M5 rear seat bar
10-14-2016, 08:47 AM
#2
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Upgrade yes, but RD Sport is what you really want to control the mass of the E61 as they are thicker and adjustable.
OEM E50 M5/ E63 M6 front= 26.5mm rear= 18mm
OEM E61 M5/ E62 M6 front= 28mm rear= 20mm
RD Sport (adjustable) front= 30mm rear= 22mm
IIRC RD is about $400 so if you can get a steal on M5 bars it may be worth running them otherwise just get the RD Sports.
Evan
OEM E50 M5/ E63 M6 front= 26.5mm rear= 18mm
OEM E61 M5/ E62 M6 front= 28mm rear= 20mm
RD Sport (adjustable) front= 30mm rear= 22mm
IIRC RD is about $400 so if you can get a steal on M5 bars it may be worth running them otherwise just get the RD Sports.
Evan
10-15-2016, 12:03 PM
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My Ride: e61 / KW V3 / JB4 / M5 Rear Sway / FDL Coded / SAT Retrofit w GKE flash / ER FMIC / BMS DCI
Model Year: 2010
Engine: N54
I haven't tried it, but another alternative would be the Dinan adjustable M5 rear for about $180. I just saw it for the first time the other day, but I'm considering upgrading my M5 rear sway to tune out a little more understeer.
Evan, where are you finding the RD's for $400? Last time I looked, they were listed for closer to $600 and I've heard availability is a challenge. I'd pick up a pair in a heartbeat for $400 though.
10-16-2016, 12:13 PM
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My Ride: e61 / KW V3 / JB4 / M5 Rear Sway / FDL Coded / SAT Retrofit w GKE flash / ER FMIC / BMS DCI
Model Year: 2010
Engine: N54
A German-sourced M5 rear stabilizer on my E61 was a noticeable improvement compared to the M-Sport stabilizer. Still could use more, though I am about to experiment with a removable strut tower brace setup. Dunno if the attachment points for a non-E61 M5 stabilizer are the same... but they're around used, so would save you money.
M5 front stabilizers do not fit US E61 Xdrive wagons, because our front struts are different. The E61 M5 front stabilizer sourced from Europe does't fit either, for the same reason.
Either *might* fit if you converted to the front suspension/hubs from a RWD E60 (528,530,535,540,550), but I am not positive that the links are the same length between the M and non-M struts, although this is more about location of the bar ends/assembly and does not influence stiffness (they aren't pre-loading the bar, in other words).
M5 front stabilizers do not fit US E61 Xdrive wagons, because our front struts are different. The E61 M5 front stabilizer sourced from Europe does't fit either, for the same reason.
Either *might* fit if you converted to the front suspension/hubs from a RWD E60 (528,530,535,540,550), but I am not positive that the links are the same length between the M and non-M struts, although this is more about location of the bar ends/assembly and does not influence stiffness (they aren't pre-loading the bar, in other words).
The M-Sport front stabilizer for US Xdrive cars fits, is larger diameter than a standard Xdrive stabilizer, though is not adjustable, as Evan notes ^.
If you want larger diameter and adjustable... you'll have to go aftermarket, but do make sure that you are comparing apples to apples, since OEM bars seem to be solid and some aftermarket stabilizers are tubular, even if adjustable. I have not found torsional data ("twist" in ft/lbs), and that's the bottom line. Tubular are likely lighter, but may not be stiffer when comparing diameters.
And once again, I am reminded that my engineering education has been most useful for car modding and beer brewing
Or, if you're feeling frisky, install a complete Dynamic Drive setup from a 550i. Tells us how that goes. 
So what was the OP's question again?
10-16-2016, 04:09 PM
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My Ride: e61 / KW V3 / JB4 / M5 Rear Sway / FDL Coded / SAT Retrofit w GKE flash / ER FMIC / BMS DCI
Model Year: 2010
Engine: N54
I see it on my M-Sport wagon measured with a digital caliper (either 25 or 28mm IIRC). See image of my bar below. Obviously much larger than the standard E60/E61 Xdrive bar, though not as large as the RD Sport's front tubular bar (Evan measured his when I was at his shop, and it was 30mm).
Given that my car was a factory M-Sport, it came with a few goodies, such as the lower rear Xbrace, supposedly stiffer/shorter front springs, and the larger stabilizer bar. My rear bags are not the same part number as the E61 M5 bags, and based on realoem, are lighter by a few ounces (what that means... I don't know). Seems reasonable to wonder if the E61 M5 bags have a higher spring rate. All the rest of the parts in the system are the same (well, save for the trailing arms and a few M5 links).
Given that my car was a factory M-Sport, it came with a few goodies, such as the lower rear Xbrace, supposedly stiffer/shorter front springs, and the larger stabilizer bar. My rear bags are not the same part number as the E61 M5 bags, and based on realoem, are lighter by a few ounces (what that means... I don't know). Seems reasonable to wonder if the E61 M5 bags have a higher spring rate. All the rest of the parts in the system are the same (well, save for the trailing arms and a few M5 links).
I would like to compare measurements of various stabilizers' torsional rigidity against the various BMW M-Sport and M factory offerings... like for like, but I doubt that sort of data exists. I wonder why BMW didn't spec a tubular bar over solid. This is not new technology.
Plus, I am pretty sure that I would not be able to perceive the difference at the front between my current bar and something with a small increase in rigidity. My body-roll issues are more at the back than the front... and currently compounded because my rear height is still in stink bug mode until I code it down, and procure some scales for a corner-weighing session.
My greater concern at the front was understeer over 50mph due to the limited tire contact patch of 245's, not body roll, which is why I moved to 255/40R 19s at the front.
I will likely futz with camber plates rather than pay a premium for a larger RD Sport tubular front stabilizer, because I think the .06º of camber would be more constant and not add more stiffness, which I don't feel I need (not to mention that there is a strong likelihood that I will have a whole new front suspension in the months ahead).
My greater concern at the front was understeer over 50mph due to the limited tire contact patch of 245's, not body roll, which is why I moved to 255/40R 19s at the front.
I will likely futz with camber plates rather than pay a premium for a larger RD Sport tubular front stabilizer, because I think the .06º of camber would be more constant and not add more stiffness, which I don't feel I need (not to mention that there is a strong likelihood that I will have a whole new front suspension in the months ahead).
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