Monday 13 May 2013

Naked Roadster

What's under that curvy body?
If you ever wondered just what is underneath the Roadster's curvy body you're in for a treat.  A few years back, Jeff @ was able to take some photos at a Mazda press event that featured an impressive display of the Roadster body shell inner structure.  The new bodyshell is larger than the previous generation and boasts a 22% improvement in bending rigidity and 47% increase in torsional rigidity, amazingly despite being larger and featuring much greater reinforcement the body weighs 247.5kg - 1.6kg lighter than the previous car.

There was a bare shell painted three different colours to highlight where weight had been saved and high strength and ultra high strength steels were used in the construction.  The integrated roll bar for example (the first in the car's history) is made from extra strong steel to provide protection in the event of landing upside down.  This is something that was missing from previous generations.  You can see from Jeff's photos of the engine bay just where Mazda was able to reduce weight using their Gram Strategy philosophy.  You can read more about that in this post, but for now just look at those large cut-outs in the front wheel arch as an example and compare that to your average car.
Mazda went to extraordinary lengths to ensure the car was as lightweight as possible within a reasonable budget.  My favourite feature of the NC's body has got to be the underside of the bonnet.  It's made of aluminium rather than steel and it sits very close to the engine components.  As a result of this to provide additional safety the bonnet features an array of "shock cones" to help absorb impact energy from an unlucky pedestrian.  But Mazda didn't just do this randomly, they've created a really cool pattern effect.  Sadly this gets hidden on the production model by an insulation cover to reduce engine noise, but I think more owners should make a feature of it.
The display also featured a fully built rolling chassis complete with engine, seats, and steering wheel.  This really emphasised how simple the roadster concept is, engine up front, two seats, and rear wheel drive.  You can see in the pictures the front and rear suspension subframes are tied together with what Mazda calls the power plant frame, or PPF for short.  This is a feature carried over from the previous generation and effectively connects the rear differential to the engine to reduce chassis flex.
The suspension arms themselves feature improvements over the old design.  You can see the newer design on the right in the above picture.  They are now made of cast aluminium so won't rust like the previous cars did.  They're also much lighter.  The steering column was made as straight and direct as possible with the minimum connections.  Not only does this save weight it also improves feedback for the driver and helps create a fun driving experience.
One day my engine will be as clean as this (I wish!).  The MZR engine uses a plastic cam cover and inlet manifold to further aid weight reduction.  The display is a fascinating insight into the engineering of the NC Roadster and shows how design and technology have progressed over the NA and NB.  Thanks to Jeff for kind permission to use his photos.  You can read the full "Inside the 2006 Miata" feature from here.

Update: Unfortunately it appears the driving enthusiast site is no longer online.