Undercar: Diagnosing And Repairing Wheel Bearing Noise
Many Miata fans love the handling and performance as much as the affordability of these little two-seaters.
In 1978, Mazda introduced the rotary-powered RX-7, which went on to become one of the most recognizable sports cars of all time. In 1989, the company introduced the MX-5 Miata, which went on to become the best-selling two-seat roadster in the world, with more than one million sold over its four generations from NA to ND models. Today, the MX-5 is a cult classic. Many Miata fans love the handling and performance as much as the affordability of these little two-seaters.
The first-generation NA model is still in demand, and many have been modified using a wide variety of suspension tuning options thanks to the aftermarket’s early production of parts for these cars. The NA, introduced at the 1989 Chicago Auto Show, was produced for 8 years, until 1997. It owed much of its success to the layout of the vehicle, which was designed for a 50/50 weight distribution. The NA was intended to be light and nimble with a basic front-engine/rear-drive configuration to achieve optimal weight distribution. Mazda designers were inspired by some classic ’60s British sports cars, namely the Lotus Elan.
The suspension combines a wishbone and multi-link system that maximizes tire performance and dynamic stability. But the stock shocks, springs and sway bar leave a lot to be desired for the spirited driving enthusiast. Many racers and street performance drivers prefer an upgraded suspension kit with sportier valving and heavier spring rates. Coilovers are available from several aftermarket companies that range from monotube, double adjustable to lower-end twin-tube, non-adjustable valving.
Prices for these kits range from a couple of hundred dollars to a couple of thousand. It depends on what your customer intends to do with the vehicle. If he or she is going to race it in Spec Miata, a popular road racing format only for MX-5s, then they may want to spend more on a fully adjustable shock with heavier springs and custom bump stops.
Currently, the most popular platform in Spec Miata is the NB, which was built from 1997-2005. They remain virtually identical to the NA in size, but have added about 200 pounds overall. However, the NB also received a bigger mill in the 1.8L DOHC that produced around 140 hp stock. Miatas were never known to be stump pullers, so many people who make performance upgrades also modify or swap engines. A popular swap is the Chevy LS, which is compact and a significant power boost for the lightweight Miata.
The NBs are distinctive from the NAs due to their flush headlights, but underneath, some changes have made the chassis a bit more tunable. The rear suspension has more travel due to extended hats, which many NA tuners also employ in their suspension upgrades. Most racers are running a “squeezed” suspension set up, meaning that they are cornering on the bump stops. Using upgraded bump stops that are available from Miata specialists such as Flyin’ Miata and others, makes a pretty significant difference in the handling. However, street drivers may not enjoy the harshness of the ride.
According to some forums (which are numerous for the Miata, from miata.net to mountainmiata.com), the stock NB ride height starts at 14 inches and is squeezed down to 12 inches on the bump stops to improve performance. The distance from the shock to the bump stop at various ride heights is highlighted in the table below. According to Mountain Miatas, the measurements were taken using an “old style” bump stop. If you use new style NB bump stops, subtract 13 mm of travel when measuring ride height from fender lip to the wheel hub center.
Ride height Rear/Front
14˝ 1.0625˝ (27mm) 1.125 (28.6mm)
13.5˝ not measured 0.5625 (14.3mm)
13˝ 0.4375˝ (11mm) 0.375 (9.5mm)
12.75˝ 0 (light contact) not measured
12.5˝ squeezed 0 (light contact)
12˝ squeezed squeezed
The bump stops are an integral part of the Miata suspension. They can be “tuned” to offer a progressive spring rate in addition to the spring itself. Because of this, it can offer a ride height that does not “bottom out” onto the bump stop. Also, some lowered or “stanced” MX-5s may need a helper spring, so the spring stays put at full droop.
Even with stock suspension, Miatas corner on the bump stops nearly all the time. Soft springs provide a nice plush ride, especially in a straight line, but as soon as cornering forces increase, the bump stops add from several hundred to a thousand lbs/in of spring rate to the equation.
These models started production in 2008-2015 (NC) and 2016 to current (ND) and feature several improvements as well as special edition models with upgraded sport packages. However, many enthusiasts continue to install aftermarket suspension packages to these models.
Mazda Motorsports and Winding Road Racing have plans to introduce a new Spec MX-5 class for the NC that is designed to be an affordable, tech-able, reliable and fun-to-drive option for club racers. The cars will feature Roush Performance cylinder heads, Penske Racing shocks, Eibach springs and sway bars, Pagid brake pads, Toyo tires, and more, and will have a curb weight of 2,500 lb (1,100 kg). Spec MX-5 plans select events starting sometime this year (no word on the schedule yet).
One of the mainstays of the MX-5 is that owners love driving them hard, whether it’s on the street or track. Aftermarket suspension companies offer kits that are geared for both types of driving. For daily driving, the suspension needs more travel to absorb the usual uneven pavement and potholes. Make sure you know what your customer intends to do with the vehicle before recommending a package. Replacing the shocks and springs is only part of the job. There are 22 bushings on a Miata that may need to be replaced as well. The mileage will indicate as to how solid the bushings are and if it’s necessary to upgrade material. Using a urethane bushing on a daily driver is not only overkill, but it will likely lead to comebacks because the ride will be too rough no matter what suspension package is installed. Inspect the bushings, ball joints, the upper and lower control arms inner tie rods and tie rod ends, and also the sway bar bushings. Look for cracked boots, dry joints and cracks in the rubber bushings.
In some cases, it may be more cost-effective to replace the control arms with ones that include the bushings as well as the upper ball joint. Or, you can order a 22-piece set from Flyin’ Miata with rubber that is 30-40% stiffer than stock but not nearly as hard as urethane. The stiffer rubber will decrease the amount of deflection in the suspension, but they are more difficult to install than polyurethane because they have to be pressed in place.
After your customer settles on the suspension package of choice for their Miata motoring, don’t forget the alignment. For racers, the alignment is critically important. Some racers will do this themselves, but if you can offer a quality alignment to their specs, which included increased camber and toe changes over stock settings, then you may win them over and gain even more Miata clients in the end.
Article courtesy ImportCar magazine.