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phate 12-30-2013 04:08 PM

MS6 Suspension Data & DIY Bilstein Coilovers & Secondary Rear Sway Bar
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.

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


Eibach's suspension worksheet (formulas and whatnot):

Suspension Worksheet |

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

phate 01-01-2014 01:51 PM

1 Attachment(s)
Potential Modifications

My goal is to have a ride-height adjustable setup using standard flat ground 2.5" or 65mm ID springs. They're available from pretty much every spring company in a wide variety of lengths and rates. Coilovers in the front, adjustable spring perch in the rear. I'm going to use Bilsteins since they're so easily rebuilt and revalved (and I already have them on the car).

After doing a TON of measuring and reading, and measuring some more, and reading of SCCA rules, I decided to not attempt a 2.5" spring in the rear. It would require modification of the lower control arm (cut OE perch out, weld in flat piece to accept a normal perch), and it would also require the bump stop mount to be modified or completely cut out. The latter modification is what I am concerned with in the SCCA SP rules.

Front Upper Spring Perches and Shock Mounts

The biggest issue is coming up with an upper spring perch to accept those springs. Both the front and rear upper perches are radiused where a 2.5" spring would sit. No bueno, they need a flat seat.

You can see the front upper perch in this picture

Rear upper perch in this picture

So they're a huge PITA. I'm planning to just have some adapters made to fit over the radiused part. To get the most space available, I'm just going to cut out the bumpstop mounts. If anything, I'll just put a small collar inside this adapter to hold a bumpstop. But, we also have hard rubber stops in both the front and rear that limit suspension movement to a max - since I'll be using hella stiff springs, I may just rely on those or retrofit softer bumpstops onto them.

Design of adapter

Adapter pics - Pic 1 - Pic 2

Update: I've decided to not run the adapter over the stock top hat. It shortens the length of available spring space quite a bit, and there doesn't seem to be much advantage to retaining the stock top hat. Along with that, there is one major disadvantage to using the stock top hat - it limits bump travel in the meat of the camber curve. If you check out the above pics of the adapters I had made, you can see the center hole is plenty wide to allow a shock to travel through it.

So, I'm going to just use the adapters under the shock tower as a spring seat. I'll build a new shock mount above the shock tower and tie it all together. Here is what the new spring perch and shock mount look like:

Pic 1 - Pic 2 - Pic 3 - Pic 4 - Pic 5

Going between the shock tower and upper spring mount plate, I made some solid threaded spacers.

The bushings in the spring mount plate are Energy Suspension 9.9126.

Update 9/30/15: You can run BC Racing's upper spring perches. I haven't measured these to see if they will limit shock travel, and I think it's likely they will limit it slightly, but it's a simple way to get an upper perch.

Suspension Bushings

Whiteline makes bushings for each point in the front suspension. From the other thread, CanyonRider noted that the front LCA inner bushings (W53396) don't hold up well.

W53396 Front Control arm - lower front inner bushing

W53397 Front Control arm - upper inner bushing

W53398 Front Control arm - upper inner bushing (camber correction)

W53394 Front Radius arm - to chassis bushing

W53395 Front Radius arm - to chassis bushing (caster correction)

W33335 Front Shock absorber - to control arm bushing

A Russian company at makes both front and rear suspension bushings for the 6, and they are much cheaper than the above whitelines. Go to this post for more information, but here are the links:

Rear suspension:

Lower Control Arm

Upper Control Arm

Trailing Arm

Three more they confirmed will work, for the FRONT suspension:

I think this is for the rearward LCA (the curved one):

Forward control arm, inner:

Forward control arm, shock mount:

This one they did not confirm will work, but should, anyway:

Front upper control arm:

Rear Upper Spring Perches and Springs

BC, Megan, and KW use an adjustable upper perch that seats a 3.5" spring. They're pretty inexpensive, but call around. If you go back to the first post, you can see the stock rear spring has a 2.5" lower ID, and a 3.5" upper ID.

Spring perches look like this: Pic 1 - Pic 2 - Pic 3 - Pic 4

Dimensions of the BC Racing upper perches

If only someone made a spring to fit that...

QA1 does. Only in a few rates and only 1 length, but they are right where we need them. You can even save a few bucks because Summit Racing and other big companies carry them.

The other option for rear springs is Suspension Spring Specialists, aka "Blue Coils". They offer a 5" OD (yes, outer diameter), 7" length series of springs starting at 700lb/in. Click here for their catalog page. Refer to this post for more information, and this post for pics.

I won't get into spring length calcs, only because we have the 1 length to choose from. But, here is a sketch of the suspension and how things will ride with a 600lb/in spring in the rear of my car - picture.

This post has some pictures of the rear spring and perch combo I've outlined above.

Bilstein front shock to coilover

So, the bilsteins have a nice ring on them where a removable perch sits, already. That's nice, because we can just get some threaded sleeves from A1 that sit on that ring.

A1 Threaded Sleeve

A1 Adjuster Nut for 2.5" ID Springs

Nut Set Screws with nylon tip

Spanner Wrench

More to come. I have a bunch of other measurements and some plans for some nice adjustable perches in the rear.
Front Spring Selection

From above, we have everything needed to closely approximate suspension frequencies. My spreadsheet looks something like this

285: 1.30 Hz (stock)
400: 1.53 Hz
500: 1.71 Hz
600: 1.87 Hz
700: 2.03 Hz
800: 2.16 Hz
900: 2.29 Hz

These are for my car, using my weights. Grab the spreadsheet and crunch some numbers for your own car to get the best results.

For spring length selection, jump to this post.

Rear Spring Selection

Sooooo, let's see where some of the available (realistic) spring rates put us:

185: 1.30 Hz (stock)
250: 1.51 Hz
300: 1.65 Hz
350: 1.78 Hz
400: 1.91 Hz
450: 2.02 Hz
500: 2.13 Hz
550: 2.24 Hz
600: 2.34 Hz
650: 2.43 Hz
700: 2.52 Hz

These are for my car, using my weights. Grab the spreadsheet and crunch some numbers for your own car to get the best results.

The beta version of the suspension frequency workbook has been attached to this post. It has suspension frequency calculations, wheel rate calculations, and just a couple notes. This is a BETA version, so it doesn't have many bells and whistles. I have a much larger workbook that will include a heck of a lot more, but I'm just slowly working on it.

TiGraySpeed6 01-02-2014 12:01 PM

Thanks Clint- great info to have.

Totally agree with your thoughts on the H&R springs too. I love the way they look, and they roll down the road fine, but heaven forbid you get aggressive with em. It's worse on my stock KYB's with 79K miles on them, 50+ of which were spent with the H&R's.

I<3Groceries 01-02-2014 12:12 PM

I can add that, with my BC COs lowered to the maxorz, that shit was constantly riding the bump stops.
Did realize there wasn't much stroke left, even with just a set of H&Rs. Crazy.

Sent from my SM-N900V using Tapatalk

phate 01-03-2014 09:08 AM

I'm changing this thread up to be an all encompassing "MS6 suspension data" thread. Reserved for actual measurements of various components, and some conceptualizing of possible modifications :)

I'll post things and update the OP as I take measurements, and if you have some info you would like to share, please post it.

Going to clean up the first couple posts and consolidate the info...

If you want some info that isn't in this thread, ask or just go measure it (and then post what you find!).

phate 01-11-2014 02:22 PM

Updated. More updates and spring selection calcs later this week, hopefully.

phate 01-17-2014 09:25 PM

Small updates above. I got new lower control arms for the front, so I have accurate measurements for them. I just need to get the angle of the front shocks so I can calculate the correction factor, then we can play with a spreadsheet I'm building to come up with specific desired suspension frequencies based on weights and motion ratios. Exciting stuff. If we know the spring rates of aftermarket springs, we can all lol at how crappy they are.

I have rear axle LCA's arriving next week. I took what I thought were pretty close measurements with them still on the car, but my motion ratios and resultant frequencies are significantly different than the most trustworthy source we have (FCM - @Code Monkey). So, once I double check my measurements with a new LCA that isn't on the car, I'll update that section.

I think I'm ~99% finished figuring out what hard parts I'm going to use, and I'll update this thread a bit more this weekend with that info.

I'm waiting on the spring adapters to be finished, which will be ~3 weeks. I might actually be able to finish this before the season starts, haha.

And damnit, I might have to rename this thread again. It's going to turn into a 'how to make your own coil overs' thread, lol.

phate 01-18-2014 09:50 AM

So, Eric ( @TiGraySpeed6) sent me a link to some BAMF doing similar BA things to his Mazda6 over here: Prepping as dedicated track car

He found near identical motion ratios using a different method, so I'm updating the above. The rear suspension requires a LOT more spring than I expected, because the motion ratio is so low. @Code Monkey, did Shaikh measure the front and rear suspension components when he had your car in? I'm trying to reconcile the difference. I'm hoping to have him revalve my bilsteins for this setup, so I'm going to call him next week, anyway.

Code Monkey 01-18-2014 09:05 PM

Shaikh did measure all the suspension components but it was not my car, @dot584; where are you? The motion ratios Shaikh came up with were .69 in the front and .75 in the rear.

phate 01-22-2014 03:20 PM

@Code Monkey and @dot584 - I received my new rear LCA's today and double checked my measurements. They were pretty dang close to my on-car measurements. The bushings aren't perfectly straight in these, so I measured each of the 4 sides and averaged my measurements (they were all within .02" of each other, so not much variance). I come up with:

Dimension A: 10.27"
Dimension B: 17.93"
Spring Angle: 0°

So we get a spring motion ratio of: .57

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

Code Monkey 01-22-2014 04:49 PM

Shaikh initially calculated the motion ratio in the rear as .57, later revised it to .75.

With the .57 ratio in the rear and .69 in the front, you would have to run stiffer springs in the rear, his initial calculations were something like 700/1000 springs for me.

After he revised the rear ratio to .75, the spring rates basically reverted to 1000/700 which makes more sense given both stock and aftermarket setups have fronts about 30%-40% stiffer in the rear.

Nevertheless, I am very curious where you will end up. :)

phate 01-22-2014 05:08 PM

Yeah, for my car with my .57 rear motion ratio figure, I come up with an 1100lb/in spring to achieve a 2.4Hz rate. If I remember right, your car is ~75lbs lighter on each rear corner, so the 1000lb/in figure puts you right at 2.4Hz. I'll give Fat Cat a call tomorrow; hopefully we can sort out what I'm doing wrong ;)

I believe there is a similar issue in the evo community, where the aftermarket companies aren't compensating for the low motion ratio in the rear, resulting in very low effective rates compared to the front.

As a small step towards proof of concept - I come up with just over 2.2Hz for your front suspension with a 1k lb/in spring and your 1085/1094 lb corner weights.

Code Monkey 01-22-2014 05:43 PM

Sorry, with my corner weights (with me in the car) and the ride frequencies of 2.2/2.4--ish, Shaikh came up with 900/672 spring rates. Then he adjusted for sway bars and said to try 1000/670 and if the car feels too pushy then we can drop the fronts to 900.

Because rear springs come in 50 lbs increments, it is easier to keep the rear at 670 and tinker with the front rates if needed. :)

phate 01-22-2014 05:53 PM

1 Attachment(s)
No doubt we're working with close estimates, but how's this for close, lol.

I'm going to take a different approach to measuring the front motion ratio this weekend to verify my LCA measurements. I'm still refining that spreadsheet so we have a good working model.

BAT-man 01-23-2014 07:35 AM

I hope this is easily adaptable to the MS3 platform... or to any platform really. Seems to be, as far as I can tell. It's all much appreciated.

zenit 01-23-2014 08:13 PM

The +0 -0 annotations, what do they mean?

phate 01-23-2014 08:25 PM


Originally Posted by zenit (Post 2426144)

The +0 -0 annotations, what do they mean?

Allowances on those measurements. 63 + 0, because the spring has to fit around it. If it's bigger, the spring won't slip past it. 92 - 0, because that cup has to sit beyond the radiused section of the current seats.

There should be a -0 on that 20mm depth, as well. If it's less, that part will sit on the radius, preventing the new perch from sitting flat. That tolerance went to the machinist. The rest weren't terribly important, lol.

One addition that I haven't talked about is a radius (fillet) on the inside cup corner (the 92mm section). These things should be plenty strong, but it was an easy addition that didn't cost me any extra.

I got word yesterday (maybe it was today, idk) that the adapters will be finished early next week. I may use them a little bit differently than I originally intended...I'm not sure yet. I'll go through it once I get the adapters and can set them in place.

phate 01-27-2014 07:30 PM

Shaikh from Fat Cat called me today. I sent in a consultation form for a coilover system many months ago and he was calling about that. I explained the situation to him about my own conversion to adjustable height suspension and what I had found so far and what I was planning. He is definitely up for reworking my Bilsteins, and I'm really excited to hear that. It will be with their new kerb blow-off valving...which should be much better suited to my normal autocross surface that isn't glass smooth.

I did ask him about the rear motion ratio, and I'll amend my figures up top. The explanation is simple - he is using a motion ratio figure based on the actual ride behavior. He did measure nearly the same spring motion ratio as what I found (.57 vs .58), so I'm not crazy ;) If I experience something different, I can swap springs very easily since I'll be using standard diameters.

I'll update my figures above.

amoosenamedhank 01-28-2014 06:48 PM

I love reading this thread even though I have no idea what the fuck you're talking about. I feel like a kid at the adults table all over again

Sent from my SCH-I535 using Tapatalk

phate 02-10-2014 01:49 PM

Making some good progress on this end. I've decided to make some changes to my original intent, but it's nothing serious, and it simplifies my life a little bit.

Front upper spring perches: The adapters were made (they're sexy) and I'm not going to use them over the stock top hats. It decreases the available space for a spring to fit, and the top hats already limit shock travel (shock top hits top hat). Limiting shock travel in bump limits wheel travel in the meat of the camber curve. No sense in doing that.

So, the adapters have a 58mm hole in the center of them...and the shock body is only ~46mm diameter. So, similar to what CanyonRider is doing in his thread, I'm going to make a shock mount up above the shock tower to allow a full range of motion where there is no limitation to shock travel. The shock will be able to travel through the spring mount and shock tower if need be, which allows full articulation of the control arms. That also lets me easily put a bump stop in and adjust the point where it engages...

In the rear, I've abandoned the idea of using a 2.5" ID spring. SCCA rules will probably put me into some nasty class I don't want to be in. In order to fit a 2.5" spring back there, you would need to modify the LCA spring perch by cutting the stock perch and welding up a new one. For the top, you have to alter or remove the bump stop mount, because a 2.5" ID spring won't even fit over it. Lame sauce. But, lots of companies who make coilovers for our car make an adjustable perch that sits at the top. So, I have a set of these coming from BC. They should be here today.

The downside to these is that they only fit 3.5" ID springs, while the bottom stock perch seats a 2.5" ID spring. These springs are really hard to find from any of the regular spring manufacturers. Luckily, and thanks to Shaikh at FCM and @Code Monkey;, we know that QA1 makes a spring for the Mustang II that has those same end diameters. Looks like I'll be going with a pair of those in the rear.

I did receive my front coilover hardware from A1. Nice pieces. I'll put up more information once I get the current spring perches off of my Bilsteins.

I did yank the Bilsteins out of my car this past weekend, so I'm nearly ready to send them out. The perches are really stuck after being on for a year, so I need to clean them up and give them hell.

Whiteline bushings came in for the front control arms. I put them in my new LCA's already - pic I did get new UCA eccentric bushings from WL, as well. I already have SPC ball joints, so you might wonder why I got the eccentrics. My thinking here is that I can lower the UCA pivot point, increasing dynamic camber that we gain through bump. Hopefully the ball joint has enough travel and doesn't neck out, lol. I'll put all of these in once I get closer to the actual racing season.

Probably more things have gone on that I can't remember right this sec. But, that's the gist of it. I've updated the 1st and 2nd posts in the thread with this info and pics.

Code Monkey 02-10-2014 02:05 PM

If you talk to Shaikh again, ask what he thinks about removing/disconnecting the RSB on our cars. :D I know I am going to try it at the track, for autox the results could be even better.

phate 02-10-2014 02:12 PM


Originally Posted by Code Monkey (Post 2448179)
If you talk to Shaikh again, ask what he thinks about removing/disconnecting the RSB on our cars. :D I know I am going to try it at the track, for autox the results could be even better.

When we talked about my setup, we went into some detail about sway bars. I'll be very near your suspension frequencies (2.2/2.4Hz front rear), and he suggested I stay with the WhiteLine rear bar and a stock front bar to get the proper balance. I'll probably end up testing it out, anyway, haha.

Let us know how it behaves when you disconnect it.

TiGraySpeed6 02-10-2014 05:02 PM

That makes me worry for how bad my suspension is (stock & trashed KYB's + H&R springs) cause the WL RSB on the stiff setting was/is a magical improvement over stock RSB stiffness.

I can't imagine how out of shape it would be without the RSB...

Code Monkey 02-10-2014 08:25 PM

The rear springs I will be running are 3.8 times stiffer than stock. Stiffer springs in the rear = more oversteer. One possible solution = soften RSB, or, in my case, eliminate it.

Or I could get a stiffer FSB, but I prefer weight reduction. :)

phate 02-10-2014 09:17 PM


Originally Posted by Code Monkey (Post 2448752)
The rear springs I will be running are 3.8 times stiffer than stock. Stiffer springs in the rear = more oversteer. One possible solution = soften RSB, or, in my case, eliminate it.

Or I could get a stiffer FSB, but I prefer weight reduction. :)

It's more proportion of roll resistance in the front vs rear of the car. Since you're also bringing the front spring rate way up, you're bringing the roll resistance proportions back to somewhere closer to nominal. My bet is that because our cars are going to be so close on spring rates, he'll suggest something similar.

Unfortunately, I don't have enough information to calculate that fun stuff, yet. So, Shaikh is the best source for that advice.

More to add on that subject...You can get enough total front/rear roll resistance with either just springs, or with springs and sway bars. But, in order for most cars to do it with just springs, it would take an INCREDIBLY stiff spring to get enough total roll resistance without any sway bars. That, in turn, makes the suspension frequencies outrageously high, and will likely decrease grip because the tire won't be able to follow the contour of the road. So, it seems that most folks get a spring rate for a desired natural frequency, then dial in the necessary front vs rear roll resistance with sway bars. [Or they just slap on HUGE sway bars because of class limitations or whatever, which has its own downsides.]

Right now, that's how I understand it. That doesn't mean it's gospel or in any way accurate, lol. I'm learning this stuff as quickly as I can. I have 4 different suspension books that I've been reading like crazy in my spare time. Steep learning curve in this side of the house, haha.

Code Monkey 02-11-2014 07:06 AM

Titles of the books please.

phate 02-11-2014 07:09 AM

1 Attachment(s)
Attachment 147461

Competition Car Suspension - Allan Staniforth (I've read this one cover to cover - it's good stuff)

Race and Rally Car Source Book - Allan Staniforth

Engineer to Win - Carroll Smith

How to Make Your Car Handle - Fred Puhn

Tune to Win - Carrol Smith (not pictured)

zenit 02-11-2014 07:15 AM

germane to the topic of spring v. sway in roll couple:
@phate If you haven't read the Mark Ortiz newsletters, they're good stuff!

phate 02-11-2014 07:26 AM

Awesome, thanks for those links. I have 3 articles up from OptimumG, right now:

phate 02-11-2014 08:56 PM

Now that I have all of the hardware for the front with the exception of springs, I thought I would get into springs lengths. It really is a simple process, there's just a lot of numbers floating around.

A few things we need to figure out first...

My maximum perch-to-perch distance is 12" with things as-is. I could cut down these adapters and gain another .75", but I don't think I'll have to.

Sprung weight on each front corner: [Corner Weight] - [Unsprung Weight] = [Sprung Weight]

For my car: 1020 - 125 = 895lb (Unsprung weight is a close estimate)
--My left/right front weights were within 1lb of each other. Use your own weights for the best numbers.

We need to know that to figure out how much our spring will compress at ride height. I know that I want around 2.2Hz natural frequency up front, which will require an 800-850lb/in spring. That much sprung weight on that spring will give us approximately 1.1" of compression at ride height.

We have 5.5" of shock travel available. We have 7.25" of wheel travel which is limited by the control arm movement. This wheel travel only requires 5.3" of shock travel (7.25*.73 = 5.3... .73 is our shock motion ratio up front). Exciting. We want the shock to sit at approximately 40-50% compression at ride height - that's .5*5.5 = 2.75". That means there will be 2.75" of bump travel at the shock. To figure out required spring travel, we just add the 2.75" bump travel to the 1.1" of compression at ride height. This will let the car sit just slightly below stock ride height so you don't have to look like a monster truck.

[Required Spring Travel] = [Bump Travel] + [Spring Compression at Ride Height]

2.75 + 1.1 = 3.85" Required Spring Travel

That lets us sort out the minimum spring length, based on usable travel of a spring. Swift and Eibach publish travel figures for their springs, Hyperco says you will get a minimum usable travel of half the free length of their spring (i.e a 7" spring will have >= 3.5" usable travel).

For the big 3 spring manufacturers, that means I need at minimum an 8" long spring. No big deal, these rates in that length are available.
If you're on the edge about going to the next longer spring, call the manufacturers to get an exact usable travel range. The shorter spring might work fine.

Note: Read the red text if you want to skip the other stuff, lol.


We could calculate a maximum spring length...but we're going to run the shortest spring possible because of weight savings. But, if you wanted to do it, it looks something like this:

We use that same ride height compression number of 2.75" to get the shock near center. 1.1" of compression means we need a gap between the spring and perch of 1.65". Meaning it will compress the shock 1.65" from full droop of the suspension until it touches the spring, then it will compress the spring by our 1.1". My max perch to perch distance is 12", so:

12 - 1.1 - 1.65 = 9.25" Max spring length...or just 9", because that's a standard length. If I wanted to cut these perches down a bit, I could (in theory) run a 10" long spring. That's really going to kill the adjustment to lower the car, though (more on that, below).

You can run a helper spring if you wanted to take up that gap, but I'll probably just secure the spring to my new spring perch. Weight savings, lol.


I suppose it would be nice to see available (approximate) ride height ranges, because I know some of you are thinking you need moar lowz (if that's true, you're probably in the wrong thread)...Sadly, no matter how awesome the car looks laying frame, you will be seriously limiting suspension travel if you do this, so I don't recommend lowering a whole bunch more than stock ride height (maybe an inch or so). Anyway, I digress.

So, we know that my max perch-to-perch distance is 12". The sleeve is 7" us a minimum perch-to-perch distance of 5". For an 8" spring in the 800-850lb/in range, we need a gap of ~1.65" to let the car ride at a decent height. That puts the lower spring perch approximately 9.65" away from the upper spring perch (8" + 1.65"). That means the spring perch can be adjusted 4.65" upward for monster truck status, or 2.35" lower for teh lowz. I think that is a totally sufficient range of adjustment.

Same sorta thing for a 9" and 10" spring. I'm going to run an 8" spring of this rate.

[Spring Length] + [Spring Gap] - 5 = available monster trucking range

12 - [Spring Length] - [Spring Gap] = Lowering range

Just remember there are real limitations to suspension travel. Refer back to the front suspension camber curve for a good visual. You can convert back to wheel travel ranges and hub to fender heights fairly easily...


So this is what the setup looks like so far:

The sleeve can be flipped to adjust the height it sits at. There is a 1" difference between the heights:
There's no way I'll ever run the perch up that high, so I'll use the second ring where the sleeve sits lower on the body.

I think I've mentioned in this thread how the bump travel is limited by the stock top hats. This is due to the top of the shock coming into contact with the top hat before we reach full bump of the suspension. In order to fix that, the shock needs to somehow travel higher. I'm planning to just use these adapters and let the shock travel right through, sorta like this:
Right now, the sleeve is too big to fit through, but I'll just cut a half inch or so off of the top of each sleeve if I have to. If I shorten the adapter, I doubt I need to. Above the shock tower will be a plate to mount the shock. It shouldn't be too far above the shock tower - maybe .5-1".

phate 02-12-2014 01:14 PM

I've added some info about the rear spring setup in the second post. I received my BC Racing adjustable perches. The QA1 springs really save the day - with the BC perches, the ride height can be raised or lowered >1" in either direction of stock ride height.

zenit 02-12-2014 04:17 PM

You bought just the perches? From BC?

Sent from my SAMSUNG-SGH-I847 using Tapatalk 2

phate 02-12-2014 04:19 PM


Originally Posted by zenit (Post 2451558)
You bought just the perches? From BC?

Sent from my SAMSUNG-SGH-I847 using Tapatalk 2

Yep. They will sell pretty much any of their components by themselves. Ground Control is the same way, and probably the other companies, too (KW offered to sell components when I called them a while back).

cnyms6 02-13-2014 04:46 AM

Wow! This is such a great thread. I've been searching for this kind of knowledge for a while. Thanks Phate for all of this intelligence for the forum. I'm hoping to learn and apply as you go along.

I have a question: How did you choose the spring frequencies you want to design for?

phate 02-13-2014 08:14 AM


Originally Posted by cnyms6 (Post 2452186)
Wow! This is such a great thread. I've been searching for this kind of knowledge for a while. Thanks Phate for all of this intelligence for the forum. I'm hoping to learn and apply as you go along.

I have a question: How did you choose the spring frequencies you want to design for?

Truthfully, where "good" suspension frequencies come from is a bit of a mystery. They're quoted in a number of places simply as magic numbers. It's a big question I have, too. Shaikh also suggested frequencies in this range. So, relying on similar wisdom from the experts seems like a safe bet to start off with.

Most of the sources quoting those numbers are at least a few years old, and they suggest those frequencies for RComp type tires. But, the rcomps of yesteryear have really been outdone by the street tires of today. So, people are getting away with these very high suspension frequencies (and higher) and having great success. I know of a couple people that are currently running ~2.6Hz on street tires and are very, very fast at autocross (by street tire, I mean non-RComp. i.e Rival/Z2). Our main autocross area is old air force tarmac that is pretty bumpy, too. I'd guess another reason for people attempting these high frequencies is the availability of highly digressive blow-off valving in their shocks.

The front/rear split in frequency is to obtain 'flat ride'. Meaning when you hit a bump, you want both the front and rear to settle at nearly the same time. [Why that's important for autocross...I'm not sure] For your average autocross speeds, that's a split of 10-20%. BUT, again, there are all kinds of people who don't follow this rule. The gentleman I referenced above actually runs 2.59Hz up front and 2.50Hz in the rear.

Probably not the answer you want to hear, and it's not the kind of answer I'd like to give. But, that's all I have for now.

Code Monkey 02-13-2014 09:09 AM

See here:

Street car: 0.8 Hz
Occasional autocrosser: 1-1.5 Hz
Full-bore autocrosser: 2.2-2.5 Hz

I bet those numbers were obtained by trial and error over a period of time and these days most everybody agrees these frequencies are a good starting point.

cnyms6 02-16-2014 07:22 AM

@phate; So I've been reading all of the links in the thread and have a question. In your buildup of the unsprung weight estimate, why do you list spring and shock twice, with different weights?
Really liking this suspension goodness - thanks

phate 02-16-2014 10:10 AM


Originally Posted by cnyms6 (Post 2455758)
@phate; So I've been reading all of the links in the thread and have a question. In your buildup of the unsprung weight estimate, why do you list spring and shock twice, with different weights?
Really liking this suspension goodness - thanks

Heh, thanks for pointing that out. They shouldn't be listed twice, so I'll check my current version and amend if it's still that way. I'm guessing I wanted them in the lower half because those weights are split between sprung and unsprung, but didn't delete the originals.

The overall difference in suspension frequencies should be negligible. I'll trim down my workbook to just the front/rear frequency calculators and post it if you'd like.

Edit: @cnyms6, and any others who are interested. I just posted a beta version of the suspension frequency and wheel rate workbook in the second post ("Potential Modifications" section). It includes both the front and rear info. Should be a good start for anyone interested. I have a lot more in my current working version, but not much else is finished.

phate 02-20-2014 06:22 AM

I posted these in my thread, but here's what most of the setup looks like.


Pic 2 - Pic 3 - Pic 4 - Pic 5 - Pic 6 - Pic 7

I found some captive studs that I think will work to make the shock mounting simple. They get here today, and I should have the shock mount plates machined by next week.


Pic 2 - Pic 3 - Pic 4 - Pic 5 - Pic 6 - Pic 7 - Pic 8 - Pic 9

I suppose I'm a little concerned with how short that rear setup is compared to stock, now that I can see them side by side. If it's too short, I'll just make a spacer for the BC perch to sit on. NBD.

Nliiitend1 02-20-2014 08:24 AM

I wouldn't worry too much. That new spring is going to compress a LOT less than the old one at static height...

Are you gonna use simple flat Torrington/needle bearings on the perches in the front?

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