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....I had to take the car and scales over to a friend's garage - with a nice flat floor. My garage floor is like a hyperbolic paraboloid (it ain't flat).
Mine was not quite that bad, but that's where I created 4 marked patches that, with the plywood "shims", created 4 places that are flat, so I park the car tires on those 4 places.

Since there was two of us, I was able to sit in the car as he read the scales. I set all the tire pressures to 35psi. I disconnected the swaybars AND the front & rear shocks. This allowed us to really bounce the car to relieve the spring bind which happens as you crank the perches up and down. After a couple of good bounces you would hear the spring go BOING. Then we'd roll it back on the scales.
That's the way to do it. But with you, or a proper substitute in the car, I had suggested shimming the pivot bushings, and/or adjusting adjustable end links, so bars are not stressed with driver strapped in.

Final point about Motion Ratio, the simple leverage IS the motion ratio, and you use the square of the MR in finding the wheel rate for the spring, and for the s-bar.

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Discussion Starter #482
I messed around with the angle of the dangle, and had trouble getting a 5% change in weight distribution. When I assume you drop the rear 3", and the front none, that angle of body tilt is 1.7 deg. And the change in the for/aft position of the CG will be the (change in CG height) x Tan(1.7). So assume change in cg height is 2", the for aft change will be .06" , but we are looking for about a 5" change to support a 5% change on a 101" wheel base.

I believe the scales, but there must be something else that was done?


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Yeah, I was just shooting from the hip and was referring back to the first time I weighed it (from memory). I went back and checked all my scale numbers:
Street driven w/battery in trunk, lite flywheel, tube headers - 58.6% front
After I gutted the car - 63.4% Front
After adding the roll bar - 62% front
After adding adjustable perches and setting ride height - 61% front

Not quite the dramatic change as I thought.

CR
 

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Discussion Starter #483
With my new found lowness, I've had to redesign the exhaust. Recall We had side exit exhaust, but it dragged a bit on hard left handers. I liked it out the side because it was out of the way as we worked on the rear suspension. This pic is before lowering the rear.



Well with the rear about 3" lower, the side exhaust ended up about an inch off the ground. So, straight out the back we go. All 2.5" with a 30" long 3"dia chamber tube at the very end. :thumbup:



Next AutoX - a week from today! :drive:
 

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I made some initial runs on my Excel model :) ...
( turns out the initial output was correct )

Input Data

3000 lb total
61% front wt bias
10% unsprung wt
F MR = .69 spring
R MR = .56 spring

Front Lever Arms, inches

to sway bar ------- 6.0
to spring ----------- 9.3
to b-jt ---------------13.5
b-jt to wheel ctr -- 3.13

Rear Lever Arms, inches

to sway bar ------- 5.5
to spring ----------10.0
to b-jt --------------18.0
b-jt to wheel ctr -- 5.5



Height, CG Sprung Weight 19
Height, CG unsprung weight 12.4
Height, Front Roll Center4
Height, Rear Roll Center 6
Height, Roll Axis to CG 4.78 ( roll couple lever)



With the RB bars as is, with rear in soft oem position: Wt Transfer is 60% up front. Very close to neutral. Roll is 1.34 deg @ 1G . Have to see how the autox goes ... looks like you have put together a great set-up !

With a 26mm front bar, Rear 27mm at oem/soft: Wt Transfer front bias is 57%, and roll is 1.47 deg @ 1G . Just checking this Steeda bar.

Note I dropped the CG & roll centers (esp rear) from my stock model.

Need to update model with your more accuratly measured MR's, roll centers, % un-sprung wt, and sprung wt CG.


Output Data

700 Front Spring, 500 Rear Spring
28.5mm Front Bar, 27 mm Rear Bar,
1.34 ROLL, deg
60% Fr WT Bias
62% Fr RS Bias
578 R Bar Link, lbs
61.2% Inside R u-load


For autox, with 2000lb GT-6, I always adjusted my 9/16" rear sway bar one spot stiffer out of 5 positions (bar was my design, no oem bar), vs on the road course.




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Discussion Starter #486
I made some initial runs on my Excel model :)

For autox, with 2000lb GT-6, I always adjusted my 9/16" rear sway bar one spot stiffer out of 5 positions (bar was my design, no oem bar), vs on the road course.
Thanks! I'll try to get some more accurate measurements for you when I get some time - trying to get the car together for Saturday.

A agree, I always like the RSB a bit stiffer for AutoX than for track. My fear is it will be spot-on for AutoX (set at full soft) and I won't have any adjustment left to soften it for track. I may be switching to the 22.5mm RSB when I head to VIR just to be on the safe side - we don't need another oversteer, off-track excursion at T10! I wish there were some way to adjust the front, but the design of the bar makes if very difficult.

Thanks again!
CR
 

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Discussion Starter #487
u got any pix of the new exhaust from the back?
Gotta wait til I get the chrome coffee-can tip installed - good for at least 10hp! JK ;)

Sit tight, pics coming.

CR
 

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I may be switching to the 22.5mm RSB when I head to VIR just to be on the safe side - we don't need another oversteer, off-track excursion at T10! I wish there were some way to adjust the front, but the design of the bar makes if very difficult.
CR
There is also a Progress 24mm rear bar. I'll check the relative changes in WT Transer Bias later.

Your spring choices are identical to D2's. Ksport has 780/200 rates, don't know about KW. I figure the D2 Bias is for hard braking.

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I may be switching to the 22.5mm RSB when I head to VIR just to be on the safe side -Thanks again!
CR
The calculated change in a variable, is more accurate than the magnitude of that variable. So I rans some RSB's with the 28.5 up front, and looked at the front WT bias. You found the weight bias was 61% .

27.0mm, 60%
24.0mm, 64%
22.5mm, 66%

Suggested Rear Sway Bar Mount Modfication.

When I designed that RSB for my GT-6, I had 5 settings for the bar, as well as the pivot, to keep the hiem link vertical at all settings. I could see that on your M6, by moving the drop bracket for the pivot rearward (to the right in pic below), and adding a spacer under the pivot for the soft setting, and removing the spacer for the stiff setting.





I also did this sort of thing on the Rx7 rear bar with 2 holes, that has a top mount pivot bracket. I made the metal clamp adjustable by slotting the bolt holes in the clamp, so it would allow the bar to be moved fore or aft, based on a stiff or a soft setting.
This kept the end link vertical in both stiff and soft settings.

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Discussion Starter #491

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Discussion Starter #492
I've noticed some excellent welding here. The big jam nut weld to the control arm is an example. Is this also done in the shop?




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Thanks, but that image is not one of my welds. Looks to be a factory robot weld actually. For those of us that learned on our dad's old stick welder, these new wire-feed mig welders make us look almost like pros. :)

CR
 

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The calculated change in a variable, is more accurate than the magnitude of that variable. So I rans some RSB's with the 28.5 up front, and looked at the front WT bias. You found the weight bias was 61% .

27.0mm, 60%
24.0mm, 64%
22.5mm, 66%

Suggested Rear Sway Bar Mount Modfication.

When I designed that RSB for my GT-6, I had 5 settings for the bar, as well as the pivot, to keep the hiem link vertical at all settings. I could see that on your M6, by moving the drop bracket for the pivot rearward (to the right in pic below), and adding a spacer under the pivot for the soft setting, and removing the spacer for the stiff setting.





I did this sort of thing on the Rx7 rear bar, that has a top mount pivot bracket. I made the metal clamp offset, so it would move the bar fore or aft, based on a stiff or a soft setting.

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I added to this post, regarding the rear sway bar attachment, and thought it was worth a bump.

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First post over here (isn't that exciting). I was directed to this thread because I'm doing similar things with my speed6....

.... I almost have enough information to finish my spreadsheet for suspension frequency calculations. !
Sounds like another interesting build ! I've seen natural frequencies show up in the literature, and I can verify that it is an important concern, especially if you will street the car. On my 2000 lb race prep'd Triumph, when I hit certain concrete highways where each "block" of concrete had a tiny pitch like a launching ramp (made by haulers), it was like riding a bucking bronko. But, In the 3 years I autox'd the car in the local non-SCCA competition, I won my class the 2nd year and bumped myself into a higher class and won that the 3rd year.

I saw your excel sheet on springs/suspension, and found this table:

Front Spring Selection

From above, we have everything needed to closely approximate suspension frequencies.

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

AFAIK, the frequency method started off with production cars, and then was applied to autox. But these target numbers change depending on the type of car ... rwd is different than awd (suggestions for AWD are in the link below), and they are often back calculated from what has worked in competition.

It is a simple up-down model, proportional to the sq-rt( K/M ). And when I back calculate, the weight used was some constant lbs, for each spring rate. For autox, I think the frequency used is for sprung-weight , which is related to body motion, including brake dive, and corner roll. (edited 3-17-14)


I did find an excellent discussion in an engineer's forum about the subject, where they made a clear distinction between wheel modes and sprung body mods:

http://www.eng-tips.com/viewthread.cfm?qid=344263 Greg and Brian are Suspension Engineers for a major auto co.

I read a bit more and you have target freq's of ~2.4 & 2.2 hz, consistent to what I have read for body motion in autox spring design. But I would assume the target freq's would be higher for a road course racer, like CR.


I made a M6 suspension spreadsheet about 8 years ago, based on Fred Puhn's book, but I did not include the nat freq calc.

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I posted more "natural frequency" based autox spring design method over at phate's excellent build thread:

MS6 Suspension Data & DIY Bilstein Coilovers - Page 2 - Mazdaspeed Forums

One thing to keep in mind is that unless someone gives target frequencies for the same or similar car and drivetrain, the numbers will be ballpark. The general published numbers are for just the springs, and don't consider the swaybars that are active as you hit a corner ... bottom line is you still need to tune the bars/springs/dampers based on performance.

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Canyon, I'm curious how the wheel bearings are holding up on the car and if you've replaced any of them?

While replacing mine this past weekend I found something I didn't expect to see; while removing the axles from the hubs there was transfer material, a grey black powder between the splines of the hub and axle. It had nearly seized the axle to the hub on the right side.

IMO the tension on the nut was inadequate and allowed a slight movement between the sets of splines. Another observation was the hub itself - you could distinctly see the parting line of the inner race on the hub once the hub was removed from the bearing. Then if you look at the mating surface of the inner race to the CV joints splines, you see it wore into the surface. See attached pic's. For me these are all signs that these parts are moving on each other. Anyway, I cleaned the hub and axle splines with a wire brush. 90% of all black dust came off.

Right wrong or otherwise at 200 ft/lbs but I could feel the nut was not done moving so I took it to 240 ft/lbs whereby I could feel something move and the wrench quit turning as if it actually came up solid. I really don't think its possible distort the inner race so time will tell what happens as its over the max spec by 40ft/lbs.

This may seem like a stretch but the car does no dart in the ruts as much as it did and brake pedal is firmer so these are tell tale signs things were moving up front. I put a dial indicator on the hub but w/out the wheel on there, I could not apply enough load to move the needle.


Something to keep in mind and good luck this season!
 

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Discussion Starter #497
Hmmm that is interesting. I replaced all four wheel bearings before the 2012 season. I didn't notice anything unusual. The fronts have held up well, but I suspect I'll be replacing the rears again at the end of this season. One of the rears is showing a tiny bit of play. I slide the rear around a lot. :D

I run my 275s on 18x10s for AutoX, but I'm thinking of dropping back to 245s on my 18x8.5s for the track just to take some of the stresses off the wheel bearings.

CR
 

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Discussion Starter #498
Heading to the track this weekend, so It was time for an oil change, brake flush and re-torque of all the suspension parts. While I was double checking my Hawk HP+ pads for wear (I only have a half dozen AutoX's on them), I thought: Hmmm wonder how close my 2011 Mustang GT brakes are to fitting?

I happen to have a set on the shelf so I checked them out. 13.22" rotors, two-piston aluminum calipers. And very reasonably priced - I bought this set complete with rotors, calipers, brackets and pads for $125. They were taken off a brand new GT by a tuner shop.



Here they are next to the MS6 rotor and my old 6s rotor:



It doesn't look like a very difficult swap. That's just great - another fabrication project. Why can't I leave well enough alone? :p

CR
 

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Discussion Starter #499
So after our latest track event I made a list of issues to resolve. One of them is the speed limiter. If you notice from my telemetry, we never get much above 113 - 115mph. The car speedo reads a bit over 120 because I'm running shorter tires than the ECU thinks I have. There have been many discussions in many threads on this subject. There is no wire to clip, no fuse to pull, etc. Vehicle speed is provided by the ABS sensors. The solution to speed limiters on other CAN-Bus cars has always been software. Since there doesn't seem to be tuners lined up to develop ECU software for the 6, we need to think of another solution.

So how about this crazy idea: What would happen if we removed every-other tooth from the ABS rings?

The speedo would read 1/2. OK - I never look at the speedo on track.
The TCS might not work as smoothly. OK - I never use it on track.
The ABS/EBD might not be quite as smooth. OK - I might care about this.

Maybe the speed limiter would be 240mph instead of 120mph. That would be good!

Wadaya think?

CR
 
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