BMW M3 Forum
BMW M3 Forum BMW M3 Gallery BMW M3 Reviews BMW M3 Social Groups BMW M3 Chat M3Forum Sponsors >>
Loading


Mobile M3forum
Go Back   BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X) > BMW M3 Discussions > E46 M3 (2001-2006)
Tire Rack Buy Winter Tires Now!
Not a member? Register Now!
Register Gallery All Albums Garage Search Today's Posts Mark Forums Read Calendar FAQ

E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


Reply
 
Thread Tools Display Modes
Old Wed, Jan-06-2016, 01:11:29 AM   #81
chatleyg
Registered User
 
Join Date: Jan 2006
Posts: 19
Reputation: 0 chatleyg is on a distinguished road





Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Great thread, now I understand why my front end feels so stiff once I installed BG springs and Bilstein HDs. I will be trimming front bump stops, thanks Shaika for the great video showing how to trim the stops, and installing GC street camber plates. Can anyone tell me the OD and ID for bump stop packers? I plan on making different thickness packers out of Delrin or UHMW.

TIA, Glenn
Jump to top chatleyg is offline   Reply With Quote
Sponsored Links
Register now and remove these ads
Old Fri, Jan-08-2016, 05:42:08 PM   #82
ShaikhA
Fat Cat Motorsports
 
Join Date: Sep 2015
Posts: 99
Reputation: 0 ShaikhA is on a distinguished road
Location: Redwood City

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by EricSMG View Post
Very eloquently stated, Shaikh.

This is something that I've known, instinctively, for years. Many people here have heard me preach that "softer is better, more travel is better" (to a point) in almost all driving situations. Sure, the car may not corner table-top-flat or be razor sharp to driver inputs and so it doesn't "feel" as sporty, but, it's ultimately the better "handling" car.

I've also MUCH preferred a larger front/rear spring rate split as opposed to a smaller split. The latter results in a very awkward feeling car as the front and rear ends of the chassis are never in phase like they are with a larger split. This is not felt on smooth surfaces but once you encounter medium/large amplitude bumps it becomes very obvious.
Thanks, Eric. I think some slight tweaking on low speed damping is what we need to get a bit sharper feedback on your setup while still maintaining optimal grip. I do like that the faster you go, the more responsive your car feels while still developing increased / maximum grip. This ties to my general understanding of yaw rate increasing as road speed goes up.

You already nailed the importance of Flat Ride noting your experience with various setups that had too much front spring or not enough rear. Also non-optimal damping screws up the potential to maintain Flat Ride. I believe the tire's spring rate also plays an important part in the unpleasant feeling of a non-Flat Ride setup. It's like trying to balance two unevenly loaded seesaws on top of each other, with a spring as your fulcrum. Once you find your equilibrium point you *might* be okay, until someone (i.e. the road) disturbs the balance. Then, good luck! Coupled oscillations and multiple chaotic resonant frequencies galore!

It's funny, I'm pretty sure in the aerospace, airplane, bridge- and skyscraper-building worlds engineers are very concerned with resonances and do their best to minimize their creation plus use tools to damp them out. Good OE vehicle manufacturers go to similar lengths, some like VW or Audi using many different springs to get ride frequencies dialed-in. But many tuners and most enthusiasts have no idea how important that choice of spring rate is beyond lowering and stiffening their cars.

Heading to Laguna Seca on Sunday, my first event in the BMW there. Stock springs, Eibach front bar on set, stock rear bar, same damping setup as you experienced (Revision 4 KBO v1.7). I think it'll be a ton of fun and useful to see how a 'street-oriented' setup works in high-speed time trial track conditions. I'm guessing you'll be swapping the Dinan springs in pretty soon.

Last edited by ShaikhA; Fri, Jan-08-2016 at 05:54:07 PM.
Jump to top ShaikhA is offline   Reply With Quote
Old Fri, Jan-08-2016, 06:12:24 PM   #83
ShaikhA
Fat Cat Motorsports
 
Join Date: Sep 2015
Posts: 99
Reputation: 0 ShaikhA is on a distinguished road
Location: Redwood City

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Oh, found an interesting couple dyno graphs



and this thread on Lotustalk forum

http://www.lotustalk.com/forums/f91/...results-27743/

I will do some analysis on what I believe the impact of those damper curves on the ride quality and behavior of those cars.
Jump to top ShaikhA is offline   Reply With Quote
Old Fri, Jan-08-2016, 06:24:32 PM   #84
ThrowinShapes
Registered User
 
ThrowinShapes's Avatar
 
Join Date: Oct 2014
Posts: 656
In the garage:
Reputation: 0 ThrowinShapes is on a distinguished road
Location: Dover, NH

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Shaikh, this thread has been a good read so far.

Would you be willing to show us a list or chart of spring rate combinations F/R that have your 'flat ride' balance for our chassis?
__________________



[06' AW/Cinnamon] [6MT] [Slicktop] [Manual Seats]
Journal - Update 2017-02-28

FS: Center Console | US Headers / Rear O2 | Rent: SIR B90-BMW Rear Wheel Bearing Tool

Jump to top ThrowinShapes is offline   Reply With Quote
Old Fri, Jan-08-2016, 07:15:31 PM   #85
Obioban
Moderator
 
Obioban's Avatar
 
Join Date: Jul 2003
Posts: 36,226
In the garage:
Reputation: 54 Obioban has a spectacular aura about
Location: SE PA

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by ThrowinShapes45 View Post
Shaikh, this thread has been a good read so far.

Would you be willing to show us a list or chart of spring rate combinations F/R that have your 'flat ride' balance for our chassis?
Depends on your cars weight, weight balance, and unsprung mass per corner
__________________

Current Cars: 2005 IR/IR M3, 2001 LMB/blk M5, 03 530i, 04 M3 wagon, and some boring stuff
Past cars: 04 M3, 96 M3, S50B32 e36 M3 CM race car
Jump to top Obioban is offline   Reply With Quote
Old Fri, Jan-08-2016, 08:28:28 PM   #86
ThrowinShapes
Registered User
 
ThrowinShapes's Avatar
 
Join Date: Oct 2014
Posts: 656
In the garage:
Reputation: 0 ThrowinShapes is on a distinguished road
Location: Dover, NH

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by Obioban View Post
Depends on your cars weight, weight balance, and unsprung mass per corner
Can you explain a bit how it depends on unsprung mass? I would the ride frequency would only depend on the sprung weight and wheel rate.

For a typical street car, which doesn't have much of any weight reduction (i.e., close to stock weight +- a few options), do you think it would realistically vary enough to even move to the next spring rate increment?
__________________



[06' AW/Cinnamon] [6MT] [Slicktop] [Manual Seats]
Journal - Update 2017-02-28

FS: Center Console | US Headers / Rear O2 | Rent: SIR B90-BMW Rear Wheel Bearing Tool

Jump to top ThrowinShapes is offline   Reply With Quote
Old Fri, Jan-08-2016, 10:18:39 PM   #87
terraphantm
Moderator
 
Join Date: Dec 2010
Posts: 11,124
In the garage:
Reputation: 11 terraphantm is on a distinguished road
Location: Philadelphia

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by ThrowinShapes45 View Post
For a typical street car, which doesn't have much of any weight reduction (i.e., close to stock weight +- a few options), do you think it would realistically vary enough to even move to the next spring rate increment?
BMW offers something like 4 different springs front and rear depending on equipment. So there could be enough variance... though I imagine most of us probably fit into 1 or 2 of combos.
__________________
Jump to top terraphantm is offline   Reply With Quote
Old Fri, Jan-08-2016, 10:28:17 PM   #88
m3 hal
Registered User
 
Join Date: Jan 2006
Posts: 21,788
Reputation: 0 m3 hal will become famous soon enough

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by ThrowinShapes45 View Post
Can you explain a bit how it depends on unsprung mass? I would the ride frequency would only depend on the sprung weight and wheel rate.
The motion of unsprung mass is what the spring is controlling. A reduction in unsprung mass = less spring rate required for a given frequency.

Quote:
Originally Posted by ThrowinShapes45 View Post
For a typical street car, which doesn't have much of any weight reduction (i.e., close to stock weight +- a few options), do you think it would realistically vary enough to even move to the next spring rate increment?
I did a quick calc assuming a spring rate of 500 lbs/in and 50 kg of unsprung mass. Dropping 5 kg off the unsprung mass (assuming lighter wheels and brakes) gives 450 lbs/in spring rate at the same ride frequency as the 500 lbs/in + 50 kg setup.
Jump to top m3 hal is offline   Reply With Quote
Old Fri, Jan-08-2016, 11:00:53 PM   #89
ThrowinShapes
Registered User
 
ThrowinShapes's Avatar
 
Join Date: Oct 2014
Posts: 656
In the garage:
Reputation: 0 ThrowinShapes is on a distinguished road
Location: Dover, NH

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by m3 hal View Post
The motion of unsprung mass is what the spring is controlling. A reduction in unsprung mass = less spring rate required for a given frequency.
I would argue the spring is controlling the sprung mass (kind of in the definition, right?). The tire and wheel is supported by the road, which is effectively rigid. No need to control its up and down motion.

Here's a reference for this:
http://eibach.com/eibach/img/ers-14s...nworksheet.pdf

As shown, Suspension Frequency = sqrt(Wheel Rate/Sprung Weight). Therefore, like your example, a rough estimate: take the sunroof for instance, a ~40lbs option, so 10lbs per corner. If the car is ~3200lbs, thats 800lbs corner weight. That represents a 1% difference in sprung weight.
__________________



[06' AW/Cinnamon] [6MT] [Slicktop] [Manual Seats]
Journal - Update 2017-02-28

FS: Center Console | US Headers / Rear O2 | Rent: SIR B90-BMW Rear Wheel Bearing Tool


Last edited by ThrowinShapes; Fri, Jan-08-2016 at 11:09:39 PM.
Jump to top ThrowinShapes is offline   Reply With Quote
Old Fri, Jan-08-2016, 11:11:16 PM   #90
m3 hal
Registered User
 
Join Date: Jan 2006
Posts: 21,788
Reputation: 0 m3 hal will become famous soon enough

United States




Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by ThrowinShapes45 View Post
I would argue the spring is controlling the sprung mass (kind of in the definition, right?). The tire and wheel is supported by the road, which effectively rigid. No need to control its up and down motion.
You're right, I had it backwards.
Jump to top m3 hal is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

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

Forum Jump



All times are GMT. The time now is 11:57:06 AM.


Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
M3Forum.com and M3forum.net is in no way sponsored, endorsed or affiliated by or with BMW NA / BMW AG or any of it's subsidiaries or vendors.
BMW and M3 (E90 M3 | E92 M3 | E93 M3 | E46 M3 | E36 M3 | E30 M3) are registered trademarks of BMW AG.
M3Forum Terms of Service
Copyright 1999-2017 M3Forum.com
Discussing Shock dynos, Fat Cat Motorsports and custom valved Bilstiens in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)