Enough of this waiting. It's time for the suspension walkaround on our 2009 BMW M3. New this week are larger clickable photos.
The overriding theme in the M3's front suspension is this: buy stock in aluminum.
It's of course a strut front suspension (yellow), but here the strut body itself is, you guessed it, aluminum.
The M3 has twin pivot steering geometry like we've seen before, and both links that feed into it (orange) are aluminum. Fanboys will appreciate the fact that most of these parts already have the "M" logo cast into them.
The steering rack and tie-rod (green) are mounted ahead of the axle, as is required to reach the level of steering feel and precision that the BMW 3-series is known for.
The stabilizer bar end link (white) shoots upward to connect drirectly to the strut housing.
Here's another view of the dual pivot setup and the bends the various parts need to have to let the steering through.
This snail's-eye view shows where the virtual steering pivot winds up when you project the links out to where they'd intersect.
By far the biggest hunk af aluminum here is the intricate welded subframe (yellow). That's some serious money.
And here you can see that the long slender stabilizer bar link attaches directly to a cast-aluminum lower spring perch. More money, that's all it takes.
Here's a close-up.
The strut's top pokes into the engine compartment, and the damping adjuster mechanism sits right at the top (white). This one looks like an external motor designed to rotate the "clicker" remotely.
Unlike the GT-R, which carries a short V6, the 3-series engine bay accomodates a straight-six or, like the M3, a deep-set V8. As a result there's no space for the permanantly-welded strut tower stiffening panels found in the GT-R, So BMW uses an external reinforcement bar (yellow) instead.
Here's a close up of the welded aluminum subframe. It extends beneath the engine to the other side, of course. I don't even want to think about how much it costs to replace one if it gets bent. Keep it on the track and you'll be OK.
Imagine my surprise when the M3 admitted to me that it uses mere single-piston sliding front brake calipers (yellow). The sliders themselves are hidden by the huge size of the calipers.
The wire goes to an electric pad wear sensor that's buried in one of the brake pads. Wear down to it and the circuit is completed, and that turns on a light on the dash.
The brakes pads themselves aren't very big (black), despite the size of the caliper. Most of the caliper mass is there for caliper stiffness and for the sake of a large thermal mass to get the heat out and away from the pads.
The same goes for the rotors. The vented and cross-drilled friction surface floats free of the aluminum hub of a series of pins (white). This allows more air circulation to remove more heat, and it isolates the wheel bearings from brake heat.
We've achieved good numbers with this M3, so an upgrade to a set of fixed-piston Brembos only seems warranted if you do a lot of track days.
Before we move to the rear, how about a shout-out for the obvious rubberized jack point (black) to go along with 4 more along the side rails, like those seen in the 135i walkaround.
This car has one tidy underside.
It's hard to see all of the rear suspension at once, so we'll break this up.
The M3 has a multilink set-up with five distinct links. So we see two upper links instead of a one-piece upper arm. Both are aluminum, of course.
The large diameter monotube rear shock (white) is also made of aluminum.
White arrows indicate the two lower links, one of which is spread wide to carry the spring. It's made of...aluminum.
Our 5th and final link is the toe-control link (yellow), another aluminum piece.
The rear subframe (orange) doesn't constitute unsprung mass, so it remains steel to help bias the weight distribution to the rear.
The rear differential sports a cover (green) that's cast out of finely-finned aluminum to draw away heat without need of an external cooler and hoses.
We can see the forward lower link (white) better in this shot, and it's the first steel piece we've set eyes on.
In the background, two eccentric cams (yellow) provide adjutability for rear camber (lower) and toe-in (upper).
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Here's a close-up of the eccentrics and the smooth, flowing exhaust bends that wrap around them.
The rear stabilizer link (white) attaches directly to the steel hub carrier (yellow) for 100% efficiency, and that allows a smaller, lighter stab bar to get the job done.
Not sure why the rear hub carrier is iron though. It may be that it's too crowded out here to use aluminum, which would need to employ a larger cross-section to achieve similar strength. This part sees a lot of high loads and stresses, so an aluminum version might have simply have been ruled-out because it would have taken up too much space.
Here we can see that the forward mounting point of steel subframe (white) has been throughly stabilized at the free end by a network of braces (green).
And, like the front, the rear brakes are single-piston sliders with electronic pad wear sensors. Also like the front, the two-piece cross-drilled and ventilated rotors are pinned to their aluminum hubs.
Of course none of this would be of much use without sticky tires. As reported before, our BMW M3 wears Michelin Pilot Sport PS2 high-performance summer rubber. The fronts ar 245/40R18, and they weigh 48.5 pounds apiece when mounted on their alloy rims.
These 265/40R18 rear tires weigh 52 lbs when mounted on their 18 x 9.5-inch rims.
Finally, here's another shot of the finned rear differential cover, for no other reason than it looks so damn ... cool.
Dan Edmunds, Director of Vehicle Testing @ "you expect me to remember that after I'll I've been through?" miles
wobbly_ears says:
02:09 PM, 06/19/09
Wheels look cool!!
sealclubb3r says:
02:41 PM, 06/19/09
Aluminum FTW!
I wonder how much the 19 inch wheels weigh? I've head that they're actually lighter because they're forged instead of cast. Is that true?
actualsize says:
02:43 PM, 06/19/09
Could be, but it might not be much. I'll let you know if I get my hands on one.
canadaphant says:
02:45 PM, 06/19/09
Cool to see an expensive, no compromises suspension
kingkhalas says:
02:47 PM, 06/19/09
Notice how much less rust compared to the Challenger.
charlesncharge says:
03:31 PM, 06/19/09
Can't Edmunds spring for some sort of two-post lift etc.? What's the relation between you (Dan) and Edmunds.com, or is it only coincidence that your last name's the same? In any case, can't you pull some strings? Hell, just put the lift in your garage.
I'd hate to think what would happen if one of these cars were to ever fall off their jack/stands, or worse - on you!
In any event, thank you for the effort - it saves me from having to put my car up onto our lift.
-Chuck
jeepsrt says:
03:33 PM, 06/19/09
Not sure why the Challenger had so much rust, I know a couple of people with them and have never seen rust, then again we are in Colorado.
ktinsd says:
03:54 PM, 06/19/09
Love these walkarounds (crawlarounds?). It would be great to see some interesting vehicles you have access to that are not a currently part of the long term test fleet. Ford GT perhaps?
In any event it's a cool way to work from home as well as ensuring you get to drive every vehicle in the fleet.
roadburner says:
04:17 PM, 06/19/09
"Not sure why the Challenger had so much rust, I know a couple of people with them and have never seen rust, then again we are in Colorado."
I live in Kentucky and most every new Jeep Grand Cherokee seems to boast several rusty suspension components when they are delivered to the dealer. Conversely, my 1999 TJ's undercarriage is virtually rust free- and it sits outside 365 days per year.
roadburner says:
04:20 PM, 06/19/09
Now THIS is a way-kewl differential cover- found on my 2007 B7 press loaner:
http://www.carspace.com/roadburner/Albums/B7/IMG_0628.JPG
the_big_al says:
04:55 PM, 06/19/09
cool cool. It is really neat to see these. I eat up everyone. I even poke around my own vehicles when I have them on jack stands to see what everything looks like. It is also neat to see what everything is supposed to do.
zjev says:
04:57 PM, 06/19/09
Great large pictures and article Dan! Very detailed and a ton of useful information. Thanks
charlesncharge says:
05:08 PM, 06/19/09
Hopefully, someone over at Nissan's taking a good look at the cooling fins on the M3's differential cover, not to mention the trick "Alpina" branded diff cover in Roadburner's post/link. Apparently, the new 370Z/Nismo, version could really benefit from more substantial cooling fins on their diff covers, as well.
ampim says:
05:23 PM, 06/19/09
The PS2's are a lust-worthy tire. All of that aluminum doesn't mean jack if you don't shoe the car with some proper rubber. Expensive to replace, but totally worth it.
uncanny_man says:
05:36 PM, 06/19/09
Any idea why they went through such great lengths to make the weird subframe? The finned differential is definitely cool though.
roadburner says:
06:40 PM, 06/19/09
Here's the B7's engine. 500 bhp, no waiting:
http://www.carspace.com/roadburner/Albums/B7/IMG_0613.JPG
0-60 in 4.4 seconds, 0-100 in 10.1. Not bad for a 4700 pound luxury sedan.
kyolml says:
08:12 PM, 06/19/09
So why the front sub frame is aluminum vs. rear steel? Front one is not sprung weight either, shouldn't matter that much. Just to keep weight distribution % even so make it aluminum?
billt9 says:
10:26 PM, 06/19/09
2008 BMW M3 E92 press release:
"Virtually every detail on the five-arm rear axle made of aluminum is new for this model. These weight-reduction measures and materials
help reduce weight by approximately 5.5 pounds when compared to the previous M3."
https://www.press.bmwgroup.com/pressclub/p/us/pressDetail.html?outputChannelId=9&id=T0017866EN_US&left_menu_item=node__2248
I don't know if the press release is referring to the entire rear axle, or just one control arm, but seriously, 5.5 lb.
Paying that much more money and spending limited resources of Earth for baby weight savings.
Personally, I wouldn't pay for that weight savings crap.
I'd pay for the fact that aluminum doesn't rust to cure my OCD rust anxiety disorder.
OMG will my car last 15 years???
bimmerjay says:
10:43 PM, 06/19/09
"So why the front sub frame is aluminum vs. rear steel? Front one is not sprung weight either, shouldn't matter that much. Just to keep weight distribution % even so make it aluminum?"
Yes, exactly. It's worth it to spend the extra $$ to save the weight up front, but not necessary in the back. There might be torsional rigidity concerns too given the serious power being routed through that rear diff.
ddoouugg says:
11:03 PM, 06/19/09
Why are the insides of ventilated rotors always rusty?
eclogite says:
07:16 AM, 06/20/09
I really enjoy these walk-arounds, Dan. Thanks for doing them. I learn every time.
rick8365 says:
07:23 AM, 06/20/09
What beautiful and impressive engineering, fabrication and build this car features behind/under the scenes. Wow.
An impressive and way informative walkaround too - thanks!
zcalvert says:
08:36 AM, 06/20/09
Nice to see that BMW is spending the profits from their soccer mom models (X3, X5, X6)on stuff that their enthusiast customers actually care about.
cartester16 says:
09:52 AM, 06/20/09
Save this link for when you hear the ricerators say "but the BMW cost 10k more" ...
slickersdrip says:
05:08 PM, 06/20/09
I really love these walkarounds. Thanks Dan-- as the others are saying I always learn something.
This walkaround also gave me a greater respect for the M3 and its price premium.
mopho says:
06:51 PM, 06/20/09
Now that's a quality machine. Great walkaround, keep em up!
athens says:
08:27 PM, 06/20/09
As an Infiniti G35 coupe owner I can attest that our multi-link front and rear suspensions are are primarily aluminum.
No the Infiniti subframes are not aluminum. They are high tensile steel. However BMW recently announced they too will forego aluminum in favor of a new generation of high tensile steel in their subframes and engine/ transmission cradles starting in the new 2011 5 series code F11.
Why is BMW abandoning aluminum alloy. Simple answer - manufacture and replacement COST. The new high tensile steel alloys are nearly as light as aluminum alloy yet stronger. They cost less to produce. Every time a BMW aluminum subframe/ cradle is damaged in a collision an insurance carrier suffers from a coronary.
True aluminum intensive suspension components are becoming more popular with manufacturers of sporty cars as a means of keeping unsprung mass down (allows for more precise control). Again there is a compromise in using aluminum. Bad roads, larger diameter wheels, lower profile tires combine to make aluminum suspension parts prone to bending or cracking in severe road impacts.
subytrojan says:
07:51 AM, 06/21/09
The rear diff cooling solution reminds me of a CPU heatsink. :o)
hondacura4 says:
08:03 AM, 06/21/09
People often complain about the M3's (and BMW's in gereral) price yet refuse to acknowledge that even the smallest details (aluminum subframe ETC ETC) can be very..very expensive.
Kudos to BMW for not going the cheap route for the sake of saving money. I enjoy seeing this level of engineering as heavy compromise leads to mediocre product.
"No the Infiniti subframes are not aluminum. They are high tensile steel. However BMW recently announced they too will forego aluminum in favor of a new generation of high tensile steel in their subframes and engine/ transmission cradles starting in the new 2011 5 series code F11."
Athens, I see nothing wrong with BMW taking this route with a drastic material change as long as there are no compromises in tactility, weight or performance. On the plus side (as you stated), its easier/cheaper to produce, repair again with little to no compromise.
yellowbal says:
10:13 AM, 06/22/09
Is that a crack or a scratch in the rim?
hurls65 says:
12:18 PM, 06/22/09
That's so much prettier than the bits on my non-m E46, that's for sure. Hopefully a bit more durable, since control arms, ball joints, bushings, etc. on the E46 wear out with alarming regularity. I suppose given the price of the M3, that's just chicken feed for owners :)
Dan... I'm eagerly awaiting you getting the A4 Avant up on the lifts. Mine's been in the driveway for a week, but before I start poking around I want someone to tell me what I'm looking at. How to explain to my wife laying beneath her car with my macbook? I'm not sure on that one yet ;)
drmillerM3 says:
01:09 PM, 06/22/09
To your responses of why they used steel for the rear subframe vs aluminum like the front... I truly don't believe cost was the main reason, and BMW could care less about insurance companies lol.
The real reason is simple: search e46 rear subframe failure (particularly rear subframe mounts). There-in lies your answer.
Particularly with the e46 M3, as it eats rear subframes and they cost $12,000 to repair. There's a class action suit against BMW for this.
They were not willing to make that mistake twice (thank goodness) so they built the rear subframe in the e9* M3 like a rock. Kudos.
Structural rigidity FTW. Seriously, take another look at the suspension walkaround... cost was not the factor.
manuelc says:
02:59 PM, 06/22/09
Dan! A4 Avant suspension walkaround! Post haste! Then the S5. Pleeeeease!! Satiate the Audi fanatics' thirst.
cwc1 says:
05:08 PM, 06/22/09
Is the rear subframe of the E46 aluminum? When designed well, isn't aluminum supposed to be just as strong as steel?
actualsize says:
07:54 AM, 06/23/09
@cwc1: not necessarily.
1) The aluminum part might need to have a larger section and that could eat up more space in the trunk and rear seat area.
2) This new M3 is putting a lot more power to the pavement than the old one (81 hp more, to be exact). It weighs a bit more. It arguably sticks better. In short, the rear subframe is under more stress. What worked for the E46 (and there are doubts about THAT) may not work here.
3) Aluminum is very advantageous for the front subframe, where you want to reduce front axle weight and shift the balance rearward. But if you use aluminum for the rear subframe too, you shift the balance back to the front again, and that's counter-productive.
cwc1 says:
06:33 PM, 06/23/09
^Thanks for the explanation. Other than putting the battery in the trunk, I had wondered how BMW was able to achieve the 50-50 weight distribution for most of its cars, considering that front engined, rear while drive vehicles usually have close to 60% of their weight on the front.
So, it's details, details, details...
tonkatoytruck says:
08:05 AM, 07/13/09
Another great technical article. Thanks. Love to hear and see the details.
911cs2 says:
07:33 PM, 10/ 1/09
REALLY appreciate the effort taken to explain 'my' car's (it's the e92 vers.) suspension bits.
Now I fully 'get it' that approx 80% of the M3's components are bespoke vs the stock 3ers. And also why a chipped 335i is no M3 substitute. Huge engineering effort expended by the M Div on the critical product they roll out ~ every 7 yrs.
Hey, how can one see all the blog entries on the M3. I followed the "2009 M3" link on a newer blog but it does not lead to all of the posts - guess I appear clueless, oh well ...