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
      05-29-2016, 10:32 AM   #1
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

true rear coil-over: possible?

I'm wondering for those of you who are probably more in the know than me, do you think it is possible to put a coil-over spring on the shock in the rear? I realize this is a major change the from the OEM design, but there are good reasons to design a coil-over that has harmonized motion ratios.

Things I'm wondering:
-top mount: how to keep the spring square?
-lower mount: threaded sleeve over shock body?
-rear shock towers: can they handle the stress?

Please let me know why this is a horrible idea.
__________________
Living the 1-life since 2013.
Appreciate 0
      05-29-2016, 01:06 PM   #2
ShocknAwe
1Addict
ShocknAwe's Avatar
3202
Rep
7,860
Posts

Drives: E82 Mutt, M57 Truck
Join Date: Jul 2012
Location: Charleston

iTrader: (22)

Top mount at body would have to be reengineered to support and withstand more force.
__________________
2010 135i 6MT Jet Black
N54/3 FE82 Mutt | BUILD THREAD | GARAGE SALE
Appreciate 0
      05-30-2016, 01:30 AM   #3
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

hmm yeah that's the major thing I was afraid of.

I guess maybe I'll look at rising rate custom rears instead.
__________________
Living the 1-life since 2013.
Appreciate 0
      05-30-2016, 03:40 AM   #4
RyanDavies
Lieutenant
63
Rep
448
Posts

Drives: 2012 128i MSport
Join Date: Sep 2015
Location: Washington, DC

iTrader: (2)

JRZ makes them. My shock bodies are already threaded on my car.
Appreciate 0
      05-30-2016, 05:45 AM   #5
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

say what? do you see any deformation on the rear shock towers?
__________________
Living the 1-life since 2013.
Appreciate 0
      05-30-2016, 08:47 AM   #6
julienjj
Private First Class
julienjj's Avatar
Canada
135
Rep
134
Posts

Drives: 135i 6MT
Join Date: May 2015
Location: Canada

iTrader: (0)

You will not gain much from having a coilspring unit VS a spring that has adjustments and a good damper with a variable height.

Actually... only the spring preload is not available but you could engineer something around that.
__________________
2016 435i xdrive Gran Coupé
2011 E82 1M Custom Frozen Brilliant White
2006 E60 M5 Alpine white SMG DELETE 6MT swap.
Gone : 135i 2008 | Gone : 2008 535i Touring|
Appreciate 0
      05-30-2016, 08:53 AM   #7
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

Quote:
Originally Posted by julienjj View Post
You will not gain much from having a coilspring unit VS a spring that has adjustments and a good damper with a variable height
I already have variable ride height springs in the rear (TC Kline perches). My point is that the motion ratio is so poor for the spring that it requires very high rates and this requires the shock to be valved for a completely different motion ratio.
__________________
Living the 1-life since 2013.
Appreciate 0
      05-30-2016, 10:34 AM   #8
RyanDavies
Lieutenant
63
Rep
448
Posts

Drives: 2012 128i MSport
Join Date: Sep 2015
Location: Washington, DC

iTrader: (2)

Wrong. The damper is in the same spot, the damper ratio will remain the same regardless of where the spring is.
Appreciate 0
      05-30-2016, 11:58 AM   #9
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

no no, I'm trying to convey the fact that the shock has to be valved for a motion ratio in the OEM setup that is way different than the spring.

there is benefit to making them the same.
__________________
Living the 1-life since 2013.
Appreciate 0
      05-31-2016, 06:05 AM   #10
John_01
Colonel
John_01's Avatar
Australia
232
Rep
2,643
Posts

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

iTrader: (0)

I can't really see any advantage in true coilover conversion. The stock setup just means using a higher spring rate than you otherwise would in a true coilover, and that's it.
There is one very minor point about the distortion of the spring perch as it is not directly aligned on axis, but it's not going to make any practical difference.
Appreciate 0
      05-31-2016, 06:17 AM   #11
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

The motion ratio I have found for the rear shock is 0.813. The rear spring is 0.563. These motion ratios are unrelated. (eg. the spring ratio is 69.25% of the shock). I fully understand that it is completely *possible* to valve shocks for a different motion ratio than the spring. What I'm saying is that its less than ideal. I would rather have a softer spring with more travel in the rear, with the same motion ratio as the shock.
__________________
Living the 1-life since 2013.
Appreciate 0
      05-31-2016, 06:44 AM   #12
John_01
Colonel
John_01's Avatar
Australia
232
Rep
2,643
Posts

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

iTrader: (0)

Quote:
Originally Posted by tuj View Post
I fully understand that it is completely *possible* to valve shocks for a different motion ratio than the spring. What I'm saying is that its less than ideal. I would rather have a softer spring with more travel in the rear, with the same motion ratio as the shock.
If that's your preference.. ok. I just can't see why its less ideal than any other spring rate or motion ratio.

The springs attach in a different place, but you use springs with higher rate spec to compensate. The end result is that its Not going to make any difference to the shock valving.
Appreciate 0
      05-31-2016, 07:16 AM   #13
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

John_01 , let's try a thought experiment: Imagine a divorced suspension with a spring motion ratio of 0.1 and a shock motion ratio of 1.0. For every 1/10th" the spring moves, the shock will move 1". We all know that shocks work by displacement per unit time via the valving, so the shock will have to be valved comparatively very soft because it is experiencing so much motion relative to the spring. This means it will be hard to do things like high-speed and low-speed digressive dampening. Maybe not impossible, but certainly harder.

Disclaimer: I am far from an expert on shocks, but I know a little bit.

Based on my calculations, I am looking at needing a 1700lb/in spring in back if I use the OEM position, which seems way extreme.
__________________
Living the 1-life since 2013.
Appreciate 0
      05-31-2016, 07:08 PM   #14
John_01
Colonel
John_01's Avatar
Australia
232
Rep
2,643
Posts

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

iTrader: (0)

Quote:
Originally Posted by tuj View Post
John_01 , let's try a thought experiment: Imagine a divorced suspension with a spring motion ratio of 0.1 and a shock motion ratio of 1.0. For every 1/10th" the spring moves, the shock will move 1". We all know that shocks work by displacement per unit time via the valving, so the shock will have to be valved comparatively very soft because it is experiencing so much motion relative to the spring. This means it will be hard to do things like high-speed and low-speed digressive dampening. Maybe not impossible, but certainly harder.
The shock should be valved to take into account the movement of the wheel in response to road shocks, and due to movement of the body of the car. That movement only depends on the motion ratio for the shock. Providing the spring rate applied to the wheel is the right one, I maintain that spring geometry and spring motion ratio won't make a difference.

Quote:
Originally Posted by tuj View Post
Based on my calculations, I am looking at needing a 1700lb/in spring in back if I use the OEM position, which seems way extreme.
1700lb/in seems high, although I think you wrote you will run some really sticky Hoosier tires on your car. Maybe you can consider adding a rear sway bar if you need that much spring rate. The stock spring location is actually good from a structural point of view because the spring perch is located directly below the rear chassis rail. I suppose the downside of the stock setup is that it is sensitive to movement of the rear subframe bushings. If you want to achieve really high rear wheel rates, you might want to consider solid rear subframe bushings.
Appreciate 0
      05-31-2016, 11:06 PM   #15
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

John_01 Yes, I am definitely considering a rear sway. The WhiteLine FSB showed up this afternoon, so that will be going on the car at some point in the future. I have some poly RSFB sitting in a box, so whenever I get the funds together for the LSD, I'll do those at the same time.

I realize 1700 seems, well, ridiculously high, but its what I calculate is about right for a NF of 2.5Hz. And NF of 2.5 is not crazy high. I know people who run NF's of higher than 3 on their track cars. The ideal front NF is, IMHO, 2.2Hz, which works out to be about 425lb/in which actually is very reasonable and is what a lot of the kits have targeted or come close to.

The spring rate really doesn't have so much to do with the tires as it does with weight transfer; eg pitch and roll. Loads are moving through different points of the suspension. Camber is changing, toe may be changing, etc. Suspension does not create grip. Suspension merely allows grip to occur more often and for longer periods when done better. Yes a sticker tire allows us to pick a NF that is higher, but some of the street tires out today like the RE71's are so responsive from what I understand, that they demand as high of spring rates as any full-bore slick autocross tire.

Of course the other thought here is to try to run progressive rears...

I'm going to stick with the 350/700 setup this year almost certainly but I want my next spring change to hopefully be my last. Famous last words?
__________________
Living the 1-life since 2013.
Appreciate 0
      06-01-2016, 08:13 AM   #16
RyanDavies
Lieutenant
63
Rep
448
Posts

Drives: 2012 128i MSport
Join Date: Sep 2015
Location: Washington, DC

iTrader: (2)

That is a *lot* of wheel rate. Maybe if you ran no bar at all or the stock bar (which at 15lbs of wheel rate is functionally the same as no bar, regardless what folks on here will say...)

Ive known zero successfully setup cars that were textbook built to natural frequencies.
Appreciate 0
      06-01-2016, 08:17 AM   #17
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

Quote:
Originally Posted by RyanDavies View Post
Ive known zero successfully setup cars that were textbook built to natural frequencies.
No? Dennis Grant?

2004 ASN/FIA Canadian D Modified Champion
2002 SCCA ProSolo Honda Street Challenge Series Champion
2002 SCCA ProSolo Street Modified Series Champion
2003, 2001, 2000 CENDIV Divisional Champion

ProSolo ain't no joke.

Yeah my math was without a rear bar. I simply ignored it to get to 1700lb/in. So I suppose I could back off those rates a little bit.
__________________
Living the 1-life since 2013.
Appreciate 1
bNks334426.50
      06-01-2016, 08:53 AM   #18
RyanDavies
Lieutenant
63
Rep
448
Posts

Drives: 2012 128i MSport
Join Date: Sep 2015
Location: Washington, DC

iTrader: (2)

SM 15 years ago wasn't exactly a hard class.

It's pretty easy to win Pros with a half second advantage leaving the tree.

Enjoy driving an STR S2000 with a higher rear NF than front. You'll die, so what kind of flowers do you want at your funeral?
Appreciate 0
      06-01-2016, 08:56 AM   #19
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

Hey bud, I didn't say it was the be-all, end-all! I'm trying out a theory here. Maybe it will work, maybe it won't. At least I'll be able to say I tried it.

I'm working on rigging up a ghetto-fabulous shock dyno right now.
__________________
Living the 1-life since 2013.
Appreciate 0
      06-01-2016, 11:09 AM   #20
RyanDavies
Lieutenant
63
Rep
448
Posts

Drives: 2012 128i MSport
Join Date: Sep 2015
Location: Washington, DC

iTrader: (2)

If that actually works (I figure you're doing a load cell deal), lmk .
Appreciate 0
      06-02-2016, 09:54 PM   #21
HP Autosport
Supreme Allied Commander
United_States
3776
Rep
54,162
Posts

Drives: F80 M3
Join Date: Mar 2007
Location: Santa Barbara, AP, Brembo, GIAC, Koni, Ohlins, Performance Friction, www.hpautosport.com

iTrader: (36)

Most high end dampers can come as true coilover rears. JRZ, MCS and Moton just to name a few.
Appreciate 0
      06-03-2016, 01:34 AM   #22
tuj
First Lieutenant
49
Rep
379
Posts

Drives: '13 135i
Join Date: May 2013
Location: Stamford, CT

iTrader: (0)

I emailed JRZ-USA over the weekend, haven't heard anything. The MCS pictures on the Vorschlag site show a divorced rear setup, as do the Moton pictures on the HPA site. I'm confused...
__________________
Living the 1-life since 2013.
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 08:50 PM.




1addicts
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, 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