Spec Miata, SCCA Touring classes, and other race or time trials classes allow the use of offset upper control arm bushings or extended lower ball joints on the front end to achieve more camber than what is available in the normal range of camber adjustment. If we use Spec Miata as a case study, one of the most competitive classes in club racing, a stock front suspension on an NA Miata or NB Miata may only be able to achieve 1.5 to 2.5° negative camber. Optimal handling for road racing on a typical race tire on this car is between 3.2 and 4.0°. The same is true for many other makes and models used in spec or touring class racing. We know we need more front camber, so what option is best and why?
One argument for extending the lower ball joint instead of pulling the upper arm further inboard is a slight increase in track width. This is valid as every bit of front track width helps reduce body roll and makes a more stable car. Both the SCCA GCR, and the NASA CCR limit front track width for Spec Miata to 1450 mm.
So why then do nearly all the front running cars use offset upper control arm bushings and not ball joints? One common justification is that the front lower ball joint is already a failure-prone part. Offsetting the ball joint from stock gives this component more leverage to fail. Quality requirements are not as stringent for the aftermarket as OEM, but no part is immune to failure under race conditions.
The real reason few are talking about this, however, is the handling advantages of removing a rubber bushing from the front suspension and replacing it with a rigid, free-spinning bushing assembly. This effectively does three important things to the front suspension:
- Allows a more linear front spring rate seen by the spindle (thus tire). Rubber bushings act as torsion springs in droop or compression once the inner sleeve is clamped to the subframe with a bolt. The spring rate increases in compression and decreases in droop, which is not ideal for keeping tires at their adhesion limit.
- Reduces the deflection of the suspension assembly under high cornering loads. Rubber bushings deflecting inboard or outboard in transient maneuvers result in poor handling performance. OEM bushings are great for reducing NVH and keeping the cabin pleasant during commutes, but we have races to win!
- Less resistance to compression in droop allows better setups. Effectively lowering the front spring rate the tire experiences will allow more level setups, thus better front/rear weight distribution. In addition to distributing the load (thus heat) more evenly amongst all four tires, this levels the roll axis since your car now handles happily at no rake, or very little rake as measured at the pinch welds.
After understanding the points above, you decide. Do all the front running drivers run offset bushings over ball joints because that’s what their teams prefer to use, or does the performance make enough of a handling difference to improve lap times and consistency?
About Race Bushing Factory’s Pre-Assembled Offset Upper Control Arm Bushings
When looking for offset bushings, do your research! There is a lot of hobbyist aftermarket junk out there that is not suitable for competition duty. ApexPAI bushings were designed specifically with ultra-high-performance materials, built to be an overkill premium product for the motorsports industry.
You can buy a set of reliable offset bushings here: https://www.racebushings.com/product/mazda-miata-offset-bushing-front-upper-control-arm-bushing-set-apexpai