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MazdaSpeed 3/6 - Suspension & Brakes Discussion for suspension items like coilovers, springs, sway bars, mounts,chassis bracing and brakes.


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 Old 11-11-2014, 07:48 AM   #201
6 mods and some Kool-Aid
 
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New thread started for blown txfer case:
Blew up my transfer case
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 Old 11-12-2014, 08:11 PM   #202
 
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Just dropping this here for future reference and collective ogling in the most active "suspension" thread.

Suspension measurement porn.

Sample:
This is one way to measure tire spring rate.


And this:
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 Old 11-13-2014, 08:31 AM   #203
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I went ahead and printed these as PDF's, because the print is so small. Kevin, let me know if you can't download these without going VIP; I can email or upload to dropbox or something similar.

I've attached two versions, one with the .57 rear MR, and one with the .75 rear MR. I've only estimated the CG and the rear roll center height because I haven't gotten those measurements. Track width is for a stock wheel. The ARB measurements are guesses, though I think I'm using front ARB info you posted previously (or maybe I'm dreaming that). Most of this is based on the Staniforth method laid out in "Competition Car Suspension". I may have said it was based on Puhn's calculations in previous posts, but that is not the case.


For anyone not familiar with these methods, there are a ton of caveats. Mainly, that this is a kinematic model. It assumes a perfectly rigid chassis and infinite spring rate for the tires, along with zero compliance in the bushings and no friction/stiction in any joints.
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File Type: pdf MS6SuspCalc_.57MR_20141113.pdf (40.7 KB, 45 views)
File Type: pdf MS6SuspCalc_.75MR_20141113.pdf (40.7 KB, 26 views)
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 Old 11-13-2014, 09:20 AM   #204
 
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Originally Posted by zenit View Post
Just dropping this here for future reference and collective ogling in the most active "suspension" thread.


Phate and I were talking about ways to measure the RSB rate, and what is shown is roughly the way I did it for my Rx7, except using a 1" dial indicator for deflection, and suspended bench weights (weighed at a shipping store) for the load. (I have the same set of stepped machined clamping blocks shown in the image, but not the Machine Shop sized base table).

We also talked about an FEA model that I could do, with phate's measurments, or test it on the car, with a load cell (the S shaped piece where the eye-bolt screws in, in the pic).

By far, the easiest way would be to ship the bar to the BMW guy that has acess to the ARB test rig. Is this possible?

Phate, I can read the data sheets fine, thanks for asking.

.
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 Old 11-13-2014, 09:44 AM   #205
 
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Originally Posted by KevinK2 View Post

By far, the easiest way would be to ship the bar to the BMW guy that has acess to the ARB test rig. Is this possible?
No idea! I just found an informational thread.

On a related note though, I have an amp/ADC board with easy usb interface to read 4/3 wire load cell inputs- my load cell is only rated to 100kg though. Here's a plug and play load cell with a 500kg rating for $50.

I guess the only other thing we'd need is an engine crane and some way to anchor the bar.

@phate, if you're interested let me know. I'm pretty sure shipping a 3"x3" pcb + load cell is much cheaper than two way shipping on a sway bar and analysis cost. That is, if you're interested.
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 Old 11-13-2014, 10:19 AM   #206
 
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Originally Posted by zenit View Post
....I guess the only other thing we'd need is an engine crane and some way to anchor the bar.

..... I'm pretty sure shipping a 3"x3" pcb + load cell is much cheaper than two way shipping on a sway bar and analysis cost.
When I ran Phates car with race springs, and an assumed 2-d 24mm bar, with no loops (stiffest assumption), the load in the end-link was only 350 lbs (160 kg) for a 1G corner.

I had considered supporting the chassis on jack stands, and bolting the bar to the chassis, grounding one end to the frame, and loading the other. If a compressive load cell could be borrowed from a ME univercity, a simple floor jack could be used for the load, and a 1" dial indicator for the loaded end. I have the set-up shown in the 1st pic of post # 202 .




For the FEA model, I located a "try-it" beam element 3D program, so I would just need measurments of oem bar. "Analysis cost" would be zero. I've been looking for a beam program like this ... I had one at work, as well as the big guns of Abaqus.

.
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 Old 11-14-2014, 09:00 AM   #207
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Originally Posted by zenit View Post
No idea! I just found an informational thread.

On a related note though, I have an amp/ADC board with easy usb interface to read 4/3 wire load cell inputs- my load cell is only rated to 100kg though. Here's a plug and play load cell with a 500kg rating for $50.

I guess the only other thing we'd need is an engine crane and some way to anchor the bar.

phate, if you're interested let me know. I'm pretty sure shipping a 3"x3" pcb + load cell is much cheaper than two way shipping on a sway bar and analysis cost. That is, if you're interested.
Heck yeah. I can probably rig something up in the shop to do this. I'll just yank the front bar while we have the subframe out, and grab my stock rear bar from storage this weekend. I'll PM you my address.
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 Old 11-14-2014, 12:09 PM   #208
 
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Originally Posted by phate View Post
Heck yeah. I can probably rig something up in the shop to do this. I'll just yank the front bar while we have the subframe out, and grab my stock rear bar from storage this weekend. I'll PM you my address.
If you get a chance, while the bar(s) are off, get the measurments on front bar, to compare actual stiffness with the usual calculated value, based on Puhn's formula, using the A, B, & C dimensions:


Puhn Sway Bar Formula, corner-carvers


For the rear bar, for an assumed stiffest shape, get the same 3 dimensions for a theoretical flat bar in a plane. I'm modifying the Puhn formula to handle the complicated rear bar shape. When done, it would be great to have more detailed measurments of the rear bar, to compare measured vs calculated stiffness using the modified formula.

Note that the measurments to bends are to centerline intersections. And the pivot bushing locations are not required.

.
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 Old 12-03-2014, 08:02 AM   #209
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Originally Posted by KevinK2 View Post
Phate, I can read the data sheets fine, thanks for asking.

.
Did you get a chance to run the numbers in your spreadsheet?
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 Old 12-03-2014, 08:44 AM   #210
 
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I got sidetracked by my weakness for political krap ... spent some time on the Ferguson cop who shot an aggressive big thug who was attacking him in self defense. I go into the den of Liers at the Huffington Post, and spread the truth by way of transcipts.

I have your parameters loaded in my program. Was looking for your basic planer rear bar dimensions, A B C, for Puhn's stiffness formula, that I requested. This would represent the stiffest version of the bar.

I'll make some runs today for sure.
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 Old 12-03-2014, 09:06 AM   #211
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Originally Posted by KevinK2 View Post
I got sidetracked by my weakness for political krap ... spent some time on the Ferguson cop who shot an aggressive big thug who was attacking him in self defense. I go into the den of Liers at the Huffington Post, and spread the truth by way of transcipts.

I have your parameters loaded in my program. Was looking for your basic planer rear bar dimensions, A B C, for Puhn's stiffness formula, that I requested. This would represent the stiffest version of the bar.

I'll make some runs today for sure.
I don't have C, but I think Staniforth's method assumes the lever arm is totally rigid, making B = C.
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 Old 12-04-2014, 01:10 PM   #212
 
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Originally Posted by phate View Post
... Most of this is based on the Staniforth method laid out in "Competition Car Suspension"....
Amazon has promised "out of stock, next week delivery" for over a month now. I can get it from ebay, but there are 2 versions:

One is a 3rd edition, sub titled "Design, Construction, Tuning" has a front shot of a yellow F1 car on the cover.

The other is 4th edition, sub titled "A Practical Handbook" , bluish, with the biggest picture a photo of the front F1 suspension, top view, with 2 smaller pic's below it.

Does it matter which one? Both published by Haynes. I would typically go with the most recent edition (2006 vs 1999).

.
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 Old 12-04-2014, 02:15 PM   #213
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Originally Posted by KevinK2 View Post
Amazon has promised "out of stock, next week delivery" for over a month now. I can get it from ebay, but there are 2 versions:

One is a 3rd edition, sub titled "Design, Construction, Tuning" has a front shot of a yellow F1 car on the cover.

The other is 4th edition, sub titled "A Practical Handbook" , bluish, with the biggest picture a photo of the front F1 suspension, top view, with 2 smaller pic's below it.

Does it matter which one? Both published by Haynes. I would typically go with the most recent edition (2006 vs 1999).

.
Mine doesn't have a cover, but I think the second one is what I have. ISBN 9781844253289
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 Old 12-04-2014, 03:30 PM   #214
 
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That's the 2006 4th edition, and likely the latest.

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Super simple, super cheap. I need to turn it down to proper diameter on the lathe, but this will be an easy test piece for bump stop adapters in the rear:



That's a 46mm bump stop. I think I will need at least the 58mm's and I will probably have room for the 76mm's from FCM.



I've been in contact with BC Racing about perches (for the bump stop engagement point) for the control arm. They think they have a couple options, and I sent them a couple pics of perches I found just searching around the interwebs. The center cylinder in the LCA spring seat is 2.17" OD and ~1.5" tall at the highest point. I'm hoping a 62mm spring perch will fit over that. Here's my most recent find that is for a 62mm spring:



It's way too tall, but I can easily cut that down.
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 Old 12-11-2014, 11:44 AM   #216
 
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Great Idea. FCM has a link to a guy with a miata that did something similar FCM rear bump stops in PVC sleeve. When I look at the force vs displacement plots for the FCM cushions, you only get about 1.4" compression before you hit the very nonlinear stiff zone. Up to that point, if these could be used, you are adding 100-200 lb/in in the usefull zone.



Roughly how much does the rear shock compress when in a hard corner (yes, I need to get my spreadsheet run) ? If more length is needed, you could consider adding part of another stop, below the main stop in the PVC, with or without the adjustment.

.
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 Old 12-11-2014, 11:59 AM   #217
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Originally Posted by KevinK2 View Post
Great Idea. FCM has a link to a guy with a miata that did something similar. When I look at the force vs displacement plots for the FCM cushions, you only get about 1.4" compression before you hit the very nonlinear stiff zone. Up to that point, if these could be used, you are adding 100-200 lb/in in the usefull zone.

http://www.fatcatmotorsports.com/iga...SpringRate.GIF

Roughly how much does the rear shock compress when in a hard corner (yes, I need to get my spreadsheet run) ? If more length is needed, you could consider adding part of another stop, below the main stop in the PVC, with or without the adjustment.

.
I'm not sure exactly, since the car doesn't actually roll on the KRC. I set it up for 3" of bump travel at the wheel and it never touched the frame stops even on mid corner bumps. With the .57MR at the spring (since the bump stops will be inside the spring), I only need ~1.7" of bump stop compression at the absolute max. For regular cornering loads, I should be operating in the mostly linear range of the stops.

Edit: Even with the 600lb/in springs and rear bar on the softer setting, it didn't touch the frame stops (ever). I think the car has room to go lower in the rear, especially if I have some bump stops. That moves it towards the flatter portion of the bump steer curve, also.
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 Old 12-11-2014, 12:25 PM   #218
 
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Keep up the good work and progress. Love reading about more progress for the 6.
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 Old 12-11-2014, 12:28 PM   #219
 
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If the red bump stop were used, and it saw1.7" of comprssion, which it should not, you would add 1000 lb/in. But if in the 30-35mm zone of compression, you add 400 lb/in. That's why I encourage creating an optimum bump stop, using part of another one below in the PVC, with a disc with a lip separating them.

Of course the very active bump stop and the coil spring create a nonlinear spring, with extension linear, and compression non-linear. So as far a roll control, you only count 1/2 of the added bump stop rate. This causes slight jacking of the rear as it starts to roll off the outside spring which is in a stiff zone, and the other side at just the sring rate wants to rise higher. Not a problem.

" ... since the car doesn't actually roll on the KRC" Could you explain this ... does K stand for Kinetic?

.
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 Old 12-11-2014, 01:51 PM   #220
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Originally Posted by KevinK2 View Post
If the red bump stop were used, and it saw1.7" of comprssion, which it should not, you would add 1000 lb/in. But if in the 30-35mm zone of compression, you add 400 lb/in. That's why I encourage creating an optimum bump stop, using part of another one below in the PVC, with a disc with a lip separating them.

Of course the very active bump stop creates a nonlinear spring, with extension linear, and compression non-linear. So as far a roll control, you only count 1/2 of the added bump stop rate. This causes slight jacking of the rear as it starts to roll off the outside spring which is in a stiff zone, and the other side at just the sring rate wants to rise higher. Not a problem.

" ... since the car doesn't actually roll on the KRC" Could you explain this ... does K stand for Kinetic?

.
Kinematic Roll Center. Just meaning I can't come close to calculating how much the springs actually compress and extend during a corner.

I see what you're saying about the rate vs distance, and I want to go with the bump stop that has the largest linear(ish) range to prevent it from going astronomically high (especially on bumps). Comparing the 58's to the 76's, it looks like the 76's stay more linear in the first 1" of travel than the 58's (which makes total sense). Flipping through a few picture from autocross, I'd guess that I only use ~2-2.5" of bump travel while cornering. At worst, that is bump stop compression of 1.42" assuming it doesn't have any spring rate. So a little less than 1.42", which should be on the edge of the linear range.


Originally Posted by KevinK2 View Post
That's why I encourage creating an optimum bump stop, using part of another one below in the PVC, with a disc with a lip separating them.
I'm not sure I understand what you mean, but that may be my fault. The PVC coupler is just being used to decrease the ID of the bump stop receiver in the subframe. Right now, the ID is 2-3mm larger than the OD of the bump stop. I'm going to cut it to length and turn down the OD so it slips in. In other words it's just going to be a sleeve inside of the bump stop receiver.

I'm really hoping to get away with a single bump stop.
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 Old 12-11-2014, 02:52 PM   #221
 
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Originally Posted by phate View Post
Kinematic Roll Center. Just meaning I can't come close to calculating how much the springs actually compress and extend during a corner.
I believe you do come close to staying on the static rollcenters if:

1) they are properly calculated, as you have done.
2) the suspension is stiffened to minimize body roll
3) springs are close to linear

Yes, the shocks can delay roll in a non-symmetric way in transition, which happens alot in autox, but for steady state corners (road course) the dampers should not be an issue, with only trivial forces

I see what you're saying about the rate vs distance, and I want to go with the bump stop that has the largest linear(ish) range to prevent it from going astronomically high (especially on bumps). Comparing the 58's to the 76's, it looks like the 76's stay more linear in the first 1" of travel than the 58's (which makes total sense). Flipping through a few picture from autocross, I'd guess that I only use ~2-2.5" of bump travel while cornering. At worst, that is bump stop compression of 1.42" assuming it doesn't have any spring rate. So a little less than 1.42", which should be on the edge of the linear range.
The way I read that 76 curve, the load starts with an arbitrary indicated displacement of about -.4", and ends at +.4", for a total useful travel of .8" of compression in those boundaries. The rate at .8" of real compression is about 500lb/in. at the half way point, it is 250 lb/in. If the slope of the curve was a constant, the rate would be linear.


I'm not sure I understand what you mean, but that may be my fault. The PVC coupler is just being used to decrease the ID of the bump stop receiver in the subframe. Right now, the ID is 2-3mm larger than the OD of the bump stop. I'm going to cut it to length and turn down the OD so it slips in. In other words it's just going to be a sleeve inside of the bump stop receiver.
That's the way I understood it. For a stock MS6, I figured there is a gap of about 1 inch before the bump stop is touched, if it is like the M6. That allows the suspension to stay at the reasonable local spring rate of the bump stop. To do the closest thing to having stiffer rear springs, I would think you want an effective bump stop that engages quickly, with a minimal static gap. But to stay away from the high rate, using two stiff bump stops (back to back in series) will get the most linear rate and stay out of the kick-up. Would have to play with the numbers to check viability, as the bump stop rates will be reduced to 50% of single stop rates (if two full bump stops are used).

.
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 Old 12-11-2014, 03:56 PM   #222
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Originally Posted by KevinK2 View Post
The way I read the 76 curve, the load starts with an arbitrary indicated displacement of about -.4", and ends at +.4", for a total travel of .8" of compression in those boundaries. The rate at .8" of real compression is about 500lb/in. at the half way point, it is 250 lb/in. If the slope of the curve was a constant, the rate would be linear.
To be specific here, and to make sure we aren't talking about two different bump stop sets, I'm looking at the 58's, here:



and the 76's, here:



In either case, I'll get the stiffest of whichever length option will work the best. So either the 260lb/in 58's or 220lb/in 76's.




From those, it looks like the 58's become more non-linear (none of them are perfectly linear, but we're working with a lot of imperfect options) sooner in travel than the 76's.
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 Old 12-11-2014, 04:38 PM   #223
 
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Yes we were talking about different bump stops earlier, when I had first posted ones from FCM for a Miata, somewhat arbitrarily. You then linked them in a quote that you used. You then linked the ones you spoke of, and we were in phase by my post # 221 . No damage done, all initial points I made were with the miata stops, but points made were still valid.

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 Old 12-11-2014, 05:48 PM   #224
 
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Originally Posted by phate View Post
Flipping through a few picture from autocross, I'd guess that I only use ~2-2.5" of bump travel while cornering. At worst, that is bump stop compression of 1.42" assuming it doesn't have any spring rate. So a little less than 1.42", which should be on the edge of the linear range.
Originally Posted by phate View Post
To be specific here, and to make sure we aren't talking about two different bump stop sets, I'm looking at the 58's, here: _ and the 76's, here: _

In either case, I'll get the stiffest of whichever length option will work the best. So either the 260lb/in 58's or 220lb/in 76's.

From those, it looks like the 58's become more non-linear (none of them are perfectly linear, but we're working with a lot of imperfect options) sooner in travel than the 76's.
I agree with those two options. For the stff version of each, you wind up at about 500lb/in at the .3 to .35 mark.

Now you noted before that the expected peak compression travel to be a max of 1.4", but the graphs show from zero lbs (-.43"), about .8" compression before they get much, much stiffer. So you would have to have a static gap of about .6" . What I'm suggesting with dual stops, is like if you put two identical linear springs in series, you have the same peak force rating at coil-bind, but 2X the displacement to get there. You could use the same logic with the stops, so you have zero static gap, and use two of the higher force 58mm stops, shortened 9mm on the stiff (bigger) ends to get zero static gap, and have a very linear curve adding about 100 - 150 averaged lb/in to the coil spring. The rate would be higher, if the trimming were done on the soft end of one of the stops.

Again, much easier said than done.

.
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 Old 12-12-2014, 12:21 PM   #225
 
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Local Spring Rate for Bump Stops

Just to clarify, the force vs crush curves are very nonlinear at the max displacement points. I sited 500 lb/in in one case. The rate is high but it only applies to the last .2" of displacement. The coil spring analogy for a bump stop is like 20 coils with progressively wider spacing between each coil. The first group of coils are closest together, but are still progressively wider spaced. With the other wider spaced coils, this creates the initial strait part of the curve, up to the .2 mark on the 58 curve. Then with more displacement, that first group of coils progressively go into coil-bind, creating the knee in the curve from the .2 mark to .35 . The remaining coils stay open, but act like a 500 lb/in spring.

.
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 Old 12-13-2014, 10:58 AM   #226
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Originally Posted by KevinK2 View Post
Local Spring Rate for Bump Stops

Just to clarify, the force vs crush curves are very nonlinear at the max displacement points. I sited 500 lb/in in one case. The rate is high but it only applies to the last .2" of displacement. The coil spring analogy for a bump stop is like 20 coils with progressively wider spacing between each coil. The first group of coils are closest together, but are still progressively wider spaced. With the other wider spaced coils, this creates the initial strait part of the curve, up to the .2 mark on the 58 curve. Then with more displacement, that first group of coils progressively go into coil-bind, creating the knee in the curve from the .2 mark to .35 . The remaining coils stay open, but act like a 500 lb/in spring.

.
Yeah. This is what the rates look like for each of the bump stops over the ranges in the above graphs (ΔF/Δx). I just eyeballed the force at each intersection.

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 Old 12-13-2014, 12:21 PM   #227
 
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Nice work. Plotted that way, the 76 provides more travel and decent rates, vs the 58 stop. The most linear is the 160, for about 100-200 lb/in up to .8" compression, then up to 300 lb/in with .2" more compression. What do you think about ~1.4" shock travel vs .8" to 1" stop compression. I guess a lot simpler to just use a single bump stop, and live with the .4" -.5" static gap, vs the double stop. To do that right, you would need a load vs displacement tester like the one at FCM, and a digital recorder. The recorder I had first used as a consultant was crude: Chart_recorder

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Originally Posted by KevinK2 View Post
Nice work. Plotted that way, the 76 provides more travel and decent rates, vs the 58 stop. The most linear is the 160, for about 100-200 lb/in up to .8" compression, then up to 300 lb/in with .2" more compression. What do you think about ~1.4" shock travel vs .8" to 1" stop compression. I guess a lot simpler to just use a single bump stop, and live with the .4" -.5" static gap, vs the double stop. To do that right, you would need a load vs displacement tester like the one at FCM, and a digital recorder. The recorder I had first used as a consultant was crude: Chart_recorder

.
I'm going to start with a single 76 for simplicity, assuming I have enough room. Since the engagement point will be adjustable, I can try it both ways. I would like it to engage as soon as possible in compression because I want the increased load transfer at initial turn in. If the mid corner stability suffers to the point that I'm slower, then I'll either have to lower the engagement point so there's a gap, or lower the engagement point and make longer bump stops.

I should be able to just reach under the car and adjust them without jacking it up. Pretty simple fine tuning, definitely easier than changing bar settings.
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 Old 12-13-2014, 03:47 PM   #229
 
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Originally Posted by phate View Post
I'm going to start with a single 76 for simplicity, assuming I have enough room. Since the engagement point will be adjustable, I can try it both ways. I would like it to engage as soon as possible in compression because I want the increased load transfer at initial turn in.....
The two curves are a bit misleading, in that they used the same stroke in compression for the 58 and the longer 76, so you see no big kick on the 76. If you assume that knee in the curve is at the same % compression, then that suggests you have about 1.1" compression before it gets very stiff. If you can live with that amount of travel, you can runn zero clearance.

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 Old 12-14-2014, 04:12 PM   #230
 
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Originally Posted by phate View Post
I'm going to start with a single 76 for simplicity, assuming I have enough room.....
I should have mentioned this before. Looking at the "local rate" plot that you made, at least I fell into the assumption that the curve reflected spring behavior. But looking back at the 58 and 76 test data, there was significant hysterysis on the unload curves. Unless specified, tests like this are done at relatively slow speeds, and the real world deflection speeds could be much faster, increasing the hysterysis drop during unload.

So in a slalom, or a quick back and forth event, the bump stop would be only partially return to the initial length before being loaded again. This effectively creates more static gap, and a stiffer initial bump stop rate.

This supports your path of using the single 76, and then testing less static gap by the ajustable seat. My concept of creating a stiffer spring with stops is loosing air ...

.
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 Old 12-16-2014, 05:21 PM   #231
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I measured the bump stop cup a bit ago. ID of the cup us 1.962", and the depth is .960". At my current ride height (~3" wheel travel to full bump), I have a 3.5" gap between the top of the LCA contact and the lowest edge of the bump stop cup. Tons of room to work with.

The PVC adapter presents a small problem. At best, it ends up having a .031" wall thickness, but its tapered all the way to the bottom edge where it would be a wall thickness of ~.021". I'm not sure I can successfully turn it down that thin, and I'm not sure if it's worth it. I might just give the bump stops a couple wraps of gaffers tape or something similar and see how it holds up.




I'm looking at some other bump stops, Eibach in particular. They offer some near-linear rate bump stops in the compression range I need.
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Originally Posted by phate View Post
The PVC adapter presents a small problem. At best, it ends up having a .031" wall thickness, but its tapered all the way to the bottom edge where it would be a wall thickness of ~.021". I'm not sure I can successfully turn it down that thin, and I'm not sure if it's worth it.
On a jawed chuck that would be pretty tough without it deforming...

Maybe if you made a holding collet. But dimishing returns for a quick and easy fix.
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 Old 12-16-2014, 06:44 PM   #233
 
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Originally Posted by phate View Post
... I'm looking at some other bump stops, Eibach in particular. They offer some near-linear rate bump stops in the compression range I need.
Do you think the hysterysis in the load/unload plots ( 58 & 76 ) could affect the desired spring behaviour? Similar to a jacking effect from cheap shocks set stiff, on a rough track.

I know you posted this info before, but what is the ID of the top of the rear spring, and the bottom?

.
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 Old 12-16-2014, 09:51 PM   #234
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Originally Posted by zenit View Post
On a jawed chuck that would be pretty tough without it deforming...

Maybe if you made a holding collet. But dimishing returns for a quick and easy fix.
Sadly, yes. I was planning to make them tomorrow. I still might, just to see if I can do it (I've never turned PVC, obviously).

Originally Posted by KevinK2 View Post
Do you think the hysterysis in the load/unload plots ( 58 & 76 ) could affect the desired spring behaviour? Similar to a jacking effect from cheap shocks set stiff, on a rough track.

I know you posted this info before, but what is the ID of the top of the rear spring, and the bottom?

.
I am unsure, really. I've never worked with bump stops, so fine tuning suspension with them is new for me. Body roll is slower than the max velocity of the suspension, so they might have time to rebound completely even in a slalom (the inner side will be completely unloaded for at least a few tenths of a second before maneuvering back the other direction). It seems that no matter what, the bump stops are more for fine tuning mid corner behavior than anything.

The top ID is 3.5", and the bottom ID is 2.5". 2.5" ID on the upper perch isn't feasible because of the flared bump stop cup's OD of just over 2.5".







Here are the Eibach bump stops that should fit with minimal work and have a mostly/somewhat linear rate for the first 1.5" compression. Click on the attached link for a higher resolution pic that you can zoom in on.



Most of them are pretty low rate, but the 770016, 770021, and 770051 (both) look to have decent rates. It looks like Summit carries them, and they're ~40% the cost of FCM's stops.
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File Type: png BumpStops_Eibach_forMS6 Rear.png (567.8 KB, 23 views)
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 Old 12-16-2014, 11:48 PM   #235
 
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Originally Posted by phate View Post
... I've never worked with bump stops, so fine tuning suspension with them is new for me. Body roll is slower than the max velocity of the suspension, so they might have time to rebound completely even in a slalom (the inner side will be completely unloaded for at least a few tenths of a second before maneuvering back the other direction).....
It might be worth an email to FCM about the rate the bump stop tests were done at.

I asked about the diameters at the rear spring coil ends, because I was checking to see if stiffer 3" race springs were available, using machined adaptors at the ends. Have not found anything stiffer.

It's tough trying to stiffen the rear springs with bump stops that have velocity based properties, when a larger sway bar would work best. I designed a bar for rear swing axles, under the axles, but with a transverse leaf spring so there was much more area to work with. If the rules allow it, I'd make sure there is no way to do this, allowing some loss of ground clearance.

.
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 Old 12-17-2014, 12:22 AM   #236
 
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Saab 900, Rear Sway Bar Install, with no endlinks.

As an example I remembered this "how to" (from my install instructions) I added to the Saab Forum. The rear bar's stiff lever arms are bolted (with bushings) to the inside of the trailing arms, so the main tubular bar's torsion is the only flex.

Pgs 5 and 6. Pic next to steps 4 and 5 show the bar hanging down, with just the bolts at the end of the lever arm in place.
Saab 900 rear swaybar install

If this were possible, the motion ratio could be much improved allowing a smaller dia bar that is much stiffer than oem. And with two sets of mounting holes at the lever arms, the arm length could have stiff and stiffer positions.
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 Old 12-18-2014, 02:54 PM   #237
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I had to get a second opinion on the sway bar rules before posting. I had interpreted it to allow additional bars, and that is the case. There are cars with this setup competing nationally, so there is also a precedent, and there is supposedly a published rule clarification that I need to find. So, relocating or adding an additional bar is OK.

Another find today was a company that makes springs that should fit the rear with no modification. They range from 700 to 1200lb/in in 100lb increments. I'm going to call them tomorrow, they're already closed for today.
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 Old 12-18-2014, 03:25 PM   #238
 
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Great! Just the possibility of getting the right springs and the right redesigned sway bar is encouraging. The bar is critical, as it could allow the existing 26mm Steeda option on the front bar, reducing body roll. Both the spring and the bar could be offered in a group buy to reduce cost.

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 Old 12-19-2014, 12:46 PM   #239
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Forgot to mention in my last post that I turned down the PVC couplers successfully. It was much easier than I expected. I cemented a PVC pipe into one side of the coupler that was ~2" long, so the chuck grabbed onto the pipe rather than the coupler. That let me really clamp down on the pipe, but the deformation was localized to the first 1" or so of the pipe, and no (or very minimal) deformation of the coupler occurred. Once the OD was turned down, I just parted that half on the lathe rather than bothering with a saw.

This same method allows me to make smaller ID sleeves, also. To do that, just cement a 2" section to one side of the coupler, then on the other side cement a short section so it sticks out just beyond the edge of the coupler. You can face that end to make it flat, cut down the OD, then cut the ID to whatever is needed. Some of the Eibach bump stops are smaller than the FCM stops, so it might come in handy.




Re: second rear bar - I've gone through the pictures I have of the rear subframe and chassis back there. There's a LOT of crap crammed into that space, so I'm not real optimistic about setting it up. I think if it can be done, it would have to be mounted rearward of the subframe. There's a small chance it will work if I didn't have exhaust back there, which has been upcoming anyway in order to shed some weight. I'll have to get back under the car and snoop around.
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 Old 12-19-2014, 04:16 PM   #240
 
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Here is "a" photo of the back side of the suspension:

Rear Suspension Assembly on Floor

There does look like there is some room back there. Eliminating the oem rear (only .33 MR) may open up some more.

What spring rates have you been using of late? 800/700 F/R ?

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