This is a 1990
model with power steering and factory 14" wheels. As the
nickname 'Shirotora' (white tiger in Japanese) suggested by a
miata mailing list member, this little white tiger is very
aggressive on race tracks. I bought it in August '95 and took it
out to a closed-club autocross event just a week afterwards. I
didn't even get a chance to familiarize the car's handling
characteristics. The result was almost a spin in the first run.
But after that, I got use to it right away.
Comparing to my previous car RWD Corolla GTS in autocrossing, the Miata has way much better handling characteristics. A better suspension design, faster steering ratio, better weight distribution, smaller angular mass (weight located closer to the center of the car), more low-end-torque and responsive engine, smaller diameter race tires (vs street tires on the Corolla), and a closer-ratio gearbox made the stock Miata at least two seconds faster than the modified Corolla.
Factory DesignMy
Modification
Not only did the higher speed in cornering, shorter distance for stopping, and better torque exiting corners of the Miata impressed me, it was the prompt responses from driver inputs that impressed me most. Lift the throttle a bit, the tail starts to swing. Give a bit more throttle and the tail stays. When the wheels start to lock up during braking, modulating brake pressure can be easily achieved by a small magnitude of foot movement. Recovering from a slide is much easier in the Miata with the relatively responsive engine and fast steering ratio.
ResponsivenessSteeringEngineTransmissionBrakesEasy
MaintenanceSimple but
Effective
All of the above behavior come from the careful design of the car. I would imagine the original theme of the car being fun-to-drive. Then FR layout must have been the first consideration dropped down onto blueprints. Responsiveness is a must-have characteristic to boost the fun-to-drive index. Responsiveness does not imply how great a car can turn or how fast it can ac/decelerate. It implies how fast an acceleration amount can be changed, both in fore/aft direction and from side to side. While a full-size sportscar can produce a 1G lateral acceleration for example, it may NOT be able to change a 0.5g-left to a 0.5g-right as fast as a Miata can. Responsiveness is the weapon for the Miata to beat many full-size sportscars including Ferrari and Porsche in an autocross course.
To be responsive "laterally", steering ratio has to be fast. Weight distribution should be more towards the rear, approaching 50/50 (52/48 I believe). Angular mass should be kept small to reduce angular momentum in the Z-axis. When I first looked under the car, it seemed funny that the inside of the front and rear bumpers can be easily visible. That means there aren't many weight hanging beyond the wheelbase, or minimal overhang in other words. Reducing angular mass also reduces the stress on the body structure which is quite important in an open-top car. Furthermore, the hood is made out of aluminum to achieve the 50/50 weight distribution and low angular mass design.
To be responsive in forward direction, Miata has its engine tuned for low-end torque (relative to my Corolla GTS) which yields relatively great throttle response (although I don't like it's sacrificed high-end power). Furthermore, the engine management unit is designed to cut fuel at any rpm above idle speed when the throttle angle is returned to idle position. That creates a greater engine braking effect to initiate drop-throttle oversteer. For comparison, my Corolla GTS cuts fuel when engine speed drops to 1800rpm and re-applies fuel below 1400rpm.
To further support the responsive engine, all Miata uses a close-ratio transmission. The open-top nature of the car makes the close-ratio transmission more suitable because a car always "feels" faster with a close-ratio transmission. That's why car critics do not complain the Miata engine being under power. Who cares if a convertible is quiet enough at highway speed!
To be responsive in braking, Miata uses a large radius master brake cylinder to reduce brake pedal travel. A small vacuum brake booster (smaller than half the size of that in a '94+ Integra) is used to give maximum braking feel for modulation. On the other hand, the rear disk brakes are not self-adjustable. It sounds retarded initially, but I make use of the manual adjustment to fine-tune my brake bias!
Reliability and easy maintenance helps further increase the fun-to-drive index indirectly. Distributorless-ignition and HLA (hydraulic valve lifters) are two examples (although I think the HLAs degrade high-end performance in the engine). Other less-known features in the Miata engine include oil jets that shoot oil right at the underside of the pistons for extra cooling and oil pan baffle to prevent foaming. These performance devices usually found in race-prepared engines allow more torture on the engine in extreme conditions.
Suspension has to be simple but effective. Thank goodness Mazda chose in-wheel double-wishbones all around. Do not mix up the legacy in-wheel double-wishbones in Miata with the so-called "double-wishbones" in Hondas. Honda's rear suspension is actually of unequal upper and lower lateral links, trailing control arm with toe control link. That's basically a multi-link suspension. There are pros and cons for multi-link suspension. See my Shop Talk for more details.
A few months before I bought the Miata, I've already had plans to modify it. First thing was to install the security system. It took me a few days to finish the whole system not because it was difficult but because I customized a number of things and I wanted to get the system done nicely.
Power door lock modules were installed such that the mechanical linkage to the door lock knobs were removed and be replaced by a single electrical switch on the driver side. The reason for replacing the mechanical linkage with an electrical switch was to be able to disable the unlocking feature when the alarm is on. A microwave sensor was installed to further deter potential theft. The alarm's starter-kill system is customized to my driving-computer-kill system, making a push start impossible.
The next thing was the hard top. Two weeks after I got the car, I bought a '92+ hard top equipped with rear window defroster. Since my Miata and all pre '92 Miatas do not have defroster, I had to do my own wiring and so the defroster had been left unhooked for more than a year.
Two weeks after I got the hard top, a series of performance and cosmetic modification was started.
Next: Come on in to see my
list of modifications, installation and tuning tips
