When talking about the handling characteristics of the tC, the term "suspension geometry" keeps coming up. We talk about ride height, spring rates, shocks, sway bars, etc and each time a comment to the effect of, yes, but don't do too much or you'll adversely affect the suspension geometry and the upgrade will be worthless.

In general terms, this makes sense. The suspension has to have enough room to work. There must be enough up and down movement to compensate for bumps and keep all 4 tires on the ground going around a turn, but not so much the car goes crazy with every imperfection in the road. But that's about all the factual data on geometry I've come up with.

Multiple people have noted that slamming your car actually hurts your cornering ability, which makes sense per my logic above. What I can't seem to resolve is what is that magic number. How low is too low? No one seems to doubt the TRD springs are acceptably low (about a 1.25" drop) but then the S-Techs get a lot a flack for being too low (about a 1.5" drop). The Eibach Pros have a 1" drop, but their Sports are advertised as having better handling and are about the same drop as the S-techs. Here are some observations I've made:

1. Obviously TRD decided the 1.25" drop would help the overall handling of the car rather than hurt it.
2. I see no benefit in Eibach falsely advertising the Sportlines as better handling than the Pros.
3. The difference between the Sportlines and the TRDs is 20% of the total drop. Is that 20% a line in the sand?

 

*bracing for assault by wall of text*

 

^ Haha, yes, I had the same thought. And I researched it online before asking and couldn't find anything that really answered my question.

 

trd drop is 1"

1.1" at most

 

So if i slam my car on racelands, it won't outhandle a Porcshe??!?!?!?




I think that hotchkis has done a great job with their springs(and swaybars), not sure on their drop though.

 

According to Scion Canada, it was 1.2" when they installed the springs on 1stOne's car.

 

I don't have a lot of good insight on this, but someone really familiar with this might be able to better help. From my basic knowledge on it, think of the angle of the control arms. The lower you go, the more of an upward angle they have. This I believe removes some of the travel that they once had and in turn doesn't allow the car to properly load and unload weight. It's like pushing your tires past the breaking point. If your suspension can only move a small amount because it's already maxed out, then it's likely to transfer all that weight to the tire and force it to breakout faster.

I think this is a bit of it, but I'm sure someone else can better assist.

 

What is the maximum drop for geometry? Every car has a different suspension geometry, so for your particular car, the practical answer is…(drum roll!)… on a flat, level surface, measure the distance from the floor to the center of the lower A-arm bolt (attaching to the chassis) and the center of the of lower ball-joint at the outboard end of the same A-arm to the floor. The distance from the floor to the bolt has to equal to or grater than the distance from the ball-point to the floor. In other words, the (effective – center of bolt to center of ball-point) lower A-arm must not exceed horizontal or be slopping downward – outboard.

 

Wall of Text hits you for: <MISS>
Wall of Text has taken a swipe at you, missed, and has become legible!

...I have barely had my coffee and I totally get this. *applaud* 2tCornot2tC concise and to the point!

 

2tCornot2tC, that was a perfect answer. Now I just have to go measure. And maybe someone with TRD springs and S-techs can go measure as well. Thanks!

 

That is a very, very generalized rule of thumb that will work to some degree, but the real answer is to figure out the motion ratio, corner weights, suspension member geometries and actually calculate effects on camber curve and roll couple to get the exact sweet spot for your vehicle. That makes sure that you are accounting for any type of suspension your car is set up with and is a much more correct answer. For the average guy just wanting to make sure he didnt screw it up too much, yes, this is an ok way of doing so I guess.

 

I don't think in most instances there is (generally) a "line in the sand". You can lower your car past the measurements as long as you compensate by changing/adjusting parts. You'll notice plenty of cars on the track lowered beyond "acceptable" measurements. They still perform at a high level because they reinforce or replace suspension components. Problem is, no one offers a lot of suspension parts for our car which makes it hard to go lower w/o biffing it.

 

You would need to relocate suspension mounting in some fashion to over lower without negative effects.

For example, you could have custom custom spindles made in front to raise the centerline of the hub, which can effectively lower the car without messing with the camber curve as much. You can do something similar with the rear (or cut the subframe bushings down to get the same effect). But other than that, if you over lower, you over lower regardless of spring rates used. Plus, if you compete with your car, changing the suspension mounting points relative to stock location typically throws you way out of your intended class. You could not autox in any ST class or stock class if you moved suspension mounting points for example. Pretty sure you couldnt even run SM classes (SP or even XP may be your only class then)... so you are stuck in a non-competitive position. So it becomes impractical at some point.

so there is, for the most part, a line in the sand where lowered CG is outweighed by camber curves and other factors of geometry. To really figure this out, doing all of the measurements and math is the way to go (not just over generalized "horizontal control arm" techniques). Fortunately, a lot of that has been done by othes (Dan Gardners team for one) and the numbers of 1.4 - 1.5" of drop are what is found for the tC1 ... the tC2 is likely to be very close to that.

I already have my corner weights from my last corner balance as well as some of the measurements. If I ever get around to it, I will get the rest and do the math, but likely will come to the same conclusions. But I will do it for sure before I build a better set of coilovers than what I have to ensure spring rates are spot on (Hyperco all the way for me... I want good springs with good spec sheets for each spring and then damping rates can be chosen from there. And all of that requires knowing what you want your overall suspension frequency to be in the end.

The act of just chosing spring rates by overall vehicle weight and a small understanding of motion ratio may get someone loosely in the ball park, but not on the money. Same goes with setting ride height. Not saying you cant make an ok handling daily driver with some rule of thumb numbers (which honestly, is what some of the companies people think are "experts" in suspension do ... incorrectly) and off the shelf parts, but if we are going to have a real discussion on the real way to do something, we should be correct ... which is why I posted in response to the above comments on the control arm angle. When people go around the forum being condescending to others and acting like they know it all, they should have the correct information to provide along with it