Let’s put together a comparison of spring rates and ride height for the tC2 (AGT20L); here is what I've got so far...



I’ll add any more so we have a quick reference.

 

The Eibach Pro-Kit is probably the TRD lowering springs…can anybody verify this?

 

you could add h&r to the list since it's supposed to come out in about ~5 weeks or so they said last time i called F/R 1.4/1.3 h&r does'nt post spring rates though..

 

I have a question for you 2tCornot2tC,

Say I have springs with a spring rate of "10K and 8K" F&R, where would that compare on that list? I know that its probably a matter of different measurement units.

Thanks,

Austin

 

Quote:

Originally Posted by greenbean24

I have a question for you 2tCornot2tC,

Without knowing the units, it would be tough to guess what that means…it could be pounds/foot…but that would be way too stiff. N/m would be way too soft. Any way you look at it, somebody does not know what they are doing if they put a stiffer spring in the front…that will make a car pitch back and forth like on a hobby horse.

In suspension design, you have to design the front and rear suspension to the design speed of the car. I don’t want to give a whole engineering lecture, so I will significantly abbreviate the explanation.

Every sprung system has a natural frequency. The weigh of one corner of the car and the stiffness of the spring combination will have a natural frequency. The stiffer the system, the shorter your period of oscillation will be…the time it take the system to go one full cycle. When your car hits a bump, your front of the car will start on its cycle. Depending on the speed of the vehicle, the rear will hit that same bump. You want a lot stiffer rear suspension to have a much shorter period of oscillation so that the rear of the car recovers at the same time the front does. If they recover at the same time, your car is back to stable and able to continue to its next imperfection, corner, bump, etc.

Did I answer your question?

 

What's the happy place for a car you drive daily and race on weekends? And why the range on the Eibachs?

 

Most people don’t know what goes on behind the scenes…
Engineering is all compromises. He who makes the best compromises wins.
Unless you weigh all 4 corners of your car, you will not know the natural frequency…and it is different on the left side from the right…plus, you sit on the left side of the car…starting to follow.

I know that TRD has a bunch of good engineers…that is why I just chose their product over anybody else’s. I know that they will work very nicely on the street and I won’t embarrass myself on the track.

It is not a range…those are multi rate springs. They are wound differently to get one rate at first and then another rate (stiffer) as the spring compresses.

 

To elaborate on my previous answer; your car is an engineering compromise. If all you are doing is parking lot racing (Auto-Xing) one weekend a month, I’d go with the Eibach Pro-Kit. I think these are the TRD springs. Since you are tracking your car only 1 day out of 30, 97% of your time will be spent DDing. If my weekend warrioring consists of going to a real road course race track, I would go for the Eibach SportLines…same argument as above. Since I’ve never straight lined…I can’t advise you on drag racing.

I’ve got the TRD springs on my car and the sway bars are in the mail…I expect to have a great handling car after this weekend.

 

Other than cost, wouldn't the Eibach Sportlines be better than the Pros under any circumstances? Lower initial spring rate (more comfy ride?) with a firmer final rate than the Pros.

The other question is, would coilovers be a better choice? I'm not looking to slam my car, but if I'm going to buy aftermarket suspension to race my car, I'd rather go the best right off the bat rather than buying 2 or 3 sets of suspension gear.

 

All true…but still a compromise. I drive where it snows…so I didn’t want to go any lower than 1-inch…just an arbitrary number. Lower is better for center of gravity. But the biggest reason is that the suspension geometry was not designed for constant operation that far down…this has nothing to do with the shock, it is all about the suspension arm angles (the geometry).

As far as the shock goes, there are quite a few misconceptions out there. The spring is what holds up the car and the spring determines the shock damping rate. Since I have not raised the spring rate any significant amount, the stock shock will work…and it does. The shock needs to critically damp the spring…that is when you bounce the car, the shock dissipates the oscillations in one and a half cycles…this is perfect. In an under damped condition, the spring will continue to oscillate and you never gain control of the car. The opposite happens in an over damped condition…it is almost like installing a solid rod in place of your shock (this is the absolute extreme), but I want you to understand what is going on…you will be skidding across the road. The misconception is that you can reduce the damping for the street and jack it way up for the track…this idiot is just making it worse in both cases.

Coil-overs…knowing what you know now, the manufacturer can make one shock and put on several springs. You just adjust the damping for your spring you have installed. Another advantage for an adjustable shock is when the shock wares out…you can just increase the damping to compensate for the ware.

 

^ Just to make sure I understand what you said, let me rephrase.

Geometry aside:
- Springs, specifically the rate, control the ride comfort and responsiveness of the suspension. Or, in other words, how quickly your wheels respond to changes in the road, direction of your car, etc.
- Shocks work like a stabilizer, to stop the springs from endlessly moving. Shocks would be adjusted to match changes in your springs.

Understanding there are limits to this comparison, the same could be said about wheels & tires. You don't increase wheel width to increase traction, you increase the tire width. You increase wheel width if you go with significantly wider tires to compensate for the change.

Last, as with the majority of auto modifications, you will reduce the life of the whatever you're modifying by doing this. However small or large that change might be, the suspension will not last as long as if you were to leave it in it's original configuration.

 

Yes…



Yes, but wider tires changes the shape of your contact patch to a more round instead of oval – along the direction of the car.



There are two sides to this coin…one; is because not too many people are qualified to properly engineer modifications / changes they attempt to do. And two; most of the time cars that are being modified are done so to go faster…you go faster, it puts a greater load on the car’s components and therefore ware them out quicker… So, I don’t necessarily agree with you here.

 

Cool and sounds good. And I realize my version has it's limits. The draw back to simplifying an explaination is it loses some of it's precision. I agree with your last statement. I was simply making a general observation.

 

Official request to have this stickied? Very good and informative conversation here.

 

So have we determined once and for all if the TRD springs are re-badged Eibach Pro-Kit?

 

We can add the H&R Sport Springs lineup as well.
http://hrsprings.com/scripts/appguid...Scion%20|%20tC

They look like they'll give a crazy raked look though...1.4" drop in the front and 1.3" in the rear?? The car is already raked enough.

 

That site doesn’t provide any spring rates…any way of getting the spring rates?

 

Just spoke with them and they said they do not release the spring rates because there is no standard in the industry for spring rates or something to that effect...

Bologna?

 

Now that is a BS line if I’ve ever heard one…

Yes there is an industry standard…it’s called pounds per inch or lb/in!

Let’s not BS-up our table and not include them for now…if they ever change their minds, we’ll add them in then.

Any objections?

 

No objections here! If it goes on the table, it needs to be complete.

I don't like the ride heights anyway.