MS6 Suspension Data & DIY Bilstein Coilovers

[phate]

This thread is for actual measurements of the various suspension components.

Here is another EXCELLENT thread from a Mazda 6 forum, where he is turning his regular 6 into a full blown racecar. More extreme than anything I'm doing, but the 6 and speed6 share suspension components. He's also doing some things a little bit differently, which just gives us more options if/when we go about these things.

Prepping as dedicated track car - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum


**Notice** This first post is just a summary of things I have done with the car. Everything here has been detailed in posts throughout the thread.


Front Suspension

Front Suspension Geometry

Basic Layout of control arm pickup points and whatnot

Instant centers and roll center at stock ride height

Instant centers and roll center at H&R ride height (just for reference)

Control arm angles through bump travel


Front Suspension Camber Profile

Did some measuring to see how much camber we gain under suspension compression (bump). I picked up a Craftsman level with digital readout to the 0.1°. Plenty accurate for what I'm doing. It has a magnetic base, so I stuck it to the rotor.

Pic of test setup

I measured the full droop height before I pulled the shock/spring out to make sure I started at true 0. Everything here is relative to that full droop point (suspension hanging freely). I took measurements at every .1°. Anyway, this is what it looks like:

Front Camber Curve Graph

I charted it like that to make it look pretty. The hub center to fender numbers start at 18" at full droop, and go to 10.75" where the UCA hits the shock tower. The stock ride height sits right where the camber curve really starts to shine.

Edit: The portion to the left of stock ride height is where the LCA is below horizontal. I didn't measure when this or the UCA get to horizontal, but I don't think it's totally necessary.

♥ Double A Arm ♥

Front Suspension Bump Steer Profile

Front Bump Steer Plot

Pics of Setup: 1 || 2 || 3

For this, I used a laser level that projects a vertical line away from the wheel surface [don't worry, sketches and even a video included below]. I had the wheel off and set it on top of the rotor. I thought this would be closer to the axis of toe rotation than the wheel face. The problem with this is that there is fore-aft wheel movement during bump travel that you have to account for when projecting onto another surface - read: the wheel center migrates forward or backward during vertical wheel movement (bump/droop). Projecting the laser onto a second surface apart from the car would require taking this movement of the laser level into account, but that's a lot of work.

So, to take care of that variable, I projected the beam onto a mirror and reflected it back onto a ruler I attached just below the laser level. With this, the projected beam and measuring stick move together, so only the rotation of the laser level via toe change will alter the projected position on the ruler. [Note: Even though I know it's not completely accurate, I'm making an assumption that the laser level travels on a completely vertical trajectory through bump travel to make the data collection and calculations simpler.] Now, because we can assume the mirror is a flat plane, we can simply measure the distance from the level to the mirror and the mirror to the ruler. The sum of this distance is the long leg of a right triangle. As the toe angle changes, the projected line moves along the ruler and we now have the measure of the short leg of a triangle measuring from the start position and the current position.

It's a simple calculation using the arctan and we have the angle. Take these measurements at different points in bump travel (I did every 1/2") and we can easily see how toe changes through bump - aka bump steer. If you want to, for whatever reason, convert these back to "toe inches", you just multiply the tire radius (1/2 height) by the tangent of the angle.

Sketch of Setup

Sketch of Calculations

Remember to work in degrees for this stuff on your calculator. Or, if you really want to work in radians, more power to you.

Stock Spring Info

I had these tested at Right Foot Performance in Wisconsin.

Front:
285lb/in
14.375" Length
2.25/3.5" ID/OD Bottom
3.375/4.5" ID/OD Top

**There is likely some variance between springs and pressure test rigs, so these are a close approximation.

Corksport had a set of stock springs tested, also:

Front: 5kg/mm - 280lb/in

Pic 1 - Pic 2 - Pic 3


Stock Front Shock Info

Stock Shock Dimensions

Pic without spring

Total Stroke - 5.3125"
Max Usable Stroke - 4.25" (Due to shock body hitting bumpstop cup when bumpstop removed - picture)


Bilstein Front Shock Info

Bilstein Shock Dimensions

Total Stroke - 5.5"
Max Usable stroke (with stock MS6 top hats) - 4.75"


BE5-A256/24-102568 and BE5-A257/24-102575 are the part #'s for the fronts


Control Arms and Motion Ratios

This is what the front (towards front of car) lower control arm looks like - Pic 1 - Pic 2

This is what the rear (towards rear of car) lower control arm looks like - Pic 1 - Pic 2

pics of the upper control arm some time in the future



Anyway - the front LCA is where the magic happens. The shock/spring mounts to the center hole. So, taking a couple measurements, we can calculate the motion ratio in the front suspension. The diagram above shows us what we need.

Dimension A - 9.050"
Dimension B - 12.425"
Spring Angle -
~62° @ Full droop
~80° @ 4.6" wheel travel (60% bump)
~93° @ full bump (frame stop touching)

Using the formula (a/b)*sin(θ), we get a shock/spring motion ratio of .73 at ride height, increasing slightly to almost .74 when the control arms are perpendicular, then decreasing a tiny amount again. I'll use .73 for calculations.

Edit: I have measured this directly, as well. I come up with an average of .73" shock travel per 1" wheel travel. Just another verification.

From my testing of the camber curve, we know that the available wheel travel from full droop to UCA frame stop is 7.25". With this spring/shock motion ratio, we know that the needed shock travel is .73*7.25 = 5.3"

Looking at the available stroke of the bilstein above (4.75"), we can see that the bilstein shock body will contact the upper perch before running out of stroke (bottoming out). The bump stops currently prevent this, and I'll probably utilize some kind of bump stop to limit this in the future.

Anti Roll Bar

Motion Ratio is the same as the shock and springs - .73

Go to this post for information about the testing methods and how these values were calculated.

Stock Front/Stock Rubber Bushing
Bar Lever Arm Length - 8.19"
Bar Vertical Rate (ItF) - 205 lb/in
Bar Vertical Rate (Average) - 208 lb/in
Bar Angular Rate (ItF) - 240 in-lb/1°
Bar Angular Rate (Average) - 244 in-lb/1°


Stock Front/Poly Bushing
Bar Lever Arm Length - 8.19"
Bar Vertical Rate (ItF) - 222 lb/in
Bar Vertical Rate (Average) - 226 lb/in
Bar Angular Rate (ItF) - 260 in-lb/1°
Bar Angular Rate (Average) - 265 in-lb/1°


Anti-Roll Bar End Links

Upper and lower studs are M10x1.5mm

Center to center of the stock links is right at 16.5cm





Rear Suspension


Rear Suspension Camber Profile

So I did the same for the rear suspension. Pulled the spring, measured from what was nearly full droop to bumpstop contact. I couldn't get it down to full droop because of the bind in the bushings. This is what the camber profile looks like starting 15/16" above full droop:

Rear Camber Curve Graph

Full droop is 17-3/8" from hub center to fender. The "0" mark is 16-7/16" from hub center to fender.

Bumpstop contact occurred at 11-5/16" hub center to fender distance. I only have H&R spring ride height data, which only leaves us with 1.7" of wheel travel before it bottoms out. Scary, and it SUCKS when you want to do anything performance oriented. The suspension is constantly bottomed out :/

If someone has ride height info for the rear for stock shocks, I'll add it to the graph. I just need center of the wheel to fender distance.


Rear Suspension Bump Steer Profile

Rear Bump Steer Plot

Refer to front suspension bump steer profile section for details on setup and procedure.

Stock Spring Info

I had these tested at Right Foot Performance in Wisconsin.

Rear: 185lb/in
13.25" Length
2.375/3.5" ID/OD Bottom
3.5/4.5" ID/OD Top

Pic 1 - Pic 2 - Pic 3

**There is likely some variance between springs and pressure test rigs, so these are a close approximation.

Corksport had a set of stock springs tested, also:

Rear: 3.5kg/mm - 196lb/in


Control Arms and Motion Ratios

This is what the rear suspension looks like

Corrections: I received new rear LCA's and remeasured them. The correct dimensions are below/

Rear LCA Pictures: Pic 1 - Pic 2 - Pic 3 - Pic 4 - Pic 5

The bump stop point is an estimate, but the three important dimensions (similar to above) are:

Dimension A: 10.27"
Dimension B: 17.93"
Spring Angle: 0° (there is some deflection because the spring is bending slightly, but I'm planning to take care of that later on)

So we get a spring motion ratio of: .57

***Edit*** - The spring motion ratio found using actual ride behavior, determined by Shaikh at Fat Cat Motorsports, acts more like a .75 MR. I will be using this figure unless I find otherwise after it's all together.

***Edit 7/20/15*** - The above note seems like a good jumping off point for frequency based equations and flat ride. After increasing rear stiffness multiple times, I firmly believe the mechanical motion ratio of .57 should be used for all weight transfer and roll resistance calculations.

If you know corner weights and unsprung weights, you can calculate suspension frequency. For my car, this looks like:

Corner Weight: 721/697 lbs left/right (these are my actual corner weights for the rear, get yours weighed)
Unsprung Weight (estimated, but probably really close): 103 lbs (with a 16lb wheel and 23lb tire, adjust yours from there)
Sprung Weight: 618/594 lbs left/right

And we grab the stock spring rate from the section below - 185lb/in

Throw that info in my handy spreadsheet, and we come up with frequencies of:

1.29/1.31 Hz left/right

That, of course, doesn't account for bind in the bushings and deflection and probably a few other very small corrections, but it should be really close. As I get better information, I'll update as necessary.



The shock motion ratio is a bit simpler:

It attaches to the knuckle, so that is nearly a 1:1 MR. But, it sits at an angle of ~67.5°. So, we get:

Shock Motion Ratio: .93


For the rear sway bar's motion ratio:

The LCA is 17-5/8", and the end link attachment point is 5-3/4" away from the inner joint. So, we get:

Rear ARB Motion Ratio: .33 (if your end links are angled away from vertical, this MR is even smaller).




Bump Stop 'Cup'

Cup Inner Diameter - 1.962"
Cup Depth - .960"
Range of Gap from Bump stop cup lip to upper edge of LCA contact - ~2" @ full bump to ~6.1" @ full droop.



Anti Roll Bar

Motion Ratio - .33

Go to this post for information about the testing methods and how these values were calculated.

Stock Rear/Poly Bushing (*Tested with oversize bushing, rate is likely higher than tested)
Bar Lever Arm Length - 7.72"
Bar Vertical Rate (ItF) - 250 lb/in
Bar Vertical Rate (Average) - 265 lb/in
Bar Angular Rate (ItF) - 260 in-lb/1°
Bar Angular Rate (Average) - 276 in-lb/1°

WL Rear - Soft/Poly
Bar Lever Arm Length - 7.65"
Bar Vertical Rate (ItF) - 393 lb/in
Bar Vertical Rate (Average) - 399 lb/in
Bar Angular Rate (ItF) - 402 in-lb/1°
Bar Angular Rate (Average) - 407 in-lb/1°

WL Rear - Stiff/Poly
Bar Lever Arm Length - 6.71"
Bar Vertical Rate (ItF) - 477 lb/in
Bar Vertical Rate (Average) - 489 lb/in
Bar Angular Rate (ItF) - 375 in-lb/1°
Bar Angular Rate (Average) - 385 in-lb/1°



Anti-Sway Bar End Links

The end links in the rear are slightly different. They are a stud on the top, and a through bolt on the bottom (double shear on the bottom).

Both the top and bottom use an M10 bolt.

Center to center is 8.25cm

The bottom section's width is 2.85cm

Here is a sketch of the dimensions




References

Eibach's suspension worksheet (formulas and whatnot):

Suspension Worksheet | eibach.com/america

Hypercoil's suspension calculator with good explanations of important aspects of all this:

Wheel Rate & Spring Rate Calculator

Competition Car Suspension by Allan Staniforth

Race and Rally Car Source Book by Allan Staniforth

Engineer to Win by Carroll Smith

How to Make Your Car Handle by Fred Puhn

Tune to Win by Carrol Smith