2009 BMW M3: Suspension Walkaround
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).
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