BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)
 





 

Post Reply
 
Thread Tools Search this Thread
      02-28-2015, 09:55 AM   #89
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by John_01 View Post
I was looking at the motion ratio calculation that was done with the spring removed. I think you settled on a figure of 0.567. It appears to me the actual motion ratio can be lower if there is too much compliance in the rear sub frame bushings. Probably with M3 bushings, there wouldn't be much significant distortion. If the stock 135i bushings are used, I reckon it would reduce the effective spring rates at the wheel. Maybe its something when analysing the factory stock configuration.
You are correct about the effect on wheel rate. The rear subframe bushings act as springs in series with the rear spring (because some of the total wheel movement is accounted for by deflection of the springs and some by deflection of the bushings). Any vertical component of the wheel reaction not carried by the spring and shock which act directly on the chassis must be carried by the subframe and reacted into the chassis at the subframe bushings. Even though the OE bushings are soft, their deflection as a function of wheel deflection will be small, so their influence on the wheel rate will be small.

Assume that at a wheel reaction force of F the bump stop is reached and at that force the wheel has moved 100 mm due to the spring and 10 mm due to the bushings. The wheel rate is F/110. Without the bushings it would have been F/100. I doubt the bushing deflection is more than this under these conditions, so the OE rear subframe bushings may reduce the wheel rate by not more than 10% as a first order approximation. This isn't strictly the same as a reduction in motion ratio, although the effect is the same.

As many have reported, NVH is scarcely affected by the change to M3 RSFBs, yet if you look at the internal structure of the OE RSFB's, they are highly complex, highly engineered structures. In comparison, the M3 RSFBs are very simple, as are all the aftermarket options. That complexity is not there to reduce NVH or to reduce wheel rate but to control compliance steer effects at the rear and to produce a benign (and annoying to anyone who tracks their car) terminal understeer well before the rear tires reach their limit of grip.
Appreciate 0
      02-28-2015, 06:49 PM   #90
John_01
Colonel
John_01's Avatar
Australia
211
Rep
2,630
Posts

Drives: E90 325i, E82 135i
Join Date: Mar 2009
Location: Sydney, Australia

iTrader: (0)

Fe1rx, Thanks for your comments. It helped me understand what is going on with the subframe bushings. I can now see how the rear subframe bushing compliance is effectively in series with the rear springs, so it makes sense to consider additional movement of the wheel due to bushing compliance as you explained in the post above. I agree there's no change to motion ratios - I was wrong about that.

I think if the wheel rates changes by 10% due to the bushing compliance, then its quite a large effect. For a road car application the chassis engineers will match the front to rear stiffness more accurately than that. I did some calculation on the standard 135i M-sport wheel rates. I was a bit concerned because it seemed the rear wheel rate could be softer than the front when the subframe bushing compliance is added in. To get a decent analysis I need a more complete understanding of the front suspension. In your rear suspension thread, you wrote that torsion of the rear control arm bushings increases the wheel rate by about 35lb/in, but I don't think you have provided any equivalent figure for the front suspension so far. Anyway I'm subscribed to your threads so I will follow with interest.

Last edited by John_01; 02-28-2015 at 06:55 PM..
Appreciate 0
      03-02-2015, 02:27 PM   #91
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

One of the things I noticed when I took my Ohlins front suspension apart after its first season was that the front springs showed signs of having coil bound. The impact marks between adjacent coils were clearly visible:

Name:  Spring Abuse.jpg
Views: 1199
Size:  156.2 KB

It was also apparent that the spring had become slightly bent, by about 3 and had sagged slightly (about 5 mm):

Name:  Bent Spring.jpg
Views: 1190
Size:  176.7 KB

The sag is quite apparent when compared to a new spring:

Name:  New vs Abused.jpg
Views: 1191
Size:  152.9 KB

I had experienced a few good thumps at the front end, but I had attributed them to what I thought were very hard bump stops on the Ohlins front strut. What I was actually experiencing was the springs bottoming out and becoming coil bound. I am using Swift 7" x 345 lb/in (178 mm x 60 N/mm) springs, which have a "usable" stroke of 107 mm and a "maximum" stroke of 117 mm. If you regularly use more than the "usable" stroke, you will damage your springs like I did. The bend in the spring arose from the fact that my GC Street camber plates kept the springs 3 bent state normally, so when they took a permanent set they adopted that angle. My new camber plates get rid of the angle, but other measures (which I will detail in a later post) are needed to avoid over-compressing the springs.

I had not actually tested the Swift springs prior to installation last year, so I decided to compare the two "abused" springs with a pair of identical new springs, and also to test the effect on spring rate of a 3 on one of the spring perches.

Here is an image of a new spring approximately at its maximum usable stroke of 107 mm. All coils are separated by a small gap so there should be no impact between adjacent coils:

Name:  Max Stroke 0.jpg
Views: 1193
Size:  204.0 KB

When retested with one perch at 3, again at approximately maximum usable stroke (as measured on the spring center line), the angle can be seen to bring the coils on the short side closer together. If you look back at the first image you will see that the coil damage is limited to one side (the outboard side) of the springs as I had installed the springs with the printing facing outward. The bent installation reduces the available stroke before coil binding.

Name:  Max Stroke 3.jpg
Views: 1194
Size:  155.9 KB

When the testing results are tabulated, it can be seen that both new springs fall very close to the nominal 345 lb/in line, as does the new spring with one perch at 3. The slightly bent condition does not contribute to significant non-linearity in the spring rate. The used springs have lost none of their original spring rate (they fall on a line with the same slope as the new springs), but they do so offset by approximately 5 mm from the new spring. In effect the abused spring has been shortened by 5 mm and has lost 5 mm of usable stroke.

Name:  Swift Front 60 Test.jpg
Views: 1197
Size:  91.5 KB
Appreciate 0
      03-02-2015, 03:02 PM   #92
Bullitt
Major
Bullitt's Avatar
55
Rep
1,107
Posts

Drives: 135i
Join Date: Apr 2008
Location: SF Bay Area

iTrader: (18)

Garage List
2008 135i  [0.00]
I have the same Swifts in the front and they also show signs of coil bind. There's more missing powdercoat on the coil installed on the damper with more preload. I have Vorshlag plates which hopefully do not have that angle you speak of. The 400 lb/in spring might be in our future.
Appreciate 0
      03-02-2015, 10:26 PM   #93
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by Bullitt View Post
I have the same Swifts in the front and they also show signs of coil bind. There's more missing powdercoat on the coil installed on the damper with more preload. I have Vorshlag plates which hopefully do not have that angle you speak of. The 400 lb/in spring might be in our future.
You raise an interesting point, but 400 lb/in springs may not be the solution.

Consider this:

Our springs have a maximum usable stroke of 106 mm and are coil bound at a stroke of 118 mm. In my case, the 3 angle reduced the coil bound stroke to 116 mm.

It is important to know the usable stroke of your front strut. If you have a visible bump stop, you can measure the stroke to the bump stop and add an amount for usable bump stop travel (I suggest half the bump stop height). In the case of the Ohlins strut, the bump stop is not visible, so I measured load vs. compression for the strut to infer the usable stroke, which from the graphs below you will see is 108 mm (at which point the bump stop is providing over 1000 lbs of resistance). The bump stop starts working at 90 mm.

When you preload your spring, you eat into the spring's usable stroke. The trick is to make sure the spring doesn't coil bind before the suspension reaches your design maximum travel.

Your first reaction might be to raise the ride height in response to coil binding. This actually requires more preload, so it will make the problem worse.

To give a concrete example, in 2014 I used a preload of 21 mm, which means my usable suspension stroke was 106 - 21 = 85 mm and my coil bind stroke was 118 - 21 = 97 mm. (actually it was only 95 mm because the 3 angle reduced it by 2 mm).

The graph below illustrates this. The important point is that at the maximum usable stroke of the spring, I still haven't even touched the bump stop! At coil bind, the bump stop is only providing a bit over 100 lbs of resistance! No wonder I was experiencing coil bind.

Name:  Front Strut 21 mm Preload.jpg
Views: 1202
Size:  114.5 KB

For 2015, I am using a preload of 3 mm. This dramatically improves things with regard to my springs. At maximum usable spring stroke I am seeing about 300 lbs of bump stop resistance, and at coil bind, the bump stop is off the scale. In other words coil binding will be impossible.

Name:  Front Strut 3 mm Preload.jpg
Views: 1269
Size:  113.0 KB

For this very reason better coil-overs allow for preload and ride height to be adjusted separately. Our front uprights (bearing carriers, knuckles) don't permit the use of such struts, so we are stuck using preload to adjust ride height. Reducing preload by 19 mm would result in a similar reduction in ride height, which is probably not tolerable, so some compromise is required. In my case I am using alternate means to decouple ride height from preload, and I will outline them in my next post.

But back to your 400 lb/in suggestion. If it is also a 7" spring it will have less usable stroke than the current spring. You will be able to use less preload because it is stiffer but if you look at the math you may find it won't solve the coil bind problem.

Last edited by fe1rx; 03-02-2015 at 11:03 PM..
Appreciate 0
      03-02-2015, 11:21 PM   #94
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by Bullitt View Post
I have the same Swifts in the front and they also show signs of coil bind. There's more missing powdercoat on the coil installed on the damper with more preload. I have Vorshlag plates which hopefully do not have that angle you speak of. The 400 lb/in spring might be in our future.
Here is a look at the Swift 7" x 400 lb/in (178 mm x 70 N/mm) spring with 3 mm preload on my strut. The problem is that the published usable stroke is only 93 mm. That means that the spring will be compressed beyond its published usable limit whenever the bump stop is engaged. It won't coil bind, but it will be over-stressed. You would have to go with an 8" spring, and that would raise other problems (i.e. tire clearance).

Name:  Front Strut with 70 N:mm Spring.jpg
Views: 1253
Size:  112.2 KB
Appreciate 0
      03-03-2015, 02:09 AM   #95
Bullitt
Major
Bullitt's Avatar
55
Rep
1,107
Posts

Drives: 135i
Join Date: Apr 2008
Location: SF Bay Area

iTrader: (18)

Garage List
2008 135i  [0.00]
Good to know. You've just persuaded me to stick with the current spring rate. I can live with the dampers set at a stiffer setting to help reduce the incidence of coil bind which appears to be only occurring in corners that have sudden dips and undulations (present in mountain and canyon roads). Fortunately, these Ohlins remain fairly compliant approaching near full hard. Did coil bind disappear for you at a certain setting/number of clicks?
Appreciate 0
      03-03-2015, 05:50 PM   #96
PeteA
Major
PeteA's Avatar
Australia
118
Rep
1,122
Posts

Drives: E30, E82
Join Date: Sep 2012
Location: Melbourne

iTrader: (3)

No coil bind for me, i checked them last night. I'll take a closer look tonight.
Appreciate 0
      03-03-2015, 06:47 PM   #97
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by Bullitt View Post
Good to know. You've just persuaded me to stick with the current spring rate. I can live with the dampers set at a stiffer setting to help reduce the incidence of coil bind which appears to be only occurring in corners that have sudden dips and undulations (present in mountain and canyon roads). Fortunately, these Ohlins remain fairly compliant approaching near full hard. Did coil bind disappear for you at a certain setting/number of clicks?
This seems to me to be the wrong approach. If you are ever getting coil bind, you are over working your springs. Also, overdamping to reduce travel kind of defeats the purpose of having a fairly refined coil-over setup.

My approach to reducing preload while maintaining ride height takes two paths. Reducing preload requires lowering the lower spring perch, which brings it closer to the tire. In order to allow the perch to be lowered without bringing it any closer to the tire, I have made a 10 mm high spacer to go between the strut and the knuckle, which raises the lower spring perch the same amount relative to the tire. This allows me to lower the spring perch by 10 mm while making no difference in tire clearance. The spacer is keyed to maintain the indexing of the strut and knuckle.

Name:  Ride Height Spacer.jpg
Views: 1406
Size:  141.1 KB

With a 10 mm spacer, the strut is still fully secured by the knuckle. Taller than this would begin to reduce the support, and it would require re-routing the ABS cable. At 10 mm I believe the effect on brake hose routing and anti-roll bar end link geometry is small enough to be negligible.

Name:  Knuckle Assembly.jpg
Views: 1273
Size:  186.1 KB

The other part of my solution is my custom camber plates, which are 5 mm taller than the GC plates they replace. You could achieve the same thing by putting a spacer on top of your camber plates.

Name:  Strut ASM.jpg
Views: 1424
Size:  47.3 KB

Therefore I can reduce my preload a total of 15 mm without any change in ride height from previously. At my selected preload of 3 mm, the lower spring perch is well clear of the tire (Nitto NT01 235/40ZR18 on Apex Arc 8 8.5 x 18 ET 45), so wider tires are also a possibility.

Name:  Spring Perch Clearance.jpg
Views: 1314
Size:  159.1 KB
Appreciate 4
      03-03-2015, 08:02 PM   #98
Nugget
Colonel
Nugget's Avatar
Australia
289
Rep
2,433
Posts

Drives: 2017 M140i, 1994 M3, 1997 M3
Join Date: Jan 2012
Location: Perth

iTrader: (2)

Garage List
2011 BMW 135i  [5.00]
So much good info as usual.
How do you do a better job of this than companies like Ohlins and Ground Control?
Is it just more time invested or more likely because they just slightly adjust products rather than tailor them specifically to a platform?
Appreciate 0
      03-03-2015, 11:57 PM   #99
dtla1
Major
dtla1's Avatar
320
Rep
1,254
Posts

Drives: 2011 135i, Space Grey
Join Date: Apr 2014
Location: Silicon Valley

iTrader: (2)

Quote:
Originally Posted by Nugget View Post
So much good info as usual.
How do you do a better job of this than companies like Ohlins and Ground Control?
Is it just more time invested or more likely because they just slightly adjust products rather than tailor them specifically to a platform?
+1, Looks like some of these suspension manufacturers need to employ you part time at least. You are contributing some of the most valuable information I have ever seen on this forum.
Appreciate 0
      03-04-2015, 02:23 AM   #100
PeteA
Major
PeteA's Avatar
Australia
118
Rep
1,122
Posts

Drives: E30, E82
Join Date: Sep 2012
Location: Melbourne

iTrader: (3)

Interesting. In Ohlins defence we are using modified spring rates and heights for tyre clearance so we can milk the patform for tyre width.

Is installing a taller bumpstop another option?
Appreciate 0
      03-04-2015, 08:25 AM   #101
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by PeteA View Post
Interesting. In Ohlins defence we are using modified spring rates and heights for tyre clearance so we can milk the platform for tyre width.

Is installing a taller bumpstop another option?
You are absolutely correct. I have no doubt they work perfectly when used as designed.

Interesting idea about the bumpstop. We need some brave soul to figure out how to disassemble the strut without screwing it up. I am thinking if you can get the adjuster knob off, then remove the nut at the bottom the shock should pull out of the housing. I am (almost) tempted to try it.
Appreciate 0
      03-04-2015, 08:33 AM   #102
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by Nugget View Post
So much good info as usual.
How do you do a better job of this than companies like Ohlins and Ground Control?
Is it just more time invested or more likely because they just slightly adjust products rather than tailor them specifically to a platform?
Thanks. As PeteA has pointed out we are just dealing with spring choices that Ohlins did not intend us to make (on a platform the kit actually wasn't designed for).

Ground Control has made a camber plate for the widest possible audience. My modification only needs to cater to my own niche requirement, hence I can optimize it for -3 1. When you reverse engineer something you get to see how thoughtful the original designer was. I am impressed by their attention to detail. They did all the hard work - I just tweaked it.
Appreciate 0
      03-04-2015, 09:13 AM   #103
Griff500
Private
25
Rep
77
Posts

Drives: 135i
Join Date: Aug 2013
Location: Home

iTrader: (0)

Aren't you effectively reducing wheel travel by implementing the spacer though?

But I appreciate you're limited by what you can do due to tyre clearance and it's better to have a controlled end of travel using the bumptstop than going coil bound.

Thanks for the really informative threads of late, I'm sure the community appreciates it as much as I do
Appreciate 0
      03-05-2015, 07:51 AM   #104
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by Griff500 View Post
Aren't you effectively reducing wheel travel by implementing the spacer though?
The spacer doesn't change wheel travel at all. It simply raises the ride height. This allows reducing the spring preload to re-establish the original ride height. In doing so you get a corresponding increase in wheel travel before coil binding occurs. Ideally you gain enough travel that the bump stop now prevents coil binding.
Appreciate 0
      03-05-2015, 01:22 PM   #105
Griff500
Private
25
Rep
77
Posts

Drives: 135i
Join Date: Aug 2013
Location: Home

iTrader: (0)

Quote:
Originally Posted by fe1rx View Post
The spacer doesn't change wheel travel at all. It simply raises the ride height. This allows reducing the spring preload to re-establish the original ride height. In doing so you get a corresponding increase in wheel travel before coil binding occurs. Ideally you gain enough travel that the bump stop now prevents coil binding.
I was thinking about available damper travel in a like for like ride height scenario.

I now see that this is your solution for resolving your coil binding issue; which was your limit on bump travel.

Is there not a better solution though? Surely you want to take advantage of the maximum available wheel envelope? Is there an opportunity for a change in spring winding (keep the rate, width and length but remove the chance of binding within he available travel?)
Appreciate 0
      03-05-2015, 08:27 PM   #106
_Ryan_
Captain
No_Country
50
Rep
750
Posts

Drives: E87 130i
Join Date: Jan 2012
Location: Melbourne, AU

iTrader: (0)

Garage List
2005 BMW 130i  [2.62]
Something like this would make me feel a little better about running 8" springs. What is the effort to replicate?
Do you consider this setup to introduce additional risk of component failure?
Appreciate 0
      03-05-2015, 10:24 PM   #107
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by Griff500 View Post
Is there not a better solution though? Surely you want to take advantage of the maximum available wheel envelope? Is there an opportunity for a change in spring winding (keep the rate, width and length but remove the chance of binding within he available travel?)
Feel free to look for a better solution!

Your choice needs to accomplish this:

1) your ride height is acceptable (to you)

2) you have clearance for your chosen wheel and tire

3) your bump travel is limited by stop, not by coil bind

4) under any normal bump, your spring is not compressed beyond the recommended maximum

5) minimal spring preload is desirable to minimize the chance of lifting a front wheel under limit cornering

I think my solution meets all of the above, so I am not looking for a better one. As they say, "better is the enemy of good".

Quote:
Originally Posted by _Ryan_ View Post
Something like this would make me feel a little better about running 8" springs. What is the effort to replicate?
Do you consider this setup to introduce additional risk of component failure?
I don't follow your questions. Replicate what? Additional risk relative to what?

What I have documented is a change to my 2014 spring setup, which resulted in spring damage (not failure). This change is intended to eliminate the cause of that spring damage. 8" springs would not work for me because they would not provide my desired tire clearance.
Appreciate 0
      03-05-2015, 10:50 PM   #108
_Ryan_
Captain
No_Country
50
Rep
750
Posts

Drives: E87 130i
Join Date: Jan 2012
Location: Melbourne, AU

iTrader: (0)

Garage List
2005 BMW 130i  [2.62]
Quote:
Originally Posted by fe1rx View Post
I don't follow your questions. Replicate what? Additional risk relative to what?

What I have documented is a change to my 2014 spring setup, which resulted in spring damage (not failure). This change is intended to eliminate the cause of that spring damage. 8" springs would not work for me because they would not provide my desired tire clearance.
To create a similar spacer setup for other 1ers.
Risk analysis of introducing another component which has [I assume] been hand machined and integrated into an existing system.
Appreciate 0
      03-06-2015, 08:23 AM   #109
fe1rx
Captain
668
Rep
604
Posts

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

Quote:
Originally Posted by _Ryan_ View Post
To create a similar spacer setup for other 1ers.
Risk analysis of introducing another component which has [I assume] been hand machined and integrated into an existing system.
This is a build thread, not a prescription. I offer up my approach as well as my solutions as food for thought. The approach (methodical, thorough, tested, documented) is probably the most important take-away. Everything made has been drawn, dimensioned, toleranced. Of course the spacer is repeatable, but it is only part of my complete "solution".

I realize that most people just want to buy a kit and have it work perfectly out of the box so they don't have to touch it again. My approach is that I would like it to work well out of the box and then I would like to improve it. That is not an imposition with a seasonal car, but it would be with a daily driver. Also, I have a certain combination of daily refinement and track manners in mind. Everyone is different in terms of how much of the one they are are willing to give up in the quest for the other. There is no perfect solution.

Obviously I design and make stuff for a living, so I have a few tools and materials at my disposal. But I don't make car parts for a living, so I don't need to rush my design to market or to convince anyone it is the best solution to their problem. I have no intention of marketing any of it. Some of it is to poke holes in marketing hype - of which there seems to be a surplus.
Appreciate 0
      03-06-2015, 10:28 AM   #110
Suprgnat
German cars and French tires.
Suprgnat's Avatar
United_States
906
Rep
1,737
Posts

Drives: 2013 128i LMB 6MT ZMP Slicktop
Join Date: Jan 2013
Location: California

iTrader: (7)

Garage List
Quote:
Originally Posted by fe1rx View Post
so I don't need to rush my design to market
Speaking of rushing your designs to market, when will you be offering your toe links for sale?
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 03:37 PM.




1addicts
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST