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      03-27-2014, 10:50 PM   #23
fe1rx
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Time to look at the front suspension. I am starting with the following constraints, selected by me:

- Ohlins 200 mm x 60 N/mm spring
- Ground Control Street Camber Plates
- Wheel Center Ride Height = 326 mm

The choice of a 60 N/mm spring is based on three things: 1) consensus on the forum that this is a good rate, 2) the fact that this spring comes with the Ohlins kit (and my testing shows it to be of good quality), and 3) the observation that this spring rate is also specified for the 1M kit (paired with a 120 N/mm rear spring). The hope is that the 200 mm length will work with respect to wheel and tire clearance, but this needs to be verified because the lower spring perch setting is affected by the choice of the Ground Control camber plates.

Ground Control street plates were chosen based on the fact that I had them previously installed and I like the idea of a urethane isolated plate for a combined street/track vehicle. I saw no reason to change, although I did need to get the upper race spring perch from GC to replace the OE spring version used previously.

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My ride heights are arbitrary and given the raging debates over ride height, I will leave it at that, except to say that form follows function.

Back to the camber plates. When I first installed the plates, I modified the indicator plate by welding a stainless cap screw in the threaded hole provided by GC to act as a locating peg. They don’t tell you the function of this hole when you buy the plates, but it is perfectly located for a locating peg, which biases the plate location in the direction of maximum camber (in the slotted holes in the strut tower).

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Without this locating peg, the indicator plate will float within the range of the slots and repeatable camber settings will not be possible. This little addition really is essential.

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One season of experience with the plates and I discovered that the shoulder bushing and washer that GC provide to contain the urethane bushings suffer a bit. In particular, the washer, which GC artistically adorns with their logo laser cut out of the part, bends in service. Also the urethane tends to extrude itself through the laser cutouts. The bushing as supplied has a countersunk lower hole to suit the OE shock top, which is not suitable for the Ohlins non-tapered top. GC can provide a non-countersunk version, but a couple of other observations prompted me to design my own 2-piece stainless steel bushings. 1) the GC parts were corroded after one year of summer use, and 2) the stack up height would prevent the top nut from being “in safety” (1.5 threads showing through the nylock nut), even with a reduced height nut.

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My bushing design also eliminates a sharp edge interface with the urethane because while I am at it, why not.

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While I had the plates apart, I replaced the urethane bushings and the steer bearings. The steer bearings are really nice, full spring diameter, units taken from BMW p/n 31-33-1-090-612, so they can be replaced without going back to GC. When you buy them from BMW they come with a metal housing that can simply be removed and discarded. These wear items should be replaced whenever the plates are apart.

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The geometry of the camber plates, the length and spring rate of the spring, and the desired ride height establish where the lower spring perch must be located. If you know the front corner weight, the front unsprung weight, the front motion ratio, the free spring length, the spring rate, and all the front geometry you can calculate the spring perch setting exactly. I know most of that, save for some of the fine points of the geometry, so my first try got me to within 2 mm of my desired ride height. A single adjustment got me right on.

My point really is this – the required spring perch height is much different than what Ohlins recommends in their instructions (for use on a 3-series with OE top mounts). The location recommended by Ohlins would be a disaster with respect to wheel and tire clearance on the 1-series. With my higher spring perch location I have tire clearance (just) with my 225 tires on OE 7.5” wheels. I will not have clearance with wider wheels and tires. Shorter front springs are in my future, but for now I will proceed with the Ohlins front springs. This is an example of the devil being in the details, but by fully understanding this installation I will be able to make an informed choice of a shorter front spring when I move to wider wheels.

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One of my original goals had been to use Swift thrust sheets on all springs. At the back it became apparent that they were only practical on the top of the spring. At the front, they are not necessary because the GC steer bearing provide for unrestricted torsion of the spring.

My front setup drawing defines the spring perch location from shock feature that locates the shock body in the steering knuckle. This is the most logical datum as it is directly tied to ride height.

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I have previously looked at the bump steer behavior and camber gain at the rear suspension so wanted to do the same at the front.

For bump steer, I wanted to look at the effect of camber changes on toe (so I would know what the toe change would be if I made a camber only change at the track). Also, toe changes will have a small but perhaps measurable effect on bump steer. Caster changes have a much more pronounced effect on bump steer, but my plates don’t permit caster changes. I suggest that anyone with adjustable caster adjust their caster to minimize bump steer rather than for any other hypothetical benefit. Quite likely this means not deviating much from the stock caster setting.

To document the bump steer behavior I used a laser pointer clamped to my hub stands and jacked the wheel through its range of motion (without a spring installed). The laser was projected on a target scaled for the projection distance (in my case 110 inches) to read directly in 0.1° increments. (A handy rule of thumb is the “1 in 60” rule familiar to pilots, that one unit at a distance of 60 units equals 1 degree of course deviation).

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The results show a toe change of approximately 0.2° toe out for each 1° of increased negative camber. The tendency towards toe out with bump at higher camber settings is worthy of consideration as this is generally considered to be an unfavorable characteristic. The results plotted below are effectively for a left front wheel, although they were actually measured on the right front.

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I have previously mentioned rule of thumb with respect to camber thrust:

"For many radial tires, 1.0° of camber produces about the same lateral force as 0.1° of steer (10:1). For bias-ply tires the effect is more pronounced: 1.0° of camber is equivalent to about 0.2° of steer (5:1). From this simple rule of thumb, it can be seen that static negative camber will require toe-out to keep the wheels from fighting each other."

This means that a slightly conservative street alignment with a bit of toe in will become a slightly aggressive track alignment with a bit of toe out with a camber change of -1° at the track.

When we looked at camber gain on the rear suspension we discovered that the rear wheel gains -0.02° camber per mm of bump travel (-0.5° camber per inch of bump travel). I presented this in tabular format but it is worth looking at it in graphical form below.

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This is a really wonderful characteristic made possible by the sophistication of the rear multi-link suspension. The camber gain on the front suspension is less favorable and inherently non-linear, a characteristic of strut suspensions. In the area of interest (positive bump travel) the camber gain is reasonably linear but will be less favorable at less aggressive static camber settings and at lower static ride heights.

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Last edited by fe1rx; 03-28-2014 at 07:33 PM..
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      03-28-2014, 07:08 PM   #24
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How much did ground control charge you for the race spring perch? I have a set of ground control street plates with BMW performance springs and was wondering what it would take to convert them to accept coil overs. Also, I could not find BMW part 31-33-1-090-060 at getbmwparts.com Is that the correct number?
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      03-28-2014, 07:36 PM   #25
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Quote:
Originally Posted by cpt97m3 View Post
How much did ground control charge you for the race spring perch? I have a set of ground control street plates with BMW performance springs and was wondering what it would take to convert them to accept coil overs. Also, I could not find BMW part 31-33-1-090-060 at getbmwparts.com Is that the correct number?
Sorry for the typo on the bearing - should be -612

http://www.ecstuning.com/ES50312/

The race spring perches were $22 each.
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      03-28-2014, 09:36 PM   #26
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Thanks for the information.
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      03-31-2014, 08:12 AM   #27
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This weekend, actually finishing something seemed like a worthy goal. The rear was basically ready to button up so I headed back there again with the idea of getting the trunk liner fitted and installed and the rear suspension aligned.

My decision to alter the rear shock top mounts meant that the adjuster knobs would now sit correspondingly higher unless I shortened the adjusters. A trial fit showed that without shortening they would rattle incessantly against the body. The adjusters are made from speedometer cable so the end needs a light touch with a TIG torch to stop it from fraying where cut, but otherwise this modification was uneventful.

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The trunk liners need to have a hole put in them for the adjuster cable to pass through. Ohlins provides detailed measurements for locating the hole, but they apply only to the 3-series. On the 1-series, the hole should be directly in below the existing fastener hole, not 20 mm aft as shown in the instructions. I made the hole with a 10 mm gasket punch, and elongated it vertically to 14 mm.

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This location and hole size worked perfectly.

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Installing the trunk liner is much easier if the rear seat side bolsters are removed first. In fact, it is probably impossible to feed the adjuster through the liner without doing so. Removing the bolsters takes a firm pull at the top of the bolster to disconnect the large white plastic clip that attaches it to the body.

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A second vertical pin feature in the bolster also holds it in place.

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The white plastic clip can be removed from the body by depressing a trigger inside the clip. The clip is then reinstalled on the bolster before pushing the bolster back into place. Done correctly the process is very easy.

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Next on the list is aligning and torqueing the rear suspension. To that end, I made myself a checklist of fasteners and torques to ensure that I didn’t miss anything. I also reconfirmed my desired alignment settings, built some decent shims to level my floor for weighing and aligning. Then I embarked on the steep learning curve …

This is the process I have figured out for aligning the rear, with my targets in brackets:

1) Set the ride height.
2) Torque all suspension arm bolts with the suspension at ride height.
3) Set the camber exactly (-2.25° ± .06°) with the toe close and then torque the camber eccentric bolt.
4) Set the toe exactly (+0.05° ± 0.03°) and then torque the toe link eccentric bolt.
5) Confirm all settings

Because static load on the suspension tends to increase negative camber and increase toe out it is important that the eccentric bolt cams engage on the face that resists these tendencies, otherwise the settings will tend to creep when torqueing the nuts. Thus the camber target should be approached in the direction of decreasing negative camber and the toe target should be approached in the direction of increasing toe in.

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It is important too that your target values are clearly known, and just as important, a realistic tolerance should be applied to those values given the technology at hand. I would say that I got the results I wanted using the hub stands I built, but doing so took a large effort. In particular, working under the car at only jack stand height does not provide much room to swing a torque wrench and those eccentric bolts are very easy to inadvertently turn while torqueing their nuts. Another 12 inches of ground clearance would have been very welcome. Removing the axle-back exhaust would make things simpler too, but I didn’t do that.

I will give some more details on the hub plates when I align the front suspension.

Here is my fastener checklist, which I initial as each fastener is torqued. The torque values generally come from the Bentley 3-Series Service Manual.

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The only fasteners not yet torqued at the rear are the anti-roll bar end links. I am leaving these disconnected until I have completed the corner balancing of the fully aligned car.
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      03-31-2014, 02:03 PM   #28
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"eccentric bolts are very easy to inadvertently turn while torqueing their nuts"

you mean, tightening a bolt with a foot of clearance with an oversized (torque) wrench, to 122 ft lbs flat on your back without any lower body leverage? How hard could it be? :Lol:

many thanks for this great write up, covers a lot of ground.
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      04-01-2014, 05:27 AM   #29
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Amazingly detailed as always.
Have you thought about what front springs you might change to?
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      04-01-2014, 07:23 AM   #30
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Quote:
Originally Posted by mlifxs View Post
"eccentric bolts are very easy to inadvertently turn while torqueing their nuts"

you mean, tightening a bolt with a foot of clearance with an oversized (torque) wrench, to 122 ft lbs flat on your back without any lower body leverage? How hard could it be? :Lol:

many thanks for this great write up, covers a lot of ground.
I am still a bit sore from the contortions. There was just enough room to swing one click on the ratcheting head of the torque wrench.

Quote:
Originally Posted by Nugget View Post
Amazingly detailed as always.
Have you thought about what front springs you might change to?
I am going to complete the installation with the Ohlins springs first, then do the calculations for a spring change to confirm what will work, then see how close I can get to ride height and corner balance by calculating the new spring perch settings for the shorter springs. Actually though, I have done the preliminary calculation and ordered the new springs but hope they don't arrive too soon to dissuade me from this path because it seems like a useful exercise. Besides, the roads are still cold and sandy here, so I need to entertain myself for a bit longer. To that end, you will have to wait until the narrative reaches that point before I tell you what spring I have chosen. I am currently being diverted by a small modification to my camber plates, but should be ready for the final spring calculations later in the week.
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      04-01-2014, 09:37 PM   #31
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I wouldn't have expected anything less. My decision was somewhat less calculated, my tyre hit the spring perch at the ride height I wanted so I got a 1" shorter spring haha.
This is what I ended up with.
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      04-03-2014, 09:35 PM   #32
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What I would really like is to have a general solution to the question of “where does the lower spring perch need to be located on the front strut?” The answer to this is useful for several reasons:

1) to assess the viability of different spring options
2) to assess the impact of those options on wheel/tire to spring perch clearance
3) to assess the impact of a change to the top mount (i.e. a camber plate vs. an OE mount)

The variables (defined by choices made by the installer) are:

- the spring free length and rate
- the height of the top mount
- the thickness of any spacers or thrust sheets
- the ride height desired

The constants (defined by vehicle) are:

- the static spring load
- the strut motion ratio

First to the “constants”.

Strut Motion Ratio:

The strut motion ratio has been published on this forum as 0.960. In fact this ratio is affected by both camber angle and wheel offset, but these two influences have only a small effect over their range. I have measured the strut motion ratio directly by recording strut extension vs. ride height and fitting a regression line to the data. My result is close enough to 0.960 as to validate this number for general purposes.

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Static Spring Load can be determined in the following manner:

1) Measure the spring length at static ride height (140 mm)
2) Subtract from the free length to get the spring compression at static ride height
200 mm – 140 mm = 60 mm
3) Multiply the static spring compression by the spring rate to get the spring load
60 mm x 60 N/mm = 3600 N = 810 lbs. We could stop here but let’s carry on to check the result for logical consistency.
4) In addition, the strut (gas spring) supports 40 lbs, so the total “spring force” is
810 lbs + 40 lbs = 850 lbs
5) Multiply this force by the Front Motion Ratio to get the resultant of the spring force at the tire
850 lbs x 0.960 = 816 lbs
6) Add the Front Unsprung Weight to get the expected corner weight based on this spring compression
816 lbs + 115 lbs = 931 lbs
7) This compares favorably (within 1.5%) to the measured front corner weights (with correction for missing brake calipers and pads) of 917 lbs.

The usefulness of knowing the static spring load is that we know now that any spring we install must provide this load to provide static equilibrium. From its free length and spring rate, we can easily calculate the amount of spring compression (and thus the static length) of any spring.

Now the “variables”:

The variables associated with the strut length and perch setting are best visualized pictorially. The following picture shows the Ohlins front strut with the Ohlins 200 mm x 60 N/mm spring installed with both the OE upper mount and the Ground Control Street camber plate. The respective settings provide for the same overall length at static load and so the same static ride height – this case 326 mm at the wheel center. The strut datum corresponds to the top of the steering knuckle so is tied directly to ride height and the rest of the suspension geometry.

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For deviations from this ride height, the static strut length changes by the Motion Ratio times the change in ride height. Therefore a 10 mm drop in ride height would result in a 9.6 mm change in overall strut length and would require a lowering of the lower spring perch by 9.6 mm to accomplish this.

More generally, the static strut length can be expressed as a function of ride height. Conveniently this is valid for any strut:

Static Strut Length = 372 + (RH – 326) x MR

For a specific example of a 20 mm drop in ride height, from 326 mm:

Static Strut Length = 372 + (306 – 326) x 0.960 = 353 mm

Once the significance of the strut settings is visualized, the next logical step is to create a spreadsheet that calculates the lower spring perch setting from the datum for any arbitrary spring configuration:

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The boxed values are input variables. The rest are constants or calculated values.

Let’s take an obvious alternate spring choice if our intention is to raise the lower spring perch for additional tire clearance, using the GC Street camber plates, two Swift Thrust Sheets, and 326 mm static ride height.

Selecting Swift spring p/n Z65-178-060 (7 inch x 60 N/mm):

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This configuration is depicted graphically below. Note that the upper spring perch has only partial thread engagement. In my view the practical maximum height of the lower spring perch is 205 mm as at this height the perch has 4 full threads engaged. Thread engagement could be increased to this amount with additional spring spacers to maintain this height or by accepting a slight lowering the car from the desired ride height.

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The criticality of the lower spring perch location on the Ohlins installation on a 1-series can be seen by mounting the de facto standard 8.5” x 18” ET45 wheel on the strut. This wheel provides 0.18” (4.5 mm) clearance from the strut tube, so clearly the lower spring perch has to be mounted well above the wheel rim to provide tire clearance. The following image depicts the approximate tire clearance for a 235/40R18 on an 8.5” ET 45 wheel without spacers. Spring perch clearance will depend on the tire corner profile, but clearly the spring perch location provided by a 7” spring is favorable when fitting wider wheels and tires.

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Shorter springs raise another concern though. They inherently have less usable stroke than longer springs. Too short and you risk bottoming out the spring before you achieve what should be full usable suspension travel. There are various approaches to determining what “full usable suspension travel” should be. A simple one is that the strut should have 50 mm travel beyond static ride height. For the Z65-178-060 spring, this implies a maximum stroke of 110 mm. The published usable stroke for this spring is 106 mm (maximum is 118 mm) so we are reasonably close to satisfying this rule of thumb. Incidentally, the front bump stop will begin engaging at 101 mm stroke, which appears acceptable to me.

As you may guess, I have selected the Z65-178-060 spring as a replacement for the Ohlins front spring. I am certainly not the first to have done so, but I hope the above explains why this spring works. Here is a picture of the maximum possible spring perch height with an 8.5” x 18” ET45 ARC 8 wheel installed without a tire showing wheel to strut tube clearance (no wheel spacer installed).

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I have taken this opportunity to complete another modification to the Ground Control camber plates. The slotted holes in the camber plate body are a loose fit on the mounting bolts. One could charitably call this a feature that permits small adjustments in caster to be made. If one intends to make camber adjustments at the track though, this slop really just results in a lack of repeatability when making such adjustments. My solution is to fit the bolts with 7/16” OD x 5/15” ID oilite bushings to take up the play. After opening the slots a few thousandths of an inch to adjust the fit, the plates now slide perfectly smoothly and without any slop in the caster direction.

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At the same time, I have re-engraved the body to provide a direct correlation between the degree readings and the actual front camber setting for my configuration (which includes M3 front suspension arms). This too will simplify making repeatable camber adjustments at the track.

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I will likely wait for my 7” Swift springs to arrive before I complete the front installation. While I am waiting, I would like to measure the actual torsional stiffness of the OE front anti-roll bar. I have removed it for that purpose. The rear bar is a lot more work to remove, but I may jury rig up something to measure its stiffness in place. With that data in hand I will be able to calculate the actual roll stiffness distribution for the car.
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      04-04-2014, 03:29 PM   #33
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I don't understand about 90% of what you said in this (impressive) thread, unfortunately I know almost nothing about technical things haha... I definitely need to learn about how the hell cars work.

I guess you do this for living, right?
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      04-05-2014, 05:57 AM   #34
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Quote:
Originally Posted by swagon View Post
I guess you do this for living, right?
No, this little project is my idea of fun.
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      04-08-2014, 11:25 AM   #35
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As always... the devil is in the details... this is analytical-car-porn at it's best on here.... keep it up

Even the "little" things... like the rear sturt adjustment knob extensions... awesome and cerebrally inspiring
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      04-08-2014, 11:56 AM   #36
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I only had the time to go through your first couple posts but wow, this is amazing. Thanks for sharing your thought process here and also have good pictures to help illustrate everything. Got to get through the rest of the stuff now
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      04-12-2014, 09:06 PM   #37
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Needing a distraction while waiting for my new front springs I decided to investigate the OE anti-roll bars.

My plan is to start out with the OE anti-roll bars because just the spring change will result in a significant increase in roll stiffness. Also, I have no data to support a decision to change the bars. So while waiting for my new front springs to arrive, I decided to collect some data on the OE bars. That means more measuring and more graphs.

The front bar is extremely easy to remove, so I pulled it out and arranged a test setup using a t-slotted machine bed as a base. A tape measured deflection, a load cell measured load and an engine hoist provided the pull.

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I have tabulated and plotted the data and fitted a regression line to find the bar rate as measured at the end link lug. The other end of the end link attaches to the strut body, so the bar has the same motion ratio as the strut. The effective bar rate at the wheels is the bar rate times the square of the strut motion ratio.

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The OE suspension had a reported front spring rate of 120 lb/in, so a wheel rate of approximately 110 lb/in. Thus the front bar contributed twice the roll stiffness that the springs did. With my Ohlins installation the springs contribute a wheel rate of approximately 320 lb/in, which, combined with the OE front bar provides approximately twice the front roll stiffness as OE.

The rear bar is not easy to remove, but is relatively easy to test in place. Whereas most of the front bar’s deflection is in the tubular torsion spring section of the bar, the rear bar is so flimsy that a significant part of the deflection is due to plain bending of the rear bar. To test the rear bar, the left wheel was blocked while the right end link was disconnected. A series of known weights were hung from the bar with the deflection measured at each test condition.

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A load of 25 lbs is sufficient to fully exercise the bar – as I said, it is very soft! The results are tabulated and plotted below:

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The OE suspension had a reported rear spring rate of 350 lb/in, so a wheel rate approximately 150 lb/in (when the bushing effects are accounted for). Thus the rear bar contributed only about 10% of the total rear roll stiffness. With my Ohlins installation the rear wheel rate is approximately 260 lb/in so the bar now contributes only 6% of the total rear roll stiffness and the total rear roll stiffness is now about 1.7 times OE.

Having an actual front bar stiffness measurement allows me to construct and validate a simple mathematical model of the bar. The usefulness of this is that, if it works, will be to allow me to estimate the stiffness of other bars that I may consider but not have the opportunity to measure. The mathematical model is based on these assumptions:

1) The arms of the bar are much stiffer than the torsion section, so all significant deflection in the bar occurs due to twisting of the torsion section (clearly not valid for the rear bar, but looks reasonable for the front bar).
2) The bar is formed from tubular material with minimal material removal at any section, so every section has approximately the same cross sectional area (possible because the bar is hollow).

As a first approximation, the cross sectional area was assumed to equal the cross section of the bar at the pin holes (assuming no hole was drilled), because the lug is formed by fully flattening the tube end.

The critical dimensions of the OE front bar are shown below:

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The bar can be simplified for analysis purpose as follows by eliminating the tapered sections.

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The stiffness of the bar follows from these assumptions and this geometry and is within 4% of the measured stiffness. By adjusting the assumed constant cross sectional area appropriately the model has been made to match the measured data:

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To get an idea as to the stiffness of a 28 mm hollow (M3) bar I have repeated the calculations with several unverified assumptions (I don’t have an M3 bar on hand to measure):

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Noting that there are several 27 mm solid bars available, I have repeated the calculation for such a solid bar:

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SWIFT FRONT SPRINGS

The new Swift front springs arrived, so I wasted no time getting them installed. I outlined the calculated spring perch height required for these springs and you may recall that it resulted in very limited thread engagement on the adjustable lower perch. I decided that 4 full threads was the minimum engagement I would be happy with, so some spring spacers were in order.

I already had some Swift thrust sheets. These consist of an HDPE (plastic) washer toped by a stainless steel washer. The HDPE provides a low friction surface for the stainless washer to rotate on, if necessary to accommodate the spring motions. Conveniently, I had some 0.060” HDPE sheet on hand so I made up some spacers with the same diameter dimensions as the thrust sheet spacers.

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Two of these in addition to the thrust sheets placed my spring perches nicely to maximize tire clearance and satisfy my thread engagement requirement, plus a little margin in case I needed to adjust the perches a bit to achieve cross balance.

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I assembled both struts completely, setting the perch positions with a vernier caliper. To prevent the shock tube from rotating while I tightened the top nut, I used a socket I had modified by machining a hex into its base. That permitted using a regular wrench while holding the strut tube from turning with an Allen key.

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FRONT ALIGNMENT AND CORNER BALANCE

I initially set the front camber to -3.25° per my engraved marks. These proved to be a bit out of calibration, plus I noted a bit of left/right asymmetry. My final settings of -3.50° RH and -3.75° LH by the engraved marks resulted in a true camber of -3.25° both sides.

Weighing showed that the RF/LR diagonal was about 1.1% lighter than the LF/RR diagonal. By taking careful notes and noting the change in corner balance and ride height with each adjustment, I achieved acceptable balance in three steps. All that was required was three complete turns (down) on the LR spring perch.

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Corner balancing was done with the bars disconnected. Connecting the bars did not change the corner balance significantly. Had it, adjustable end links would have been an appropriate fix to remove any bias from the bars.

The % figure shown on the scales is the cross balance ((RF+LR)/(LF+RF+LR+RR) as %), which should ideally be 50.0%

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At this point I wanted to determine how sensitive the balance was to various factors. Here is what I found:

1) the weight of a full washer fluid bottle changes the cross balance by 0.05%
2) the weight of a 170 lb front passenger or driver changes the cross balance by 0.10% each
3) a mis-leveling of a single scale by 0.08” (2 mm) changes the cross balance by 0.40%
4) cross balance changes with fuel load (because the c.g. of the car is offset to the left, but the c.g. of the fuel is on center).

This does raise the question of just how finely the cross balance hair should be split, because it does vary with occupant and operating fluid loads. I have settled on setting it to within 0.1% of 50% with the expectation that it will remain within 0.5% of 50% under most operating conditions.

Incidentally the car was weighed with 170 lb driver, full fuel, full washer, half fuel, roof racks, on hub stands not wheels, no brake pads, no front calipers, so the weight is not the true “empty weight”. This car has no sunroof. I will measure a true empty weight on wheels later. Wheels, calipers and pads, being unsprung, don’t change the cross balance %.

Final alignment is as follows:

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As with the rear, I put together a checklist of torques so that each fastener was torqued correctly and not were inadvertently forgotten.

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BRAKE INSTALLATION AND BRAKE PISTON BOOT REPLACEMENT

Not strictly part of the Ohlins installation, but a necessary part of the project – the front brake calipers needed the dust boots changed on the pistons because they had become charred from previous track days. I had removed the calipers early in the process, which made the replacement of the piston boots much easier. I had also fabricated a set of piston wrenches to assist removing and reinstalling the pistons (4 different sizes are needed to cover both the front and rear calipers). They definitely made the task of removing, cleaning, lubricating and installing the boot easier.

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Another simple tool was fabricated from a piece of 2 x 4 lumber, cut to fit in the space normally occupied by the rotor. With this in place, a few careful puffs of compressed air extend the pistons for removal. Without it, inevitably one piston will pop out easily, then the rest won’t budge. The correct width of wood allows all pistons to fully extend without any of them becoming unsealed. The wood also provides a cushion so that the fragile phenolic piston nose is not damaged by slamming into its opposite piston.

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I lubricate the pistons with a light coat of Permatex Ceramic Brake Lube before installing them. I believe this helps protect them from galling in the cylinder bores. The piston seal keeps the lube away from the fluid, but in any case the lube is brake fluid compatible.

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Although I have Hawk DTC track pads, at this moment I am installing OE brake pads, which will be changed before heading to the track.

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Because I will be switching pads frequently, the brake pad wear sensors are a bother that I want to dispense with. To that end, I have cut off the sensor leads, soldered them together, and sealed the ends with heat-shrink.

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This is the rear lead installed:

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Brake bleeding was done with a Motive Pressure Bleeder and Castrol SRF fluid. Bleeding was uneventful

Final tasks:

- Reset the service indicators for the work done (oil change, front and rear brake pads, brake fluid)
- Set dampers per Ohlins recommendation (10 clicks Front, 10 clicks Rear)
- Check tire pressures (36 psi all around) and install wheels
- Install front undertray
- Final inspection for anything amiss

Go for a drive …
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      04-12-2014, 09:07 PM   #38
fe1rx
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Quote:
Originally Posted by Fume View Post
I only had the time to go through your first couple posts but wow, this is amazing. Thanks for sharing your thought process here and also have good pictures to help illustrate everything. Got to get through the rest of the stuff now
Quote:
Originally Posted by yllwwgn View Post
As always... the devil is in the details... this is analytical-car-porn at it's best on here.... keep it up

Even the "little" things... like the rear sturt adjustment knob extensions... awesome and cerebrally inspiring
I am glad to have an appreciative "audience"!
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      04-12-2014, 10:59 PM   #39
arcticcat522
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read further and got my answer....delete had my car on the scales today...3275lbs no driver, 1/2 tank, full washer fluid

Last edited by arcticcat522; 04-12-2014 at 11:05 PM..
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      04-13-2014, 06:34 PM   #40
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FIRST IMPRESSIONS

1) Stiffer than OE ride is immediately apparent, however ride over small bumps is very noticeably more refined than OE.
2) Cornering attitude is much flatter than OE.
3) Turn-in is very immediate and responsive, attributed to less body roll (less time to take a set in a corner).
4) Steering wheel is perfectly centered – no issues with my alignment.
5) Ultimate grip and handling balance is confidence-inspiring.
6) A local skid pad (parking lot) shows that the car is safely understeer at the limit with a smooth turn-in response to lifting the throttle at the limit. Very confidence inspiring. Lots of front grip.
7) The car is not afraid of bumps at all. Most, up to a speed bump, are absorbed quietly and smoothly. It is hard to overstate how much BMW cheaped out on the OE dampers. Luckily they gave us a half-decent base to work with (OE rear subframe bushings notwithstanding).
8) At extreme lock there are a few ticking noises from the front suspension that I want to chase down. I suspect a little silicone spray on the thrust sheets may help.
9) Large bumps do produce a “thunk” from the front, but these are rare.
10) Trying the recommended 10 clicks front and rear, and ±4 clicks from there, I have to say that the recommended setting seems like a really good starting point for the street. 4 clicks produces a very noticeable change in feel.
11) I look forward to exploring the limits at an auto slalom and a race track.
12) One point I want to make is that OE is not the baseline. Way too many changes have been made to meaningfully assess the effect of each individual change. The current state is the new baseline from which refinements can be made and measured.
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      04-23-2014, 07:07 PM   #41
arcticcat522
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a question for you. the piece the stock rear springs sit in at the top, im having a shop install my coilovers, and they removed it....the cup type thing....to install the height adjuster. is that going to cause any issues? they said it was a challenge to remove, but they did. Any thoughts would be great. Thanks in advance
Adam
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      04-23-2014, 08:55 PM   #42
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Quote:
Originally Posted by arcticcat522 View Post
a question for you. the piece the stock rear springs sit in at the top, im having a shop install my coilovers, and they removed it....the cup type thing....to install the height adjuster. is that going to cause any issues? they said it was a challenge to remove, but they did. Any thoughts would be great. Thanks in advance
Adam
It depends on what type of adjuster you are using. The Ohlins adjuster sits in the cup. In this respect it is similar to the AST adjuster.

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The HPA adjuster has a spigot that fits in the hole the cup sits in, so it replaces the cup.

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Images are from the HPA website.
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      04-23-2014, 09:32 PM   #43
arcticcat522
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im assuming they need the piece removed than. they came with the TCK coilovers. the shop is highly reputable. thanks for the insight
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      04-23-2014, 09:48 PM   #44
fe1rx
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That does appear correct based on the design of the TCK adjuster.

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