Suspension Tips, for those who want to lower this car.

[BRZranger]

Originally Posted by Racecomp Engineering

1.5 inches is a lot and I would recommend the whiteline roll center kit at that point.

It's much easier to deal with things if you stick with a medium/milder drop.

- Andrew

What is the lowest you would recommend on coilovers without requiring aftermarket camber plates and RCA?

Seems like 20mm-40mm is recommended per Moto-P, but he doesn't mention using plates or adjusters.

[spitz]

Great thread! Quality posts by the OP, and very informative as well.

[fatoni]

Originally Posted by WestZ

Not necessarily true. There's that aspect of them, but they do serve a purpose both on track and on the street.

Look up "bump stop tuning." I'm not saying you HAVE to ride them the whole time, but if/when they engage, they act as a secondary spring, which actually has a benefit to the suspension's handling.

From Modified: "As for bumpstop use on race cars, according to Peter, Often they are used truly as just a bumpstop, but the progressive spring rates can be used to help cars when they are riding the curbs or jumping them (as is often seen). In a controlled racing formula like a spec or one-make series where every car must use the same shocks and springs, the bumpstop becomes the one tunable spring on the car. It could even be in contact at ride height if a long enough bumpstop is used or the main springs are short enough. Bear in mind that the rate will be rising steeply into compression but will be dropping off into rebound, so the car is likely to roll up a lot on the inside rather than just down on the outside."

As you told me, "read and read some more," I strongly urge you to do the same.

I used to think that bump stops just prevented the shock from totally bottoming out and destroying itself, but I learned later that it serve an underlying purpose. It really does factor in a perfect suspension equation.

i feel like this is especially true on cars with limited suspension travel (pretty huge for miata guys) or cars using stock suspension. itseems just about every car from the factory is designed to corner on the bumpstops. its a cheap effective way to have a decent ride quality and composed handling in a cheap package.

[czar07]

I want to retain the stock handling characteristics as much as possible while achieving a 0.8-1inch drop. So all I need for this is some lowering springs? Should I get camber correction kit or anything of that sort?

[Phaedrus29]

Originally Posted by czar07

I want to retain the stock handling characteristics as much as possible while achieving a 0.8-1inch drop. So all I need for this is some lowering springs? Should I get camber correction kit or anything of that sort?

I'm in the same boat in terms of my goals. I decided to go with the RCE Yellow springs LITE starter pack that comes with the 20mm drop springs, oem front camber bolts, and whiteline rear camber bushings. I don't have it installed yet so I can't give real feedback. But after doing lots of reading on the forum and asking for advice from people, this sounded like one of the best options for a slight drop with an emphasis on handling.

[czar07]

Originally Posted by Phaedrus29

I'm in the same boat in terms of my goals. I decided to go with the RCE Yellow springs LITE starter pack that comes with the 20mm drop springs, oem front camber bolts, and whiteline rear camber bushings. I don't have it installed yet so I can't give real feedback. But after doings lots of reading on the forum and asking for advice from people, this sounded like one of the best options for a slight drop with an emphasis on handling.

Thank. Let me know how it goes. I wonder if the from camber bolts and rear camber bushings are really required for the mild drop?

[Racecomp Engineering]

Originally Posted by czar07

Thank. Let me know how it goes. I wonder if the from camber bolts and rear camber bushings are really required for the mild drop?

Required, no. But I definitely recommend them.

The front bolts are like 10 bucks and an easy install. They really help handling a LOT too. Zero reason not to do those in my opinion.

The rear camber bushings are recommended but they are a little bit of a pain to install. It does help you dial camber down to a better range for more ideal handling and tire wear, but you can get away without them. You just end up with a little too much rear camber.

- Andrew

[SubieNate]

I'd like to add something that I've been lead to understand. Correct me if I'm wrong.

The car diving does not cause weight transfer. Weight transfer causes dive. What dive does give you is a gentler weight transfer (There's some time delay as the springs are weighted, compressed, and then transfer weight to the front tires), which gives the driver A. a bit more time to react and B. more obvious feedback as to how much weight is being transferred.

Weight transfer is a function of CG and acceleration force only.

Say you're braking at 1 g (Pulling that out of my rear because I know the math, dunno what a realistic hard braking g loading is). That means your car is decellerating at ~32ft/s^2. Basically, for each second that goes by, your car is going 32 ft/s slower. or 9.81 m/s slower per second, 9.81 m/s^2.

I'm going to use metric from here on out because it makes my life easier and the numbers are as if not more easy to understand. I don't feel like getting into slugs or pound mass units and the accompanying explanation in this thread.

A=9.81 m/s
M=1270 kg (~2800 lb)

So. Force = mass x acceleration.

F = 1270 kg * 9.81 m/s^2 = 12458.7 kg*m/s^2 = 12358.7 Newtons.

Now that we have our braking force, we can determine our effective weight transfer. The weight of the car doesn't really transfer front to rear. There is a moment arm between the tire's contact patch and the center of gravity that basically "twists" the car forward.

Because of the nature of moments, centers of gravity etc, it doesn't really matter if the force is coming from the front or rear. It affects whether the tires can take the strain and keep their grip, but total force wise it works out approximately the same, so lets say that our moment arm goes directly down from our CG and acts in plane with the tire's contact patch. The CG is proportedly at 18" above this point, which is ~.457 m

.457 m * 12358.1 N = 5693.63 N-m.

This is our moment caused by our braking decelleration.

To find out the effective weight transfer, we take this moment, and balance it with a reacting force at the front tires. Because we're taking everything in reference to the CG, we can neglect the static forces present at all times from the actual force of the car being pressed down by gravity as it will be equal front and rear. Additionally, when pitching forward, there is no added force in the rear as the tires do not have suction cups on them.

So. Knowing the weight distribution (53/47) and the wheelbase (101.2 in) we can determine the horizontal distance from the front wheels to the CG. (101.2 * .47 = 47.564 in = 1.21 M)

Taking this number and dividing our moment by it results in 4705.48 N.

This is equal to 1057.8 lb of force being applied to the front wheels and effectively taken away from the rear. It's taken away from the rear because the total reaction force applied by the ground to the car must always equal that of gravity pushing the car down (or the combined forces of gravity and aero), otherwise the car would cease to be a car and become an airplane.

Pitching of the car does very little to change the magnitude of this weight transfer. It does not change the car's weight, and it usually changes the car's Cg location very little in the vertical plane.

What it does do, as I said before, is give the driver a good indication of what is happening, giving a novice driver big hints as to how the weight is being transferred. It also has a delaying effect on the weight transfer, making things more gradual. If the car had no suspension this weight transfer would be instantaneous. This is why riding on the bumpstops gives such unpredictable handling.

Moto-P is definitely right on one thing. Too stiff a suspension on weak tires can lead to scary things, as the tires load and unload so quickly and the threshold is so low that it can be difficult for even a good driver to feel things in time.


Nathan

[ATL BRZ]

bump, I love this thread!

[Mikepage]

Me to ;p

[Coaster]

Great thread. I hope the Eibach Pro kit maintains balance of car for me.

[mit_peid]

So is the consensus Eibach Pro kit for moderate aesthetic-driven drop to still maintain the good handling with stock struts/shocks? Seems like the Pro kit is still stiffer than stock, though. Also, how would sway bars and strut bars add to this equation / artform?

[whataboutbob]

I've got a set of RaceCompEng springs in a box on the floor waiting for a full Whiteline setup to arrive. I plan to start a personal build thread once everything arrives. Stay posted for details.

[diirk]

I've been holding out for the new Sprint springs.