2012 McLaren MP4-12C: Suspension Walkaround


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As cool as this naked chassis is,I wouldrather have a 2012 McLaren MP4-12C at home in my driveway, up on jackstands with the wheels off. Why? Gettingone to my home would involve me driving it, of course.

But McLaren isn't quite ready to hand out keys just yet, not even for those who come armed with a quarter-million dollars in cash.No, even the paying customersmust wait.

Inthis unfortunate reality,a de-bodied protoype like this is a more-than-acceptable substitute.

Already, we can see something interesting. The McLaren MP4-12C is not a unibody machine: the car gets all the strength it needs from what liesbeneath the skin.The body itself adds a bit of rollover crash structure, aerodynamic scuplting and, of course, a heaping helping of bad-assedness, but you could drive one that looks like this with little trouble.

But the MP4-12C isn't a body-on-frame vehicle either, not really. That's because the heart of the"frame" is a single-piece carbon-fiber monocoque (yellow) that weighs just 80 pounds. I guess we can callthis body-on-monocoque construction. Whatever the term, it's put together very muchlike a prototype racecaryou might see at Le Mans or Daytona.

The engine, transmission and rear suspension are carried by analuminum trusswork (orange) that's bolted behind. This sort of trusswork isn'tfound in racing applications where the engine block itself is a so-called "stressed member" that doubles as the rear half on the frame. Here the engine is "unstressed", so the trussworkis needed to do exactlywhat it looks like it's doing.

Meanwhile, that aluminumbeam up front isnot much more thana deformable crash structure and a place to hang the nose.

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Even though it's hard tosee now, I can tell you from a test-sit in a full-bodied example that themonocoque provides plenty of space for occupants that stand well over 6 feet tall.In fact, McLaren tells me that 6-foot 7-incheswas the upper end of their design envelope. Partial credit goes to the generously telescopic steering wheel that's supported by thatmagnesium dash support bracket.

Meanwhile, the gas tank sits beneath that shelf behind the seats.

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Finally, some suspension bits to look at. To the surprise of no one, the McLaren's front suspension is comprised ofdouble wishbones,a front-mounted steering rack and a coil-over shock absorber. And, of course, it's all made of "aluminium".

But this looks too clean and simple. Something's missing. What could it be?

I'll give you a few panels to figure it out.

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In keeping with a constructiontheme we'll see repeated throughout, the MP4's upper control arm bushingshave a tie-bar (yellow) that's bolted directly into bosses thatare bonded into the side of the monocoque.

The shock absorbers have independent external adjustments (black)for compression and rebound damping force, with the uppermost onefor compression and the lowermost for rebound. The electrical connectors at the ends (white)indicate that the adjustmentsare computer-controlled.

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Here again, we can see how the upper shock tower bolts toanother boss molded into the monocoque.

Are those hoses making you curious? Don't worry if the light bulb stillhasn't flicked on.

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Enough torture. The missing front suspension element is...a front stabilizer bar. The MP4-12C hasn't gotone.Go ahead. Scroll back a couple of pictures and have another look. I'll wait.

What the McLaren has fitted instead is a complex series of tubes. These hoses (yellow) connect to the opposite side to form a hydraulic stabilizer bar that can be computer controlled.But to make it work they must cross overone another: the compression valve on this side connects to the reboundvalve on the other side, and vice-versa.

Imagine you're in a sweeping bend. Naturally, the body wants to roll toward the outside, and this causes the outer shock to compresswhile the inner one grows. With this system, the pressure rise in the outer shock is re-routed across the car so it can repel the extension of theinner one, and vice-versa. But this only works if thehoses are"cross-wired", rebound to compression.

Here'sanother cool bit. There are valves, accumulators and electronics between the two interconnected hoses, and their presence allows the roll stiffness to be continuously variable, evenduring a single corner. For example: the system can be programmed to roll-in softly then firm-up as g-forces rise.

You can't do anything like thatwith a regular anti-roll bar, a simple bent piece of steel that tries tocounteract body roll by simple torsion. Such a bar can only haveone roll stiffness value. Even the adjustable ones have to be physically moved and "set" into one position.

Sebastian Loeb's all-conquering Citroen world-rally caronce had a setup like this,and it wasso effective it waslater banned. More recently, a similar (but far less exquisite-looking) system is offered as an option in the new 2011 Infiniti QX-56 SUV. (We'll see more of that in an upcoming walkaround.)

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Still not getting it?Here'sthe pair of crossover pipes (green)that plumb one side to the other. Bothare connected via pressure lines toa control valve assembly (yellow)that sits on the floor of the front sub-frame. Those black dumbbell ends are the accumulators. Onething that's missing from this rolling chassisis a pair ofmatching pressure linesrunningup from the rear of the car.

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Keep looking at the control valve assembly if you want, but this picture is all about the steering. The MP4-12C usesrack-and-pinion steering, and McLaren engineers told me they wanted to use hydraulic power steering for its superior feel. Butelectric power steering would have helpedengine-bay packaging and parasitic power loss by eliminating the belt-driven pump, the belt hardware itself and the need for long hose runs.

To get both benefits, McLarenfitted this electric-driven hydraulic pump (black), which feeds the rack directly via short lines (yellow). This,then,is electro-hydraulic or electric-over-hydraulic power steering, and it's the best of both worlds.

Meanwhile, this small gap (green) shows that the front suspension and steering subframe is independent of that front crash structure.

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In order to give the carbon monocoque the maximum possible stiffness despite door cutouts, clearances must betight. They're so tight, in fact that there's no place for traditional door hinges. Instead, the door hinges attach higher-up (yellow). And that's why...

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...the McLaren MP4-12C has "dihedral" scissor doors. Please don't call them Lambo doors.

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The standard front brakes use 4-piston fixed calipers and two-piece front rotors made up of aluminum hubs andventilated and cross-drilled cast-iron rotors. But there is an upgrade available, even though most owners won't need it.At this price range, it's a "want" thing.

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I give you 6-piston fixed calipers and cross-drilled carbon-ceramic rotors. The little thingy above (yellow)is a brakecooling duct.

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Moving to the rear, we can see another pairof wishbones and another coil-over shock. But wait? Is that (yellow) a stabilizer bar? No, it isn't.

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See? Here on the right-rear there's nothing where thelink on the other side attached to. This is something we've never seen before, so let's look at this again.

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This is what they call a "z-bar" or "heave spring", and it's not something you see outside of high-level racing. And by high-level I mean high levels of aerodynamic downforce.

A stabilizer bar is u-shaped (albiet a wide U), so it does nothing when both wheels compress together. Its job is to resist body roll, to dampen the suspension from being fully independent, in effect, when the wheels are moving in opposite directions, such as they do in body roll.

Because one leg goes forward and the other aft, a z-bar (or heave spring)is exactly the opposite animal. In corners, it does nothing to inhibit roll. If one wheel hits a bump, it's not going to put up much of a fight. Butwhen both wheels compress together, as they might when a huge wing is creating a ton of downforce, the z-bar becomes a spring that counteracts that force. This allows the coil springs at the wheels to be relatively soft for good mechanical grip and drivable comfort.

You don't see this often because not many cars make enough downforce, either because they don't really have a big rear diffuser or wing, or because they don't go fast enough. The MP4-12C goes fast enough, and it's got a real, functional diffuser. The rear downforce is significant.

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Like we saw up front, tie-bars (green)hold the rear control arms in place.The toe-link (yellow) pivots on an inner ball-and-socket joint.

No, that's still not a stabilizer bar. Sorry.

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In order to clear a path for the shock, the aluminum upper control arm is L-shaped instead of A-shaped.

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Like the front, the "stabilizer bar" is really just a pair of hoses.

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Don't be distracted by the pretty exhaust system that exits high so the rear diffuser can make gobs of rear downforce. Because this is a suspension walkaround, the thing to look at here is the pair of hoses that cross-links the shocks.

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Maybe this stretches the definition of suspension, butthe engine is "suspended" in the rear frame by these (yellow) links. Fuel is suspended in this well-protected tank (black). That green thing? Oh, that's nothing much. Just one of two turbochargers, that's all.

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The back half of the engine and transaxle is suspended from this frame crossmember.

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Like the front, braking duties are handled by a 4-piston fixed caliper and two-piece cross-drilled and ventilated cast-iron rotors that ride on aluminum hubs. Unlike the front, there's a smallerbrake caliper strictly for parking brake duty.

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Upgraded rear brakes consist of carbon-ceramic rotors andsilverycalipers. I prefer to use the term black chrome.

If we play our cards right, we may get a chance to put one of these on the track fairly soon. I'm crossing my fingers and toes. I could use your help.

Photos by Kurt Niebuhr. Arrows, as usual,by me.

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