E90Post
 


Evolution of Speed
 
BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > True Coilover Rear Conversion: Benefits?



Reply
 
Thread Tools Search this Thread
      07-17-2012, 06:07 PM   #1
turugara
Major
turugara's Avatar
71
Rep
1,321
Posts

Drives: 335i Coupe, 6 Speed
Join Date: May 2011
Location: NYC

iTrader: (5)

Garage List
2011 BMW 335i  [4.72]
True Coilover Rear Conversion: Benefits?

I've seen a true rear coilover setup for the E9x, mainly on track/race cars.

What's the benefit? Why don't we all have that type of setup?

Example:
Appreciate 0
      07-17-2012, 07:15 PM   #2
cvc 22349a
Colonel
cvc 22349a's Avatar
United_States
113
Rep
2,486
Posts

Drives: 335i
Join Date: Sep 2007
Location: SF Bay

iTrader: (11)

That set up might tear the subframe away from the chassis and would require extensive reinforcement of the shock towers and solid subframe mounts.
Those spherical joints don't look so hot btw.
__________________
2007 E90 335i, TiAg, 6AT, ZPP, ZSP, ZCW, 6FL, HD
Quaife lsd, ETS fmic, GIAC s/w, Dinan intake/exhaust/oc, Koni/M3 susp, Apex Arc 8, Mich PSS
Appreciate 0
      07-17-2012, 09:53 PM   #3
CJ421
Brigadier General
CJ421's Avatar
United_States
418
Rep
3,578
Posts

Drives: 2017 F30 340i
Join Date: Feb 2011
Location: Blue Bell PA

iTrader: (1)

Garage List
Actually I think the coilover rear would be less stress on the subframe.

The inboard spring setup puts a substantial amount of stress on the subframe. The spring sits in the camber link (which is connected to the subframe) and is connected at the top to the body; so every time the spring compresses, it's acting on the subframe (literally pushing it away from the body).

The spring has to be quite stiff to begin with because the spring's inboard location means the wheel rate is 1/3 of the spring rate (there are exact numbers on this forum somewhere). In the front the wheel rate is 1/1.
That's a problem because it greatly limits how much lb/in we can use in the rear. The maximum rear rate is about 800 lb/in; evidence for this is that none of the coilover kits available for our cars or the M3 go above that in the rear. We can increase the front spring rate FAR more than the rear, but to maintain a front-rear balance we can't go nearly as high in the rear and that limits the front.

So if you switch to a coilover type rear, your wheel rate is much closer to one (about 4/5ths I imagine) and that means you can increase the spring rates back there a lot more (and therefore the fronts too). The spring will now put much more force on the body of the car (no longer on the subframe) so I think cvc is right that some reinforcement will be needed in that area.

Edit: I don't know what is involved in the rear coilover conversion. VAC Motorsports runs it on their E92 M3 w/ Nitron NTR R3s. And I know there's other benefits from what I've researched so far. I stopped looking into it after I realized I was not going to go with a really high spring rate.
__________________
2017 BMW 340i (F30) - M Sport, Mineral Gray/Coral Red, 6MT; Dinan exhaust
Past: 2011 335i (E92) - M Sport, Le Mans Blue/Black, 6MT

Last edited by CJ421; 07-17-2012 at 10:25 PM.
Appreciate 1
feuer2392.00

      07-17-2012, 10:27 PM   #4
dvpouldar26
Major
dvpouldar26's Avatar
56
Rep
1,498
Posts

Drives: 2008 e92 328i, Porsche 987.1
Join Date: May 2008
Location: Beverly Hills, CA

iTrader: (4)

The reasoning behind a rear coilover is because of the motion ratio of the rear suspension. In current form, the motion ratio is about 50%, meaning that with an 800lb spring in the rear, there is an effective rate of 400lb at the wheel. With this current geometry, an extremely high spring rate will need to me run in the rear, however, this causes a lot of stress on the rear subframe. The subframe would need to be reinforced. By going to a rear coilover, the spring is moved out closer to the wheel, increasing the motion ratio. In doing this, the spring rates that can be used are not limited by how much force the subframe can handle. This is the same reason why so many subframe problems were seen in the e46 m3's. Hope this helps.
__________________
E92 328i
Jet Black / Gloss Black Grilles / 8000k D1S low beam / 6000k HID fogs / GP Thunder 8500k angels & cornering bulbs / black reflectors / gloss black vinyled window trim / tints / smoked rear turn signals / black roundels / AC Schnitzer roof spoiler / VRS style decklid spoiler / Matte black Stripes / Rear fogs / matte mirrors / 19" LM reps / APR lip
Appreciate 0
      07-17-2012, 10:28 PM   #5
turugara
Major
turugara's Avatar
71
Rep
1,321
Posts

Drives: 335i Coupe, 6 Speed
Join Date: May 2011
Location: NYC

iTrader: (5)

Garage List
2011 BMW 335i  [4.72]
Quote:
Originally Posted by CJ421 View Post
I stopped looking into it after I realized I was not going to go with a really high spring rate.
This is only partially true. Edited for truth.


I shouldn't have stopped looking into it because eventually I know I going to go with a really high spring rate because racecar.
Appreciate 0
      07-17-2012, 10:29 PM   #6
turugara
Major
turugara's Avatar
71
Rep
1,321
Posts

Drives: 335i Coupe, 6 Speed
Join Date: May 2011
Location: NYC

iTrader: (5)

Garage List
2011 BMW 335i  [4.72]
Quote:
Originally Posted by dvpouldar26 View Post
The reasoning behind a rear coilover is because of the motion ratio of the rear suspension. In current form, the motion ratio is about 50%, meaning that with an 800lb spring in the rear, there is an effective rate of 400lb at the wheel. With this current geometry, an extremely high spring rate will need to me run in the rear, however, this causes a lot of stress on the rear subframe. The subframe would need to be reinforced. By going to a rear coilover, the spring is moved out closer to the wheel, increasing the motion ratio. In doing this, the spring rates that can be used are not limited by how much force the subframe can handle. This is the same reason why so many subframe problems were seen in the e46 m3's. Hope this helps.
So it's better for the subframe?
Appreciate 0
      07-17-2012, 10:31 PM   #7
CJ421
Brigadier General
CJ421's Avatar
United_States
418
Rep
3,578
Posts

Drives: 2017 F30 340i
Join Date: Feb 2011
Location: Blue Bell PA

iTrader: (1)

Garage List
Great post dvpouldar26.
Quote:
Originally Posted by turugara View Post
So it's better for the subframe?
Unquestionably. I added some more info to my post above.

Subframe problems:
http://www.m3post.com/forums/showthread.php?t=659693
Page #2 is where there is good info.
__________________
2017 BMW 340i (F30) - M Sport, Mineral Gray/Coral Red, 6MT; Dinan exhaust
Past: 2011 335i (E92) - M Sport, Le Mans Blue/Black, 6MT
Appreciate 0
      07-17-2012, 10:36 PM   #8
turugara
Major
turugara's Avatar
71
Rep
1,321
Posts

Drives: 335i Coupe, 6 Speed
Join Date: May 2011
Location: NYC

iTrader: (5)

Garage List
2011 BMW 335i  [4.72]
Very cool. I'll inquire as to how much work it'll take to get this done. I don't imagine much given all that we've done already CJ.
Appreciate 0
      07-17-2012, 11:16 PM   #9
dvpouldar26
Major
dvpouldar26's Avatar
56
Rep
1,498
Posts

Drives: 2008 e92 328i, Porsche 987.1
Join Date: May 2008
Location: Beverly Hills, CA

iTrader: (4)

Quote:
Originally Posted by CJ421 View Post
Great post dvpouldar26.

Unquestionably. I added some more info to my post above.

Subframe problems:
http://www.m3post.com/forums/showthread.php?t=659693
Page #2 is where there is good info.
+1. I can't tell you how many cracked and damaged subframes i've seen on e46 m3's because of this reason. A friend of mine is running an 1100lb rear spring with motons on his e92 m3. I think this is the highest spring rate I have seen run on the rear of these cars. KW CS's come with 800lb rears out of the box.
__________________
E92 328i
Jet Black / Gloss Black Grilles / 8000k D1S low beam / 6000k HID fogs / GP Thunder 8500k angels & cornering bulbs / black reflectors / gloss black vinyled window trim / tints / smoked rear turn signals / black roundels / AC Schnitzer roof spoiler / VRS style decklid spoiler / Matte black Stripes / Rear fogs / matte mirrors / 19" LM reps / APR lip
Appreciate 0
      07-20-2012, 03:12 PM   #10
turugara
Major
turugara's Avatar
71
Rep
1,321
Posts

Drives: 335i Coupe, 6 Speed
Join Date: May 2011
Location: NYC

iTrader: (5)

Garage List
2011 BMW 335i  [4.72]
Talked to VAC. You need extensive shock tower reinforcement and not a mod recommended on a street car. Otherwise it is very likely that you may damage the chassis.
Appreciate 0
      07-21-2012, 04:17 PM   #11
CJ421
Brigadier General
CJ421's Avatar
United_States
418
Rep
3,578
Posts

Drives: 2017 F30 340i
Join Date: Feb 2011
Location: Blue Bell PA

iTrader: (1)

Garage List
Quote:
Originally Posted by turugara View Post
Talked to VAC. You need extensive shock tower reinforcement and not a mod recommended on a street car. Otherwise it is very likely that you may damage the chassis.
Thanks for the report.

Going off that train of thought - given reinforcement is required, it makes me reconsider doing solid subframe bushings. I really do think there needs to be some flex where the subframe connects, there otherwise there'd be too much stress on where the shock connects to the body.
__________________
2017 BMW 340i (F30) - M Sport, Mineral Gray/Coral Red, 6MT; Dinan exhaust
Past: 2011 335i (E92) - M Sport, Le Mans Blue/Black, 6MT
Appreciate 0
      07-21-2012, 05:05 PM   #12
turugara
Major
turugara's Avatar
71
Rep
1,321
Posts

Drives: 335i Coupe, 6 Speed
Join Date: May 2011
Location: NYC

iTrader: (5)

Garage List
2011 BMW 335i  [4.72]
All I know is that at my current setup level, Im limited by tires and personal skills. Perhaps when because racecar with full aero in a year or so, I'll revisit this.

Quote:
Originally Posted by CJ421 View Post
Thanks for the report.

Going off that train of thought - given reinforcement is required, it makes me reconsider doing solid subframe bushings. I really do think there needs to be some flex where the subframe connects, there otherwise there'd be too much stress on where the shock connects to the body.
Appreciate 0
      07-21-2012, 10:44 PM   #13
CALWATERBOY
Major
CALWATERBOY's Avatar
95
Rep
1,051
Posts

Drives: 2009 E93 N54
Join Date: Jan 2011
Location: San Francisco

iTrader: (0)

Quote:
Originally Posted by turugara View Post
Who's selling this setup?

Or is it home-grown?
Appreciate 0
      07-22-2012, 10:34 AM   #14
turugara
Major
turugara's Avatar
71
Rep
1,321
Posts

Drives: 335i Coupe, 6 Speed
Join Date: May 2011
Location: NYC

iTrader: (5)

Garage List
2011 BMW 335i  [4.72]
I know a lot of high end brands are like moton/AST, JRZ's, or nitron are offering it.
Appreciate 0
      07-22-2012, 11:45 AM   #15
CALWATERBOY
Major
CALWATERBOY's Avatar
95
Rep
1,051
Posts

Drives: 2009 E93 N54
Join Date: Jan 2011
Location: San Francisco

iTrader: (0)

Quote:
Originally Posted by turugara View Post
I know a lot of high end brands are like moton/AST, JRZ's, or nitron are offering it.
Looks like Ground Control
Appreciate 0
      07-22-2012, 05:05 PM   #16
DaveOH32
New Member
0
Rep
15
Posts

Drives: 335i
Join Date: Oct 2011
Location: Greensboro, NC

iTrader: (0)

Quote:
Originally Posted by CALWATERBOY View Post
Looks like Ground Control
How so?

The shock is an inverted Moton.
Appreciate 0
      07-23-2012, 12:38 PM   #17
Doyle
Hellafunctional
27
Rep
426
Posts

Drives: 335xi
Join Date: Nov 2010
Location: N/A

iTrader: (2)

I would avoid full true coilover until you run a full cage. The added rigidity will allows the higher spring rate to function better. Think of the body as a third spring.
__________________
Go: Cobb S2+, Big Tom FMIC, CP-E DP & DCI, Royal Muffler, AR OC
Turn: TC Kline/Swift SA, Vorshlag Plates, UUC Front Bar, H&R M3 Rear Bar, VAC endlinks & spacers, Forgeline 18x9.5/NT05 265 Square
Stop: Endless MX72, Stoptech Rotors/Lines, Motul RBF600
Appreciate 1
N54POWR46.50

      07-23-2012, 06:08 PM   #18
mike-y
just another bmw douche bag
United_States
165
Rep
3,669
Posts

Drives: 1.9L of fury
Join Date: Nov 2008
Location: Los Angeles, CA

iTrader: (4)

Quote:
Originally Posted by CALWATERBOY View Post
Looks like Ground Control

That setup is using an Eibach Race Spring (ERS line), which just happen to be used/sold by Ground Control - but anyone can buy them for custom setups, similar to what HPA does with the swift line.
Appreciate 0
      07-24-2012, 11:03 PM   #19
CALWATERBOY
Major
CALWATERBOY's Avatar
95
Rep
1,051
Posts

Drives: 2009 E93 N54
Join Date: Jan 2011
Location: San Francisco

iTrader: (0)

Quote:
Originally Posted by DaveOH32 View Post
How so?

The shock is an inverted Moton.
Spring color & hat.

But like Mike-y says, OEM'd by Ground Control; in this thread wasn't a Ground Control setup.
Appreciate 0
      07-28-2012, 04:57 PM   #20
HP Autosport
General
United_States
1944
Rep
33,078
Posts

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

iTrader: (34)

Less stress on the subframe bushings and the sheetmetal around the subframe mounts, but more on the shock towers. You will likely need to reinforce the towers or run a cage.

More consistant spring rates(no spikes) since you will no longer have the slight bending of the springs due to their current location between the lower camber link and the frame of the vehicle and the arc the lower camber link must travel through.

You can also swap this coilover setup(spring and shock) in minutes.

The list goes on and on...
Appreciate 0
      09-05-2012, 12:24 PM   #21
ajm8127
Private
ajm8127's Avatar
0
Rep
80
Posts

Drives: '07 335i
Join Date: Aug 2012
Location: Pittsburgh

iTrader: (0)

Looks good, Andrew. Why no tubes to the structural support seen at the top of the first picture?
Appreciate 0
      09-05-2012, 01:59 PM   #22
ajm8127
Private
ajm8127's Avatar
0
Rep
80
Posts

Drives: '07 335i
Join Date: Aug 2012
Location: Pittsburgh

iTrader: (0)

Quote:
Originally Posted by AndrewLang View Post
Do you mean the rear parcel shelf? I didn't see anything up there of significant structural integrity worth attaching to, although this is just my opinion. The other issue was cost and weight. The owner probably would have prefered I use less tubing to save weight but this is what I felt was needed at a bare minimum considering the lack of the cage. The way his build is going I expect him to come back for a half or full cage in the near future so I wanted to design the rear bracing structure to work well with a cage.
There is a piece of sheet metal formed into a 'U' channel shape that runs along the top of the inside of the trunk from one side to the other. I remember thinking it looked structural after looking inside my trunk. I would think what you have is fine though, I was just curious.
Appreciate 0
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 -4. The time now is 04:49 PM.




e90post
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
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