individual bumps and dips that only affect the left or the right of the car will still experience a bit of a tougher ride from increased wheel rate due to the tying together of the two sides.

Strut tower tie bars are designed to reduce the, "spring effect," of a car's chassis or unit body. Because cars have their own mass to deal with and have to carry things like humans and their stuff, compromises are made to the stiffness of the car itself, so in turning and particularly in transitional situations, the car itself will flex a little, resulting in changes to the suspension geometry that can affect handling and grip.

The strut tie bars reinforce the car's chassis against flex by trying to tackle the chassis flex where it is inherently worst; as a car turns, the suspension tower on the outside wheel tends to lean inward; in some extreme cases of very heavy braking, both towers will lean inward at the front, and in the most unlikely case (particularly for a car as slow as ours), the rear towers may tilt inward from heavy accelerative forces. By physically attaching the two sides together at the top, it should significantly reduce this effect. Just picture an open cardboard box, and then a cardboard box with a piece of cardboard glued across the top--the latter is much stiffer.

The strut tie bars are the least likely to provide a noticeable change in handling because most modern cars are built with fairly rigid unit bodies to begin with thanks to modern advances in computer design technologies as well as overall superior engineering experience. Only in very high performance and extreme situations (for example, a car on the track shod with slicks and very firm suspension) will the car really benefit from this. Granted, having the additional bracing will help keep the car's unit body firmer longer, which is a nice thing for people who plan to keep the car a long time, and strut tie bars are the easiest thing to show off, since it's just under the hood, not under the car.

Please note that in many (I may even say, most) cases, the car's suspension is optimal for real world use as it is from the factory. Manufacturer's spend thousands of man hours fine tuning a car's suspension before releasing the car to the real world for consumption. Generally, the only ways to improve upon a stock car's handling, other than to install improved tires (which should always be done regardless, as it is the easiest and least expensive way to dramatically improve grip and handling), will almost always compromise ride comfort for either superior control and/or grip at the limit. There is pretty much little chance of improving handling/control while still maintaining factory ride quality.

Let me know if you need me to discuss dampers (struts/shocks).

-Ed

EDIT: Spaced out the paragraphs with extra line breaks (not grammatically correct either, but at least it makes for easier reading).
 

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OK, it's been a minute...it should read like this:

QUOTE
The TRD sport springs do several things for you. First, they lower the car's center of gravity. This makes the car less prone to rollover events.  Unfortunately, at the same time it lowers the center of gravity, it also lowers the roll center of the suspension, and quite a bit more than the center of gravity.  The distance between the center of gravity and the roll center is called the roll couple, and cornering forces are applied to the suspension through the roll couple.  This means a lowered car will need stiffer springs to resist the lowered suspension’s increased tendency to roll in corners.
TRD sport springs are stiffer than the stock springs to counteract this. This is an unfortunate compromise because the spring rate should be as soft as possible to provide wheel compliance – meaning the wheel should follow the contour of the road including bumps, while still being stiff enough to keep the suspension from hitting maximum compression.  When the spring rate increases, the damping rates must also increase.  These two changes conspire to make the tire lose traction especially over bumps under braking, the time you really need maximum grip.
On the positive side, stiffer springs will make the car’s suspension resist transitional roll changes better and reduce the amount of pitch the car experiences under braking.  The suspension is optimally tuned when the wheels are at the best angle to get maximum traction on all four wheels under all conditions.  This never happens in real life, but it is the goal of any suspension designer.  Maximum grip is achieved when all four wheels are sharing the car’s load equally.
Factory suspension designs work best at stock height with stock springs, so springs designed to lower the car without becoming significantly firmer will not help handling—TRD’s springs work because they make a reasonable compromise between changing the car's suspension geometry and making the ride stiffer to compensate for the drop without requiring a kidney belt or frequent dental work to replace loose fillings.  Some aftermarket springs are so stiff that they are a joy to every chiropractor and dentist around the globe.
Anti-sway bars are designed to further reduce lateral body roll in turns without increasing wheel rate. Basically, they tie the left and right sides of the suspension system together so that the wheel on the side under compression transfers part of that force to the wheel on the opposite side, resulting in less roll. In situations where both wheels must move together, the sway bar also moves with both wheels in the same direction, so the ride is not affected (like in speed bumps, dips and other sorts of bumps that cross the whole lane). Individual bumps and dips that only affect the left or the right of the car will cause part of the force applied to the affected wheel to be transferred to the other side, much the same as in cornering, giving the sensation of a stiffer ride.
Strut tower bars are designed to reduce the, "spring effect," of a car's chassis. Because cars can’t be infinitely stiff and still economical to move, the car’s chassis will flex, resulting in changes to the suspension geometry that can affect handling and grip.
The strut bars reduce flex by limiting chassis flex where it is inherently worst.  As a car turns, the strut tower on the outside wheel tends to lean outward and reduce camber.  Under heavy braking, both towers will lean inward at the front.  By physically attaching the two sides together at the top, it significantly reduces this effect.
The strut bars are the least likely to provide a noticeable change in handling because most modern cars are built with fairly rigid chassis thanks to computer aided finite element analysis and modern machine tools. Only in very high performance and extreme situations (for example, a car with slicks and very firm suspension) will the car benefit noticeably from this kind of chassis modification.  However, the additional bracing will reduce flex over the life of the car, which may be a nice thing for people who plan to keep the car a long time, and strut tie bars are the easiest thing to show off, since it's just under the hood, not under the car.
Please note that in many (I may even say, most) cases, the car's suspension is optimal for real world use as it is from the factory. Manufacturer's spend thousands of man hours fine tuning a car's suspension before releasing the car to the real world for consumption. Generally, the only way to improve upon a stock car's handling after mounting improved tires, (the easiest and least expensive way to dramatically improve grip and handling), will almost always compromise ride comfort for either superior control and/or grip at the limit. There is no chance of improving high performance handling and control while maintaining factory ride quality.[/b]
If you want me to cover the problems with the original document point by point, I'll address it, but it will take even more time.
 

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Discussion Starter · #3 ·
Originally posted by lo bux racer@Jan 15 2006, 11:00 AM
This is going to take a minute to fix...I'll be back...
Thanks, Lance; I need that.

No better way for me to learn than to screw up.


-Ed
 

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I don't really have anything to add about the content, but I think it could stand some indented paragraphs or some blanks lines in between the paragraphs... that left margin is hard on the eyes.
At least you did hit the return key a few times... I know some people who make a single paragraph that long with no returns at all.


Yeah, sorry to be like the grammar police, but that stuff really bothers me somtimes (I think I've got OCD). It's great of you to take the time to write that up, Ed... I really appreciate all the information available on this site. It's all good stuff.
 

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Discussion Starter · #6 ·
Originally posted by neo-truth@Jan 15 2006, 08:44 PM
I don't really have anything to add about the content, but I think it could stand some indented paragraphs or some blanks lines in between the paragraphs... that left margin is hard on the eyes. 
  At least you did hit the return key a few times... I know some people who make a single paragraph that long with no returns at all.


Yeah, sorry to be like the grammar police, but that stuff really bothers me somtimes (I think I've got OCD).  It's great of you to take the time to write that up, Ed...  I really appreciate all the information available on this site.  It's all good stuff.
I tried to do TAB indents but that just tabs me through the page.

-Ed

EDIT: I tried to the, "five spaces," indents but it cleaned them all out on me!
 

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I would suggest using the ampersand command for a space ( ) x 5 to make indentations, but I doubt it will work with BB Code overwriting everything. Oh well.. thanks for trying, Ed.


EDIT: Yeah the ampersand command didn't work lol
 

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Wow, that seemed fairly well written and definitely well thought out. I'm interested in seeing what changes are to be made on this. Way to take initiative on this one, this is definitely a topic that pops up often and becomes a bit redundant to read through every time.
 

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Ed, I would also like to learn about the TRD shocks
. Very well writen, I learned a lot just from that. Thanks.

-Eric
 

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Discussion Starter · #11 ·
Springs are springs--ever seen how slinkies work? Or if you dangle something down with a spring, then give it a tug or push and let it go? It keeps going up and down and up and down, boing boing boing...

So basically the job of the shocks/struts, or what I consider the dampers, is to literally restrict the springs from continuous reciprocating motion. If you've ever driven a car with weak or blown dampers, the car gets floaty or worse, straight up bouncy (a lot of older SUVs and pickups with undamped leaf spring suspensions were known for their bouncy, bouncy rides).

Bouncy suspension also has another drawback, one that's worse than a wallowy ride--without proper damping, wheels will not maintain proper contact with the road after hitting sharp bumps or tight little dips like expansion joints. Rather than resettle their motion, they keep bouncing a little bit. I'm sure everyone has seen (maybe not really paid attention to, but at least sort of noticed) on some older cars, particularly with heavier wheels, where the car (particularly an older Econoline van, as an example) will pass over an expansion joint or something similar and then the wheels keep bouncing rapidly for a few meters--this is improper damping.

The job then, of the shocks/struts, is to dampen this excessive wheel motion without overly restricting the springs from doing their job--allowing the car to pass over irregularities without breaking the passengers' backs. Various technologies in shock valving allow different shocks to behave in different ways (for example, shocks that can compress quickly but don't decompress as quickly) and in the case of many aftermarket shocks, is even adjustable for amount of damping. I'm not good enough to go into serious detail as to how they are designed and exactly how they work (particularly since some have separate reservoirs and some don't, some are inverted, some are multivalve or multistage etc.).

The important thing to note is simply that stiffer springs have a tendency to be more, "boingy," when loaded by a heavy mass like a car (this is a generalization and isn't necessarily true in all cases, but in most cases is) so stiffer springs necessitate stiffer damping. A car with too soft springs and too stiff dampers will have a good deal of dive, squat and lean but yet will be stiff when driving over small irregularities. A car with too stiff springs and too soft dampers will have a harsh ride in general but will not have as much lean, dive or squat; however, small irregularities will easily allow the wheels to break loose and the car will have a quick, hard bounciness to its motion over dips and humps in the road. A car with soft springs and dampers will have a good deal of lean, dive and squat but will have a fairly smooth ride overall. A car with hard springs and stiff dampers will have very little lean, squat or dive and the wheels will be extremely well controlled, but the ride will be very, very bad, particularly over small irregularities.

In comparison to the stock struts and shocks, the TRD ones are designed to handle stiffer springs, so they offer a higher level of damping. It is also important to note that the stock dampers are designed for a certain default level of load; when a car is lowered on sport or lowering springs, the tC's stock dampers become preloaded more heavily, and if the car is particularly low, the stock dampers will wear out very quickly from being loaded all the time (shocks are designed to dampen, not to maintain the car's level). The TRD dampers are designed to handle a lower default ride level than the stock ones.

Again, please don't take my word as gospel; anyone who feels I've said something incorrect here, please feel free to correct me at any time.

-Ed

PS Spell check hated this post.
 

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Discussion Starter · #12 ·
Btw just saw your edit, Lance; thanks again! I see the primary error was n my description of what happens to the outside strut tower when loaded in a turn; thanks for clarifying that!

Is there any chance manufacturers tune the factory camber to deal with this flex? In that case, wouldn't a strut tower bar actually make things worse? Or better said, would it be a good idea at all to dial in a tiny bit of positive camber up front after installing a strut tower tie bar?

-Ed
 

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That one's pretty good as is.

Just one note to add: Stiff springs and stiff damping will cause the wheels to lose contact over washboard bumps especially under braking. This can be very problematic with cars using EBFD and ABS, since the wheel locks up completely every time it loses contact with the pavement. It extends stopping distance dramatically, and may be highly unsuitable for street use. Tein SS-Ps on full stiff damping demonstrate this very effectively on the tC.

Ideal springs with ideal damping never allow the tires to lose contact with the road surface, and never bottom out under cornering, braking, or uneven road surfaces. This is a goal that cannot be achieved with the passive suspension systems currently used on automobiles, and only shows promise with active susension control systems like this Bose system.
 

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Originally posted by EddNog@Jan 16 2006, 12:49 PM
Btw just saw your edit, Lance; thanks again! I see the primary error was n my description of what happens to the outside strut tower when loaded in a turn; thanks for clarifying that!

Is there any chance manufacturers tune the factory camber to deal with this flex? In that case, wouldn't a strut tower bar actually make things worse? Or better said, would it be a good idea at all to dial in a tiny bit of positive camber up front after installing a strut tower tie bar?

-Ed
I dialed in a bunch of positive camber up front because it works for me.

The strut bar is supposed to help retain the camber you've set by limiting tower flex. The towers do flex in both directions depending on what kind of forces are being applied (cornering, braking, etc.) The ideal brace connects the towers to the firewall in a triangle (the way the AE92 GTS Corolla did from the factory) so not only do the towers maintain their distance from each other, but they remain better fixed relative to the rest of the chassis, which is what you wanted to happen in the first place.

The factory frowns on camber in the front. They set front camber to a minimum to promote understeer. Understeer is safer than oversteer for untrained drivers, so ALL manufacturers set up their cars to understeer heavily from the factory. The tC is no exception there, and even the Supra came that way (-1.5 degrees in the rear, and only -0.5 degrees camber in the front).
 

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Discussion Starter · #16 ·
Does anybody feel like now would be a good time to discuss tire pressure level and its effects on handling and ride?

Actually Lance I wanted to ask a random side question--if you compare two tire with the same outside diameter and the same profile, but one is wider than the other, and both are inflated to the same amount of pressure, then one tire obviously has more air volume and mass than the other. Would it be reasonable at all to say that the wider tire would experience less of a pressure increase from a quick bump compared to the narrower tire? Assuming this is true, would the wider tire have a slightly softer ride to it? Let's assume both tires are mounted to correctly matched with wheels. I understand the increased weight of the wider wheel & tire combo will also come into play with regards to road compliance, wheel control and possibly ride quality as well.

Or is my question leaving out too many variables?

-Ed
 

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Discussion Starter · #17 ·
Originally posted by lo bux racer+Jan 16 2006, 01:02 PM-->QUOTE (lo bux racer @ Jan 16 2006, 01:02 PM)
<!--QuoteBegin-EddNog
@Jan 16 2006, 12:49 PM
Btw just saw your edit, Lance; thanks again!  I see the primary error was n my description of what happens to the outside strut tower when loaded in a turn; thanks for clarifying that!

Is there any chance manufacturers tune the factory camber to deal with this flex?  In that case, wouldn't a strut tower bar actually make things worse?  Or better said, would it be a good idea at all to dial in a tiny bit of positive camber up front after installing a strut tower tie bar?

-Ed
I dialed in a bunch of positive camber up front because it works for me.

The strut bar is supposed to help retain the camber you've set by limiting tower flex. The towers do flex in both directions depending on what kind of forces are being applied (cornering, braking, etc.) The ideal brace connects the towers to the firewall in a triangle (the way the AE92 GTS Corolla did from the factory) so not only do the towers maintain their distance from each other, but they remain better fixed relative to the rest of the chassis, which is what you wanted to happen in the first place.

The factory frowns on camber in the front. They set front camber to a minimum to promote understeer. Understeer is safer than oversteer for untrained drivers, so ALL manufacturers set up their cars to understeer heavily from the factory. The tC is no exception there, and even the Supra came that way (-1.5 degrees in the rear, and only -0.5 degrees camber in the front). [/b]
Perhaps I should check the tech manual on this but I'm going to ask you anyway: how does one adjust the camber of the tC's front suspension and what's the adjustability range? Is it simply a matter of playing with excess slack in the assembly?

-Ed
 

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The only way to adjust it is to get a camber kit, or to use different bolts on the struts. There is a big table in the FSM with the different bolts and how to choose them to correct for improper camber, but it's a LOT easier to get adjustable hats (camber kit items) and do it that way.

AFA the tire pressure stuff. This is as much art as it is science. I couldn't possibly have anything useful to say when you can refer to the tyre bible link previously provided. There is SO much to know about tires, and I barely scratch the surface compared to real experts in tire science.
 

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Discussion Starter · #19 ·
Originally posted by lo bux racer@Jan 16 2006, 01:23 PM
... tyre bible link...
Oh shnikies!


-Ed

EDIT: Hey this article indicates that going with wider tires only re-shapes your contact patch (does not necessarily mean more contact area), since the weight of the car has not changed and neither has the amount of air pressure. Aaaaaargh I be [email protected]#
 

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I've read over that Tyre Bible several times... I've learned a lot from it, but I've certainly not absorbed all of the info there. I don't recall seeing anything going into detail about tire pressures affecting handling and ride, but there was a nice little bit about tire pressure affecting gas mileage... and it's kinda crazy how much it affects it.

There's several other Car Bibles if you go to the root link there, including a Suspension Bible which goes through the basics (including progressively wound springs and anti-roll bars and strut braces). Even a mechanical doofus like myself can understand most of it.
 
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