Do front spacers REALLY belong on the E39? Scrub radius examination... - BMW M5 Forum and M6 Forums

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Old 26th February 2013, 08:26   #1
Landerholm
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Do front spacers REALLY belong on the E39? Scrub radius examination...

Alright folks,

Its been argued that E39s have an ET20 front offset due to TUV requirements for chain clearance etc. It does state in some of our manuals that chains are not to be used with 17" wheels (or on M5s I believe it states they are not to be used). The M5 rear wheels have NO clearance for chains. TUV chain theory out the window.

When you add spacers to front wheels you are changing the scrub radius. This changes the effective spring rate and steering effort and kickback. An explanation of scrub radius...
Camber Scrub Radius and Handling.

In putting REAR wheels on the M5... BMW went so wide they had to factory roll the fenders.....yet the front wheels remained ET20, just like a 540i on 15" wheels. (Change in wheel width does not change wheel centerline location).

What I am offering is that BMW never intended the front offsets that some of us are using for the E39 steering/suspension geometry....Another possibility I've contemplated is that in 2000 or so it wasn't as "fashionable" to push front wheels outward along with the rears.

Thoughts on this? Have people noticed a change in ride quality over bumps etc after adding front spacers?
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Old 26th February 2013, 12:23   #2
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PLEASE NOTE THAT THIS POST MIGHT CONTAIN SARCASM. IF SARCASM BOTHERS YOU PLEASE STOP READING THIS POST IMMEDIATELY! YOU HAVE BEEN WARNED! PROCEED AT YOUR OWN RISK!!!


Why would anyone consider suspension geometry when people assume wider tires have more traction and that a "Square" set up is a lot cooler?


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Last edited by rao; 26th February 2013 at 12:31.
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Old 26th February 2013, 14:58   #3
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doubt it had anything to do with chains as you mention BMW recommends against chains, imo due to the performance of the car, i still drive pretty hard in snow with snow tires... chains would be ridiculous and likely cause damage


i run 5mm in front for PSS9

without spacers i still had no rubbing on OE wheels and Michelin PSS, but i wouldn't go against bilstein suggestion

ride quality unaffected, i'm sure there's a lot of leeway between offsets before you start having problems:

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Old 26th February 2013, 15:11   #4
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Quote:
Originally Posted by Landerholm View Post
Thoughts on this? Have people noticed a change in ride quality over bumps etc after adding front spacers?


nope.

scrub radius effect feels minimal to me vs. the traction gained (285/35 on 18x10 +13).


your camber angle and the condition of your control arm (lateral and longitudinal) bushings will affect your scrub radius more than wheel offset (within reason).

Last edited by mattmartindrift; 26th February 2013 at 15:19.
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Old 26th February 2013, 16:25   #5
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I also forgot to mention - the E39s steering axis is dynamic (two front lower ball joints), so your scrub radius would vary as you change steering angle and displace the suspension - up and down.


those silly engineers!!!
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Old 26th February 2013, 16:41   #6
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Quote:
Originally Posted by mattmartindrift View Post
I also forgot to mention - the E39s steering axis is dynamic (two front lower ball joints), so your scrub radius would vary as you change steering angle and displace the suspension - up and down.


those silly engineers!!!

So that means that the location of the center of the front wheel tread isn't important? Those silly engineers indeed!
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Old 26th February 2013, 16:56   #7
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Quote:
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So that means that the location of the center of the front wheel tread isn't important? Those silly engineers indeed!


I haven't seen treaded wheels since playing Oregon Trail in very early grade school.
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Old 26th February 2013, 23:13   #8
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Quote:
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So that means that the location of the center of the front wheel tread isn't important? Those silly engineers indeed!
Those silly engineers put a lot of R&D time into the E39 platform. All across the platform its ET20 up front. While the scrub radius may vary throughout a turn, BMW set what that radius should be. Increasing an already positive scrub radius tends to worsen turn-in, allow more kickback....

Last edited by Landerholm; 26th February 2013 at 23:15.
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Old 26th February 2013, 23:25   #9
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Quote:
Originally Posted by Landerholm View Post
Alright folks,

Its been argued that E39s have an ET20 front offset due to TUV requirements for chain clearance etc. It does state in some of our manuals that chains are not to be used with 17" wheels (or on M5s I believe it states they are not to be used). The M5 rear wheels have NO clearance for chains. TUV chain theory out the window.

When you add spacers to front wheels you are changing the scrub radius. This changes the effective spring rate and steering effort and kickback. An explanation of scrub radius...
Camber Scrub Radius and Handling.

In putting REAR wheels on the M5... BMW went so wide they had to factory roll the fenders.....yet the front wheels remained ET20, just like a 540i on 15" wheels. (Change in wheel width does not change wheel centerline location).

What I am offering is that BMW never intended the front offsets that some of us are using for the E39 steering/suspension geometry....Another possibility I've contemplated is that in 2000 or so it wasn't as "fashionable" to push front wheels outward along with the rears.

Thoughts on this? Have people noticed a change in ride quality over bumps etc after adding front spacers?
The fronts were chosen for 3 reasons.

1) Aerodynamics
2) Straight line stability (wider tires up front = more tramlining)
3) To introduce understeer at the limit.

Plain and simple, BMW has been doing this since the E36 M3 in 1996.

Running spacers up front for those of us running a square setup has to do with suspension clearance. On a good set of spacers, with the right length bolts, you should not notice them there. Not even a little bit.

Last edited by E55AMG2; 26th February 2013 at 23:26.
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Old 26th February 2013, 23:33   #10
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R&D can't compare to the overwhelming real world uses accumulated by the M5b community. Oh yes those engineers, guess how many of us had engineering degrees. I wouldn't add spacers for cosmetic reasons, but going wider up front dictates it unless you custom build your rims.
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